histology

Classification of histological tissuesThe tissues of the body are divided into four types:

- epithelial

- tissues of the internal environment - muscle - nervous

Structural and functional units that form tissues are -

histological elements. The cell is the main tissue-forming unit and the main histological element. Other histological elements:

Symplast- a multinuclear structure formed by the fusion of identical cells.

Syncytium- a structure consisting of cells connected by cytoplasmic bridges.

Components of the intercellular substancemake up the tissue matrix.

Produced and secreted by cells.

EPITHELIAL TISSUE:

Many cells, little intercellular substance --- a layer is formed

cells

presence of a basement membrane: proteins - collagen type 4, laminin, entactin, fibronectin - in any basement membrane.

presence of intercellular contacts

belongs to avascular tissues and is nourished diffusely through the basement membrane

regenerate well: especially pronounced in the integumentary epithelium; due to stem cells, the possibility of DNA replication with subsequent uitokinesis or without it (hepatocytes).

can occur from all germ layers

intermediate filaments are formed by the protein cytokeratin

Some have polar differentiation: the apical part (microvilli, stereocilia, cilia, secretory material, formation of tight and intermediate junctions); the basal part contains various organelles, mainly associated with the need for ATP for the operation of ion pumps.

the border arrangement of cells is the epithelial layers

spatial organization:

layer - always borderline location (epidermis, epithelium of the mucous membrane of the skin and intestinal type, mesothelium)

tubule - a variant of a layer rolled into a tube (sweat glands, nephron tubules)

islet - always immersed in the internal environment of the body and performs an endocrine function

follicle - a cavity-containing island of epithelium (follicles

thyroid glands)

cord - liver parenchyma

network - in the thymus gland the supporting framework consists of

epithelial cells that branch out and contact each other.

INTERNAL ENVIRONMENTAL TISSUES

Few cells, lots of intercellular substance

Rich species composition of cells

Presence of fibers: collagen (cell strength), elastic (elasticity), reticular (mesh structures).

Intermediate filaments are formed by the protein vimentin.

A lot of water in the intercellular substance, --- most often a gel-like consistency

Most cells are derivatives of mesenchyme

Motility of most cells (ability to migrate)

The ability to proliferate most cell types The tissue system of the internal environment includes blood, connective tissues

fabricsand skeletal tissues (cartilage and bone).

BLOOD - contains two main components: liquid intercellular substance (plasma) and cells suspended in it.

Connective tissues maintain the integrity of other tissues, form the stroma of organs, contain blood and lymphatic vessels, and participate in the trophic supply of all tissues and organs. Among connective tissues are:

fibrous tissues (loose and dense)

tissues with special properties (fat, reticular, etc.)

SKELETAL TISSUES

Cartilaginous tissue consists of cartilage cells (chondrocytes) and

intercellular substance - cartilaginous matrix. A distinction is made between hyaline, elastic and fibrous cartilage.

Bone tissue: two processes are going on in parallel:

new bone formation, carried out by osteoblasts

destruction is carried out by osteoclasts

CONNECTIVE TISSUES

Connective tissue cells: fibroblasts, fibrocytes, chondroblasts,

chondrocytes, osteoblasts, osteocytes, macrophages, mast cells, leukocytes, plasma cells, pericytes, adipocytes.

The basement membrane is a special type of extracellular matrix, has the appearance of a sheet or plate and consists of special proteins (various types).

MUSCLE TISSUE

Carries out the motor functions of the body. Some of the histological elements of muscle tissue have contractile units - sarcomeres. Two types of muscle tissue: striated (skeletal and cardiac) and smooth.

Contractility

Acto-myosin chemomechanical energy converter

Mesodermal origin

Intermediate filaments are formed by the protein desmin.

Structural-functional. The unit of skeletal muscle is a muscle fiber, which is a symplast. In smooth muscle tissue - SMC.

NERVOUS TISSUE

Histological elements of nervous tissue are neurons and gliocytes. Neurons are the main cell types of nervous tissue. These excitable cells conduct electrical signals and provide the brain with the ability to process information.

Neuroglia - almost half of the brain volume. Ependymal glia, macroglia (from astrocytes and oligodendrocytes) and microglia are distinguished.

In the peripheral nervous system, there are Schwann cells and a group of accessory cells surrounding neurons in the ganglia.

Cell cycle, phases of the cell cycle. Interphase. MitosisThe cell cycle consists of mitosis and interphase.

Mitosis, or indirect division, is most common in

nature. Mitosis is the basis for the division of all non-reproductive cells (epithelial, muscle, nerve, bone, etc.).

Interphase. The interphase is divided into the periods G1, S and G2 (Fig. 3-1). • Presynthetic G1 phase (from the English gap) is a period of high metabolic activity and cell growth between the telophase of mitosis and DNA replication (doubling). During this phase, the cell synthesizes RNA

proteins, the formation of the nucleolus is completed. The duration of the phase is from several hours to several days. In rapidly dividing cells (embryonic and tumor), this phase is shortened.

Synthetic S phase (from English synthetic) is the period of DNA synthesis and replication; the second chromatid is formed in the chromosome. Mitochondrial DNA is synthesized insignificantly, its main part is replicated in the postsynthetic period of interphase. In the S phase, protein synthesis continues in the cell, and centrioles separate. In most cells, the S phase lasts 8-12 hours.

Postsynthetic G2 phase. During this period, the doubling of the total cell mass is completed, the daughter centrioles reach the size of definitive organelles. In this phase, RNA and protein synthesis continues (for example, tubulin synthesis for the microtubules of the mitotic spindle), ATP accumulates to provide energy for subsequent mitosis. This phase lasts 2-4 hours.

G0 phase is a period of proliferative rest. At the end of the G1 phase, there is a restriction point (Checkpoint 1) — a safe point in the cell cycle at which the cell can stop and exit the cycle into the G0 phase. In the G0 phase, cells begin to differentiate, reaching terminal (final) differentiation (e.g. neurons), or remain in a resting state (stem cells). The stimulus for passing through the restriction point or returning the cell from the G0 phase to the cell cycle is the action of mitogens (e.g. growth factors) — molecules that interact with specific receptors in the target cell membrane and initiate its proliferation.

Prophase. Chromosomes condense, chromatin threads form a ball (mother ball). Each chromosome is represented by two closely adjacent daughter (sister) chromatids.

The nucleolus is reorganized. The nuclear membrane disintegrates into membrane vesicles. The number of structures of the granular endoplasmic reticulum and the number of polysomes in the cytoplasm decreases. The Golgi complex disintegrates into vesicles. The synthesis of RNA and protein in the cell ceases. The centrioles in two pairs (diplosomes) diverge toward the poles of the cell, and the mitotic (proliferative) apparatus is formed, which includes the centrioles and the division spindle, consisting of microtubules.

Prometaphase. The formation of the spindle is completed. The chromosomes move toward the division equator.

Metaphase. Maximally condensed chromosomes line up

plane of the cell's equator (metaphase plate or mother star). By the end of the phase, the chromatids retain only an apparent connection in the centromere region. Their arms are parallel to each other with a clearly visible gap between them. Cytogeneticists use specially prepared preparations of metaphase chromosomes to study the karyotype.

Anaphase. The shortest phase of mitosis. Chromosomes become like hairpins. Daughter (sister) chromatids, now independent chromosomes, with their centromeric regions oriented toward one of the poles and their telomeric (end) regions toward the cell equator, move toward the cell poles. The divergence of chromosomes along microtubules is provided by a motor protein (dynein). Upon completion of the movement, two equivalent sets of chromosomes (daughter stars) are assembled at the poles, intended for the daughter cells.

Telophase. The final phase of mitosis is often divided into early and late telophase. The most important event of early telophase is the reconstruction of the nuclei of future daughter cells. The chromosomes that have reached the cell poles by the end of anaphase come into contact with vesicles, which are derivatives of the membranes of the nuclear membrane disassembled in prophase. In accordance with the presence of two poles in the dividing cell, two polar groups are formed, where daughter nuclei (daughter balls) are formed. Important events of telophase also include decondensation of chromosomes, formation of the nucleolus, and destruction of the division spindle. The result of late telophase is the division of the body of the mother cell (cytotomy, cytokinesis). In animal cells, this occurs by forming a constriction in the equatorial region. In plant cells with their rigid (unyielding) cell walls, the division of the mother cell into two occurs by constructing a partition from the vesicles of the Golgi complex.

3. Mitosis and its phases. The concept of ploidyPhases - see ticket 2.

Plóidentity— the number of identical sets of chromosomes located in the cell nucleus or in the nuclei of cells of a multicellular organism.

There are haploid cells (with a single set of unpaired chromosomes), diploid cells (with paired chromosomes), and polyploid cells.́id (they are also called tri-, tetra-, hexaploid, etc., depending on how many times the haploid set is repeated in the cell nucleus) and aneuploid (when the doubling or loss - nullosomy, monosomy, trisomy or tetrasomy - does not affect the entire genome, but only a limited number of chromosomes).

Polyploidy should not be confused with an increase in the number of nuclei in a cell and an increase in the number of DNA molecules in a chromosome (polythenization of chromosomes).

Endomitosis is characterized by doubling the number of chromosomes inside the nucleus without destruction of the nucleolus and formation of the division spindle. This leads to an increase in the number of chromosomes in the cell, sometimes tens of times compared to the diploid set. This is how polyploid cells arise.

Hepatocytes (liver epithelial cells). 25% of hepatocytes have two nuclei. The cells are characterized by polyploidy: 55-80% of hepatocytes are tetraploid, 5-6% are octaploid, and only 10% are diploid.

Cardiomyocytes (cardiac muscle cells). As a rule, cardiomyocytes have one nucleus. Along with the growth of myocardial mass, the number of diploid cells decreases and the number of polyploid cardiomyocytes increases (Fig. 3-5). Polyploidy can reach 64n.

Meiosis

The biological role of meiosis:

Doubling of the number of chromosomes in each generation is prevented, since during the formation of sex cells by meiosis, a reduction in the number of chromosomes occurs.

It is the main stage of gametogenesis, as it leads to the formation of haploid cells (gametes).

Meiosis is a process by which cells with a haploid set are formed.

chromosomes. During meiosis, two divisions occur in a row.

interphasethe cell is preparing for division, doubling the DNA.

prophase Iconjugation of homologous chromosomes occurs. Between them

crossing over occurs between chromatids, which leads to recombination.

metaphase Ibivalents line up at the cell equator. In anaphase I

independent segregation of homologous chromosomes to the poles occurs

(Mendel's third law). In telophase I of meiosis, haploid nuclei are formed

cytokenesis occurs. In the interphase between two divisions of meiosis, chromosome doubling does not occur, since they are already double. The second division of meiosis is no different from mitosis. As in mitosis, in anaphase II of meiosis, single sister chromatids diverge to the poles of the cell.

During meiosis the following events occur:

Genetic recombination by crossing over between homologous chromosomes

Reduction in the number of chromosomes

Decrease in DNA content

Reduction in ploidy of cell descendants

Significant RNA synthesis

The first division of meiosis is reductional.Prophase I (2n4c)- the longest and most complex phase. Several stages occur sequentially:

Leptotena(2n4c).Chromatin is condensed, each chromosome consists of two chromatids connected by a centromere

Zygotene(2n4c).The stage of merging threads. Homologous chromosomes begin to attract each other with similar regions and conjugate. The contact allows the chromosomes to exchange genetic material (crossing over). Two adjacent pairs of chromosomes form a bivalent. Pachytene (2n4c). The chromosomes thicken due to spiralization.

Individual sections of conjugated chromosomes cross each other and form chiasmata. Crossing over occurs here.

Diplotene(2n4c). The bivalent composition clearly distinguishes 4

chromatids (tetrad). In the chromatids, areas of unwinding appear, where

RNA is synthesized.

Diakinesis(2n4c). Chromosome shortening and splitting of chromosome pairs continue. Chiasmata move to the ends of chromosome pairs. The nuclear membrane is destroyed, the nucleolus disappears, and the mitotic spindle appears.

Metaphase I.Chromosomes are distributed randomly on one side or the other of the mitotic spindle equator (Mendel's second law - genetic differences between individuals) Anaphase I. Whole chromosomes move to the poles

Telophase I.Nuclei with 23 doubled chromosomes are formed, cytokinesis occurs, and daughter cells are formed.

InterphaseII(1n2c )is a break between the first and second meiotic divisions, the duration of which varies among organisms - in some cases both daughter cells immediately enter the second division, and sometimes the second division begins several months or years later. But since the chromosomes are dichromatid, no DNA replication occurs during interphase 2.

The second division of meiosis is equational.- proceeds in the same way as mitosis (but much faster) Daughter cells receive a haploid set of chromosomes (22 autosomes and 1 sex chromosome)

Prophase 2 (1n2c)

Metaphase 2 (1n2c)

Anaphase 2 (2n2c)

Telophase 2 (1n1c in each cell)

Through meiosis, mature sex cells receive a haploid (n) number of chromosomes, and during fertilization, the diploid (2n) number characteristic of the species is restored. During meiosis, homologous chromosomes enter different sex cells, and during fertilization, the pairing of homologous chromosomes is restored.

Meiosis ensures the transfer of genetic information from organism to organism during sexual reproduction, since upon fertilization the resulting zygote contains the genetic information of both parents.

Meiosis creates the possibility for the emergence of new combinations of genes (combinatorial variability), since during meiosis, genetically different gametes are formed. As a result:

Independent divergencechromosomes duringmeiosis(Anaphase I);

Recombinationsgenes as a resultcrossing over(In prophase I, during conjugation, in some places homologous chromosomes are tightly connected, forming chiasmata. In them, crossing over occurs—the exchange of sections between homologous chromosomes, i.e., the exchange of genetic material)

Renewing cell populations. Concept, examplesThe renewing population is characterized by multiple mitoses

rapid cell death. The number of newly formed cells slightly exceeds the cell losses.

Examples: epidermis, intestinal epithelium, cells of internal tissues.

Among the cells of this population there are two types: highly differentiated and undifferentiated (stem or cambial cells). Highly differentiated cells do not live long (hours, days, months), are incapable of division, and constantly die. For example, cells of the superficial layer of the epidermis, blood cells, and intestinal mucosa cells.

Undifferentiated (stem) cells of this population constantly divide, differentiate and replace dead ones. Thus, epidermal stem cells are located in the lowest (Malpighian) layer; intestinal mucosal stem cells are in the deep sections of intestinal crypts, and blood stem cells are in the red bone marrow.

Thus, the life cycle of cells of a stable population and differentiated cells of a renewing population is equal to G0; there is no mitotic cycle in their life cycle.

The life cycle of stem cells in a renewing population consists of preparation for division

division, i.e. equal to the MC (the G0 period in this case can be neglected, since the cells are functionally inactive,

(are in a state of rest). Malignant tumor cells also have such a life cycle, since they do not differentiate into normal cells, but divide again and again.

The life cycle of cells of a growing population consists of G0+(G1+S+G2+M)

Chemical composition, organization of the cell membrane

(plasmolemma). Functions of the plasmalemma

The plasma membrane contains lipids, cholesterol, proteins and carbohydrates.

Lipids(phospholipids, sphingolipids, glycolipids) make up to

45% of the membrane mass.

Phospholipids consist of a polar (hydrophilic) part (head) and an apolar (hydrophobic) double hydrocarbon tail. In the aqueous phase, phospholipid molecules automatically aggregate tail to tail, forming the framework of the biological membrane in the form of a bilayer.

Sphingolipids contain a long-chain base (sphingosine); sphingolipids are found in significant quantities in the myelin sheaths of nerve fibers, layers of the modified plasma membrane of Schwann cells and oligodendrogliocytes of the central nervous system.

Glycolipids are oligosaccharide-containing lipid molecules present in the outer part of the bilayer, with their sugar residues oriented toward the cell surface. They constitute 5% of the lipid molecules of the outer monolayer.

Cholesterolnot only a component of biological membranes, cholesterol is also used to synthesize steroid hormones - sex hormones, glucocorticoids, mineralocorticoids.

Squirrels- 50% of the membrane mass. Plasmalemma proteins are divided into integral and peripheral.

Integral membrane proteins are firmly embedded in the lipid bilayer. Examples include ion channel proteins and receptor proteins.

Peripheral membrane proteins (fibrillar and globular) - on one of the surfaces of the cell membrane (outer or inner). Associated with integral membrane proteins.

Examples: cytoskeleton-associated proteins, second messenger system proteins.

Functions:

transmembrane transport of substances;

endocytosis - the absorption of water, substances, particles, microorganisms by a cell;

exocytosis - secretion, intracellular secretory vesicles merge with the plasma membrane, and their contents leave the cell.

intercellular information interactions

receptor function of the membrane - is carried out due to the work of peripheral membrane proteins

maintaining cell volume

Nucleus. Structural components of the nucleus (membrane, chromatin, nucleolus,nucleoplasm)

The nucleus is the largest organelle of a eukaryotic cell, with a diameter of 3 to 10 µm. The nucleus can be of various shapes (e.g., round, oval, rod-shaped, bean-shaped, segmented). As a rule, the cell has one nucleus, but there are binuclear (liver cells) and multinuclear osteoclast cells. Mammalian erythrocytes have lost their nucleus during evolution. The nucleus consists of chromatin, nucleolus, and nucleoplasm, surrounded by a nuclear membrane.

Nucleolus— a round body with a diameter of 1-5 μm. It is not an independent organelle; it is a compact structure in the nucleus of interphase cells containing DNA loops of chromosomes 13, 14, 15, 21, and 22. The dense fibrillar component (pars fibrosa) consists of transcriptionally active DNA regions. The granular component (pars granulosa) contains mature precursors of ribosomal subunits (SU). The main functions of the nucleolus are rRNA synthesis (transcription

rRNA processing) and the formation of ribosome SE.

Nuclear envelope

The nuclear envelope consists of the inner and outer nuclear membranes and the nuclear lamina.

•On the surface of the outer nuclear membrane are ribosomes, where proteins are synthesized that enter the perinuclear cistern. The perinuclear cistern is localized between the outer and inner membranes, 20-40 nm wide. Nuclear pores are located at the fusion sites of the two membranes.

The inner nuclear membrane is externally bordered by the perinuclear cistern and internally separated from the contents of the nucleus by the nuclear lamina. • The nuclear lamina, 80–300 nm thick, contains intermediate filament proteins—lamins A, B, and C—and is involved in organizing the nuclear membrane and perinuclear chromatin.

• The nuclear pore complex is formed by 8 protein granules, composed of approximately 100 different proteins, which control nuclear import (transcription factors) and export (RNA)

Nucleolasmaenclosed in a nuclear membrane, consists of a nuclear matrix (ribonucleoprotein network) and nuclear particles (associates of different molecules - ATPase, GTPase, NAD pyrophosphatase, DNA and RNA polymerase, transcription factors, nuclear receptors).

ChromatinThe term "chromatin" refers to the complex of nuclear double-stranded DNA

proteins (histones, non-histone proteins). Chromatin is represented by chromatin fibers with a diameter of 11 nm, consisting of spherical structural units - nucleosomes. Histones (H2A, H2B, H3 and H4) in the nucleosomes contain a large number of positively charged amino acids arginine and lysine, which

increases	affinity	histones to
negative	charged	DNA..
A distinction is made between hetero- and euchromatin.
•	Heterochromatin			—
	transcriptionally		inactive,
	condensed-	ny	chromatin
	interphase nucleus.	It is located
	mainly on the periphery
	nuclei and around the nucleoli, is
	10% of total chromatin.
	Typical			example
	heterochromatin - Barr body
•	Euchromatin	—	less
	condensed
	(dispersed)		Part

Golgi complex: structure, functions

The Golgi apparatus is a single-membrane organelle formed by a stack of 3-10 flattened and slightly curved cisterns in which substances synthesized on the membranes of the ER accumulate. The cisterns of the Golgi complex form three main compartments: the cis-compartment, the intermediate compartment, and the trans-compartment.

Substances are delivered to the Golgi complex in membrane vesicles that are pinched off from the endoplasmic reticulum and attached to the Golgi cisterns. Here, these substances undergo various biochemical transformations and are then repacked into membrane vesicles, and most of them are transported to the cytoplasmic membrane. The membrane of the vesicles fuses with the cytoplasmic membrane,

the contents are removed from the cell by exocytosis.

The Golgi complex of plant cells synthesizes cell wall (membrane) polysaccharides.

Another important function of the Golgi complex is the formation of lysosomes.

In general, the Golgi complex is involved in segregation - this is the division, separation of certain parts from the main mass, and the accumulation of products synthesized in the ER, in their chemical rearrangements, maturation.

The secretory function of the Golgi complex is that the exported protein synthesized on the ribosomes, separated and accumulated inside the cisterns of the ER, is transported to the vacuoles of the lamellar apparatus.

The Golgi complex can increase sharply in size in cells that actively perform a secretory function, usually accompanied by the development of the EPS, and in the case of protein synthesis, the nucleolus.

Sarcoplasmic reticulum. Structure, meaning

The diagram of skeletal muscle is shown below. The T-tubules extend deep into the center of the cell between the two terminal cisterns of the sarcoplasmic reticulum.

Sarcoplasmatíchesky retícoolum(SR) is a modified smooth ER of muscle cells.

The main function of the SR is storageionscalcium(Ca2+). The calcium level in the cell is maintained relatively constant, and

The concentration of calcium inside cells is maintained at 100,000 times less than outside cells.

The sarcoplasmic reticulum contains numerous small vesicles (caveolae) under the sarcolemma. Ca-ATPase constantly pumps Ca from the cytoplasm of SMC into the cisterns of the sarcoplasmic reticulum. Through the Ca channels of calcium depots, Ca ions enter the cytoplasm of SMC. Activation of Ca channels occurs with a change in membrane potential and with the help of ryanodine and inositol triphosphate receptors.

Smooth endoplasmic reticulum, structural organization, functions

The EPS is a single-membrane organelle, which is a collection of membrane vacuoles, tubes and flat sacs (cisterns), distributed in one way or another in the cytoplasm.

Smooth (agranular) EPS- a single-membrane organelle, represented by a system of anastomosing membrane channels, vesicles and tubes.

Functions: Hydroxylation (or microsomal oxidation) enzymes are built into the membranes of smooth ER.

- synthesis of lipids and steroid hormones: in steroid-producing cells (adrenal cortex, sex glands), the smooth ER serves for the metabolism of steroids and the formation (with the participation of mitochondria) of the final forms of steroid hormones.

- detoxification of cellular metabolism products and substances coming from outside (ethanol, barbiturates) by means of hepatocyte oxidases. These substances are converted into water-soluble compounds, which facilitates their elimination from the body.

- deposition of calcium ions. The cisterns of the hepatic endoplasmic reticulum of many cells are specialized for the accumulation of calcium in them by constantly pumping calcium out of the cytoplasm. Similar depots exist in the skeletal

cardiac muscles, neurons, chromaffin cells, oocytes, endocrine cells, etc. Various signals influence cell functions

by changing the concentration of the intracellular mediator, calcium, in itosol.

Inside the cisterns are Ca-binding proteins. In the membrane of the cisterns - calcium depots are built Ca-pumps (Ca-ATPase), constantly pumping calcium into the cisterns, and Ca-channels, through which Ca is released from the depot when a signal is received.

Granular endoplasmic reticulum. Structural organization, functions

It is a network of channels, tubes, closed cavities that are formedmembrane. Rough endoplasmic reticulum - contains on its surfaceribosomes, i.e. protein synthesis occurs on it.

Functions.

synthesis of proteins intended for removal from the cell ("for export");

separation (segregation) of the synthesized product from the hyaloplasm, that is, the removal of the metabolic product from the liquid part of the cytoplasm.

condensation (transition of a substance from a gaseous state to a liquid state) and modification (change in the structure of their radicals and structure aimed at improving functional properties, when

with the help of chemical or enzymatic reactions) of synthesized protein;

transport of synthesized products into the cisterns of the lamellar complex (membrane organelles of the eukaryotic cell) or directly from the cell;

synthesis of bilipid (with a double layer of lipids) membranes.

Genesis, structure and functions of mitochondria. Participation in apoptosisMitochondria -double-membrane organelles of cylindrical shape

length up to 7 microns.

The mitochondrion is bounded by two membranes - a smooth outer membrane and a folded inner membrane, which has a very large surface area. The folds of the inner membrane penetrate deeply into the mitochondrial matrix, forming transverse partitions - cristae. The space between the outer and

The inner membranes are usually called the intermembrane space.

The mitochondrial membranes contain integral membrane proteins. The outer membrane includes porins, which form pores and make the membranes permeable to substances with a molecular weight of up to 10 kDa. The inner mitochondrial membrane is impermeable to most molecules; the exception is O2, SO2, N20. The inner mitochondrial membrane is characterized by an unusually high protein content (75%). These include transport proteins, enzymes, components of the respiratory chain, and ATP synthase. In addition, it contains the unusual phospholipid cardiolipin. The matrix is also enriched in proteins, especially enzymes of the citrate cycle.

Functions of mitochondria:

oxidation in the Krebs cycle

electron transport

chemiosmotic coupling

ADP phosphorylation

coupling of oxidation and phosphorylation

control of intracellular calcium concentration

protein synthesis

heat generation

apoptosis. Mitochondria play an important role in regulated cell death - apoptosis, releasing factors into the cytosol that increase the likelihood of cell death. One of them is cytochrome C - a protein that transfers electrons between protein complexes in the inner membrane of mitochondria. When released from mitochondria, cytochrome C is included in the apoptosome, which activates caspases (representatives of the killer protease family).

13. Lysosomes: formation; lysosomal proteins, functionsLysosomes -single-membrane structures formed by fusion

perinuclear endosomes containing lysosomal hydrolases and lysosomal membrane proteins, with vesicles subject to degradation (peripheral endosome, phagosome or autophagocytic vacuole).

perinuclear endosomesare formed by the fusion of vesicles containing lysosomal hydrolases after their synthesis in the granular EPs and processing in the Golgi complex, and vesicles in whose membrane specific lysosomal membrane proteins are embedded.

peripheral endosomesare formed as a result of endocytosis.

multivesicular bodiesare formed by the fusion of perinuclear and peripheral endosomes.

phagolysosomeformed by the fusion of a perinuclear endosome and a phagosome.

autophagolysosomeis formed by the fusion of a perinuclear endosome and an autophagocytic vacuole containing endogenous molecules and organelles to be degraded.

residual bodies- lysosomes of any type containing undigested material (lipofuscin, hemosiderin).

Function:

Catalysis of hydrolytic (in an aqueous environment) breakdown of nucleic acids, proteins, fats, polysaccharides and mucopolysaccharides, and other chemical compounds at low pH values. In cytobiological terms, it is the intracellular digestion of substances and structures.

Peroxisomes -single-membrane organelles, vesicles with an electron-dense core. The membrane of the organelle contains specific proteins - peroxins, and the matrix contains more than 40 enzymes that catalyze anabolic (biosynthesis of bile acids, H2O3, dependent respiration, degradation of xenobiotics) processes.

Origin:are formed by the fusion of perinuclear endosomes (formed by the fusion of vesicles containing lysosomal hydrolases synthesized in the granular ER and processed in the Golgi complex, and vesicles in whose membrane specific lysosomal proteins are embedded) with vesicles subject to degradation: a peripheral endosome (formed as a result of endocytosis), a phagosome (formed as a result of phagocytosis), or an autophagocytic vacuole (contains endogenous molecules and organelles subject to degradation).

Lysosomal proteins- these are enzymes: ribonucleases, deoxyribonucleases, cathepsins B and L (proteases), sulfatases, B-glucuronidases, B-galactosidases, glycosidases, lipases, esterases, phosphatases

others. They are most active in an acidic environment, to maintain which a proton pump is built into the lysosome membrane.

Cytoskeleton. Structure and functions of microtubules, intermediate filaments, microfilaments

Cytoskeleton(intracellular cytoplasmic skeleton)— component part

cytoplasm, its mechanical framework. The cytoskeleton is a complex

three-dimensional network of microfilaments

and microtubules.

Microtubules

Microtubules are hollow cylinders about 25 nm in diameter, the walls of which are composed of 13 protofilaments (threads), each of which is a linear polymer of the dimer of the protein tubulin. The dimer consists of two subunits - the alpha and beta forms of tubulin. Microtubules grow from one

end by way additions

tubulin subunits. Growth can only begin in the presence of a matrix.

Functions:Microtubules take part in various intracellular processes; they regulate the separation of chromatids or chromosomes (this is accomplished by sliding microtubules), and they participate in the movement of various cellular organelles (example: in the movement of Golgi vesicles to the forming cell plate).

Microfilaments

About 7 nm in diameter, microfilaments are two chains of actin monomers twisted into a helix. They are mainly concentrated near the outer membrane of the cell. In complex with actin-binding proteins, actin filaments form various intracellular structures (thin filaments of myofibrils, cortical perimembrane skeleton, encircling desmosomes, microvilli, stereocilia). Like microtubules, microfilaments are polar: the addition of new G-actin molecules occurs at the (+) end, and depolymerization (disassembly of the polymer) occurs at the (-) end of the microfilament.

Functions: They are responsible for the shape of the cell and are capable of forming protrusions on the cell surface (pseudopodia and microvilli). They also participate in intercellular interactions (formation of adhesive contacts), signal transmission and, together with myosin, in muscle contraction. Vesicular transport can be carried out along microfilaments with the help of cytoplasmic myosins.

Intermediate filaments

Intermediate filaments resemble a rope, about 8-10 nm thick, consisting of fibrillar monomers. They are localized mainly in the perinuclear zone and in bundles of fibrils extending to the periphery of cells and

located under

plasma membrane. They are found in all types of animal cells, but are especially abundant in those exposed to

mechanical effects: epidermal cells, nerve processes, smooth and striated muscle cells. Not found in plant cells.

Intermediate filaments contain 4 types of proteins:

First type- keratins, acidic and neutral, found in epithelial cells; they form heteropolymers of these two subtypes.

Second typeproteins include three types of proteins: vimentin,

characteristic For cells

mesenchymal origin,

part of the cytoskeleton of connective tissue cells, endothelium, cells

blood. Desmin - characteristic For muscular cells, How smooth, So And

striated. Glial fibrillar protein. Peripherin - is part of peripheral and central neurons.

Third type- neurofilament proteins are found in the axons of nerve cells.

The fourth type- proteins of the nuclear lamina.

Functions:They serve as a true support system in cells subjected to significant physical stress. They create an intracellular component

cytoplasm, coordinate the connections between the extracellular substance, cytoplasm and nucleus.

Structure and role of cilia. Examples

Cilium is a cell outgrowth 5-10 µm long and 0.2 µm wide, containing an axoneme. Cilia are present in the epithelial cells of the airways and genital tracts, move mucus with foreign particles and dead cell debris, and create a fluid flow near the cell surface.

The entire length of the cilium or flagellum is made up of microtubules - hollow protein cylinders with an external diameter of 25 nm.

Functions: framework, provide elasticity of the cell, maintain orderly arrangement

In humans, bronchial epithelial cells have many cilia. They force the mucus layer with dust particles and dead cell debris to constantly move upward. With the help of the cilia of the oviduct cells, the egg cells move along it. Flagella differ from cilia only in length. Thus, mammalian spermatozoa (Fig. 75) have one flagellum up to 100 μm long. Usually, cilia are shorter than flagella by more than 10 times. Thousands of cilia of one cell move in a coordinated manner, forming traveling waves on the surface of the plasma membrane (Fig. 29). Each cilium works like a whip: a forward blow, during which the cilium straightens out completely and transmits maximum force to the surrounding fluid, pushing it, and then, bending to reduce the resistance of the environment, it returns to its original position

16. Microvilli. Structure, functions. Examples of localizationA bundle of parallel microfilaments forms the core

microvilli 1 µm high. Each enterocyte (the epithelial cell of the small intestine that carries out absorption) contains more than 1000 microvilli, which increase the area of the apical surface of the cell by 20 times.

About 30 parallel microfilaments form the core of the microvilli. The (+)-ends of two intertwined F-actin filaments of the microfilaments are directed toward the apex of the microvilli. The microfilaments cross-link the actin-binding proteins fimbrin and villin. The microfilaments are attached to the inner surface of the plasma membrane by myosin I. At the base of the microvilli, the (-)-ends of the actin filaments are anchored in the terminal network - a peri-membrane plexus of microfilaments cross-linked by fodrin.

Example: microvilli of the small intestine, which carry out absorption.

17. Classification of intercellular contacts. Examples of localization of various contacts

(briefly) ADHESION: determine the strength of the bond. These include:

1) desmosome (point desmosome): the plates are formed by the protein desmoplakin; between them are fibers - desmocollin and desmoglein ???

2) hemidesmosome (with its help cells are attached to the basement membrane)

3) encircling desmosome (intermediate contact) - with the help of actin protein; along the entire perimeter of the cell membrane.

CLOSING, or LOCKING

tight contact (no charge; common membrane)

septate contact

CONDUCTING CONTACT - ensures the transport of NMS, ions and mediators.

gap junction - a pore surrounded by six subunits of the protein connectin; consists of two parts (there is a connexon)

chemical synapse.

(in detail) Adhesion is the ability of cells to selectively attach to each other or to components of the extracellular matrix. Adhesion is necessary to maintain tissue structure. There are several groups of adhesion molecules (special glycoproteins that implement adhesion processes):

cadherins (for example, E-adherins bind cells of embryonic tissues, P-cadherin binds cells of the placenta and epidermis).

nerve cell adhesion molecules.

macromolecules of the extracellular matrix.

Adhesion molecules are specific to each tissue type.

Intercellular contacts are specialized cellular structures that hold cells together to form tissues, create permeability barriers, and serve for intercellular communication. They are subdivided into adhesive, closing (tight), and communication (conductive).

ADHESION CONTACT:

intermediate contact: the membranes of adjacent cells are separated by a gap 10-20 nm wide, filled with amorphous or fibrillar material. The electron-dense plate on the cytoplasmic side of the cell membrane within the contact contains the proteins plakoglobin,

vinculin, alpha-actinin and radixin. The ends of actin-containing microfilaments are woven into the plate. Transmembrane adhesion proteins from the cadherin family participate in the formation of contact. Function: fastening membranes, stabilizing the cytoskeleton, uniting cells with their contents into a single rigid system.

Example: intestinal border epithelium (girdling desmosome), secretory epithelium, intercalated discs in the myocardium, ependymal cells of the central nervous system.

Desmosomes: they bind cells of the same type (keratinocytes, cardiomyocytes) and different types (tactile epithelial cell-keratinocyte). Desmosome consists of two components: cytoplasmic plate formed by desmoplakin protein and desmogleia. The sections of cell membranes that make up desmosomes are separated by a 20-30 nm thick desmogleia layer. Function: desmosomes maintain the structural integrity of tissue by binding cells together. They give tissue elasticity.

hemidesmosome: provides cell attachment to the basement membrane (e.g. keratinocytes of the basal layer of the epidermis, myoepithelial cells). Contains a cytoplasmic plate with

with intermediate filaments woven into it.

CLOSING

CONTACT

1) tight contact

forms a regulated permeability barrier in the cell layers, separating environments with different chemical compositions. They look like ribbons consisting of proteins: integral, plaque proteins, contact, cytoplasmic.

Example of localization: intestinal border epithelium, capillary endothelium, alveolar cells,

renal tubular epithelial cells.

septate contact

COMMUNICATION CONTACTS (CONDUCTIVE)

gap junction: provides ionic and metabolic coupling of cells. The gap is 2-4 nm wide. Connexon is a transmembrane protein of cylindrical configuration, consisting of 6 connexin subunits. Two connexons of adjacent cells connect in the intermembrane space and form a channel between the cells. The channel with a diameter of 1.5 nm passes ions and molecules up to 1.5 kD, NMS, regulating cell growth and development. Gap junctions provide excitation propagation.

18. Desmosome and hemidesmosome. Structure, meaning, examples of localization (Fig. on the right)

DesmosomeThe plasma membranes of cells are separated by a gap of 20-30 nm, in which the extramembrane parts of the Ca-binding proteins desmoglein and desmocollin are located.

The cytoplasmic plate with intermediate filaments interwoven into it is adjacent to the inner surface of the plasma membrane. This plate contains desmoplakins, plakoglobin

part of the desmoglein molecule.

Two components:

cytoplasmic plate (with intermediate filaments woven into it)

Hemidesmosome.Provides attachment of the cell to the basement membrane. Like the desmosome, it contains

cytoplasmic plate with intermediate filaments interwoven into it. For example, attachment

keratinocytes of the basal layer of the epidermis.

Gap junction. Structure, function, localization examples

Provides ionic and metabolic coupling of cells.

Slot width 2-4nm.

Connexon is a transmembrane protein of cylindrical configuration, consisting of 6 connexin subunits. Two connexons of neighboring cells connect in the intermembrane space and form a channel between the cells. The channel with a diameter of 1.5 nm passes ions and molecules up to 1.5 kD, NMS, regulating cell growth and development. Gap junctions provide excitation propagation.

The drawing is above and to the right.

Six protein subunits in the plasma membrane form a connexon. When connexons of adjacent plasma membranes are combined, a channel with a diameter of 1.5 nm is formed.

Function: conducting NMS, regulating cell growth and development. Ensuring the spread of excitation - the transfer of ions between myocardial muscle cells and between SMCs.

Tight junctions. Structure, localization, functions

The drawing was above.

Tight junction (or closing junction) forms an adjustable permeability barrier in cell layers, separating environments with different chemical compositions (for example, internal and external). Examples of localization: intestinal border epithelium, capillary endothelium, alveolocytes, epithelial cells of the renal tubules. Tight junctions look like

tapes consisting of chains of rounded zones (plaques) 10 nm in size and with a distance between the centers of adjacent plaques of approximately 18 nm. The proteins that make up the multimolecular tight junction complex can be divided into three groups: integral, plaque proteins, and cytoplasmic proteins.

Pinocytosis: characteristics, examples

Pinocytosis- the process of absorption of liquid and dissolved substances with the formation of small bubbles.

Pinocytosis is considered a non-specific method of expulsion of extracellular fluids and the substances contained therein, when some area of the cell membrane invaginates, forming a pit and then a vesicle containing intercellular fluid.

The bubbles that form are often very small.

In this case, we speak of micropinocytosis and the vesicles are called micropinocytic. Pinocytosis is characteristic of many cells, both animal and plant.

Examples: capture by epithelial cells of the intestine and renal tubules, vascular endothelium.

Axovasal synapses. Localization, structure, functionsAxovasal synapses are the endings of axons of neurosecretory

neurons on the capillaries.

Localization: in the hypothalamic-pituitary system.

Function: secretion of ADH and oxytocin into the capillaries of the posterior pituitary gland, secretion of releasing hormones and capillaries of the median eminence.

They are formed by neurons of the hypothalamus.

I couldn't find the structure, it's not in the textbook or on the Internet.

Cholinergic synapse, structure

Cholinergic synapses are synapses in which the transmission of excitation is carried out by means of acetylcholine.

When ACh binds to the nicotinic cholinergic receptor (n-cholinergic receptor), an ion channel opens within the latter, through the pore of which sodium and potassium ions pass, leading to depolarization of the postsynaptic membrane (postsynaptic potential).

The cholinergic synapse includes 5 protein subunits (α, α, β, γ, δ) surrounding the ion (sodium) channel and passing through the entire thickness of the lipid membrane. Two acetylcholine molecules interact with two α-subunits, which leads to the opening of the ion channel and depolarization of the postsynaptic membrane.

Cholinergic receptors of different localizations have different sensitivity to pharmacological substances. This is the basis

the allocation of the so-called
	muscarinic sensitive	cholinergic receptors	—m-
		cholinergic receptors(muscarine — alkaloid from a number of poisonous mushrooms	,

		for example fly agarics) and
	nicotine-sensitive	cholinergic receptors	— n-

cholinergic receptors (nicotine is an alkaloid from tobacco leaves)

Structure - neuromuscular synapse.

Neuromuscular synapse. Structure, functioning, neurotransmitter

At the neuromuscular synapse, a distinction is made between the presynaptic and postsynaptic regions, separated by a synaptic cleft.

The presynaptic part contains synaptic vesicles with neurotransmitter (each vesicle contains a quantum of neurotransmitter), cytoskeleton elements and mitochondria. Potential-dependent Ca-channels are built into the presynaptic membrane.

The synaptic cleft is a space between membranes 20-35 nm wide. Neurotransmitter molecules are released from synaptic vesicles into the synaptic cleft and reach the postsynaptic membrane by diffusion. The synaptic cleft contains enzymes that break down neurotransmitter molecules (ACh esterase, hydrolyzing ACh), and the presynaptic membrane contains carriers that carry amino acid neurotransmitters and biogenic amines (glutamate, aspartate, norepinephrine) to the presynaptic terminal.

The postsynaptic region contains many large mitochondria with well-developed cristae and a large number of ribosomes. The postsynaptic membrane contains receptors for the neurotransmitter acetylcholine.

Structure of spermatozoon

human ejaculate

contains 3*108spermatozoa. In the female reproductive tract, they retain the ability to fertilize for a maximum of two days. About 200 of them reach the funnel of the fallopian tube.

Acrosome is formed

during spermatogenesis as

productcomplex

Golgi and can be considered as an analogue

lysosomes. The acrosome is located in the head of the sperm, in front of

nuclei and just below the plasma membrane.

In frontmembrane

The acrosome (outer) is in contact with the sperm cell membrane, and the back (inner membrane) is in contact with the nuclear membrane.

Head of spermThe human sperm head is ellipsoidal in shape, compressed laterally, with a small pit on one side, which is why people sometimes talk about the "spoon-shaped" shape of the human sperm head. The nucleus carries a single set of chromosomes. The centrosome is the center of microtubule organization, which ensures the movement of the sperm tail, and is also presumably involved in the convergence of the zygote nuclei and the first cell division of the zygote.

The middle part is separated from the head by a small narrowing, the "neck". Behind the middle part is the tail. The cytoskeleton of the flagellum, which consists of

microtubules. In the middle part around the cytoskeleton of the flagellum there is a mitochondrion consisting of 28 mitochondria. The mitochondrion has a spiral shape and seems to wrap around the cytoskeleton of the flagellum. The mitochondrion performs the function of synthesizing ATP and thus ensures the movement of the flagellum.

Tail,or flagellum, is located behind the middle part. It is thinner than the middle part and significantly longer than it. The tail is the organ of movement of the sperm. Its structure is typical for the cellular flagella of eukaryotes.

Fertilization. Main events and their characteristics

During fertilization, male and female haploid gametes interact; their nuclei (pronuclei) merge, chromosomes unite, and a diploid cell of a new organism, a zygote, emerges. The beginning of fertilization is the moment of fusion of the membranes of the sperm and egg cell, the end of fertilization is the moment of unification of the material of the male and female pronuclei.

Acrosome reaction --- Fusion of gametes --- Activation of the egg cell --- Fusion of pronuclei --- Cortical reaction --- Formation of the fertilization membrane.

During the fusion of the plasma membranes of gametes and the unification of nuclear genomes, significant changes in the intracellular ionic composition occur, leading to a decrease in the volume of the zygote, depolarization of its plasma membrane, and the development of a cortical reaction. A direct consequence of the decrease in volume is the formation of the perivitelline space. The perivitelline space contains both polar bodies and has a characteristic ionic composition (homeostatic environment for the conceptus), creating an additional obstacle to the penetration of other spermatozoa to the zygote. Depolarization of the plasma membrane prevents the penetration of spermatozoa into the zygote.

Pronuclei fusion: During the first 12 hours after the sperm penetrates the egg, the nuclei of the fused gametes undergo a restructuring. The nuclei swell and nucleoli appear. The pronuclei migrate to the center of the egg and come closer together. Their nuclear membranes

disappear, and the maternal and paternal chromosomes mix - a synacryon is formed. This process (syngamy) is actually fertilization.

The fertilized egg, as a result of divisions, forms an embryo (conceptus), consisting of blastomeres. Later (before gastrulation), the embryo goes through the stages of morula and blastocyst.

Interaction of sperm with egg membranes during fertilization

In order for fertilization to occur, the sperm must sequentially overcome three barriers:

Radiant Crown

easily penetrates through the corona radiata between the loosely located follicular cells and reaches the transparent membrane.

Transparent shell

When a sperm interacts with the zona pellucida, the following occurs: binding of the sperm to its receptor --- acrosomal

reaction --- cleavage of transparent membrane components by enzymes

acrosomes --- penetration of the sperm to the plasma membrane of the egg.

plasma membrane

Acrosome reaction- exocytosis of the acrosome contents for local destruction of the zona pellucida and overcoming of this barrier by the spermatozoon. The acrosome reaction is initiated by the interaction of oligosaccharides of the glycoprotein ZP3 of the zona pellucida with its lectin-like receptor (the protein bendin) in the membrane of the sperm head. During the acrosome reaction, the outer membrane of the acrosome and the cell membrane of the sperm merge and form small vesicles that separate from the head, hyaluronidase, protease and other enzymes that break down the molecules of the zona pellucida are released.

Fusion of gametes has occurred, the nucleus of the spermatozoon in the cytoplasm of the cell.

Acrosome reaction, its importance. Events occurring during the acrosome reaction

Before the sperm meets the egg, it spends several hours in the female reproductive tract. During this time, it is exposed to the pH of the environment, mucus, progesterone, etc. The final maturation of the sperm occurs - this is the process of capacitation.

In order for fertilization to occur, the sperm must sequentially overcome three barriers: the corona radiata (follicular cells) - easily overcome, the zona pellucida (acrosomal reaction) and the plasma membrane of the egg.

Acrosome is an organelle of the sperm located in the anterior part of its head.

This is an exocytosis of the acrosome contents for local destruction of the zona pellucida and overcoming of this barrier by the spermatozoon. The acrosome reaction is initiated by the interaction of oligosaccharides of the glycoprotein ZP3 of the zona pellucida with its lectin-like receptor (the protein bendin) in the membrane of the sperm head. During the acrosome reaction, the outer membrane of the acrosome and the cell membrane of the sperm fuse and form small vesicles that separate from the head, releasing hyaluronidase, protease and other enzymes that break down the molecules of the zona pellucida.

Fusion of gametes has occurred, the nucleus of the spermatozoon in the cytoplasm of the cell.

The event that prevents polyspermy and occurs several minutes after the sperm penetrates the egg is the cortical reaction.

Fertilization membrane. Formation, structure, meaning

Cortical granules containing enzymes (hydrolases) are located along the periphery of the egg. Immediately after the spermatozoon penetrates the egg, a cortical reaction begins - the release of the contents of these granules, which is caused by an increase in the concentration of Ca in the cytosol. Under the action of cortical granule enzymes, proteolysis of ZP2 and modification of the spermatozoon receptor to ZP3 occur. ZP molecules lose their ability to initiate the acrosome reaction in other spermatozoa.

As a result of the cortical reaction, the transparent membrane (containing ZP proteins) undergoes changes - it is stabilized, and the fertilization membrane is formed. In the stabilized state, the membrane protects the conceptus passing through the fallopian tube. Without the fertilization membrane, zygote cleavage is impossible.

30. Transparent zona pellucida of the oocyte. Formation, structure, significanceAs the egg develops, synthesis and subsequent

secretion of glycoproteins that gradually form the zona pellucida. Mature

The zona pellucida contains a dense network of fine filaments consisting of glycoproteins (mainly ZP proteins). One of them, ZP3, is the main sperm receptor, and ZP2 is a secondary receptor that provides additional binding of gametes. Binding of sperm to ZP glycoproteins is a signal for the acrosome reaction.

Formation: Follicular cells of secondary follicles begin to proliferate, resulting in several layers of cuboidal cells forming around the first-order oocyte. A thick transparent membrane appears between the oocyte and the follicular cells surrounding it.

Meaning: Prevents more than one sperm from entering the egg (called a "polyspermy block"). Holds the cells of the early embryo together. Blastomeres (cells of the embryo at the cleavage stage)

Mammals do not form cellular contacts and are not capable of independently forming a single embryo.

Zygote. Its formation and characteristics

Acrosome reaction --- Fusion of gametes --- Activation of the egg cell --- Fusion of pronuclei --- Cortical reaction --- Formation of the fertilization membrane.

disappear, and the maternal and paternal chromosomes mix - a synacryon is formed. This process (syngamy) is actually fertilization.

The fertilized egg, as a result of divisions, forms an embryo (conceptus), consisting of blastomeres. Later (before gastrulation), the embryo goes through the stages of morula and blastocyst.

The zygote is the first stage of the embryo's life and lasts no more than two days. The zygote begins to divide very quickly and moves along the fallopian tubes until it gets inside the uterus. The zygote is fixed inside the uterus.

Cleavage in the human embryo. Character of cleavage, compaction, morula, blastocyst. Intercellular contacts.

Crushing- mitotic division of diploid cells without increasing their total volume. After the first cleavage division, 2 blastomeres are formed. One of them is darker and larger, the other is smaller and lighter. After the second cleavage division, 4 blastomeres are formed, at this stage the main types of RNA are synthesized. The third cleavage - 8 blastomeres.

The embryo and almost all provisional organs develop from a large blastomere.

(connective tissue of the chorion and fetal part of the placenta, amnion, yolk sac,

allantois). The trophoblast develops from the small blastomere.

In the process of fragmentation, small cells divide faster than large ones. As a result, small cells become surrounded by large ones on the outside. Therefore, the resulting cell mass - morula - consists of two groups of cells. Large cells are located inside. Their collection is called embryoblast. Small cells, called trophoblast, are located on the outside.

Nature of fragmentationdetermined by the number of yolk inclusions; in humans, the yolk is distributed evenly, i.e., the egg is isolecithal. The zygote undergoes holoblastic (divided into 2 blastomeres), then asynchronous and partly uneven cleavage.

Classification of cleavage (By the completeness of zygote division: )

Complete - the zygote divides completely and two separate cells (blastomeres) are formed

Incomplete - the cleavage furrow does not completely separate the daughter cells and individual cells do not form

By the size of the resulting blastomeres:

Uniform - blastomeres are of equal size

Uneven - blastomeres are of different sizes

By time intervals between divisions:

Synchronous - the intervals between divisions of all blastomeres are the same

Asynchronous - the intervals between divisions of all blastomeres are different.

HUMAN - COMPLETE, UNEVEN, ASYNCHRONOUS CRUSHING

Compactization- compaction of the structure of the early embryo due to the convergence of blastomeres. After compaction, blastomeres are connected by gap junctions,

tight contacts are formed between the outer blastomeres.

As a result of cleavage, a morula is formed - a dense (without a cavity) cluster of blastomeres. Morula cells divide homoblastically. After several divisions, the cells of the embryo form a spherical structure resembling a mulberry. Blastomeres, morula cells, secrete serous fluid that fills the interior of this conglomerate and form a cavity in it. The centrally located morula cells form gap junctions, the peripheral ones form tight junctions, forming a barrier for the internal environment of the morula. In this state, blastulas are a primitive organism, similar in shape to a hollow ball attached to the walls of the uterus.

On the 5th day, a cavity filled with liquid, the blastocoel, appears in the embryo. Such an embryo is called a blastocyst.

Formation and structure of the blastocyst

The blastocyst is formed with the appearance of the blastocoel (a fluid-filled cavity) by 4-5 days after fertilization. The blastocoel increases in volume and the conceptus takes the form of a bubble. The transparent membrane becomes thinner and disappears.

blastocysts are distinguished by:

Trophoblast- a single-layer wall of small light cells connected by tight junctions. Trophoblast cells "pump" fluid into the blastocoel. The chorion is subsequently formed from the trophoblast.

Embryoblast, or inner cell mass - a compact mass of small cells protruding into the blastocoel. These cells originate from the central part of the morula and are connected by gap junctions. The embryoblast then forms the embryo proper and some membranes associated with it.

Blastocoel- a cavity filled with liquid

The nature of gastrulation in humans

Gastrulation is a complex process of morphogenetic changes, accompanied by reproduction, growth, directed movement and differentiation of cells, resulting in the formation of germ layers (ectoderm, mesoderm and endoderm) - the sources of tissue and organ rudiments.

Gastrulation in humans occurs in two stages. The first stage occurs by delamination (splitting), and the second by migration.

The first phase occurs on the 7th day, simultaneously with implantation.

During the first stage, two germ layers (ecto- and endoderm, or epiblast and hypoblast)), two provisional organs (amnion and yolk sac) are formed. In addition, immediately before the beginning of the first stage, such a provisional organ as the chorion is formed. The formation of the chorion is the second stage in the formation of the placenta.

The first phase leads to the isolation of the embryonic epiblast and the beginning of the formation of extraembryonic organs.

The second phase begins only a week later (from the 14th to the 17th day). During the second stage, another germ layer is formed - the mesoderm and its derivative - the mesenchyme, a provisional organ - the allantois, and further formation of another provisional organ - the placenta - occurs: tertiary chorionic villi are formed, which subsequently join with the decidua basalis and form the placenta. Axial organs are formed - the chord, neural tube, intestinal tube, mesoderm.

Between these two phases, the formation of extraembryonic organs occurs, which are necessary for the successful development of the embryo.

Hypoblast. Formation, derivatives of the hypoblast

Hypoblast. The formation of the hypoblast (primary endoderm) occurs along the caudal-cronial gradient. The cells of the ventral part of the inner cell mass facing the blastocoel are separated into a thin layer - the hypoblast. The hypoblast cells (small, cubic, light) are evicted from the inner cell mass due to weak adhesive interaction between them. Intensively proliferating hypoblast cells move along the inner

surface of the trophoblast and form the extraembryonic endoderm adjacent to the trophoblast wall of the yolk sac.

Trophoblast. Its formation and functions

The trophoblast is formed by the peripheral cells of the morula

Trophoblast is a single-layer wall of small light cells connected by tight junctions. Trophoblast cells "pump" fluid into the blastocoel. The trophoblast subsequently forms the chorion.

Yolk sac. Formation, wall structure, functions

Yolk sacin humans (umbilical or umbilical vesicle) - a rudimentary formation that has lost its function as a receptacle for nutrients. It is formed on the 11th day of embryogenesis

Sources of development: Lower layers - extraembryonic endoderm (from the hypoblast) and visceral layer of extraembryonic mesoderm. Extraembryonic endoderm, growing to the periphery from the embryonic shield, delimits part of the space inside the trophoblast: first, the primary yolk sac, which adjoins the trophoblast with its wall, quickly reduces, then the secondary yolk sac is formed. Extraembryonic mesoderm covers the outer surface of the yolk.

Functions of the yolk sac:

Up to 7-8 weeks of embryogenesis - hematopoietic.

Formation of primary germ cells - gonoblasts, which migrate into it from the area of the primitive streak.

Formation of primary blood vessels, including umbilical cord vessels

In the 3rd month of intrauterine development, the yolk sac ceases to function as an organ of hematopoiesis and blood circulation, is reduced and remains in the form of a small cystic formation at the base of the umbilical cord.

The wall of the yolk sac is lined with yolk epithelium, a special subtype of intestinal epithelium. The epithelium consists of a single layer of cubic or flat cells of endodermal origin with light cytoplasm and round, intensely staining nuclei. After the formation of the trunk fold, the yolk sac is connected to the midgut cavity by means of the yolk stalk. Later, the yolk sac is found as a narrow tube in the umbilical cord.

Allantois. Development, structure, functions

Allantóis— embryonic respiratory organ of higher vertebrates

The allantois is laid down at 14-15 weeks of embryogenesis, i.e. during the 2nd phase of gastrulation. It is formed as a small finger-like outgrowth of the posterior section of the primary intestine, developing into an amniotic stalk.

Sources of development

Extraembryonic endoderm, derived from intestinal mesoderm (from within)

Extraembryonic mesoderm derived from embryonic mesoderm

(outside)

The allantois completely disappears by the 5th month of intrauterine life.

Functions:

In birds it is a urinary sac (it is believed that in mammals it is also associated with the excretion of metabolic products)

In mammals and humans, it is involved in the formation of blood vessels, the umbilical cord and the placenta (in the wall)

Embryonic respiratory organ in higher vertebrates

Embryogenesis. Formation, structure and significance of the primitive streak

The human primitive streak is formed from the future caudal edge of the embryonic disk. In the center of the primitive streak, the primitive groove is formed, and along the edges - the primary ridges. At the head end of the primitive streak, a thickening appears - Hensen's node, and in it the primary pit. The cells of the primary ectoderm, passing through the primary (Hensen's) node, form a chord. The remaining cells of the primary ectoderm, passing through the primitive streak, migrate in the lateral direction and form the mesoderm and endoderm. The primitive streak can be considered the first axial structure around which the entire embryogenesis is built, since cells participating in the formation of primary germ layers and extraembryonic structures migrate through it.

Embryogenesis: Cleavage. Compaction. Morula. Characteristics of blastomeres

Cleavage is a mitotic division of diploid cells without increasing their total volume. After the first cleavage division, 2 blastomeres are formed. One of them is darker and larger, the other is smaller and lighter. After the second cleavage division, 4 blastomeres are formed; at this stage, the main types of RNA are synthesized. The third cleavage - 8 blastomeres.

The embryo and almost all provisional organs develop from a large blastomere.

(connective tissue of the chorion and fetal part of the placenta, amnion, yolk sac,

allantois). The trophoblast develops from the small blastomere.

HUMAN - COMPLETE, UNEVEN, ASYNCHRONOUS CRUSHING

Compaction is the compaction of the structure of the early embryo due to the convergence of blastomeres. After compaction, the blastomeres are connected by gap junctions, and tight contacts are formed between the outer blastomeres.

Characteristics of blastomeres: from the very first divisions of the zygote, two types of blastomeres are formed - "dark" and "light". The "light", smaller, blastomeres divide faster and are located in one layer around the large "dark" ones, which end up in the middle of the embryo. From the superficial "light" blastomeres, the trophoblast subsequently arises, connecting the embryo with the maternal organism.

providing it with nutrition. The internal, "dark" blastomeres form the embryoblast, from which the body of the embryo and extraembryonic organs (amnion, yolk sac, allantois) are formed.

Germ and extraembryonic layers. Examples of their derivatives

Derivatives of the extraembryonic ectoderm - the trophoblast - participate in the formation of the chorion and amnion.

Derivatives of the embryonic ectoderm: all nervous tissue, outer layers of skin and

derivatives (hair, nails, tooth enamel) and partially the mucous membrane of the oral cavity, sensory organs, anterior and posterior sections of the intestine.

Derivatives of the embryonic endoderm are the organs of the digestive and respiratory systems.

Derivatives of the extraembryonic endoderm are the yolk sac and allantois.

Epiblast cells, which form the mesoderm, migrate through the posterior part of the primitive streak. First, the cells of the future extraembryonic mesoderm migrate, and then the cells for the mesoderm of the embryo. The notochord is formed by mesodermal cells located along the midline of the embryo. They migrate through the head end of the primitive streak in the area of the primary node in the direction of the future head part of the embryo. Bones, cartilage, muscle tissue, some tissues of the genitals, blood and excretory systems are formed from the mesoderm.

The embryonic endoderm originates from the portion of the epiblast located anterior to the primitive streak.

Embryonic and extraembryonic mesoderm. Epiblast cells migrate through the posterior portion of the primitive streak to form the mesoderm. First, the cells of the future extraembryonic mesoderm move, followed by the cells for the mesoderm of the embryo. The notochord is formed by mesodermal cells located along the midline of the embryo. They migrate through the head end of the primitive streak in the region of the primary node toward the future head portion of the embryo.

Extraembryonic ectoderm. From the peripheral areas of the epiblast cells, cells lining the polar trophoblast from the inside are evicted.

The ectoderm of the embryo is formed by cells that do not migrate from the epiblast.

Dorsal (presomitic) mesoderm and somite formation. Somite structure and their derivatives

Presomitic mesoderm. The cells that passed through the primitive streak,

migrate laterally and form a continuous layer with a thickness of

several cells. In close proximity to the neural tube and chord

mesodermal cells form clusters - concentric layers of cells

metameric organization in the form

potential somites, or

somitomeres. Somitomeres

determine the segmentation of the chord,

neural tube, intermediate and

lateral mesoderm (mesoderm

lateral plate).

Somites. As a result of cell proliferation, migration and

Subsequent aggregation of somitomeres forms the dorsal mesoderm - somites. Somite formation occurs from the head to the tail end of the embryo. A new pair of somites is formed approximately every 6.6 hours. In the somite there is a cavity limited by cells connected to each other by tight junctions. In each somite, a sclerotome, dermatome and myotome are distinguished; their cells have their own migration paths and serve as a source for various structures.

Formation of the somite and subsequent eviction of cells from it. Left -

mesodermal cells are concentrated lateral to the neural groove around

small cavity; on the right -

ventral and ventral cells

medial part of the somite,

located laterally

neural tube, begin

migrate in the direction

chords; the totality of these

cells - sclerotomes.

Intermediate and lateral (splanchnic) mesoderm, its derivatives

The mesoderm located lateral to the nephrotome (the lateral mesoderm)

plate) is split into two sheets: dorsal (parietal) and ventral

(visceral). The parietal layer is the somatic mesoderm (from which the

serous membranes). The visceral layer is the splanchnotic mesoderm (from which

the heart, adrenal cortex, gonadal stroma, connective tissue and

smooth muscle tissue of internal organs and blood vessels).

Between these two layers, a secondary body cavity is formed - the coelom, which extends from the future cervical region to the posterior end of the body. At later stages of development, the somatic mesoderm forms folds that divide the coelom into separate cavities. In mammals, the coelom is subdivided into the pleural, pericardial, and peritoneal cavities.

Derivatives of the embryonic and extraembryonic mesoderm

Thus, the derivatives are:

Chord

Somites

Nephrogonotomes (rudiments of the genitourinary tract)

Splanchnotome (forms the epithelium lining the internal cavities of the body)

Mesenchyme (forms smooth muscle tissue, tissues of the internal environment, large vessels)

Derivatives of the embryonic and extraembryonic endoderm

Derivatives of the embryonic endoderm are the organs of the digestive and respiratory systems.

Derivatives of the extraembryonic endoderm are the yolk sac and allantois.

Neurulation. Onset and sequence of events during neurulation

Stages of neurulation - induction (primary embryonic induction) of the neural plate → lifting of the edges of the neural plate and formation of the neural groove → appearance of neural folds - formation of the neural crest and the beginning of the eviction of cells from it - closure of the neural folds with the formation of the neural tube

fusion of the ectoderm over the neural tube. Some structures of the nervous tissue develop from neurogenic placodes.

Primary embryonic induction. Neural, or primary embryonic induction - the formation of the neural plate from the dorsal ectoderm. This process is determined by the organizer - the chordomesoderm. During primary embryonic induction, the fate of the cells that give rise to the nervous system is determined.

The neural plate is the thickened part

dorsal ectoderm, forming along a cranio-caudal gradient. The prismatic cells of the newly formed neural plate are located on a basement membrane containing fibronectin, sulfated glycosaminoglycans, and laminin. The cells of the neural plate in the apical part are connected at

with the help of tight junctions, and in the basal part - gap junctions.

Neural tube. Soon after the formation of the edge of the neural plate

are raised, and neural folds are formed. Between the folds is the neural groove. Later, the edges of the neural folds close along the midline, and a closed neural tube is formed. The cranial and caudal sections of the neural tube remain unclosed for a long time, they are called the anterior and posterior neuropore, respectively. The anterior neuropore closes on the 23rd-26th day of development, and the posterior one - on the 26th-30th day.

Neural crest. After the ridges close and the neural tube is formed, the part of the ectoderm located between the neural and non-neural (cutaneous) ectoderm forms a new structure - the neural crest and its derivatives.

Examples of epithelia of ecto-, ento- and mesodermal origin

Table according to Khlopin:

Types of single-layer epithelia. Single-row and multi-row epithelia. Examples of localization

All cells of the simple epithelium are associated with the basement membrane.

Single-layer epithelium can be single-row or multi-row.

Single-row - the nuclei of all cells are located at the same level - in one row; Multi-row - the nuclei are located in several rows, since the multi-row contains cells of different types that contact the basal membrane, but at different levels.

Single-layer epithelia are localized in the intestine from the stomach to the sigmoid colon inclusive, as well as:

-mesothelium: covers the serous membranes (pleura, pericardium, peritoneum)

-endothelium: lines the inside of the walls of the heart, blood vessels and lymphatic vessels

-epithelium of some renal tubules

Transitional epithelium. Origin, structure, localization

This type of multilayered epithelium is typical for urinary organs - renal pelvis, ureters, urinary bladder, the walls of which are subject to significant stretching when filled with urine. Several layers of cells are distinguished in it - basal, intermediate, superficial.

The basal layer is formed by small, almost round (dark) cambial cells. The intermediate layer contains polygonal cells. The superficial layer consists of very large, often bi- and trinucleate cells, which have a dome-shaped or flattened shape depending on the condition of the organ wall. When the wall is stretched due to the organ filling with urine, the epithelium becomes thinner and its superficial cells flatten. During contraction of the organ wall, the thickness of the epithelial layer increases sharply. In this case, some cells in the intermediate layer are “squeezed” upward and take on a pear-shaped form, and the superficial cells located above them take on a dome-shaped form. Tight contacts have been found between the superficial cells, which are important for preventing fluid penetration through the organ wall (for example, the bladder).

Cell adhesion in a single-layer epithelium. Examples

(sorry for this, but this is the most complete info(()

Locking,or tight junction is characteristic of single-layer epithelia (Fig. 9). This is the zone where the outer layers of the two plasma membranes are maximally

brought together. The three-layer structure of the membrane is often visible in this contact: the two outer osmophilic layers of both membranes seem to merge into one common layer 2-3 nm thick.

The fusion of membranes does not occur over the entire area of the tight junction, but is a series of point-like approaches of membranes. Such structures can be seen with special stains in a light microscope. Morphologists call them closing plates. The role of the closing tight junction is not only in the mechanical connection of cells with each other. This area of contact is poorly permeable for macromolecules and ions, and thus it locks, blocks off the intercellular cavities, isolating them (and with them the internal environment of the body) from the external environment (in this case, the lumen of the intestine).

Closing,or tight contact occurs between all types of single-layer epithelium (endothelium, mesothelium, ependyma).

Simple contact, which occurs among most adjacent cells of different origin (Fig. 10). Most of the surface of contacting epithelial cells is also connected by simple contact, where the plasma membranes of the contacting cells are separated by a space of 15-20 nm. This space represents the supramembrane components of the cell surfaces. The width of the gap between the cell membranes can be more than 20 nm, forming expansions, cavities, but not less than 10 nm.

On the cytoplasmic side, no special additional structures adjoin this zone of the plasma membrane.

Toothed contact("lock") is a protrusion of the surface of the plasma membrane of one cell into the invagination of another (Fig. 11).

In section, this type of connection resembles a carpenter's seam. The intermembrane space and cytoplasm in the "lock" zone have the same characteristics as in the zones of simple contact. This type of intercellular connections is characteristic of many epithelia, where it connects cells into a single layer, facilitating their mechanical fastening to each other.

The role of mechanically tightly adhering cells to each other is played by a number of special structured intercellular connections.

Desmosomes, plaque- or button-like structures also connect cells to each other (Fig. 12). In the intercellular space, a dense layer is also visible here, represented by interacting integral membrane cadherins - desmogleins, which adhere cells to each other.

On the cytoplasmic side, a layer of desmoplakin protein is adjacent to the plasma membrane, with which the intermediate filaments of the cytoskeleton are associated. Desmosomes are most often found in epithelia, in which case the intermediate filaments contain keratins. In the cardiac muscle, the cells, cardiomyocytes, contain desmin fibrils as part of the desmosomes. In the vascular endothelium, the desmosomes include vimentin intermediate filaments.

Hemidesmosomes, in principle, are similar in structure to desmosomes, but represent a connection of cells with intercellular structures. Thus, in epithelia, linker glycoproteins (integrins) of desmosomes interact with proteins of the so-called basement membrane, which includes collagen, laminin, proteoglycans, etc.

The functional role of desmosomes and hemidesmosomes is purely mechanical - they firmly connect cells to each other and to the underlying extracellular matrix, which allows epithelial layers to withstand large mechanical loads.

Similarly, desmosomes tightly bind cardiac muscle cells together, allowing them to bear enormous mechanical loads while remaining linked into a single contracting structure.

Unlike tight contacts, all types of adhesive contacts are permeable to aqueous solutions and play no role in limiting diffusion.

Slotted contacts(nexuses) are considered to be communication connections of cells; these are structures that participate in the direct transfer of chemical substances from cell to cell, which can play a major physiological role not only in the functioning of specialized cells, but also ensure intercellular interactions during the development of the organism, during the differentiation of its cells (Fig. 13).

Characteristic of this type of contacts is the convergence of the plasma membranes of two adjacent cells at a distance of 2-3 nm. It was this circumstance that for a long time did not allow this type of contact to be distinguished from a tight separating (closing) contact on ultrathin sections. When using lanthanum hydroxide, it was noticed that some tight contacts let the contrast agent through. In this case, lanthanum filled a thin gap about 3 nm wide between the converging plasma membranes of adjacent cells. This led to the emergence of the term

gap junction. Further progress in deciphering its structure was achieved using the freeze-fracture method. It turned out that on the membrane cleavages, the gap junction zones (0.5 to 5 µm in size) are strewn with hexagonally arranged particles with a period of 8-10 nm, 7-8 nm in diameter, having a channel in the center about 2 nm wide. These particles were called connexons.

gap junction zones can contain from 10-20 to several thousand connexons, depending on the functional characteristics of the cells. Connexons

were isolated preparatively, they consist of six subunits of connectin - a protein with a molecular weight of about 30 thousand. By combining with each other, connectins form a cylindrical aggregate - a connexon, in the center of which a channel is located.

Individual connexons are embedded in the plasma membrane so that they pierce

through and through. One connexon on the plasma membrane of a cell is precisely opposed by a connexon on the plasma membrane of an adjacent cell, so that the channels of the two connexons form a single unit. Connexons act as direct intercellular channels through which ions and low-molecular substances can diffuse from cell to cell. It has been found that connexons can close, changing the diameter of the inner channel, and thus participate in the regulation of the transport of molecules between cells.

Such cells, due to their size, can easily be inserted with microelectrodes in order to study the electrical conductivity of their membranes. If electrodes are inserted into two adjacent cells, their plasma membranes exhibit low electrical resistance, and a current flows between the cells. This ability of gap junctions to serve as a place for transporting low-molecular compounds is used in those cellular systems where a rapid transfer of an electrical impulse (excitation wave) from cell to cell is required without the participation of a nerve mediator. Thus, all muscle cells of the cardiac myocardium are connected by gap junctions (in addition, the cells there are also connected by adhesive contacts). This creates the condition for the synchronous contraction of a huge number of cells.

When growing a culture of embryonic cardiac muscle cells

(cardiomyocytes) some cells in the layer begin to divide independently of each other

spontaneously contract at different frequencies, and only after the formation of inter

with them gap junctions they begin to beat synchronously as a single

a contracting layer of cells. In the same way, joint

contraction of smooth muscle cells in the wall of the uterus.

Synaptic contact(synapses). This type of contact is characteristic of nervous tissue and occurs both between two neurons and between a neuron and some other element - a receptor or effector (for example, a neuromuscular ending) (Fig. 14).

Synapses are areas of contact between two cells, specialized for one-way transmission of excitation or inhibition from one element to another.

In principle, this type of functional load, the transmission of impulses can be carried out by other types of contacts (for example, gap junctions in the heart muscle), but in the synaptic connection, high efficiency in the implementation of the nerve impulse is achieved.

Synapses are formed on the processes of nerve cells - these are the terminal sections of dendrites and axons. Interneuronal synapses are usually pear-shaped

extensions, plaques at the end of a nerve cell process. Such a terminal extension of a process of one of the nerve cells can contact and form a synaptic connection both with the body of another nerve cell and with its processes. Peripheral processes of nerve cells (axons) form specific contacts with effector cells or receptor cells. Consequently, a synapse

This is a structure formed between the areas of two cells (like a desmosome). The membranes of these cells are separated by an intercellular space - a synaptic cleft about 20-30 nm wide. Often, a thin-fibrous material located perpendicular to the membranes is visible in the lumen of this cleft. The membrane in the area of synaptic contact of one cell is called presynaptic, and that of the other, which receives the impulse, is called postsynaptic. Under an electron microscope, both membranes look dense and thick. Near the presynaptic membrane, a huge number of small vacuoles, synaptic vesicles filled with mediators, are revealed. Synaptic vesicles release their contents into the synaptic cleft at the moment of passage of a nerve impulse. The postsynaptic membrane often looks thicker than ordinary membranes due to the accumulation of many thin fibrils near it on the cytoplasm side.

Plasmodesmata. This type of intercellular connections is found in plants. Plasmodesmata are thin tubular cytoplasmic channels that connect two adjacent cells (Fig. 15). The diameter of these channels is usually 20-40 nm. The membrane that limits these channels directly passes into the plasma membranes of adjacent cells.

Plasmodesmata pass through the cell wall separating the cells. Thus, in some plant cells, plasmodesmata connect the hyaloplasm of neighboring cells, so formally there is no complete demarcation, separation of the body of one cell from another, it is rather a syncytium: the unification of many cellular territories by means of cytoplasmic bridges.

Membranous tubular elements that connect the cisterns of the endoplasmic reticulum of neighboring cells can penetrate into plasmodesmata. Plasmodesmata are formed during cell division, when the primary cell membrane is being built. In newly divided cells, the number of plasmodesmata can be very large (up to 1000 per cell); as cells age, their number decreases due to ruptures with an increase in the thickness of the cell wall.

The functional role of plasmodesmata is very important: with their help, intercellular circulation of solutions containing nutrients, ions and other compounds is ensured.

Basement membrane of epithelia. Structure, functions

basement membrane- is a layer of intercellular substance 20-100 nm thick and a complex protein and polysaccharide composition. (collagen type IV, fibronectin, laminin, glycosaminoglycans). These substances determine the adhesion, elasticity, permeability, colloidal state, electrical charge and other properties of the basement membrane. The basement membrane includes a luminous plate,

which the epithelial cells are directly attached and the dark plate, into which the loops of anchor collagen fibrils are woven. The cells are attached to the basal membrane by special structures - hemidesmosomes. In general organization, they resemble half a desmosome, but the set of proteins is somewhat different. Thin anchor filaments extend from the attachment plates into the light plate of the basal membrane. From the side of the connective tissue, collagen fibrils are fixed into the loops of anchor fibrils.

A layer of loose connective tissue almost always underlies the epithelial layer. In mucous membranes, it is called the proper lamina of the mucous membrane. Capillaries are located here, thanks to which the nutrition of epithelial cells is carried out, since there are no blood vessels in the epithelium itself. The influx of substances occurs by the diffusion mechanism (necessarily crossing the basement membrane), and it is this feature that limits the thickness of the epithelia. The cells farthest from the vessels die.

Functions of the basement membrane.

The basement membrane provides a mechanical connection between the epithelial and connective tissue, regulates the transport of substances between them. The basement membrane also regulates the migration and differentiation of cells during development and growth. It controls the position and movement of epithelial cells, preventing them from growing into connective tissue. In malignant growth, this function is disrupted, and the tumor forms metastases.

Changes in the properties of the basement membrane are the cause of a number of serious diseases. For example, in diabetes mellitus, this membrane thickens in the capillary wall, which leads to degenerative changes in many organs - the retina, kidneys, etc.

Polar differentiation of epithelial cells. Examples of epithelia

The basal and apical parts of the cell differ both structurally,both functionally and.This feature is obligatory for single-layered epithelia of border location.(at the boundary of the external and internal environments,on the surface of serous membranes),and also for epithelial cells,closely associated with blood capillaries(For example,in the endocrine glands,liver).Polar differentiation of epithelial cells is genetically determined.So,the lipid composition of the plasma membrane of the apical and basal parts of epithelial cells differs significantly.Phosphatidylethanolamine and phosphatidylserine predominate in the plasma membrane of the apical part of the cell..The plasma membrane of the basal part contains predominantly phosphatidylcholine,sphingomyelin and phosphatidylinositol.The membrane of a virus that has penetrated a cell contains lipids from the plasma membrane of that part of the cell,where the virus entered the cell(apical or basal).Genes identified,defects of which disrupt the polar differentiation of the epithelial layer.

The apical part contains microvilli,stereocilia,cilia,secretory material and participates in the formation of tight and intermediate junctions.

The basal part contains various organelles.The localization of mitochondria predominantly in the basal part is associated with the need for ATP for the ion pumps built into the plasma membrane of this part of the cell.(For example, Na+,K+‑ATPase).The basal part of the cell contains receptors for hormones and growth factors.,transport systems of ions and amino acids.Basal Glucose Transporters(ensuring the release of glucose from the cell along the concentration gradient)differ from those embedded in the apical membrane.Polar differentiation is also manifested in the nature of protein distribution,cytoskeleton related.So,ankyrin and fodrin predominate in the basal part,localized together withNa+,K+‑ATPase.Hemidesmosomes link the basal part of the epithelial cell with basement membrane.

Spatial organization of epithelia. Examples

Epithelial cells are organized into associates at the boundary of the internal and external environment of the body,and also in the internal environment as follows:layer,heavy,island,follicle,tube,net.

Plast.Epithelial cells,forming layers,always have a borderline position.For example:epidermis,epithelia of the mucous membrane of the skin and intestinal type,mesothelium.Polar differentiation is characteristic of cells in a single-layer layer.,and multilayered layers have significant morphological differences between epithelial cells of different layers.

A tubule is a type of layer rolled into a tube. For example, sweat glands, nephron tubules.

Islet. Epithelial islets are always immersed in the internal environment of the body and, as a rule, perform an endocrine function. For example, the islets of Langerhans of the pancreas.

A follicle is a cavity-containing island of epithelium. A typical example is the thyroid follicle.

Cord. The liver parenchyma is organized according to the principle of anastomosing cords from epithelial hepatocytes.

Network. In the thymus gland, the supporting framework consists of epithelial cells that branch and contact each other.

Myoepithelial cells

Myoepithelial cells (myoepitheliocytes) make up the second layer of cells in the terminal secretory sections of the salivary glands. They are epithelial cells by origin and contractile elements resembling muscle cells by function. They are also called stellate epithelial cells because they are stellate in shape and their processes envelop the terminal secretory sections like baskets. Myoepithelial cells are always located between the basal membrane and the base of the epithelial cells. Their contractions facilitate the secretion from the terminal sections.

Types of epithelial cell secretion

There are several options for separating the secretion.

Eccrine (merocrine) - secretion of fluid by exocytosis (salivary glands).

Apocrine - secretion of a secretion together with a fragment of the apical part of the secretory cell (mammary gland).

Holocrine - complete destruction of the secretory cell (sebaceous gland).

Sweat glands. Origin, structure, secretion and its regulation

They develop in the 3rd month of embryogenesis from the epidermis of the skin, which in the form of epithelial strands grows into the subepithelial mesenchyme

Sweat glands are simple, unbranched tubular glands, the terminal sections of which are located deep in the reticular layer of the dermis at the border with the adipose tissue.

their sections contain light (producing water and ions) and dark (secreting organic metabolic products) secretory cells, on the periphery-

myoepithelial cells, which by their contractions promote the secretion of secretions. They are affected by sympathetic nerve fibers, stimulating sweating.

The ducts of the sweat glands are lined with multilayered cuboidal epithelium.

Stem cells of epithelial tissues, properties. Examples

1. Stem cells are poorly differentiated, their cytoplasm appears primitive and contains few, if any, differentiation products.

2. Stem cells have high self-renewal capacity with high potential for error-free proliferation and cell division.

3. Stem cells are characterized by a long lifespan, which can be equivalent to the lifespan of the organism.

4. Stem cells have a long cell cycle or low mitotic activity. Although stem cells have high proliferative potential, under normal conditions they exhibit a very low proliferation rate.

5. Divisions within stem cells may be asymmetric with respect to the fate of the daughter cells or symmetric. In asymmetric divisions, one daughter cell remains as a parent and replenishes the stem cell pool, while the other daughter cell is destined to divide and differentiate according to the characteristics of a specific tissue. Asymmetry in divisions may be due to local forces that cause similar daughter cells to behave differently. Finally, cell divisions may be symmetric, but self-renewal takes only half the time.

Intercellular substance of connective tissues. General characteristics and structure. Distribution in different connective tissues

The intercellular substance (matrix) of connective tissue consists of collagen and elastic fibers, and the ground substance.

The intercellular substance, or extracellular matrix (substantia intercellularis), of connective tissue consists of collagen and elastic fibers, as well as the basic (amorphous) substance. The intercellular substance in both embryos and adults is formed, on the one hand, by secretion by connective tissue cells, and on the other hand, from blood plasma entering the intercellular spaces.

In human embryogenesis, the formation of intercellular substance occurs starting from the 1st-2nd month of intrauterine development. During life, the intercellular substance is constantly renewed - resorbed and restored.

Intercellular substance

Fibers:

Collagen fibers are formed from the protein collagen structure: there are 5 levels of organization:

a polypeptide chain consisting of repeating sequences of 3 amino acids, 2 of which are proline or lysine and glycine, and the third is any other

molecule - three polypeptide chains form a collagen molecule

protofibril - several collagen molecules cross-linked by covalent bonds

connections

microfibril - they are formed by several protofibrils

fibril - formed by bundles of protofibrils

Depending on the amino acid composition, the number of cross-links, the attached carbohydrates and the degree of hydroxylation, there are 15 different types of collagen. Collagen fibers are strong and do not stretch.

Elastic fibers structure: on the outside there are microfibrils consisting of microfibrillar protein, and inside there is protein - elastin; elastic fibers stretch well, after which they acquire their original shape

Reticular fibers - a type of collagen fibers are well stained with silver salts, therefore they have another name - argyrophilic fibers

Elastin. Synthesis of elastin, formation of elastic fibers and their localization

Elastin is a protein responsible for the elasticity of connective tissues and it has elasticity and allows tissues to recover, for example, when the skin is pinched or cut. The precursor of elastin is proelastin, a globular molecule that is formed by fibroblasts in connective tissue and smooth muscle cells in blood vessels. Proelastin polymerizes to form elastin, an amorphous, rubber-like glycoprotein that predominates in mature fibers. Elastin contains two unusual amino acids, desmosine and isodesmosine, formed by covalent reactions between four lysine residues. By holding elastin strands together, they form a rigid framework. Elastin is also found in a non-fibrillar form - it forms fenestrated membranes (elastic plates present in the wall of some blood vessels). Fibrillin is a family of proteins that perform a kind of supporting function necessary for the deposition of elastin. Elastic fibers are composed of disordered plexuses of fibrils

elastin around a microfibrillar core consisting of acidic glycoprotein (fibrillin). This structure provides the unique elasticity of these fibers. Elastin is destroyed by elastase, which can be secreted by bacteria and cells at the site of inflammation.

Loose fibrous connective tissue. Loose fibrous connective tissue cells. Localization and functions of loose connective tissue

Signs:

The main amorphous substance predominates in terms of volume occupied over the fibers

The fibers lie rather involuntarily

Localization:

forms the stroma

is located around the vessels

forms the papillary layer of the skin

Between the fibers there is a large amount of ground substance with various cells immersed in it: fibroblasts, migrating and resident macrophages, mast cells, pericytes, adipocytes, plasma cells, leukocytes. Glycosaminoglycan molecules, intertwining, form a network, in the cells and channels of which a large amount of tissue fluid with substances dissolved in it is retained. Leukocytes, macrophages, mast and plasma cells take an active part in defense reactions.

Fibroblast. Origin, localization, structure, functions

Fibroblasts (fibroblastocytes) develop from stem cells of mesenchymal origin.

Fibroblast is the most common type of connective tissue cell; it secretes extracellular matrix components, participates in wound healing, and is capable of proliferation and migration. Fibroblast is a flattened, star-shaped cell that forms wide wedge-shaped processes; it contains a large oval nucleus with several nucleoli. The cell size is variable. Fibroblast intensively synthesizes protein, so its cytoplasm contains a large number of cisterns of the granular endoplasmic reticulum, a well-defined Golgi complex, and many mitochondria. There are lysosomes and secretory granules, glycogen, numerous microfilaments, and microtubules.

Fibroblast (active form of the cell) contains well-defined organelles: granular endoplasmic reticulum, Golgi complex, mitochondria. Fibroblast forms large elongated processes. Fibrocytes have significantly fewer organelles, the cell lacks processes and has a spindle shape.

Functions:

Mature ones produce proteins (collagen and elastin) and proteoglycans and glycoproteins.

Pericryptal fibroblasts are present in the intestinal mucosa

— stromal cells that exhibit morphological features of SMCs. They are thought to regulate the growth and differentiation of epithelial cells. These fibroblasts express smooth muscle actin.

Myofibroblasts are contractile cells that have common features with SMC. Myofibroblasts exhibit properties of fibroblasts and SMC. During wound healing, some fibroblasts begin to synthesize smooth muscle actins and myosins. Differentiating myofibroblasts help bring wound surfaces closer together. Myofibroblasts are also found in fibromatosis, pulmonary fibrosis, liver, and kidney fibrosis.

Lipofibroblasts are present in the interstitium of the interalveolar septa of the lungs. In a number of characteristics, lipofibroblasts are similar to adipocytes, SMC, myofibroblasts, pericytes, and Ito cells of the liver. Lipofibroblasts contain numerous fat droplets, glycogen granules, contractile proteins, and accumulate retinoids.

Fibrocyte: origin, structure, localization, functions

Fibrocyte is a mature form of fibroblast present in dense, formed connective tissue. Fibrocyte has a spindle-shaped form. The dense nucleus is elongated and located along the cell. There are scattered cisterns of the granular endoplasmic reticulum and a small number of mitochondria. The Golgi complex is poorly developed. The cell contains relatively few secretory granules. The function of the fibrocyte is to maintain tissue structure by continuous (albeit slow) renewal of extracellular matrix components. During wound healing, fibrocyte can be stimulated to synthetic activity. Activated fibrocyte acquires fibroblast features: the nucleus becomes rounded, the number of cisterns of the endoplasmic reticulum and mitochondria increases; the Golgi complex becomes more pronounced.

Adipocytes and white adipose tissue. Structure, functioning, influence of hormones.

Adipose tissue develops from mesenchyme during embryogenesis. It constitutes almost all of the body's adipose tissue.

Fat cells formclusters (lobules) separated by a partition of loose connective tissue in which blood vessels and nerves pass. Individual adipocytes are surrounded by a network of reticulin and collagen fibers. In the partitions are fibroblasts and mast cells.

Adipocytes— large (from 25-50 to 150-250 μm in diameter) spherical cells, which in fat lobules, tightly adjoining each other, often acquire the shape of polyhedrons. The nucleus is flattened and shifted to the edge of the cell together with a thin rim of the cytoplasm surrounding it. The cytoplasm of the adipocyte contains one large fat droplet, occupying the main part (up to 95-98%) of its volume. The cytoplasm is characterized by a developed aER, numerous pinocytotic vesicles, a small Golgi complex, a small number of mitochondria, intermediate filaments.

White zht- in subcutaneous fat tissue. Especially abundant: skin area of the thighs, abdomen, buttocks, in the omentums.

Function:Participates in the absorption from the blood, synthesis, storage and mobilization of neutral lipids (triglycerides).

Influence of hormones:The distribution of adipose tissue in the body is influenced by sex hormones and adrenal cortex hormones. Regulation of adipocyte differentiation from precursors is carried out by the growth hormone (GH) of the pituitary gland, thyroid hormones and insulin-like growth factor-1. Lipolysis in adipose tissue is stimulated by a large number of hormones: norepinephrine; pituitary hormones: adrenocorticotropic (ACTH), thyroid-stimulating (TSH), melanocyte-stimulating (MSH), lipotropic (LPH), luteinizing (LH) and growth hormone (GH). When these hormones interact with the corresponding receptors, cAMP production is increased, which increases the activity of hormone-dependent lipase in adipocytes. This enzyme breaks down accumulated triglycerides into fatty acids and glycerol (glycerol), which are released into the bloodstream. Insulin has the opposite effect.

Brown adipocyte and brown adipose tissue. Structure, functioning.

Brown adipocytesare more modest (compared to white) and contain many small drops of fat (while white has one large one), and the diameter is 10 times smaller. They contain a lot of mitochondria, with iron-containing pigments (cytochromes) of which the brown color of cells and tissue as a whole is associated. The nucleus is usually in the center or eccentric, but not shifted to the periphery.

It is found in small quantities in humans and, unlike white adipose tissue, is concentrated only in a few clearly defined areas of the body: between the shoulder blades, in the armpits, on the back of the neck and between its vessels, in the renal hilum. It is relatively well represented in human fetuses and newborns. In adults, brown fat

It is found in small quantities in the mediastinum, along the aorta, and under the skin between the shoulder blades. Brown adipose tissue is abundantly supplied with blood capillaries that form a network around each adipocyte and has a pronounced sympathetic innervation. An important feature of brown adipose tissue is that its content changes little with insufficient and excessive nutrition.

In general, the structure of the BurZhT is similar to that of the BelZhT, but has a more abundant blood supply (which also gives the tissue its characteristic color).

Main function: thermogenesis. A special protein, UCP (short for uncoupling protein), or thermogenin, has been identified in the mitochondria of adipocytes, which causes the uncoupling of metabolic processes of oxidation and phosphorylation. Therefore, the result of fat oxidation in these cells is not the accumulation of energy in the form of macroergic compounds, but the formation of a significant amount of heat.

65. Connective tissue macrophage. Origin, structure, receptors, bioactive substances, functions

Macrophage- differentiated form of monocytes. Macrophages are professional phagocytes, they are found in all tissues and organs. This is a very mobile population of cells. Life expectancy is months.

Macrophages are divided into resident (or resting - have low functional activity - are in the tissue normally, in the absence of inflammation) and mobile (or wandering - high FA). Among resident macrophages, there are free (having a rounded shape) and fixed macrophages - star-shaped cells that attach with their processes to the extracellular matrix or other cells. Mobile macrophages are a population of migrating macrophages. (Do you want to know the formula for success? Here it is: resident macrophages = histiocytes)

Structure of a macrophage: depends on its activity and localization.

The cell diameter is about 20 µm. The nucleus is irregular in shape, with depressions. The cytoplasm contains mitochondria, free ribosomes, a well-defined Golgi complex, multivesicular bodies, rEPS, lysosomes, and phagolysosomes. Lysosomes contain bactericidal agents (myeloperoxidase, lysozyme, proteinases, acid hydrolases, cationic proteins, lactoferrin, superoxide dismutase - an enzyme that promotes the formation of H2O2, OH-, O2-). The cell forms cytoplasmic processes that participate in migration and phagocytosis. In activated cells, the expression of rEPS and the number of lysosomes are increased.

Under the plasma membrane there are a large number of actin microfilaments, microtubules, and intermediate filaments necessary for migration and phagocytosis.

Receptors:determine the cell's chemotaxis and its phagocytic activity.

MFs migrate along the concentration gradient of certain factors (otherwise I don’t know what receptors we’re talking about, if not receptors for these factors***), produced by other cells:

Macrophage chemotactic factors - secreted by activated T-lymphocytes;

Neutrophils that have migrated to the site of inflammation also secrete;

Factors secreted by bacteria;

Lymphokines from activated lymphocytes;

5) Fibronectin fragments;

6) Complement components C5a, C3 and leukotriene LTB4;

Opsonin receptors - macrophages attach to opsonized bacteria and engulf them (specific phagocytosis).

If you or your loved ones have more precise information, please contact us by calling the hotline: 89063218996.

Bioactive substances:Activated MF secretes more than 60 factors. Among them:

Contents of lysosomes: during phagocytosis, the contents of lysosomes are secreted with the formation of H2O2, OH-, O2-), which have high antibacterial activity.

Inflammatory mediators: in the MF, arachidonic acid is oxidized to form lipid mediators - prostaglandin PGE2, leukotrienes (LTC4, LTD4, LTE4), and platelet activity factor.

a-Interferon - blocks virus replication

Cytokines:

a) IL-2 - activates T-lymphocytes (and to a lesser extent - B-lymphocytes). Together with lipid mediators, it causes symptoms of acute inflammation;

b) Tumor necrosis factor (TFN) - has an effect similar to IL-1, including stimulating the formation of myeloid tissue.

Enzymes: elastase, hyaluronidase, collagenase (destroy the extracellular matrix)

Growth factors:

a) Platelet (PDGF);

b) Transforming -αAndβ(TGFαand TGFβrespectively); c) Alkaline fibroblast growth factor (bFGF);

d) Colony-stimulating (M-CSF and M-CSF).

Functions of MF:

Phagocytosis: Recognition, absorption and digestion of damaged, infected, tumor and dead cells, components of the intercellular substance, as well as exogenous materials and microorganisms (including denatured proteins and aged erythrocytes);

Participation in the induction of immune responsesby capturing, processing antigens and presenting them to lymphocytes (they act as antigen-presenting cells);

Regulation of the activity of other cell types(fibroblasts, lymphocytes, mast cells, endothelial cells, etc.). Including regulating hematopoiesis and the functions and differentiation of blood cells.

Bactericidal activity- lysozyme, acid hydrolases, cationic proteins, and lactoferrin are released from lysosomes.

Antitumor activity- direct cytotoxic action H2O2, cytolytic proteinases and tumor necrosis factor.

Tissue reorganization and wound healing: On the one side - its phagocytic activity (as well as the action of elastinase, collagenase and hyaluronidase), and on the other hand, the secretion of growth factors that stimulate cell proliferation.

Plasma cell. Formation, structure, function, localization.

Plasma cell (plasmocyte):immunologically activated B-lymphocytes responsible for the synthesis of Ig (immunoglobulins). An activated B-lymphocyte divides for about 5 days and, forming a clone, differentiates into a plasma cell or a memory B-cell. Plasma cells produce immunoglobulins and serve as the main effector cells of humoral immunity.

Structure: has a round or fan shape, with a diameter of 8-15 µm. The plasma cell contains a large oval eccentrically located nucleus with characteristic clumps of heterochromatin. Euchromatin occupies a smaller volume of the nucleus, but it is with it that the transcription of genes encoding immunoglobulins is associated. In the cytoplasm there is a well-developed Golgi complex and a mass of large cisterns of the granular endoplasmic reticulum, concentrically

located around the core.

The life span of a plasma cell is 4-5 days.

Functional propertiesplasma cells. The function of plasma cells is to provide humoral immunity by producing antibodies. The immunoglobulins produced belong to five classes (IgA, IgD, IgE, IgG And IgM), and plasma cells are capable of switching from producing immunoglobulins of one class to another. However, each plasma cell simultaneously synthesizes AT of only one type.

Localization: Plasma cells are rarely found in the peripheral blood, they are mainly present in the bone marrow, lymph nodes and spleen, as well as in the loose connective tissue of the mucous membranes.

Pericytes.Origin, localization, morphology, functions.

Pericytes- dendritic cells, adjacent to the capillaries on the outside, are most numerous in postcapillary venules. Formed (presumably) from adventitial cells.

Morphology:The oval-shaped cells form long primary processes located along the vessel, from which thinner and shorter secondary processes extend at right angles, embracing the capillary or postcapillary venule. Pericyte is characterized by a disc-shaped nucleus, a normal set of organelles, multivesicular bodies, microtubules, and glycogen. In the area facing the vessel wall, the pericyte cytoplasm contains vesicles. Contractile proteins, including actin and myosin, are present near the nucleus and in the processes. Pericytes are covered by a basement membrane, but are closely associated with the endothelial cell, since the basement membrane between them may be absent.

Functions: remain a mystery, as they have not been clearly established. It is assumed:

Contractile properties:Pericytes have common properties with SMCs

(expression of smooth muscle actin, vimentin) and are capable of contracting in response to angiotensin II,serotonin,acetylcholine, ATP, endothelin-1, regulating the lumen of the vessel;

Source GMK:during wound healing and vascular restoration, pericytes differentiate into SMCs;

Secretory function:synthesis of components of the capillary basement membrane;

Participation in phagocytosis(mainly remnants of the basement membrane);

Effect on endothelial cells: control the proliferation of endothelial cells (both during normal growth and during vascular regeneration).

Take part in the competition: come up with a new function for pericytes and send an SMS to the hotline number! The most original versions will be awarded, and every second one will get a funny joke in response (everyone else will get jokes of their own composition, sorry)!

Mast cells. Origin, localization, structure, granule contents, functions.

Mast cell- refers to the descendants of the blood stem cell. Like the basophil (with which m(orphologically and functionally similar), originates from a precursor in the bone marrow, but final differentiation occurs in connective tissue (growth factors - IL-3 and IL-10).

Localization: mast cells are resident cells of connective tissue. They are especially numerous in the skin, in the mucous membrane of the respiratory and digestive systems, and around blood vessels.

Structure:contains numerous modified lysosomes - large metachromatic granules. Various receptors are built into the cell membrane, including receptors for the Fc fragment of IgE. In the cytoplasm - several rounded mitochondria and moderately developed hepatic endoplasmic reticulum. The nucleus is relatively small, non-segmented, oval or round, with a moderate content of heterochromatin.

Contents of granules:

Heparin(heparin sulfate);

Histamine(causes a reduction in the SMC, hypersecretion of mucus, increase vascular permeability with the development of edema);

Proteases: tryptase, elastase, dipeptidase, plasminogen activator - together with carboxypeptidase cause destruction of the tissue matrix;

Himase- a specific protein involved in the breakdown of extracellular matrix components;

Acid hydrolases- lysosomal enzymes;

Chemoattractants: eosinophil chemotactic factor (ECF), chemotactic factor

neutrophils (NCF).

Main componentmast cell granules - a negatively charged sulfated glycosaminoglycan heparin, synthesized and stored exclusively by mast cells.

Functions: mast cell is involved in inflammatory and allergic reactions. Activation

Degranulation of mast cells, like basophils, is mediated by IgE.

Histamine. Sources of histamine, its receptors. Secretion, effects.Histamine is mainly found in the granules of mast cells and basophils.

Almost everything said below was (or will be?..) taken from the Internet, since our textbooks, including Bykov, do not have more precise material.

In clinical practice, histamine secretion (or mast cell/basophil activation) is usually associated with allergies - when an antigen is re-exposed to a previously sensitized organism, an allergic reaction develops.

***IF YOU HAVE ANY ADDITIONS - POST THEM IN THE GENERAL CHAT OR CALL THE HOTLINE!!!***

Histiocyte.

Remember, macrophages inquestion 65Macrophages were divided into wandering and resting? Well, the latter are also called histiocytes. Everything else was already mentioned in question 65.

Reticular tissue. Structure, functions, examples of localization.

Structure: has a reticular structure and consists of reticulin fibers (collagen type III) and reticular cells with long processes. Microphages are usually present in the RT. Function and examples of localization:

Reticular cells together with reticulin fibers form a loose network (stroma)

bone marrow,lymph nodes, spleen and tonsils. Also, the RT surrounds the liver sinusoids.

In hematopoietic organs it creates a microenvironment for developing blood cells. Synthesizes hematopoietic growth factors (IL-3, IL-7, GM-CSF, G-CSF, etc.)

The concept of mesenchyme, its structure. Derivatives of mesenchyme.

Mesenchyme- embryonic connective tissue - the source of cells of all connective tissues.

Mesenchymal cells are stellate or spindle-shaped with delicate branching processes forming a network. The gelatinous extracellular material consists almost exclusively of ground substance and a minimal amount of reticulin fibers. The oval nucleus contains dispersed chromatin and nucleoli.

The mesenchymal stem cell of the red bone marrow is a self-renewing cell population that gives rise to stromal cells expressing stem cell markers. The mesenchymal stem cell and its daughter stromal cells can differentiate into fat, bone, cartilage, muscle, and reticular cells.

Mesenchyme exists only in the embryonic period of human development. After birth, only poorly differentiated (pluripotent) cells remain in the human body as part of loose fibrous connective tissue (adventitial cells), which can divergently differentiate in various directions, but within a certain tissue system.

Tendon. Structure, regeneration.

Structure of the tendon:These assholes are elongated cylindrical or flattened structures that connect striated somatic muscle to bone. They are formed by tightly packed parallel bundles of collagen fibers, between which are rows of fibrocytes, also called tendon cells, or tendinocytes (from the Latin tendo - tendon).

The latter are characterized by elongated nuclei oriented along the tendon axis (parallel to the collagen bundles) and weakly oxyphilic cytoplasm. The peripheral areas of the cytoplasm form flattened lamellar processes that envelop the collagen fiber bundles. In transverse sections of the tendon, its cells have a stellate shape; they laterally contact each other with their processes, forming typical gap junctions that connect the cells electrically and chemically. In this case, fibrocytes form a single system (similar to that which unites osteocytes in bone tissue).

Tendonas an organ includes:

Components formed by dense fibrous connective tissue - bundles of collagen fibers of various orders with fibrocytes located between them;

Shells (layers) of loose and dense unformed connective tissues,

surrounding bundles of collagen fibers and supporting blood vessels and nerves.

The tendons are divided into primary, secondary and tertiary tendon bundles:

Primary tendons(collagen) bundles (first-order bundles) are located between the rows of fibrocytes.

Secondary tendons(collagen) bundles (second-order bundles) are formed by a group of primary bundles surrounded on the outside by a sheath of loose fibrous irregular connective tissue - endotendinium, in which blood and lymphatic vessels and nerve fibers pass.

Tertiary tendons(collagen) bundles (third-order bundles) consist of several secondary bundles, which are surrounded on the outside by a sheath of dense fibrous irregular connective tissue - peritendinium, extending into the tendon layer of endotendinium.

Tendon as a wholemay be a tertiary bundle, in some cases it consists of several tertiary bundles, surrounded by a common membrane - epitendinium.

Regeneration:When a tendon is damaged, activated fibrocytes and fibroblasts synthesize collagen for new fibers.

Chondroblast. Origin, localization, structure, functions.

Deferoon of cartilaginous tissue: chondrogenic cells - chondroblasts - chondrocytes. Like any cell of connective tissue - a derivative of the mesenchyme.

Origin and functions:During the development of cartilaginous tissue, chondrogenic cells differentiate into chondroblasts. Chondroblasts proliferate and begin synthesizing substances for the construction of the cartilaginous matrix, releasing them as part of secretory vesicles (matrix vesicles). Chondroblasts ensure the development of cartilaginous tissues during embryogenesis, persist in mature tissues and are their cambial elements.

Localized:in the inner (cellular) layer of the perichondrium, where chondrogenic cells are located.

Structure:Chondroblasts are large, round, synthetically active young cells that retain the ability to proliferate. They are characterized by a large, bright nucleus and extensive cytoplasm with numerous ribosomes, a developed ER, and a large Golgi complex.

Perichondrium. Structure, functions.

Structure: in the fetus, the perichondrium is formed by a layer of compacted mesenchyme around the cartilaginous rudiment. In postnatal ontogenesis - dense fibrous unformed connective tissue. In the perichondrium, a distinction is made between: a fibrous outer layer (collagen type I) and a cellular inner layer containing chondrogenic cells. The blood vessels of the perichondrium provide nutrition to the cartilage. The inner layer contains a vascular network that nourishes the cartilage,

also cambial elements - chondrogenic cells that morphologically have the characteristics of dormant, poorly differentiated cells that are capable of being activated, proliferating and differentiating into chondroblasts with appropriate stimulation. The formation of chondroblasts in this layer ensures the appositional growth of cartilage in the embryonic period and in childhood. In an adult, upon completion of cartilage growth, the signal for activation of cambial elements is usually damage to the perichondrium.

Thus, the functions of the perichondrium:

Trophic— the perichondrium provides nutrition to the cartilage, which occurs diffusely from its vessels adjacent to the surface of the cartilaginous tissue. Removal of the perichondrium or its separation from the cartilage (for example, its rupture as a result of injury) over a sufficiently large area inevitably causes the death of the corresponding section of cartilage due to the cessation of its nutrition;

Regenerative— the perichondrium contains cambial elements (prechondroblasts), which, with appropriate activation, are capable of transforming into chondroblasts — synthetically active cells that produce cartilage matrix and ensure cartilage regeneration;

Mechanical, support— the perichondrium provides a mechanical connection between the cartilage and other structures (tendons, ligaments, etc.) attached to it.

The structure of the intercellular substance of various types of cartilaginous tissue.

The cartilaginous matrix containsup to 75% water, which allows substances from the vessels of the perichondrium to diffuse into the matrix and provide nutrition to the chondrocytes. Proteins of the cartilage matrix are of great importance for ensuring the strength and elasticity of the cartilage. The most functionally significant are collagens (II - forms collagen fibers and makes up to 40% of the dry mass of cartilage; IX, VI - in hyaline and elastic; X), proteoglycans and chondronectin.

The proteoglycan molecule binds (structures) a large volume of water, much greater in mass than its own. When cartilage is compressed, water is forced out of the areas around the sulfated and carboxyl groups of the proteoglycan, the groups come closer together, and the repulsive forces between their negative charges prevent further compression of the tissue. The water returns to its original place when the pressure is removed. Thus, if collagen determines the strength of cartilage, then proteoglycan determines its elasticity (due to chondroitin sulfate).

intercellular substance of hyaline cartilage collagen fibers II are located

type and fibrils, wriggling, surround isogenic groups of cartilage cells, protecting them from mechanical pressure.

elastic cartilage: in its intercellular substance along with collagen fibers elastic fibers, penetrating the intercellular substance in all directions. The matrix consists of more than 90% of the protein elastin (which forms elastic fibers). Contains less lipids, glycogen and chondroitin sulfates.

The intercellular substance of fibrocartilaginous tissue contains parallel collagen bundles, which gradually loosen and turn into hyaline cartilage. It is 90% formed by type I collagen, less than 10% is type II collagen.

Growth, nutrition, regeneration of cartilage.

Height: cartilage growth occurs both from within (interstitial growth) and from the perichondrium (appositional growth). Interstitial growth is provided by chondrocyte proliferation

increase in matrix volume. Appositional growth - superposition of layers of newly formed cartilaginous tissue along the periphery of the cartilage due to differentiation of cartilaginous cells from chondrogenic cells of the perichondrium.

Nutrition: is carried out diffusely due to the perichondrium (cm. question 75) or, if speech If we are talking about articular cartilage, then nutrition occurs with the help of synovial fluid.

Cartilage regenerationif it is damaged, it can be carried out due to the presence cambial elements in the perichondrium (and you thought there was a miracle of God there? Read question 75, damn!). Contained in the perichondrium, chondrogenic cells that are activated, proliferate and differentiate into chondroblasts, which in turn produce the intercellular substance of the cartilage, gradually filling the resulting defect. However, almost complete regeneration is observed only with minor cartilage damage in childhood. In adults, the regeneration of cartilage tissue is preceded by the development of fibrous connective tissue originating from the perichondrium, which quickly fills the defect in the cartilage tissue, eventually turning from loose fibrous tissue into dense tissue (scar). Sometimes bone tissue develops in this area of connective tissue. Such healing, although it ensures the binding of undamaged areas of cartilage, is incomplete and under loads can lead to a repeated rupture of the cartilage along the scar line.

Hyaline cartilage. Origin, localization, structure.

Origin:Here everything is simple - chondrogenic cells spin - chondrocytes become muddy (for more details see question 74). Histogenesis of cartilage is stimulated by thyroxine, testosterone and somatotropin, and inhibited by cortisol, hydrocortisone and estradiol.

Localization:hyaline cartilage is localized in the ribs, joints, and walls of the airways. In the fetus, hyaline cartilage forms the skeleton, and in the growing organism and in bone fractures, it is the site of bone tissue formation.

Structure:matrix + chondrocytes. Chondrocytes are cartilage cells surrounded by matrix, located closer to the surface of the cartilage, have an oval shape, their long axis is parallel to the surface of the cartilage. In deeper layers, chondrocytes form groups within one lacuna - the so-called isogenic groups of cells (clone).

intercellular substance of hyaline cartilageType II collagen fibers and fibrils are located, wriggling, surrounding the isogenic groups of cartilage cells, protecting them from mechanical pressure.

Elastic cartilage. Structure, localization.

Elastic cartilageThe tissue forms cartilages that are flexible and capable of reversible deformation. It comprises the cartilages of the auricle, external auditory canal, Eustachian tube, epiglottis, some cartilages of the larynx, as well as the cartilaginous plates and islets of the middle bronchi.

Elastic cartilage tissue, like hyaline, consists of chondrocytes and intercellular substance (vot_eto_povorot.jpg).

Chondrocytesin elastic cartilaginous tissue they are located in lacunae, where they lie singly or in the form of small (up to 4 cells) isogenic groups.

elastic cartilage: in its intercellular substance along with collagen fibers elastic fibers, penetrating the intercellular substance in all directions. The matrix is more than 90% elastin protein (which forms elastic fibers). Contains less lipids, glycogen and chondroitin sulfates than hyaline.

80. Fibrocartilage: structure, localization.

Fibrous (collagen fibrous) cartilaginous tissue forms cartilages that have considerable mechanical strength. It is found in intervertebral discs, pubic symphysis, areas of attachment of tendons and ligaments to bones or hyaline cartilage. This tissue is never found in isolation, it always transforms into dense fibrous connective tissue and hyaline cartilaginous tissue.

Chondrocytesin fibrocartilaginous tissue they have a round or elongated shape and are located in lacunae singly or in the form of small isogenic groups, often lining up in columns along bundles of collagen fibers. Morphologically they are similar to chondrocytes of other cartilaginous tissues, but functionally they occupy an intermediate position between typical chondroblasts and fibroblasts, since, in addition to type II collagen and components of the main substance of cartilage, they produce type I collagen in significant quantities. The similarity with fibroblasts is clearly evident in the areas of cartilage-tendon junction, where fibrocyte-type cells (on the tendon side) are gradually replaced by typical chondrocytes (on the cartilage side) through a series of intermediate forms.

There is no perichondrium!

Intercellular substancefibrocartilaginous tissue contains parallel collagen bundles that gradually loosen and turn into hyaline cartilage. 90% is formed by type I collagen, less than 10% is type II collagen.

Bone tissue cells: osteocytes and osteoblasts. Structure, localization in bone, functioning.

Osteoblast. Origin, localization, structure, function.

There are two cell lines in the bone - creative and destructive, which reflects the constant ongoing restructuring of bone tissue. The differentiation of the creative cell line in bone tissue: osteogenic cell → osteoblast → osteocyte. The destructive cell line is osteoclasts.

OSTEOBLASTS

Origin:formed from osteogenic cells (descendants of the mesenchyme). Osteogenic cells originate from the mesenchyme, have a spindle-shaped form and are located in the periosteum and endosteum. At high pO2, osteogenic cells differentiate into osteoblasts, and at low pO2 - into chondrogenic cells.

Structure:non-dividing (according to Chelysheva et al., but capable of proliferation - according to Afanasyev) dendritic cells, have a cubic, polygonal or cylindrical shape. The nucleus is located eccentrically, the cytoplasm is sharply basophilic. Osteoblasts synthesize and secrete substances of the bone matrix. In this regard, osteoblasts have well-developed GEPS and the Golgi complex, there are many secretory granules containing procollagen and mitochondria. Procollagen is secreted almost through the entire surface of the cell, which allows the osteoblast to surround itself with a matrix from all sides. With the help of processes, osteoblasts establish contacts with neighboring osteoblasts and osteocytes.

Localization:In formed bone, they are found only in the deep layers of the periosteum and in places of bone tissue regeneration after injury.

Functions: in general, they synthesize and secrete non-mineralized intercellular substance (matrix) of bone (osteoid), participate in its calcification, regulate the flow of calcium and phosphorus into and out of bone tissue. In general, active and inactive forms of osteoblasts are distinguished.

Active - indulge in synthesis;

Inactive (resting) osteoblasts (cells that line bone)are formed from active osteoblasts and cover 80-95% of the bone surface in a resting bone. The organelles are reduced, but the receptors for various hormones and growth factors, as well as the ability to respond to them, are preserved. Between the resting osteoblasts and the bone surface there is a thin (0.1-0.5 μm) layer of non-mineralized matrix - the endosteal membrane, which protects the bone surface from possible attack by osteoclasts. The endosteal membrane differs from osteoid in its structural organization, biochemical composition, and also in the fact that it is never mineralized. It is assumed that resting osteoblasts maintain connections with each other and with osteocytes, forming a system that regulates the mineral metabolism of bone tissue. They play an important role in the initiation of bone tissue remodeling.

Osteoid- non-mineralized organic bone matrix around osteoblasts that synthesize and secrete its components. Later

osteoid is mineralized, which is preceded by the appearance of matrix vesicles secreted by osteoblasts in the osteoid. The membrane-surrounded matrix vesicles contain lipids, a large amount of Ca2+, various phosphatases. For normal mineralization of osteoid, 1a,25-dihydroxycholecalciferol (the active form of vitamin D) is especially necessary.3calcitriol).

OSTEOCYTES.

Osteocytes— the main cell type of mature bone tissue. They are formed from osteoblasts when, as a result of their synthetic activity and mineralization of osteoid, they are surrounded on all sides by a calcified matrix. In this case, osteoblasts lose the ability to divide, decrease in size, their organelles are reduced, and the intensity of synthetic processes drops sharply. The flattened bodies of osteocytes lack polarity and are located in narrow bone cavities

—lacunae, where they are surrounded by collagen fibrils and a narrow strip of osteoid. Their processes (up to several hundred in number) are located in narrow bone canals and connect neighboring cells thanks to gap junctions between them (through which low-molecular nutrients and ions are transferred).

Osteocyte functionconsists in maintaining the normal state of the bone matrix (and the balance of Ca and P in the body). At the same time, they not only produce its components, but apparently have the ability to limitedly dissolve the matrix, which leads to an increase in the volume of lacunae (osteocytic osteolysis). This phenomenon is observed in 3-4% of lacunae in healthy people; it increases several times with elevated levels of parathyroid hormone or a lack of vitamin D. Osteocytes can secrete substances for the formation of a matrix of new bone, but this ability is less pronounced than in osteoblasts.

INTERESTING TO KNOW:The lacunar-tubular system is filled with tissue fluid, through which the exchange of substances between osteocytes and blood is carried out. Fluid constantly circulates in the tubules, which supports the diffusion of metabolites and the exchange between the lacunae and the blood vessels of the periosteum. The barrier separating the plasma and the lacunar-tubular fluid is called the bone membrane. The barrier is formed by osteoblasts and osteocytes.

Osteoclast. Origin, cytology, localization, functions. Regulation of functions.

Origin:osteoclast precursors - monocytes. To be completely honest - colony-forming unit for granulocytes and monocytes (CFU-GM). Osteoclasts are classified as part of the mononuclear phagocyte system. For this reason, they are classified as

mononuclear phagocytes.

Monocytes fuse and form large (giant) multinucleated cells (up to 50 nuclei):

Structure and localization:have acidophilic cytoplasm and are located in the region

bone resorption (destruction) in the Howship lacunae. - Our textbooks

The localization of osteoclasts is almost identical to that of osteoblasts: they too

are located in the developing bone - on the surface of the bone beams (forming in them

recesses);

in mature bone- in the periosteum, endosteum, perivascular space of osteons

and, in addition, as part of multicellular complexes that carry out bone remodeling. - Our Internet

In an activated osteoclast, a corrugated border, light,

vesicular and basal zone.

Corrugated edging- numerous cytoplasmic outgrowths directed toward the bone surface and reaching it. The locus of active bone tissue resorption. A large amount of H+ and Cl- is released from the osteoclast through the membrane of the outgrowths, which creates and maintains an acidic environment in the closed space of the lacuna, which is optimal for dissolving calcium salts of the bone matrix (pH 4.5). The enzymes of numerous lysosomes of the vesicular zone destroy the organic part of the bone matrix.

Marginal light zones are areas of dense attachment of its cytoplasm to the bone, located on both sides of the corrugated border. Creates a closed space necessary for maintaining a high concentration of H+ and proteolytic enzymes. There are many actin filaments here, which participate in the formation of the contact of the ostaclast-surface of the matrix.

Vesicular zone- contains numerous lysosomes.

Basal zonecontains nuclei, mitochondria, the Golgi complex and the ER element.

Function:Osteoclasts that have mobility carry out the destruction, or resorption (from the Latin resorptio - absorption) of bone tissue. Since bone resorption

accompanied by the release of calcium bound to its matrix, these cells play a vital role in maintaining calcium homeostasis.

Regulation of functions:

General factorsinclude:

Parathyroid hormone (parathyroid hormone), 1,25 hydroxyvitamin D3 (activate osteoclasts and increase their number by stimulating the fusion of mononuclear precursors).

The thyroid hormone calcitonin and female sex hormones (estrogens) inhibit osteoclast activity. Calcitonin binds to specific receptors on the surface of osteoclasts, and parathyroid hormone, which has no receptors on osteoclasts, has an indirect effect on them, apparently mediated by osteoblasts.

Local factors,causing activation of osteoclasts in specific areas of bone tissue remain poorly understood. There is evidence that mechanical stress creates local electric fields to which these cells are sensitive. The role of mediators in this case is probably performed by collagen fibers, which have piezoelectric properties. It has been shown that osteoclast activity is stimulated by a special factor activating osteoclasts (FAO), which is produced by lymphocytes. It is influenced by prostaglandins produced by macrophages and osteoblasts. The formation and activity of osteoclasts is also influenced by a number of interleukins (IL-1, IL-3, IL-6) and growth factors. - Bykov

Intercellular substance of bone tissue, its physical and chemical properties and structure.

Bone matrixmakes up 50% of the dry weight of bone and consists of inorganic (50%) and organic (25%) parts and water (25%). The inorganic part contains two chemical elements - calcium (35%) and phosphorus (50%), which form hydroxyapatite crystals, and are also part of other inorganic substances. Hydroxyapatite crystals combine with collagen molecules through osteonectin. The inorganic part of the bone also includes bicarbonates, citrates, fluorides, salts of Mg2+, K+, Na+. The organic part - collagens (collagen type I - 90-95% and collagen type V) and non-collagen proteins (osteonectin, osteocalcin, proteoglycans, sialoproteins, morphogenetic proteins, proteolipids, phosphoproteins), as well as glycosaminoglycans (chondroitin sulfate, keratan sulfate). Organic substances of the bone matrix are synthesized by osteoblasts.

Osteoid- non-mineralized organic bone matrix around osteoblasts synthesizing and secreting its components. Later, osteoid is mineralized, which is preceded by the appearance of matrix vesicles secreted by osteoblasts in the osteoid. The matrix vesicles surrounded by a membrane contain lipids, a large amount of Ca2+, and various phosphatases. 1a,25-dihydroxycholecalciferol (the active form of vitamin D3 calcitriol) is especially necessary for normal mineralization of osteoid.

Periosteum; periosteum and endosteum. Structure, localization in bone, functions.

Periosteumcovers the entire bone from the outside, with the exception of the articular surface. The periosteum is a source of osteogenic cells for the development, growth and regeneration of bone tissue. The periosteum has two layers - outer and inner.

Thick outer layer- fibrous, represented by dense connective tissue. In the fetus, the cells of the compacted mesenchyme, located outside the osteogenic cells of the bone rudiment, differentiate into fibroblasts. The periosteum passes into the areas of attachment of ligaments and muscles without sharp boundaries.

Inner layer- (in adults it is weakly distinguishable) consists of loose fibrous connective tissue, in which flat spindle-shaped cells are located - resting osteoblasts and their precursors (preosteoblasts). Osteogenic cells and osteoblasts are part of the inner (osteogenic) layer of the periosteum. Bundles of piercing collagen fibers (Sharpey's fibers), sharpening towards the bone and going into its matrix from the periosteum, provide strong attachment of the inner layer to the bone surface. The periosteum is a source of osteogenic cells for the development, growth and regeneration of bone tissue.

Endoste -a thin membrane lining the bone from the bone marrow side. It covers the trabeculae in the spongy substance and also lines the Haversian canals of the compact substance. In other words, the endosteum is present on the surface of all bone cavities. The endosteum consists of a layer of inactive flat osteogenic cells. During the period of bone growth and remodeling, the integrity of the endosteum is often damaged by osteoclasts. It consists of the same layers as the periosteum, but less pronounced.

Function of the periosteum:

Trophic— the periosteum provides nutrition to the bone, since it contains vessels that (together with nerves) penetrate from it into the bone through special nutrient openings on its surface and are directed into the penetrating (Volkmann) canals located at an angle (often right) to the long axis of the diaphysis. These canals inside the bone contain vessels that connect the vessels of the osteons and nourish the bone marrow. Traumatic separation of the periosteum from the bone over a significant distance deprives the latter of nutrition and causes necrotic changes in it;

Regenerative— is caused by the presence of cambial elements in its inner layer - osteogenic cells, which, when stimulated, turn into active osteoblasts that produce bone matrix and ensure bone regeneration;

Mechanical, support— the perichondrium provides a mechanical connection between the bone and other structures (tendons, ligaments, muscles) attached to it.

Bone plate.Bone plate systems.

Bone plate- a layer of bone matrix 3-7 microns thick. Between adjacent plates

Osteocytes are located in the lacunae, and their processes pass through the thickness of the plate in the bone canals. Collagen fibers within the plate are oriented in an orderly manner and lie at an angle to the fibers of the adjacent plate, which provides significant strength to the lamellar bone.

Osteon, or Haversian system - a set of 4-20 concentric bone plates.

Osteon canal: in the center of the osteon is the Haversian canal (osteon canal), filled with loose fibrous connective tissue with blood vessels and nerve fibers.

Folkman channels: connect the osteon canals with each other, as well as with the vessels and nerves of the periosteum.

Cementation line: from the outside, the osteon is limited by a commissure line separating it from fragments of old osteons.

Formation of osteons: during osteon formation, osteogenic cells located in the immediate vicinity of the Haversian canal differentiate into osteoblasts. On the outside is a layer of osteoid formed by osteoblasts. Subsequently, the osteoid mineralizes, and osteoblasts, surrounded by mineralized bone matrix, differentiate into osteocytes. The next concentric layer arises in a similar way from the inside. A calcification front passes along the outer surface of the osteoid at the border with the mineralized bone matrix, where the process of deposition of mineral salts begins. The diameter of the osteon (no more than 0.4 mm) determines the distance over which substances effectively diffuse to the peripheral osteocytes of the osteon through the lacunar-tubular system from the centrally located blood vessel.

If the pictures are hard to see, click/tap/say sweet words and you will get the result.

Lamellar (mature) bone tissue. Concept of bone plate. Types of bone plates in tubular bone.

Mature (secondary) or lamellar bone tissueformed by bone plates.

Lamellar bone tissue forms the spongy and compact substance of bone.

Spongy substance- intertwined bone trabeculae, the cavities between which are filled with bone marrow. The trabecula consists of bone plates and is surrounded on the outside by one layer of osteoblasts. The trabeculae are arranged according to the direction of compression and tension forces. The spongy substance fills the epiphyses of long tubular bones and forms the internal content of short and flat bones of the skeleton.

Compact substanceforms the diaphysis of long tubular bones and covers all other (short and flat) bones of the skeleton with a layer of varying thickness. The bulk of the compact substance consists of osteons.

Organization of lamellar bone tissueIn lamellar bone tissue, osteocytes, collagen fibers, bone plates and blood vessels are arranged in an orderly manner.

Osteocyteslie in the lacunae between adjacent plates. From the lacunae, anastomosing bone canals containing osteocyte processes extend into the thickness of adjacent plates.

Collagenthe fibers in each plate run parallel to each other and at an angle to the fibers of adjacent plates.

Bone plates:In the compact substance, bone plates mainly form osteons, oriented along the long axis of the tubular bone. Between the osteons are intercalated bone plates: A) external (covering the bone) and B)

internal(lining the cavity of the bone) common (general) bone plates lie parallel to each other. Blood vessels lie in the canals of osteons.

bone plate - see question 86.

Coarse fibrous bone tissue. Development, structure, localization.

Between the thick bundles of randomly arranged collagen fibers there are elongated lacunae with long anastomosing canals. Osteocytes are located in the lacunae. Such immature bone (characterized by a large number of proteoglycans and glycoproteins and a low content of mineral salts) is present in the fetus. In an adult, it is preserved in places where tendons attach to bones, near cranial sutures, in dental alveoli, in the bone labyrinth of the inner ear. Immature bone is also formed during fracture healing.

They have little mechanical strength and are usually formed when osteoblasts form osteoid at a high rate.

The content of osteocytes in fibrous bone tissue is higher than in lamellar bone tissue, and its matrix contains more basic substance and fewer mineral components. During normal development and regeneration of bone tissue, fibrous bone tissue is gradually replaced by lamellar bone tissue.

In fractures, as calcification occurs, young cartilage is replaced by immature coarse fibrous bone tissue, in place of which spongy substance is formed.

Development of bone in place of cartilage (enchondral, or endochondral, osteogenesis).

Endochondral (indirect)Osteogenesis occurs in the rudiment of future bone (cartilage model) consisting of hyaline cartilage. During this process, long tubular bones are formed. Bone morphogenetic proteins (BMPs) induce enchondral osteogenesis. There are two stages in enchondral osteogenesis: the formation of primary and then secondary ossification centers. Cartilage does not turn into bone, but is replaced by it. Osteogenic cells penetrate the cartilage model with blood vessels. Osteoclasts disassemble the mineralized cartilage matrix, and osteoblasts build bone tissue.

Ossification centers:

Primary (diaphyseal) ossification centeris formed during the following events: increased blood supply to the perichondrium in the cartilaginous model → increased pO2 - commitment of skeletal tissue stem cells in the osteogenic direction - appearance of osteoblasts - formation of coarse fibrous bone tissue (bone cuff) in the middle part of the diaphysis by intramembranous osteogenesis (aka direct osteogenesis). In parallel, hypertrophy of chondrocytes, their degeneration, calcification of the matrix, fusion of cartilaginous cell lacunae and formation of cavities occur in the central part of the cartilaginous model. Osteoclasts of the bone cuff resorb primary bone tissue, which leads to the formation of pathways through which blood vessels, osteogenic and other cells of mesenchymal origin penetrate from the periosteum into the cavities formed during the death of cartilage. Differentiation of osteogenic cells that have penetrated into the center of the cartilaginous model leads to the formation of bone tissue. In the diaphysis, the primary bone tissue is replaced by compact matter. The bone marrow cavity is formed as a result of active resorption of the "calcified cartilage - calcified bone" complex by osteoclasts. The previously formed bone cuff thickens and grows toward the epiphyses.

Secondary (epiphyseal) ossification center.Its formation is associated with the growth of the bone cuff. In the epiphyses, ossification occurs similarly to the formation of the diaphyseal ossification center, but in place of the primary bone tissue, spongy substance is formed. When the newly formed bone tissue fills the entire epiphysis, the cartilaginous tissue remains in the form of narrow strips only on the surface of the epiphysis (articular cartilage), as well as between the epiphysis and diaphysis (metaphysis) in the form of an epiphyseal cartilaginous plate.

During endochondral osteogenesis, chondrocytes express a rare form of collagen - collagen type X.

Direct osteogenesis(intramambranous).

This is how flat bones are formed. In areas of mesenchyme containing capillaries, groups of mesenchymal cells form primary ossification centers. The mesenchymal cells then differentiate into osteoblasts.

Osteoblasts begin to produce osteoid. Osteoid mineralizes, and differentiating osteocytes become immured in the lacunae of the mineralized bone matrix. The immature coarse fibrous bone tissue that forms exists in the form of trabeculae. Individual trabeculae formed in different areas grow and merge with each other. The thickest trabeculae (over 0.4 mm in diameter) contain a blood vessel located in a central narrow channel lined with osteogenic cells. The surface of the trabeculae is covered by a layer of osteoblasts and osteogenic cells. Due to this layer, bone plates are formed on the surface of the immature bone tissue.

Gradually, osteoclasts destroy the primary bone and in its place, layers of parallel plates are formed by appositional growth, forming bone trabeculae from mature bone tissue. The anastomosing network of bone trabeculae forms a spongy substance. With thickening of the trabeculae and reduction of the cavities between them, up to their disappearance, the spongy substance

can be reconstructed into a compact one, consisting of osteons. The length of the osteons of flat bones is quite small compared to the osteons of long tubular bones. In flat bones, the spongy substance is preserved in the form of a very thin middle layer - diploe.

SECTION "QUESTIONS FROM READERS"

(or questions not included in the list, but you never know).

Fracture healing.

In the fracture area, the tissue is damaged, the blood supply is disrupted, and the osteocytes in the adjacent areas of the osteons die. The dying bone undergoes resorption. New tissue, the bone callus, forms between the ends of the fragments (Fig. 6-66). The bone callus occurs as a result of the intensive proliferation of osteogenic cells in the periosteum. Some of these cells differentiate into osteoblasts, which form new bone trabeculae that are firmly attached to the matrix of the fragment. The rate of proliferation of osteogenic cells in the outer part of the bone callus exceeds the growth rate of blood vessels, which determines the appearance of chondroblasts and the formation of hyaline cartilage. Subsequently (as calcification occurs), the cartilage is replaced by immature coarse fibrous bone tissue, in place of which spongy substance is formed. After this, the bone callus is rebuilt: the spongy substance between the fragments is transformed into a compact one, and the original configuration of the bone is restored.

Fig. 6-66.

Fracture healing. Formation of bone callus by proliferation of cells, predominantly osteogenic layer of periosteum (A). Appearance of hyaline cartilage in the outer part of bone callus and gradual spread of cartilage throughout its volume (B). Replacement of cartilage by bone (C). In this case, spongy substance is formed first, later rebuilt into compact (D).

Growth of tubular bones.

lengthening of the diaphysistubular bones involve the epiphyseal plate, represented by hyaline cartilage (Fig. 6-63). It exists until the postnatal growth of the bone in length is completely completed, after which it is replaced by bone tissue. The epiphyseal plate consists of four zones - reserve (resting cartilage); reproduction (proliferating young cartilage); cell hypertrophy and maturation of cartilage; calcification of cartilage and ossification.

Resting cartilage reserve zoneis located in the epiphyseal part of the plate. It consists of hyaline cartilage containing small, randomly scattered chondrocytes. This zone does not participate in the growth of the epiphyseal plate, but serves to fix the plate to the epiphysis.

Breeding area. In this zone there are numerous dividing chondrocytes. These small cells, stacked on top of each other, form isogenic groups in the form of columns located perpendicular to the plane of the plate.

Zone of cell hypertrophy and cartilage maturation. Here are located large vacuolated cells that have left the reproduction zone and are also grouped into columns, having stopped mitosis. The most mature of them, increasing in size even more, shift closer to the diaphysis and actively secrete alkaline phosphatase, which promotes the accumulation of calcium ions and phosphate ions. As the cartilage calcifies, the third zone passes into the fourth.

Cartilage calcification zone, bordering the diaphysis, is very thin; its thickness corresponds to the diameter of one to three cells. In this zone, mineralization of the cartilaginous matrix and death of chondrocytes occur. Blood vessels with accompanying osteogenic cells grow into the forming cavities of the calcified cartilaginous matrix from the diaphysis side. Bone tissue is formed in place of the calcified cartilage. Osteoclasts immediately appear, destroying the "calcified cartilage-calcified bone" complex.

Growth of tubular bones in widthoccurs due to the formation of new layers of bone tissue (formed by appositional growth) by osteogenic cells of the periosteum. From the inside, the bone is resorbed by osteoclasts. As a result, the wall of the diaphysis does not thicken, while the bone marrow cavity increases. As the bone growth is completed, external general plates are formed under the periosteum (also by the appositional mechanism).

Blood. Types of leukocytes. Leukocyte formula.

Leukocytes: quantity, classification. Properties and functions of leukocytes.

Blood- one of the tissues of the internal environment. The liquid intercellular substance (plasma) and the cells suspended in it are the two main components of blood. In an adult, the total blood volume is about 5 liters; about 1 liter is in the blood depot, mainly in the spleen.

Blood circulates in a closed system of vessels and carries gases, nutrients, hormones, proteins, ions, and metabolic products. Blood maintains the constancy of the internal environment of the body, regulates body temperature, osmotic balance, and acid-base balance. Blood cells participate in the destruction of microorganisms, in inflammatory and immune reactions. Blood contains platelets and plasma coagulation factors.

Plasmaconsists of water (90%), organic (9%) and inorganic (1%) substances. Proteins make up 6% of all plasma substances. Among the hundreds of different plasma proteins

They secrete proteins of the blood coagulation system, proteins involved in immune reactions, and transport proteins.

Clotted bloodconsists of a thrombus (clot), which includes blood cells and some plasma proteins, and serum - a clear liquid similar to plasma, but lacking fibrinogen.

Blood cells (formed elements):

Erythrocytes;

Leukocytes;

Platelets.

Leukocytes: 1 liter of blood of an adult healthy person contains 3.8-9.8x109 leukocytes - spherical cells. Their number varies significantly under physiological conditions, changing in the same person due to the time of day, the nature and severity of the work performed, food intake and other factors. Leukocytes in the bloodstream and lymph are capable of active movement, can pass through the wall of blood vessels into the connective tissue of organs, where they perform basic protective functions. Some leukocytes are able to repeatedly return from tissues to the blood (recirculate).

Movement of leukocytescan be divided into passive and active. Passive movement is caused by the transfer of leukocytes with the blood flow. Active movements are accomplished due to the presence of numerous actin microfilaments and proteins associated with them in the cytoplasm of leukocytes; they are accomplished with energy expenditure.

The cytoplasm of leukocytes contains granules - specific (secondary) and azurophilic (lysosomes). Depending on the type of granules, leukocytes are divided into granulocytes (granular) and agranulocytes (non-granular).

Granulocytes(neutrophils, eosinophils, basophils) contain specific and azurophilic granules. Granulocytes are characterized by a lobed segmented nucleus (however, their relatively few less mature forms circulating in the blood have a rod-shaped nucleus) of various shapes, which is why they are called polymorphonuclear leukocytes. Also, granular leukocytes, when staining blood according to Romanovsky-Giemsa, reveal specific granularity in the cytoplasm (eosinophilic, basophilic or neutrophilic)

In the cytoplasm of agranulocytes (monocytes, lymphocytes) there are only azurophilic granules. They are characterized by the absence of specific granularity and non-segmented nuclei.

Leukocyte formula:When conducting a clinical blood test, a differential count of the relative content of individual types of leukocytes is performed on its smears.

The results of such a count are recorded in tabular form in the form of the so-called leukocyte formula, in which the content of cells of each type is presented as a percentage in relation to the total number of leukocytes, taken as 100%:

Kroch, in Russian: leukocyte formula - percentage ratio of the main types of leukocytes.

Blood basophils.

Basophilsmake up 0-1% of the total number of leukocytes in the circulating blood. Basophils remain in the blood for 1-2 days. They are formed in the bone marrow. Like other granulocytes, basophils can leave the bloodstream when stimulated and activated, but their ability to move amoeboidally is limited.

Structure: size - 10-12 µm. Lifespan and fate in tissues are unknown. The compacted nucleus consists of 2-3 indistinct lobes, curved in the shape of the letter S. The cytoplasm contains all types of organelles, free ribosomes and glycogen.

Specific granulesrather large (0.5-1.2 µm), stained metachromatically (from reddish-violet to intense violet). They have a varied, often oval or round shape with dense content. The granules contain various enzymes and mediators. The most significant of these include heparin sulfate (heparin), histamine, serotonin, neutral proteases tryptase and chymase, and inflammation mediators.

Receptors: basophils have high-affinity surface receptors for Fc fragments of IgE produced in response to the action of Ag (allergens).

Functions:Activated basophils, leaving the bloodstream, migrate to the foci of inflammation and participate in allergic reactions. Activation and degranulation of basophils occurs when an allergen enters the body and is mediated by IgE. IgE molecules attach to the basophil (the IgE-basophil complex is formed). When the antigen (allergen) enters again, it binds to two or more IgE molecules on the surface of the basophil, which leads to degranulation of the latter - rapid exocytosis of the contents of the granules. In parallel, metabolites of arachidonic acid are formed. The release of histamine and other vasoactive factors during degranulation and oxidation of arachidonic acid cause the development of an immediate-type allergic reaction. Such reactions are typical, for example, of allergic rhinitis, some forms of asthma, anaphylactic shock.

Eosinophil. Quantitative characteristics, structure, granule contents, functions

Quantitative characteristics and other figures

1-5%of the total number of leukocytes. Their number changes during the day and is highest in the morning

Eosinophils remain in the bone marrow for several days after formation, then circulate in the blood for 3-8 hours, most of them leave the bloodstream and migrate to tissues that are in contact with the external environment (mucous membranes of the respiratory and genitourinary tracts, intestines). Life expectancy is 8-14 days. (In Bykov it is written that the exact life expectancy in tissues has not been established). They can also penetrate into secretions and are found in the composition of nasal and bronchial mucus. They are also found in the lymph nodes and thoracic duct lymph.

The size in the blood is 14-15 microns, after entering the connective tissue the size increases to 20 microns

Structure

The eosinophil (oxyphil) nucleus consists of two large segments connected by a thin bridge (segmented eosinophil). The cytoplasm contains a well-developed granular endoplasmic reticulum, a small number of cisterns of smooth endoplasmic reticulum, clusters of ribosomes, individual mitochondria and a lot of glycogen. They are easily recognized in smears due to numerous eosinophilic granules.

Receptors:mmembrane receptors of Fc fragments of IgG, IgM and IgE, complement components C1s, C3a, C3b, C4 and C5a, as well as eotaxin and IL5.

Contents of granules

The cytoplasm of the eosinophil contains large and small specific granules with pronounced acidophilia (red-orange).

Large granules (specific, eosinophilic):0.5-1.5 µm. They have an ovoid shape and contain a crystalloid of ANTIPARASITIS AGENT - MAIN ALKALINE PROTEIN (MBP). Also present are NEUROTOXIN (PROTEIN X), EOSINOPHILE PEROXIDASE EPO,

HISTAMINASE, PHOSPHOLIPASE D, HYDROLYTIC ENZYMES, ACID PHOSPHATASE, ZINC, CATHEPSIN Small granules (non-specific, azurophilic, primary) (represent

lysosomes): ARYL SULFATASE (inactivates leukotrienes), ACID PHOPHTASE,

PEROXIDASE, CATIONIC PROTEIN OF EOSINOPHILS ECP.

Functions

Prevents the development of allergic reactions.

The contents of the granules block mast cell degranulation, inactivate histamine and LTC4Eosinophils also secrete an inhibitor that blocks mast cell degranulation.

cells. The slow-reacting factor anaphylaxin, secreted by mast cells and basophils, is also inhibited by activated eosinophil.

Antiparasitic.

Provided by the presence in eosinophil granules of basic cationic proteins that destroy the cuticle of parasitic organisms and lipid mediators.

Eosinophil migration is stimulated by eotaxin, histamine, eosinophil chemotactic factor ECF, IL5, etc.

In this case, the contents of the granules are secreted and a respiratory burst occurs simultaneously. a state of phagocytic cells (neutrophils, eosinophils, macrophages), occurring soon after the reception and capture of foreign material. It is manifested by a sharp increase in their metabolic activity. It is accompanied by increased oxygen consumption and the formation of toxic reactive biooxidants - H2O2, superoxide O2- and hydroxyl radical OH-.

After degranulation, eosinophils undergo apoptosis and their fragments are phagocytized by macrophages.

ADDITIONAL INFO FROM BYKOV

Eosinophils differ from neutrophils in their lower mobility and weaker phagocytic activity. At the same time, they are the leading cellular elements in the fight against helminths and protozoa.

Eosinophilia (increased content) - allergic conditions, parasitic diseases, physiological eosinophilia in the first three months of life.

Eosinopenia -acute infections, administration of glucocorticoids, ACTH.

Neutrophil. Quantitative indicators, structure, granule contents, functions Quantitative characteristics and other figures

40-75%of the total number of leukocytes - the most numerous of leukocytes

circulate in the blood for 8-12 hours, after which they are phagocytosed by macrophages

diameter in a blood smear is 12-13 µm, when migrating into tissue it increases to almost 20 µm

Structure

Plasmalemmahas receptors for adhesion molecules, cytokines, colony-stimulating factors (CSF), inflammatory mediators, opsonins (Fc fragments of IgG and C3b component of complement), and some microbial products.

Corehas a different structure in cells of different degrees of maturity, therefore a distinction is made

segmented-lobed nucleus of 2-5 segments connected by constrictions, chromatin is strongly condensed. Sex chromatin is visible in 3% of neutrophils in a woman's blood smear. The most mature and numerous among neutrophils (60-65%).

band-shaped -the nucleus is rod-shaped or horseshoe-shaped, unsegmented or contains only emerging constrictions that deepen as they mature. Contains less heterochromatin. Younger, relatively few in number (3-5%)

young neutrophil granulocytes -the core is bean-shaped and the lightest. The youngest and extremely few in number (up to 0.5%)

Cytoplasm:the number of mitochondria and organelles needed for protein synthesis is minimal, so the life expectancy is minimal. A lot of glycogen, so they can exist in poor O2damaged tissues. Many actin filaments are found mainly in the peripheral part of the cytoplasm, where pseudopodia are formed.

Granules

Azurophilic (non-specific primary): contain proteins that destroy components of the extracellular matrix and have antibacterial activity:

MYELOPEROXIDASE, PROTEINASE 3, AZUROCIDIN, ELASTASE, CATHEPSINS, DEFENSINS, CATIONIC PROTEINS, LYSOZYME, ARYLSULPHATASE, BACTERICIDAL PERMEABILITY-INCREASING PROTEIN (BPI-PROTEIN). These enzymes are active mainly in an acidic environment and ensure intracellular destruction of microbes.

Larger, but fewer in number.

Specific (secondary):proteins with bacteriostatic properties and

destructive extracellular matrix:

LACTOFERRIN, LYSOZYME, METALLOPROTEINASES (GELATINASE AND COLLAGENASE), ALKALINE PHOSPHATASE, partially CATIONIC PROTEINS.

They participate in the intracellular destruction of microbes and are also secreted into the intercellular substance, where they play a role in the mobilization of inflammatory reaction mediators and activation of the complement system. These granules contain adhesive proteins.

Numerous, smaller ones.

Functions

The main cellular elements of the body's non-specific defense.

Destruction of microorganisms: phagocytosis of opsonized microorganisms, since neutrophils are microphages. In the inflammation focus, neutrophils participate in the formation of detritus (pus).

Phagocytosis and digestion occur in parallel with the formation of arachidonic acid metabolites and a respiratory burst..

It is also possible to destroy microorganisms by extracellular, non-phagocytic mechanisms.

Secrete pyrogens - factors that increase body temperature), thereby causing protein denaturation. This is what the lecture says, but the textbook doesn't say a word about it. It lists this function in monocytes.

ADDITIONAL INFO

In addition to specific and azurophilic granules, there are also "incompletely described, recently studied" tertiary gelatinase granules. They contain gelatinase, lysozyme, some other enzymes, adhesive proteins. It is assumed that they participate in the digestion of substrates in the intercellular space, adhesion processes.

Secretory vesicles -are another recently described membrane structure. They have not been found to have any specific content, but it has been established that their membrane carries a large number of adhesive proteins and receptors for chemotactic factors. By fusing with the plasma membrane, they provide an influx of adhesive molecules necessary for the formation of a connection between the neutrophil and the endothelium -FROM BYKOV

3 pools of neutrophils:circulating - in the bloodstream, borderline - associated with the endothelium of small vessels of many organs, reserve - mature neutrophils of the bone marrow - FROM THE RED TEXTBOOK

Monocyte. Quantitative characteristics, structure, functions Quantitative characteristics and other figures

2-9%from all leukocytes in the blood

Diameter approximately 15 µm (up to 20 µm) - the largest leukocytes

They remain in the blood for about 2-4 days (according to the lecture, several hours), after which they go into the tissue and become specific macrophages of this tissue.

Structure

CoreThe large, eccentrically located horseshoe-shaped nucleus has a mottled appearance due to unevenly condensed chromatin.

Cytoplasm:pale bluish-gray (on stained smear) includes numerous lysosomes containing ACID HYDROLASES, ARYLSULPHATASE CATHEPSIN C, ACID PHOSPHATASE, PEROXIDASE, a large number of ribosomes and polyribosomes, Golgi complex, small elongated mitochondria.

Membrane:receptors of the Fc fragment of Ig, complement proteins, cytokines, inflammatory mediators, bacterial products, cholinergic receptors, adrenergic receptors.

Functions

Phagocytosis.

Monocytes phagocytize opsonized particles. Their digestion involves lysosomal enzymes of monocytes, as well as intracellularly formed H2O2, OH, O2. When a large number of monocytes merge to neutralize foreign bodies,

giant complexes of foreign bodies.

participation in immune reactions as antigen-presenting cells, for which the membrane contains proteins of the main histocompatibility type MHC II

form the mononuclear macrophage system

activated monocytes (macrophages) synthesize endogenous pyrogens

ADDITIONAL INFO

Monocyte activation:various substances formed in the foci of inflammation and tissue destruction - agents of chemotaxis and activation of monocytes (IL2, IL4, TNF, IFNgamma, FAT, colony-stimulating factor). As a result of activation, the size increases, metabolism increases, biologically active substances are released (IL1, IL6, tumor necrosis factor alpha-TNFalpha, CSF, prostaglandins, interferons, neutrophil chemotaxis factors). - FROM THE RED STUDY BOOK

Erythrocyte. Quantitative characteristics, structure, functions. Hemoglobin and its types. Destruction of erythrocytes

Quantitative characteristics

The most numerous blood cells. Number of erythrocytes: in women - 3.9-4.9x1012/l, for men - 4.0-5.2x1012/l. (if shorter 3.8-5.5 million erythrocytes in 1 µl of blood). The higher content of erythrocytes in men is due to the erythropoiesis-stimulating effect of androgens.

Hematocrit-the percentage ratio of the volume of red blood cells to the volume of blood. Normally, hematocrit is 40-50% for men, 35-45% for women, and 45-65% for children under 10.

Structure

An anuclear cell with a diameter of 7-8 µm. It has the shape of a biconcave disk with d=8 µm - normocyte.

FROM THE LECTURE: Anisocytosis is a pathological condition in which the size of the red blood cell changes.

d<7 - microcyte, d>9 - macrocyte.

poikilocytosis-change in the shape of the red blood cell. A poikilocyte is formed.

The biconcave shape is due to 3 reasons:

Allows passage through the smallest vessels

Maximum surface area with minimum hemoglobin consumption

Provides minimum distance for gas diffusion

Erythrocyte cytoskeleton proteins:

Actin

Spectrin

ankyrin

Glycophorin

Band 4.1 protein

Band 3 protein

Plasmalemma:is quite plastic, which allows the cell to deform and easily pass through narrow capillaries. The main transmembrane proteins of the erythrocyte are band 3 protein, glycophorins, and the glucose transporter GLUT1. Band 3 protein, together with the proteins of the near-membrane cytoskeleton, maintain the shape of the erythrocyte as a biconcave disk. Glycophorins - their polysaccharide chains contain antigenic determinants (agglutinogens A and B of the AB0 blood group system)

Functions

Respiratory - due to the connection of gases with hemoglobin

Protective and regulatory - due to the ability to carry a number of biologically active substances on the surface, including immunoglobulins, complement components, and immune complexes.

Hemoglobin

Almost the entire volume of the erythrocyte is filled with hemoglobin (Hb). The Hb molecule is a tetramer consisting of four polypeptide chains of globin, each of which is covalently linked to one heme molecule. The main function of Hb is to transfer O2.

Types of hemoglobin.There are several types of hemoglobin, formed at different stages of development and differing in the structure of the globin chains. These types include:

embryonic (HbE)-for a 19-day embryo up to 3-6 months of pregnancy

fetal(HbF) - 8-36 weeks of pregnancy and make up 90-95% of fetal hemoglobin.

definitive hemoglobin (96-98% HbA, 1.5 - 3% HbA2) - in an adult.

Forms of hemoglobin. The following forms of hemoglobin are distinguished: oxyhemoglobin,

carbhemoglobin, methemoglobin(iron +3), carboxyhemoglobin (HbCO), glycosylated hemoglobin.

Destruction

The destruction of red blood cells that have completed their life cycle occurs mainly in the spleen, as well as in the liver and bone marrow.

Since enzyme synthesis is impossible in the erythrocyte, over time, its metabolism decreases, its shape is disrupted, proteins degrade, and new antigens appear. Such aging cells are recognized by macrophages and phagocytized. In erythrocytes, the so-called "aging antigen" is presented as a degraded protein of band 3. 0.5-1.5% of the total mass of erythrocytes is removed from the bloodstream per day (40,000-50,000 cells/μl).

Hemolysis-destruction of red blood cells due to internal defects and under the influence of microenvironmental factors. Leads to a decrease in circulating red blood cells - hemolytic anemia.

Platelet. Quantitative indices, structure, granule contents, functions

THE CORRECT MODERN NAME IS BLOOD PLATELES, not thrombocytes.

Quantitative indicators and other numerical characteristics

190 - 400 thousandin 1 µl of blood. Two-thirds of the platelets circulate in the blood, the rest are deposited in the spleen

8 dayslife expectancy. Old and defective platelets are phagocytized in the spleen, liver and bone marrow.

3-5 micronsdiameter

Structure

Fragments of the cytoplasm of megakaryocytes located in the red bone marrow.

Glycocalyx. The platelet is surrounded by a thick layer of glycocalyx, rich in acidic glycosaminoglycans. The glycocalyx forms fibrillar bridges between the membranes of adjacent platelets during their aggregation.

Plasma membranecontains glycoproteins that act as adhesion and aggregation receptors.

Cytoplasmon a stained smear - purple and granular. Platelets contain a large number of mitochondria, elements of the Golgi complex and ribosomes, as well as glycogen granules and enzymes for aerobic and anaerobic respiration.

The peripheral part of the cytoplasm contains actin, myosin, gelsolin and other contractile proteins involved in platelet rounding and thrombus retraction.

There are also bundles of microtubules, circularly located under the plasma membrane.

These microtubules are essential for maintaining the oval shape of the platelet.

Along the periphery of the platelet are anastomosing marginal membrane canals opening into the extracellular environment; their membranes are associated with cytoskeletal elements. The system of these canals participates in the secretion of the contents of α-granules. In addition to α-granules, platelets contain 3 more types of granules - δ-, λ-granules and microperoxisomes.

STRUCTURE BY LECTURE

The platelet consists of 2 parts:

Peripheral zone - hyalomer

Central zone with granules - granulometer

Contents of granules

α-Granules(300-500 nm) are most important for the implementation of platelet functions and contain a variety of substances.

THROMBOCYTE FACTOR 4 - regulates the permeability of the vascular wall, mobilization of Ca2+from bone, chemotaxis of monocytes and neutrophils, is able to neutralize the anticoagulant properties of heparin

PLATELET GROWTH FACTOR (PDGF), TRANSFORMING GROWTH FACTOR β (TGFb) - chemoattractants for leukocytes and fibroblasts. Stimulate fibroblast proliferation, accelerating healing.

THROMBOSPONDIN binds to other molecules and promotes platelet adhesion and aggregation

FACTOR V BLOOD COAGULATION - cofactor for factor Xa-mediated activation of prothrombin and conversion to thrombin

P-SELECTIN is a membrane protein adhesion receptor.

Glycoproteins - fibronekin, fibrinogen, von Willebrand factor.

δ-Granules(250-300 nm) have a compacted core and accumulate

inorganic phosphate (P), ADP, ATP, Ca2+, serotonin and histamine (serotonin and histamine come from plasma)

λ- Granules(200-250 nm) contain lysosomal enzymes. May participate in thrombus dissolution.

Microperoxisomes- a few granules with peroxidase activity.

Functions

Participation in blood clotting processes in 2 ways:

a) formation of a thrombus due to adhesion

b) secretion of internal factors regulating the cascade mechanism of blood coagulation

More details from the red textbook: Under physiological conditions, platelets do not attach to the vascular endothelium. When the integrity of the vascular wall is compromised, a thrombus is formed with the direct participation of platelets. In particular, platelets release fibrinogen (in addition to that already present in the plasma under normal conditions), which, with the help of coagulation factors, is converted into fibrin, which forms a dense fibrous base to which more and more platelets and other blood cells attach.

restoration of vascular integrity

Lymphocytes. Formation, quantitative characteristics, structure, morphological and functional classification.

Education

Lymphocytopoiesis:

The hematopoietic stem cell (CFU-blast) gives rise to a pluripotent colony-forming unit of lymphocytopoiesis (CFU-Ly). B-lymphocytes are formed in the bone marrow, and T-lymphocytes mature in the thymus.

In the formation of lymphocytes, two stages are distinguished - lymphoblast and prolymphocyte. Lymphoblast is much larger than mature lymphocyte. The main feature of lymphocytopoiesis

gradual and significant decrease in cellular volume.However, many circulating lymphocytes respond to antigenic stimulation by increasing cell volume, acquiring lymphoblast morphology.

Unlike other blood cells, lymphocytes can proliferate outside the bone marrow. This occurs in the tissues of the immune system in response to antigen stimulation.

Quantitative characteristics

20-45% of the total number of leukocytes circulating in the blood.

Blood is the medium in which lymphocytes circulate between the organs of the lymphoid system

other tissues. Lymphocytes leave the vessels into the connective tissue in response to appropriate signals. Lymphocytes can migrate through the basement membrane and penetrate the epithelium (for example, in the intestinal mucosa). Life expectancy is from several months to several years.

Structure

The nucleus is round with small indentations or bean-shaped. The chromatin is highly condensed. The cell

has a small volume of cytoplasm, forming a narrow rim around the nucleus. The cytoplasm contains a minimal amount of normal organelles. The lymphocyte forms short cytoplasmic processes

Classification

Functional: B-lymphocytes, T-lymphocytes and NK cells (3 subpopulations)

Morphological: small (4.5-6 µm or <7 µm), medium (7-10 µm or <10 µm) and large lymphocytes (10-18 µm or >10 µm).

B-lymphocytes. Formation, structure, functions. Structure and function of plasma cells

Formation of B-lymphocytes

Differentiation of B lymphocytes begins in the liver at the 9th week of development and continues in the red bone marrow, where it is maintained throughout life.

The signal to initiate differentiation comes from the stromal cells of the bone marrow. The following stages of B-lymphocyte maturation are distinguished: early pro-B-lymphocyte → late pro-B-lymphocyte → large pre-B-lymphocyte → small pre-B-lymphocyte → immature B-lymphocyte → mature B-lymphocyte. From the red bone marrow, B-lymphocytes migrate to the thymus-independent zones of the lymphoid organs. The activated mature B-lymphocyte differentiates into a lymphoblast and then into a plasma cell that secretes immunoglobulins.

Structure

Morphologically, it belongs to small lymphocytes. It has a round nucleus with small notches, containing condensed chromatin, the cytoplasm forms a narrow ring around the nucleus. The activated AG B-lymphocyte already belongs to medium and large lymphocytes. Short processes (microvilli) are formed.

Functions of B-lymphocytes

They make up less than 10% of blood lymphocytes. On their surface they have a receptor Ag-monomer Ig M, which interacts with AG. B-lymphocyte processes AG and presents its fragment in connection with the MHC II molecule on their surface. This complex recognizes T-helper, selected with the help of the same AG, B-lymphocyte is activated and differentiates into plasma cell and memory cell.

Plasma cell

The activated B lymphocyte divides for about 5 days and, forming a clone, differentiates into a plasma cell and a memory B cell.

Function: Plasma cells produce immunoglobulins and serve as the main effector cells of humoral immunity. A plasma cell synthesizes AT of one type. Secretion of Ig is stimulated by IL 6, released by activated T-helpers. Plasma cells are rare

peripheral blood, they are mainly present in the bone marrow, lymph nodes and spleen, as well as in the loose connective tissue of the mucous membranes.

Structure: The plasma cell has a round or fan-shaped form, with a diameter of 8-15 μm. It contains a large oval eccentrically located nucleus with characteristic clumps of heterochromatin. Euchromatin occupies a smaller volume of the nucleus, but it is with it that the transcription of genes encoding immunoglobulins is associated. The ratio of the volume of the nucleus to the volume of the cytoplasm is very large and fluctuates from 2:1 to 1:1. In the cytoplasm, there is a well-developed Golgi complex and a mass of large cisterns of the granular endoplasmic reticulum, concentrically located around the nucleus. The life span of a plasma cell is 4-5 days.

T-lymphocytes

T-lymphocytes include:

Lymphocytes proliferating and differentiating in the thymus

Doing this in other organs of defense, but under the influence of thymus hormones (thymosin,

thymopoietin, thymostimulin).

Education

Differentiation of T lymphocytes occurs in the thymus from precursor cells that enter the thymus gland from the bone marrow. Differentiation is an antigen-independent maturation of T cells. Here, T lymphocyte precursors begin to express specific markers (differentiation molecules): αβT cell receptor, CD2, CD3, CD4 or CD8. After leaving the thymus, T lymphocytes express either CD4 or CD8, cells of the CD4 phenotype+CD8+are absent.

Mature T-lymphocytes leave the thymus, circulate in the peripheral blood and lymph, and settle in the lymphoid organs.

Function

T-lymphocytes (thymus-dependent) make up the majority of blood lymphocytes (more than 80%), are responsible for the cellular immune response, and also help B-lymphocytes react to antigens when

humoral immune response. T-lymphocytes recognize antigen that has been previously processed and presented on the surface of antigen-presenting cells. T-lymphocytes destroy abnormal cells in their own body, participate in allergic reactions, and rejection of foreign transplants. T-cells consist of functional subtypes CD4+ and CD8+.

Classes of T-lymphocytes

T-helpers (TH) - CD4+ T-cells.

They enhance both humoral and cellular immunity by synthesizing cytokines (lymphokine hormones): IL2, IL4, IL5, IL6, γ-interferon. Thus, they support the number of the entire pool of lymphocytes in the body. They are a target of HIV. During the immune response, they recognize MHC class II molecules.

Cytotoxic T lymphocytes (TC) - CD8+ T cells, T-killers

They ensure the development of cellular immunity, which is understood as:

A) destruction of altered cells of the body (infected with a virus, tumor, old, mutated cells)

B) transplant rejection

These cells are destroyed using perforin, which interacts with the MHC class I molecule embedded in the plasma membrane of the target cell.

T-suppressors (TS)- representatives of CD8+ T cells - regulate the intensity of the immune response by suppressing the activity of Tncells; prevent the development of autoimmune reactions; protect the body from the undesirable consequences of the immune reaction.

The lecture highlights memory T cells as a separate class. They live for 30-50 years and ensure the development of cellular immunity when AG is repeatedly introduced.

T-helpers. Formation, functions- see question 101

T-killers -see question 101

Age-related changes in the cellular composition of the bloodErythrocytes

1. At birth and in the first hours of life, the number of red blood cells in the blood is increased and is 6-7 million in 1 μl. During the first day of the postnatal period, the number of red blood cells decreases, by 10-14 days it reaches the level of an adult, but continues to decrease.

The minimum indicator is observed at 3-6 months of life (physiological anemia), when the level of erythropoietin is reduced. This is due to a decrease in the synthesis of erythropoietin in the liver and the beginning of its production in the kidney.

In the 3rd-4th year of life, the number of erythrocytes is reduced (lower than in an adult), i.e. there are less than 4.5 million of them in 1 liter.

The red blood cell count reaches adult levels during puberty.

2. In newborns, anisocytosis with a predominance of macrocytes, as well as an increased content of reticulocytes, is observed.

Leukocytes

The number of leukocytes in newborns is increased and amounts to 10-30 thousand per µl.

The number of neutrophils is 60.5%, eosinophils - 2%, basophils - 0.2%, monocytes - 1.8%, lymphocytes - 24%.

During the first two weeks of life, the number of leukocytes decreases to 9-15 thousand, by the age of 4 it decreases to 7-13 thousand, and by the age of 14 it reaches the level typical for an adult. The ratio of neutrophils and lymphocytes changes, which causes the occurrence of so-called physiological crossovers. (there is a graph in the lecture)

First cross. In a newborn, the ratio of these cells is the same as in an adult. Subsequently, the content of neutrophils decreases, and lymphocytes increases, so that on the 3-4th day their number is equalized. Subsequently, the number of neutrophils continues to decrease and by 1-2 years reaches 25%. At the same age, the number of lymphocytes is 60-65%.

Second cross. Over the next few years, the number of neutrophils gradually increases and the number of lymphocytes decreases, so that at 3-4 years of age these indicators equalize again and make up 35% (40%) of the total number of leukocytes. The number of neutrophils continues to increase and the number of lymphocytes decreases, and by the age of 14 these indicators correspond to those of an adult.

The structure of the bone marrow, its functions

Structure: Red bone marrow contains a large number of maturing erythrocytes, which gives the bone marrow foci of hematopoiesis a red color.

The stroma consists of reticular cells with long processes, reticulin fibers, sinusoidal capillaries and adipocytes, which make up almost half of the volume of the bone marrow.

Bone marrow stromal cells express a wide range of adhesion molecules that mediate the binding of hematopoietic stem cells to elements of the extracellular matrix. Reticulin fibers, together with the processes of reticular cells, form a three-dimensional network and form cavities filled with islands of hematopoietic cells. Mature blood cells enter the bloodstream through gaps in the wall of sinusoidal capillaries. Bone marrow contains a large number of macrophages located near the sinusoids.

Functions:

hematopoiesis

removal of old and defective blood cells from the bloodstream, such as those in the spleen and liver

plays a central role in immune defense, since B-lymphocytes are formed in it, and a large number of plasma cells that synthesize antibodies are also present.

Red bone marrow is located mainly inside the pelvic bones, ribs, sternum, skull bones, inside the epiphyses of long tubular bones, and to a lesser extent, inside the vertebral bodies.

Yellow bone marrow.In adults, most of the bone marrow becomes inactive; fat cells predominate in it. Yellow bone marrow, however, can restore its activity if it is necessary to enhance hematopoiesis (for example, in chronic hypoxia or severe bleeding)

Hematopoietic stem cell (HSC), its properties

The hematopoietic stem cell is morphologically similar to a small lymphocyte and is capable of differentiating into all blood cells. Such a cell was called CFU-blast (CFU - Colony Forming Unit).

A hematopoietic stem cell divides continually but rarely.However, it can be involved in proliferation with significant blood loss and under the influence of growth factors. The division of HSC is stimulated by stem cell factor (SCF), which is produced by bone marrow stromal cells and is fixed on the surface of stem cells by the proto-oncogenic protein c-kit.

Daughter cells choose symmetrical or asymmetrical division, i.e. they either remain hematopoietic stem cells or differentiate into pluripotent descendants with their subsequent differentiation into blood cells.

The cells formed during division differentiate into proliferating pluripotent cells.

precursors (colony forming units) of lymphocytopoiesis (CFU-Ly)and myelopoiesis (CFU-

GEMM).As a result of division of CFU-Ly and CFU-GEMM, their descendants remain pluripotent or

differentiate into one of several types of committed unipotent cells

(colony-forming units), also actively proliferating, but differentiating only in

in one direction.

Unipotent committed cellsare capable of differentiating into one cell type, proliferate, and differentiate into progenitor cells in the presence of growth factors. Unipotent cells are morphologically indistinguishable from stem cells. Programming of a cell to a particular differentiation pathway (commitment) apparently occurs randomly.

Progenitor cells- cells of the same line, differing morphologically and formed sequentially in each line, starting with a committed unipotent cell and ending with the formation of a mature blood cell.

All this was info from the textbook. And now there will be signs of hematopoietic stem cells from the lecture:

self-sustaining population of cells

external resemblance to a small lymphocyte

not sensitive to request

microenvironment (osteoblasts, osteoclasts, fat cells, reticular cells, macrophages, developing blood cells) can influence the rate of HSC proliferation, but does not affect the direction of differentiation

the rate of proliferation of HSCs is unlimited

SC differentiation is irreversible

PROPERTIES OF BYKOV

They are capable of forming all types of formed elements of the blood (i.e. they have true pluripotency).

Resistant to the effects of damaging factors (compared to more differentiated cells).

They are located in places that are well protected from external influences (cells in bone tissue) and have an abundant blood supply.

. They circulate in the blood, migrating to other hematopoietic organs.

Hematopoiesis in the embryo and fetus. Main stages, their characteristics

In the embryo and fetus, sequentially and with partial overlap in the time of occurrence and attenuation, megaloblastic, hepatosplenothymic stages and bone marrow hematopoiesis are distinguished.

Megaloblastic stage.

In the extraembryonic mesoderm of the yolk sac, during the 3rd week, clusters of mesenchymal cells are formed - blood islands. Cells located along the periphery of the island differentiate into endothelial cells of the primary blood vessels. In the central part of the island, the first blood cells are formed - primary erythroblasts - large cells containing a nucleus

embryonic hemoglobins. There are no leukocytes or thrombocytes at this stage. At the 12th week, hematopoiesis in the yolk sac ends.

Hepatosplenothymic stage

It begins in the second month of development, when hematopoietic stem cells populate the liver, spleen and thymus.

Liver.In the liver, hematopoiesis begins at 5-6 weeks of development. Erythrocytes, granulocytes, and thrombocytes are formed here. By the end of the 5th month, the intensity of hematopoiesis in the liver decreases, but continues to a small extent for several weeks after birth.

Spleen. Hematopoiesis in the spleen is most pronounced from the 4th to the 8th month of intrauterine development. Erythrocytes and a small number of granulocytes and thrombocytes are formed here. Immediately before birth, the most important function of the spleen becomes the formation of lymphocytes.

Thymus.In the thymus gland, the first lymphocytes appear at 7-8 weeks.

Bone marrow hematopoiesis.

During the 5th month of development, hematopoiesis begins in the bone marrow, and by the 7th month, the bone marrow becomes the main organ of hematopoiesis. After birth and until puberty, the number of foci of hematopoiesis in the bone marrow decreases, although the bone marrow fully retains its hematopoietic potential. In adults, hematopoiesis is limited to the bone marrow and lymphoid tissue. When the bone marrow is unable to satisfy the increased and prolonged demand for blood cell formation, the hematopoietic activity of the liver, spleen, and lymph nodes can be restored (extramedullary hematopoiesis).

Erythropoiesis. Differentiation of erythrocytes and characteristics of cells of different stages as the erythrocyte matures. Hormonal regulation of erythropoiesis

The beginning of the erythroid series is the burst-forming unit of erythropoiesis (BFU-E), which originates from CFU-GEMM. From BFU-E, a unipotent colony-forming unit of erythropoiesis (CFU-E) is formed. At further stages of erythropoiesis, proerythroblasts, erythroblasts, reticulocytes and erythrocytes differentiate from CFU-E. The duration of erythropoiesis (from stem cell to erythrocyte) is 2 weeks.

Stages of erythropoiesis

Erythropoiesis burst-forming unit(BFU-E) and unipotent colony-forming unit of erythropoiesis (CFU-E). The differences between the burst-forming unit of erythropoiesis (BFU-E) and the unipotent colony-forming unit of erythropoiesis (CFU-E) are that the former responds to IL3 but is not sensitive to erythropoietin, while CFU-E is dependent on erythropoietin for proliferation and differentiation. BFU-E is separated from cells in a state of terminal differentiation by 12 cell generations, and six or fewer cell divisions occur from the CFU-E stage to mature cells.

Proerythroblasts- the first morphologically recognizable precursors of erythrocytes - large cells (diameter 20-25 µm) with numerous organelles, but without hemoglobin (Hb). The pale nucleus is located centrally. The volume of the cytoplasm is about 20% of the total cell volume; it contains quite a lot of polyribosomes, which causes the basophilia of the cell. Proerythroblasts undergo multiple mitoses.

Erythroblasts. At further stages of differentiation, there is a decrease in cell size, chromatin condensation and a decrease in the diameter of the nucleus, progressive loss of organelles and RNA, a gradual increase in the Hb content, and elimination of the nucleus. Basophilic, polychromatophilic and oxyphilic (normoblasts) erythroblasts are successively distinguished.

Basophilic erythroblastsomewhat smaller (diameter 16-18 μm) than the proerythroblast, contains a nucleus with denser chromatin. The cytoplasm is more basophilic. The cell retains the ability to undergo mitosis and actively synthesizes Hb, contains a well-developed protein-synthesizing apparatus that synthesizes globins for the construction of Hb. At the same time, receptor-mediated endocytosis of iron-bound transferrin occurs. Iron enters the erythroblast, and free transferrin returns to the plasma.

Polychromatophilic erythroblast- a cell with a diameter of 12-15 μm, contains a significant amount of Hb. The gray tone of the cytoplasm is due to the basophilic staining of ribosomes and oxyphilic staining of Hb. The size of the nucleus decreases. The cells continue to synthesize Hb and can divide.( according to the lecture at this stage the division stops)

Oxyphilic erythroblast (normoblast)) has small dimensions (diameter 10-12 microns) and

acidophilic cytoplasm with traces of basophilia. The nucleus is small, contains condensed chromatin. At this stage, erythroid cells lose the ability to divide and push out the pycnotic (degenerating) nucleus. The protein synthesizing apparatus disintegrates almost completely.

Reticulocytes (diameter of 6-8 μm) contain remnants of ribosomes and RNA, forming network-like structures. Reticulocytes enter the bloodstream and make up to 1% of the total number of circulating red blood cells. They are capable of performing all gas exchange functions. After entering the bloodstream, during the first 24-48 hours, the reticulocyte completes its maturation and becomes an erythrocyte. In this case, the cell acquires the shape of a biconcave disk, and the last remaining organelles are destroyed by enzymes.

Discocyte.(the textbook does not highlight this stage separately)

Hormonal regulation of erythropoiesis

The regulation of the erythropoiesis process is carried out by a number of humoral factors, of which the most important are:

IL-3 -stimulates proliferative activity of BFU-E

erythropoietin- stimulates proliferation of CFU-E

Erythropoietin In adults, 90% is produced by the kidney and 10% by the liver (the latter,

however, serves as its main source in the fetus) in response to hypoxia. Its action

is enhanced by androgens, growth hormone, thyroxine and weakened by estrogens

(that is why women have lower levels of red blood cells and hemoglobin in their blood than men).

Iron, folic acid and vitamin B12 are also necessary for normal erythropoiesis.

Granulocytopoiesis. Characteristics of cells at different stages as neutrophils, eosinophils, and basophils mature

Granulocytes are formed in the bone marrow. Neutrophils from the pluripotent colony-forming unit of neutrophils and monocytes/macrophages (CFU-GM), and basophils and eosinophils from the unipotent colony-forming units of basophils (CFU-B) and eosinophils (CFU-Eo), respectively.

As differentiation occurs, the size of the cells decreases, chromatin condenses, the shape of the nucleus changes, and granules accumulate in the cytoplasm.

Specific granules appear at the myelocyte stage; from this point on, the cells are named according to the type of mature granulocytes they form.

Cell division ceases at the metamyelocyte stage.

Stages.

Myeloblast- a poorly differentiated cell with a diameter of about 15 µm. A large round or oval nucleus is located eccentrically, contains 1-3 nucleoli. The cytoplasm is slightly basophilic, devoid of granules.

promyelocyte. Large cells (15-24 µm) containing more condensed chromatin. The round nucleus is located eccentrically. The cytoplasm contains azurophilic granules.

Myelocyte. The cell size is smaller (12-16 µm), a significant number of specific granules appear, which allows us to distinguish 3 types of myelocytes: neutrophilic, eosinophilic and basophilic. The nucleus gradually acquires a bean-shaped form, the chromatin becomes more condensed.

Metamyelocyte. As a result of myelocyte division, neutrophilic, eosinophilic and basophilic metamyelocytes are formed. The size of these cells is even smaller (12-14 µm); the content of specific granules is significantly greater than at the previous stage. Deep notches appear in the nucleus, chromatin is even more condensed. The ability to undergo mitosis is lost.

Band granulocyte- cells that immediately precede mature forms. Their diameter is 10-12 µm, the nucleus is horseshoe-shaped. These cells can already enter the bloodstream and make up 3-5% of the total number of circulating leukocytes.

SegmentedGranulocyte - mature forms. The segmented nucleus contains dense chromatin.

Monocytopoiesis

Monocytes and granulocytes (neutrophils) have a common precursor cell, the colony-forming unit of granulocytes (neutrophils) and monocytes (CFU-GM), which is formed from the pluripotent colony-forming unit of myelopoiesis (CFU-GEMM). CFU-GM gives rise to the unipotent colony-forming units of monocytes (CFU-M) and granulocytes (neutrophils) (CFU-G).

Before reaching the mature monocyte stage, the cells undergo three divisions. The size of the cells gradually decreases, and notches appear in the nucleus. All mature monocytes leave the bone marrow shortly after formation. For 2-4 days, monocytes remain in the bloodstream and then migrate into the tissues.

Differentiation of monocytes. CD14+ monocytes leave the bloodstream and enter tissues where they differentiate into dendritic cells and macrophages, the totality of which (together with monocytes) constitutes the mononuclear phagocyte system.

Stages:

monoblast - active division

promonocyte - division stops

monocyte

macrophage

Thrombocytopoiesis

Platelets are formed by the largest (up to 100 µm) cells of the bone marrow - megakaryocytes, their precursor - the megakaryoblast - a descendant of the unipotent megakaryocyte precursor cell (CFU-Meg), originating from the pluripotent colony-forming unit of myelopoiesis (CFU-GEMM).

Megakaryocytes are characterized by a polyploid and lobed nucleus with diffusely distributed chromatin.

The cytoplasm is weakly basophilic, contains small granules and demarcation membranes - a system of interconnected vesicles and tubes associated with the cell membrane. Demarcation membranes perform a demarcation function in the formation of future blood platelets (thrombocytes) as part of the thrombocyte fields.

Thus, platelets are formed by fragmentation of the cytoplasm of the megakaryocyte.

Stages of platelet formation

megakaryoblast- actively shares

promegakaryocyte- cells increase in size, lipids, glycogen, and DNA accumulate.

MegakaryocyteA piece of cytoplasm breaks off from it.

Mononuclear system of phagocytes. Properties and types of cells united in the system. Examples

Connective tissue macrophages are part of the mononuclear phagocyte system.

Cells of the mononuclear phagocyte system differ from other phagocytic cells in three ways:

have macrophage morphology

originate from monocytes or their precursors in the bone marrow, which circulate in the blood for several hours and then migrate into the tissues.

Their phagocytic activity is modulated by Ig and complement components.

Macrophages belong to a heterogeneous population of cells (histiocytes, liver stellate macrophages, osteoclasts, microglia) expressing phenotypes that differ in morphological and functional properties.

Examples:bones - osteoclasts, lungs - alveolar macrophages, skin - Largenhans cells (intraepidermal dendrocytes), connective tissue - histiocytes, peritoneal fluid - peritoneal macrophages, nervous tissue - microglial cells, placenta - Hofbauer cells, liver - Kupffer cells (stellate macrophages), also foreign body giant cells and macrophages of hematopoietic organs.

Skeletal Muscle Tissue. Connective Tissue in Skeletal Muscle. Signs: 1) contractility

actomyosin chemomechanical transducer

mesodermal origin

4) intermediate filaments are formed by the protein desmin

transverse striation

Function: Provides conscious and aware voluntary movements of the body and its parts. Structure: 1) Structural and functional unit of skeletal muscle - muscle fiber, which is a symplast (contraction function)

satellite cells (cambial reserve)

*Symplast-a large multinucleated cellular formation that appears as a result of the fusion of a large number of cells.

The transverse striations are due to the presence of sarcomeres, which are a consequence of the special packaging of proteins.

Connective tissue:

Endomysium -loose fibrous connective tissue between individual muscle fibers, contains blood and lymphatic vessels, nerve fibers.

2. Perimysium - fibrous connective tissue surrounds groups of muscle fibers in the form of a sheath and forms bundles.

3. Epimysium - a dense connective tissue sheath surrounding the set of bundles that form the muscleDevelopment is not asked in the question, but it is in the textbook, so I will include it just in case.

Sources of development histological elements of skeletal muscle tissue - myotomes The myogenic cell type is sequentially composed of the following stages: myotome cells (migration) → mitotic myoblasts (proliferation) → postmitotic myoblasts (fusion) → muscle tubes (synthesis of contractile proteins, formation of sarcomeres) → muscle fibers (contraction function).

• Muscular tube.After a series of mitotic divisions, myoblasts acquire an elongated shape, line up in parallel chains and begin to merge, forming muscle tubes (myotubes). In muscle tubes, contractile proteins are synthesized and myofibrils are assembled - contractile structures with characteristic transverse striations. The final differentiation of a muscle tube occurs only after its innervation.

• Muscle fiber. The movement of the symplast nuclei to the periphery completes the formation of striated muscle fiber.

Skeletal muscle fiber. General characteristics of the structureThe structural and functional unit of skeletal muscle is the symplast - the skeletal muscle fiber has the shape of an extended cylinder with pointed ends. This cylinder reaches 40 mm in length with a diameter of up to 0.1 mm.

“fiber sheath” - sarcolemma = plasmalemma symplast + basement membrane.

Satellite cells with oval nuclei are located between the plasma membrane and the basement membrane.

The rod-shaped nuclei of muscle fibers lie in the cytoplasm (sarcoplasm) under the plasma membrane.

The sarcoplasm of the symplast contains the contractile apparatus - myofibrils (SFU of muscle fiber, and the sarcomere - SFU of myofibrils), the Ca2+ depot - the sarcoplasmic reticulum (smooth ER), and

also mitochondria and glycogen.

From the surface of the muscle fiber, tubular invaginations of the sarcolemma - transverse tubules (T-tubules) - extend to the expanded areas of the sarcoplasmic reticulum.

Myofibrils

The transverse striation of skeletal muscle fiber is determined by the regular alternation

myofibrils of differently refracting polarized light sections (disks) - isotropic and anisotropic: light (Isotropic, I-disks) and dark (Anisotropic, A-disks) disks. Different refraction of disks is determined by the ordered arrangement of thin and thick threads along the length of the sarcomere. Thick threads are dark disks (their length does not decrease during contraction!), thin threads are light disks. Each light disk is crossed by a Z-line. The section of the myofibril between adjacent Z-lines is defined as a sarcomere.

Sarcomere. Structural organization

The sarcomere is formed by thin (actin) and thick (myosin) filaments located parallel to each other. The I-disk contains only thin filaments. The Z-line runs through the middle of the I-disk. One end of the thin filament is attached to the Z-line, and the other end is directed toward the middle of the sarcomere. The thick filaments occupy the central part of the sarcomere, the A-disk. The thin filaments partially enter between the thick filaments. The section of the sarcomere containing only thick filaments is the H-zone. The M-line runs through the middle of the H-zone. The I-disk is part of two sarcomeres. Therefore, each sarcomere contains one A-disk (dark) and two halves of the I-disk (light), the sarcomere formula is 1/2 I + A + 1/2 I.

Proteins:• titin - connects myosin and Z-lines

α-actinin (in the textbook nebulin)- connects actin filaments and Z-lines

desmin-connects the Z-lines of adjacent myofibrils

vimentin -intermediate filament protein of the Z-line

Triads of skeletal muscle fiber and dyads of cardiomyocytes. Structure, function

On the membrane of the muscle fiber there are invaginations - transverse T-tubes.

In skeletal myofibrils they approach the myofibrils at the level of the boundaries between the dark and light discs, and in cardiomyocytes - at the level of the Z-lines.

In addition, each myofibril is surrounded by regularly repeating elements of smooth muscle fiber - anastomosing membrane tubes ending in terminal cisterns.

Skeletal MV: each T-tube is adjacent to 2 cisterns of the SPRtriad Cardiomyocyte: each T-tubule is adjacent to 2 cisterns of the SPRdyad Sarcoplasmic reticulum - modified smooth ER, Ca depot2+ Function of triads and dyads- coupling of excitation and contraction.

*When an action potential arises in a muscle, it spreads along the superficial plasma membrane, as along an unmyelinated nerve fiber. Then, along the T-system, the action potential spreads deep into the fiber. In this case, excitation is transmitted to the membrane of the sarcoplasmic reticulum. As a result, the permeability of the sarcoplasmic reticulum for Ca2+ ions increases and they enter the interfibrillar space.

Structure of thin (actin) filaments of the sarcomere

They contain the contractile protein actin and two regulatory proteins, troponin and tropomyosin. The latter form a functionally unified troponin-tropomyosin complex.

Actin In monomeric form, it is represented by polar globular subunits with a diameter of 4-5 nm (G-actin), which have active centers capable of binding to myosin molecules. G-actin aggregates to form polymeric fibrillar actin (F-actin), the molecule of which has the appearance of two twisted threads with a thickness of 7 nm and variable length.

Tropomyosin is represented by thread-like molecules that are connected at their ends, forming a long thin strand lying in a groove formed by intertwined F-actin threads. Since there are two such grooves on an actin molecule, there are also two tropomyosin threads. In total, the thin thread contains approximately 50 tropomyosin molecules.

Troponin is a globular protein, each molecule of which is located on the tropomyosin molecule near its end. Troponin consists of three subunits: TnC, which binds calcium, TnT, which attaches to tropomyosin, and TnI, which inhibits the binding of myosin to actin.

There is no question about thick threads, but they are in the textbook and lectures, so read them just in case

Each myosin filament consists of 300-400 molecules of myosin and C-protein. The giant protein titin links the free ends of the thick filaments to the Z-line.

Myosin: the molecule is a dimer. It consists of 2 heavy chains - heavy meromyosin (sections

headsand necks that connect them to the stem part) and 4 light chains - light meromyosin

("kernel"myosin molecules). The light chains are attached to the heads by electrostatic force.

interactions. 2 hinge areas: in the area of the connection of heavy and light meromyosins and in the neck area. Myosin heads have ATPase activity, but in the absence of its interaction with actin, the rate of ATP hydrolysis is negligible.

WITH-proteinstabilizes the structure of myosin filaments. Affects the aggregation of myosin molecules, ensures uniform diameter and standard length of thick filaments.

The role of calcium in muscle fiber contraction

When an impulse is received, Ca is released from the cisterns.2+, which diffuses to the thin filaments of the sarcomere, where it binds to troponin C. This leads to a change in the transformation of the troponin-myosin complex, as a result of which the actin regions necessary for interaction with the myosin heads are released.

At the same time, Ca2+ leads to the appearance of ATPase activity, as a result of which energy appears, phosphorylation processes occur and myosin heads begin to walk along actin.there is a reduction

Satellite cells of skeletal muscle fiber. Origin, localization, structure, functions

Fig. Histogenesis of skeletal muscle tissue. MGCs — myogenic cells give rise to myoblasts (MBL) of two different types — MBL1 and MBL2. MBL1 form chains (a), merge with each other (b) and with myosatellite cells (MSC) — derivatives of MBL2, forming a muscular tube (c), which gradually turns into a muscular fiber (d). MF — myofibrils, BM — basement membrane.

Origin:myosatellites- G1 myoblasts isolated during myogenesis, which do not participate in the formation of symplasts, but remain as separate independent cells.

L: They are located between the basement membrane and the plasmalemma of muscle fibers. The nuclei of these cells make up 30% of the total number of skeletal muscle fiber nuclei in newborns, 4% in adults, and 2% in the elderly.

F: Satellite cells are a cambial reserve of skeletal muscle tissue. They retain the ability to myogenic differentiation, which ensures the growth of muscle fibers in length in the postnatal period. Satellite cells also participate in the reparative regeneration of skeletal muscle tissue.

WITH: retain a poorly differentiated state, have a large nucleus and little cytoplasm.

Contractile (working) cardiomyocytes. Structure, organization of muscle fibers

Working cardiomyocytes are morpho-functional units of cardiac muscle tissue, have a cylindrical branching shape. With the help of intercellular contacts (intercalated disks), working cardiomyocytes are united into so-called cardiac muscle fibers - a functional syncytium - a collection of cardiomyocytes within each chamber of the heart.

The cells contain one or two centrally located nuclei elongated along the axis, myofibrils and associated cisterns of the sarcoplasmic reticulum (depot of Ca2+). Numerous mitochondria lie in parallel rows between the myofibrils. Their denser clusters are observed at the level of the I-disks and nuclei. Glycogen granules are concentrated at both poles of the nucleus. T-tubules in cardiomyocytes - unlike skeletal muscle fibers - pass at the level of the Z-lines.

In this connection, the T-tubule contacts only one terminal cistern. As a result, instead of triads of skeletal muscle fiber, dyads are formed.

Contractile apparatus. The organization of myofibrils and sarcomeres in cardiomyocytes is the same as in skeletal muscle fiber. The mechanism of interaction of thin and thick filaments during contraction is also the same.

Insert discs.There are interdigitations at the ends of the contacting cardiomyocytes.

(finger-like protrusions and depressions). The outgrowth of one cell fits tightly into the depression of another. At the end of such a protrusion (the transverse section of the intercalated disk) contacts of two types are concentrated: desmosomes and intermediate. On the lateral surface of the protrusion (the longitudinal section of the intercalated disk) there are many gap junctions (nexus), transmitting excitation from cardiomyocyte to cardiomyocyte.

Atrial and ventricular cardiomyocytes. Atrial and ventricular cardiomyocytes belong to different populations of working cardiomyocytes.

Atrial cardiomyocytes:smaller. The T-tubule system is less developed in them, but there are significantly more gap junctions in the area of the intercalated discs.

Ventricular cardiomyocyteslarger, well-developed T-tube system.

The contractile apparatus of atrial and ventricular myocytes contains different isoforms of myosin, actin and other contractile proteins.

Smooth muscle cell: origin, structure

Development. Cambial cells of the embryo and fetus (splanchnomesoderm, mesenchyme, neuroectoderm) differentiate into myoblasts in the places of smooth muscle formation. Then into mature SMCs, which acquire an elongated shape. Their contractile and auxiliary proteins form myofilaments. SMCs in smooth muscles are in the G1 phase of the cell cycle and are capable of proliferation.

Structure: elongated spindle-shaped, often branched form. The length of the SMC is from 20 µm to 1 mm (for example, the SMC of the uterus during pregnancy).

The oval nucleus is located centrally.

sarcoplasmAt the poles of the nucleus there is a well-defined Golgi complex, numerous mitochondria, free ribosomes, and sarcoplasmic reticulum. Myofilaments are oriented along the longitudinal axis of the cell.

basement membrane, surrounding the SMC, contains proteoglycans, collagen types III and V. Components of the basement membrane and elastin of the intercellular substance of smooth muscles are synthesized both by the SMC themselves and by fibroblasts of the connective tissue.

Contractile apparatus:actin and myosin filaments do not form myofibrils!!!

MoleculesGThe smooth muscle actin forms stable actin filaments attached to dense bodies (analogs of Z-lines) and oriented predominantly along the longitudinal axis of the SMC.

Myosin filamentsare being formed between stable actin myofilaments only during contraction of the SMC. The assembly of thick (myosin) filaments and the interaction of actin and myosin filaments are activated by calcium ions coming from the Ca depot2+.Essential components of the contractile apparatus - calmodulin (Ca2+ -binding protein), kinase and phosphatase of the light chain of smooth muscle myosin.

Depot Ca2+-a collection of long narrow tubes (sarcoplasmic reticulum) and numerous small vesicles (caveolae) located under the sarcolemma.

Mechanism of contraction and relaxation of smooth muscle cells

Reduction

In SMC, as in other muscle tissues, the actomyosin chemomechanical converter operates, but the ATPase activity of myosin in smooth muscle tissue is approximately an order of magnitude lower than the ATPase activity of myosin in striated muscle. Slow formation and destruction of actin-myosin bridges require a smaller amount of ATP. This, as well as the fact of the lability of myosin filaments (their constant assembly and disassembly during contraction and relaxation, respectively), leads to an important circumstance - in SMC, contraction develops slowly and is maintained for a long time. When a signal is received by SMC, cell contraction is triggered by calcium ions coming from calcium depots. The Ca2+ receptor is calmodulin.

Relaxation

Ligands (atriopeptin, bradykinin, histamine, VIP) bind to their receptors and activate G protein (Gs), which in turn activates adenylate cyclase, which catalyzes the formation of cAMP. The latter activates the work of calcium pumps that pump Ca2+ from the sarcoplasm into the cavity of the sarcoplasmic reticulum. At a low concentration of Ca2+ in the sarcoplasm, myosin light chain phosphatase dephosphorylates the myosin light chain, which leads to inactivation of the myosin molecule. Dephosphorylated myosin loses affinity for actin, which prevents the formation of cross-bridges. Relaxation of the SMC ends with the disassembly of myosin filaments.

Reparative and physiological regeneration of muscle tissue

Physiological regeneration.In skeletal muscle, physiological regeneration - renewal of muscle fibers - constantly occurs. In this case, satellite cells enter into proliferation cycles with subsequent differentiation into myoblasts and their inclusion in the composition of pre-existing muscle fibers.

Reparative regeneration.After the death of the muscle fiber, activated satellite cells differentiate into myoblasts under the preserved basement membrane. Then, postmitotic myoblasts merge, forming muscle tubes. Synthesis of contractile proteins begins in the myoblasts, and in the muscle tubes, myofibrils assemble and sarcomeres form. Migration of nuclei to the periphery and formation of the neuromuscular synapse complete the formation of mature muscle fibers. Thus, during reparative regeneration, the events of embryonic myogenesis are repeated.

The concept of regeneration, physiological and reparative. Stem cells, their importance

Physiological regeneration- continuous renewal of structures at the cellular (replacement of blood cells, epidermis, etc.) and intracellular (renewal of cellular organelles) levels, which ensures the functioning of organs and tissues.

Reparative regeneration- the process of overcoming the consequences of structural damage caused by the action of pathogenic factors.

physiological and reparative regeneration are accompanied by cell proliferation and differentiation.

Stem cells

Stem cells are undifferentiated cells that, under certain conditions, are capable of reproducing similar cells for a long time and, during life, giving rise to specialized cells that form tissues and organs.

Stem cells have a number of properties:

Self-renewal and self-maintenance - the ability of a stem cell to maintain itself in an undifferentiated state due to the microenvironment under the influence of specific factors

High proliferative capacity.

Plasticity is the ability of a stem cell from one tissue to differentiate into specialized cells of another tissue of an adult organism.

Potency is the ability to produce offspring in the form of specialized cells (differentiation). Distinguish between: totipotency, pluripotency, multipotency, unipotency.

Meaning -provide physiological and reparative regeneration.

Development of nervous tissue and system. Neuroectoderm, neural tube, neural crest, neurogenic placodes

Stages of neurulation-

induction (primary embryonic induction) of the neural plate

elevation of the edges of the neural plate and formation of the neural groove

appearance of nerve folds

formation of the neural crest and the beginning of the eviction of cells from it

closure of the neural folds to form the neural tube

fusion of the ectoderm over the neural tube.

Primary embryonic induction. Neural, or primary embryonic induction - the formation of the neural plate from the dorsal ectoderm. This process is determined by the organizer - the chordomesoderm. During primary embryonic induction, the fate of the cells that give rise to the nervous system is determined.

Neural plate(19th day) - the thickened part of the dorsal ectoderm, formed along the cranio-caudal gradient. Prismatic cells of the newly formed neural plate are located on the basal membrane containing fibronectin, sulfated glycosaminoglycans and laminin. The cells of the neural plate in the apical part are connected by tight junctions, and in the basal part - by gap junctions. During its formation, the cells of the dorsal

ectoderm, with the microtubules in them oriented parallel to the dorsoventral axis.

Neural tube (22nd day). Soon after formation, the edges of the neural plate rise and neural folds are formed. Between the folds is the neural groove (20th day). Later, the edges of the neural folds close along the midline, and a closed neural tube is formed. The cranial and caudal parts of the neural tube remain unclosed for a long time, they are called the anterior and posterior neuropore, respectively. The anterior neuropore closes on the 23rd-26th day of development, and the posterior one - on the 26th-30th day.

day.

The neural tube contains neural stem cells (also known as matrix or ventricular cells) - the source of almost all CNS cells. Ventricular cells multiply and give rise to neuroblasts and glioblasts, which are the precursor cells of neurons and gliocytes. Some ventricular cells remain in situ, which is the future ependyma.

Neural tubecontains:

internal limiting membrane

ependymal (ventricular, matrix) layercontains cambial elements and mitotically dividing cells. Some of the cells that form the inner lining of the neural tube give rise to ependymal glia

mantle layerreplenished mainly by the migration of cells from the ependymal layer, which differentiate into neuroblasts (which give rise to neurons) or spongioblasts (glioblasts), which give rise to astrocytic glia and oligodendroglia. One type of glioblasts is transformed into radial glial cells, which extend through the entire wall of the neural tube and serve as guides for the migration of neuroblasts. Later, radial glial cells differentiate into astrocytes

marginal veil, contains processes of cells located in two deeper layers

external limiting membrane

Neuroblasts: AN-apolar, BN-bipolar, UN-unipolar, MN-multipolar

Matrix (ventricular) cellsependymal layer - the source of almost ALL CNS cells. They are concentrated near the internal limiting membrane. Due to their active reproduction, their nuclei move cyclically within the ependymal layer and the shape of the cells changes.

Cells that have completed proliferating (neuroblasts), as well as glioblasts that are potentially capable of proliferating, migrate to the mantle layer. Some of the ventricular cells remain - they form the future ependyma.

Neural crest. After the ridges close and the neural tube is formed, the part of the ectoderm located between the neural and non-neural (cutaneous) ectoderm forms a new structure - the ill-fated neural crest. Its derivatives:

Sensory neurons of the spinal ganglia and cranial nerves: superior ganglion of the glossopharyngeal nerve, jugular ganglion, part of the neurons of the ganglion of the trigeminal nerve, part of the neurons of the ganglion of the geniculate nerve

Sympathetic neurons

Parasympathetic neurons

Schwann cells (lemmocytes, if you like) and satellite cells of the spinal nodes and ganglia of the cranial nerves

Melanocytes

Carotid body cells

Calcitonin-producing cells (thyroid C cells)

Chromaffin cells

Cartilage, bones, muscles and connective tissue of the face

Peripharyngeal mesenchyme

Maxillary and mandibular processes

Hypoglossal arches and 3rd pharyngeal arch

Odontoblasts

Corneal endothelium

Cells in the wall of the aortic arch

Neurogenic placodes- thickenings of the ectoderm located laterally on both sides of the forming neural tube in the cranial part of the embryo. They form neurons of the olfactory lining, vestibular and auditory ganglia, as well as sensory neurons of the geniculate, petrosal, nodose and trigeminal ganglia of the cranial nerves.

(wikipedia)Dorsolateral placodes, located in the upper part of the embryo's head (the back part later), take part in the development

head nerves

auditory vesicle and its derivatives (vestibular apparatus)

lateral line organ (mechano- and electroreceptors)

Epibrachial, located in the lower (later front) part of the embryo's head, partially give rise to:

crystal lens

olfactory epithelium

head nerves

Neuroblasts- cells with a large round nucleus, dense nucleolus and pale cytoplasm - give rise to neurons. Neurons belong to a static population. Under no conditions are they capable of proliferation and renewal in vivo. The exceptions are the olfactory neurons of the epithelial lining of the nasal passages, as well as some neurons of the hippocampus and olfactory bulb.

Glioblasts- macroglia precursors (astrocytes and oligodendrocytes). All types of macroglia are capable of proliferation.

Information not in the question, but may also be asked: NeuroblastsAt first they have no processes (apolar neuroblasts), then processes are formed at the opposite ends of their bodies (the cells are transformed into bipolar neuroblasts). One of the processes undergoes reverse development (the cells are transformed into unipolar neuroblasts), in place of the lost process several new ones (dendrites) subsequently appear, and the neuroblasts become multipolar, gradually differentiating into mature neurons that lose the ability to divide. Differentiation of a neuroblast into a neuron is accompanied by the accumulation of GREP cisterns in its cytoplasm, an increase in the volume of the Golgi complex, and the accumulation of cytoskeletal elements.

Neuron: structure, morphological classification

Neurons (neurons; the term neuron was proposed by Wilhelm von Waldeyer)- the main cellular types of nervous tissue. Their total number in the human nervous system exceeds 100 billion. (1011), and according to some estimates reaches one trillion (1012)These excitable cells conduct electrical signals and provide the brain with the ability to

information processing. The perikaryon (the body of the neuron), the processes extending from it

(axon (neurite; carrying impulses from the body of the neuron) and dendrites (bringing impulses to the body of the neuron)) are the standard parts of neurons.

Neuron body (perikaryon)includes the nucleus and the cytoplasm surrounding it (except for that which is part of the processes). The perikaryon contains the nucleus, the Golgi complex, the granular endoplasmic reticulum, mitochondria, lysosomes, and elements of the cytoskeleton.

Neuron nucleus—usually one, large, round, light, with finely dispersed chromatin (predominance of euchromatin), one, sometimes 2-3 large nucleoli. These features reflect the high activity of transcription processes in the neuron nucleus. Near the nucleolus in neurons of females, a Barr body is often found - a large lump of chromatin containing a condensed X chromosome (especially noticeable in the cells of the cerebral cortex and sympathetic ganglia).

Cytoplasm of a neuronrich in organelles and surrounded by a plasma membrane, which

has the ability to conduct nerve impulses (spread

depolarization)due to local current Na+ into the cytoplasm and K+ from it through potential-dependent membrane ion channels. The plasma membrane contains Na+-K+pumps that maintain the required ion gradients.

grEPSwell developed, its cisterns often form separate complexes of parallel flattened anastomosing elements, which at the light-optical level, when stained with aniline dyes, have the appearance

basophilic lumps, collectively called the chromatophilic substance (substance, or Nissl bodies, tigroid substance, tigroid). The nature of the distribution and size of the complexes of cisterns of the GRPS (chromatophilic substance) vary in individual types of neurons (the largest are found in motor neurons) and depend on their functional state. With prolonged irritation or damage to a neuron, the complexes of cisterns of the GRPS disintegrate into individual elements, which at the light-optical level is manifested by the disappearance of Nissl bodies (chromatolysis, tigrolysis).

Axon hillock- a region of the perikaryon free of granular endoplasmic reticulum and ribosomes, containing many microtubules and neurofilaments, this is the site where the axon begins and the action potential is generated.

aEPS (smooth EPS)formed by a three-dimensional network of anastomosing cisterns and tubes involved in synthetic processes and intracellular transport of substances.

Golgi complexwell developed (first described in neurons) and consists of multiple dictyosomes (a structural unit of the Golgi complex, which is a system of flat membrane sacs (ciscerna),

arranged in a stack of 5-8 pieces), usually located around the nucleus, which reflects the powerful transport of proteins synthesized in the granular endoplasmic reticulum of the perikaryon into the axon.

Mitochondria—are very numerous and provide high energy needs of the neuron, associated with significant activity of synthetic processes, conduction of nerve impulses, activity of ion pumps. They usually have a rod-shaped form and are characterized by rapid wear and tear and renewal (short life cycle).

Lysosomal apparatus(intracellular digestion apparatus)has high activity and is represented by endosomes and numerous lysosomes of various sizes. Intensive autophagy processes ensure constant renewal of neuron cytoplasm components. With defects of some lysosomal enzymes, undigested products accumulate in the neuron cytoplasm, which disrupts their functions and causes storage diseases, such as gangliosidosis (Tay-Sachs disease).

Cytoskeleton(see next question)

Inclusions in the cytoplasm of a neuronare represented by lipid droplets, granules of lipofuscin (ageing pigment, or wear, which, however, is revealed even

neurons of the fetus), (neuro)melanin - in neurons of the substantia nigra

and the blue spot (locus coeruleus).

Offshoots

Axon (neurite)- a long process, occupies most of the neuron's volume (99%). Almost along its entire length it is covered by a glial membrane. Nissl bodies are absent in the axon. The axon can give branches (collaterals) along its course, which usually depart from it at a right angle. In the final section, the axon often breaks up into thin branches (telodendria) containing synaptic vesicles. The axon ends in specialized terminals (nerve endings) on other neurons or cells of the working organs.

Dendrites- branching processes ending near the body of the neuron.

postsynaptic receptors are embedded in the plasma membrane, and dendrites conduct excitation to

perikaryon. Dendrites integrally form up to 95% of the entire receptor surface

(receptive field) of a neuron. They branch heavily near the neuron's body. Large stem

dendritescontain all types of organelles, and as their diameter decreases, they disappear

elements of the Golgi complex, and the cisterns of the GREP are preserved. Neurotubules and

neurofilaments are numerous and arranged in parallel bundles; they

provide dendritic transport, which is carried out from the cell body along

dendrites at a rate of about 3 mm/h.

They receive signals from other neurons through numerous interneuronal contacts (axo-dendritic synapses) located on them in the area of special cytoplasmic protrusions - dendritic spines. Many spines have a special spine apparatus consisting of 3-4 flattened cisterns separated by areas of dense substance. Spines are labile structures that are destroyed and formed again; their number drops sharply with aging, as well as with a decrease in the functional activity of neurons.

Morphological classification of neuronstakes into account the number of their processes and divides all neurons into three types: unipolar, bipolar and multipolar.

Unipolar neuronshave one process. According to most researchers, they are not found in the nervous system of humans and other mammals. Some authors still include amacrine neurons of the retina and interglomerular neurons of the olfactory bulb among such cells.

Bipolar neuronshave two processes - an axon and a dendrite, usually extending from opposite poles of the cell. They are rare in the human nervous system. They include bipolar cells of the retina, spiral and vestibular ganglia.

Pseudounipolar neurons— a type of bipolar cells, in which both cell processes (axon and dendrite) extend from the cell body as a single outgrowth, which then divides into a T-shape. These cells are found in spinal and cranial ganglia.

Multipolar neuronshave three or more branches: an axon and several dendrites. They are the most common in the human nervous system. Up to 80 variants of these cells have been described: spindle-shaped, stellate, pear-shaped, pyramidal, basket-shaped, etc. According to the length of the axon, Golgi cells of type I (with a long axon) and Golgi cells of type II (with a short axon) are distinguished.

Neuron cytoskeleton: microtubules, microfilaments, intermediate filaments, their structure and functions. Axonal transport, its types, functions

Cytoskeletonneurons are well developed and represented by all elements -

microtubules (non-tubules), microfilaments and intermediate filaments (neurofilaments).They form a three-dimensional support-contractile network that plays an important role in maintaining the shape of these cells and, in particular, their long process, the axon. Numerous intermediate filaments (neurofilaments) are connected to each other and to neurotubules by cross-bridges; when fixed, they stick together into bundles that are stained with silver salts. Such formations (which are actually artifacts) are described at the light-optical level

called neurofibrils - threads 0.5-3 µm thick that form a network in the perikaryon.

Microtubules (neurotubules) and microfilamentshave the same structure as in other cells. They are associated with intracellular, including axonal, transport. Various substances (proteins, neurotransmitters, etc.), organelles (mitochondria, cytoskeletal elements, vesicles, etc.) move from the perikaryon along the processes. Microtubules in the perikaryon and dendrites (unlike the axon) do not have a directional orientation. Most axon microtubules are directed with the (+) end toward the terminal, and the (-) end toward the perikaryon. The nature of the orientation of microtubules is important for the distribution of various organelles along the processes. Mitochondria move to the (+) end

secretory vesicles, and towards the (-)-end - ribosomes, multivesicular bodies, elements of the Golgi complex. The cellular center is present in all neurons, its main function is the assembly of microtubules.

Axonal transport (current)—movement of various substances and organelles along the axon (see Fig. 14-4); is divided into anterograde (direct - from the neuron body along the axon) and retrograde (reverse - from the axon to the neuron body). Substances are transported in the cisterns of the aER and vesicles, which move along the axon due to interaction with elements of the cytoskeleton (mainly with microtubules through the contractile proteins associated with them - kinesin and dynein); the transport process is Ca2+-dependent.

Anterograde axonal transportturns on slow (speed - 1-5

mm/day), providing a current of axoplasm (transporting enzymes and cytoskeletal elements), and fast (100-500 mm/day), carrying out the transport of various substances, cisterns of the GREP, mitochondria, vesicles containing neurotransmitters.

Retrograde axonal transport(100-200 mm/day) promotes removal

substances from the terminal area, the return of vesicles, mitochondria. It is assumed that due to axonal transport, neurotropic substances that have penetrated into the neuron

viruses (herpes, rabies, poliomyelitis) can spread along neural circuits. The phenomenon of transport is used to study interneuronal connections by introducing a marker into the area of terminals or cell bodies and identifying areas of its subsequent spread by the described mechanisms.

AAT - anterograde axonal transport (from the neuron body along the axon), PAT - retrograde axonal transport (from the axon to the neuron body), DT - dendritic transport (from the cell body along the dendrites).

Nervous tissue: microglia. Origin, morphology, localization, functions

Microglia- a collection of small, elongated, stellate cells (microgliocytes) with dense cytoplasm and relatively short branching processes, located mainly along the capillaries in the central nervous system (see Fig. 14-6). Unlike macroglial cells, they are of mesenchymal origin, developing directly from monocytes (or perivascular macrophages of the brain) and belong to the macrophage-monocyte system. They are characterized by nuclei with a predominance of heterochromatin and a high content of lysosomes in the cytoplasm.

Microglial function- protective (including immune).Microglial cells are traditionally considered as specialized macrophages of the central nervous system - they have significant mobility, becoming activated and increasing in number during inflammatory and degenerative diseases of the nervous system, when they lose processes,

are rounded offand phagocytize the remains of dead cells (detritus). Activated microglial cells express MHC class I and II molecules and the CD4 receptor, perform

CNS function of dendritic APC, secrete a number of cytokines. These cells play a very important role in the development of nervous system lesions in AIDS. They are credited with the role of a "Trojan horse" that carries (together with hematogenous monocytes and macrophages) HIV throughout the CNS. Increased activity of microglial cells, which secrete significant amounts of cytokines and toxic radicals, is also associated with increased neuronal death in AIDS by the mechanism of apoptosis, which is induced in them due to a violation of the normal balance of cytokines (what stinking bastards).

Oligodendrocytes and Schwann cells. Origin, localization, morphology, functions

Oligodendroglia(from the Greek oligo - little, dendron - wood and glia - glue, i.e. glia with a small number of processes) - a large group of various small cells (oligodendrocytes) with short, few processes that surround the bodies of neurons, are part of the nerve fibers and nerve endings. Found in the central nervous system

(gray and white matter) and the PNS, in the gray matter they are in direct contact with the perikarya, in the white matter they lie between the nerve fibers; they are characterized by a dark nucleus, dense cytoplasm with a well-developed synthetic apparatus, a high content of mitochondria, lysosomes and glycogen granules.

With the help of thin, unbranched processes, oligodendrocytes contact axons and, moving relative to the axon with the flattened ends of the processes, surround it.

circular myelin plate(a good analogy is that by rotating around axons, myelin is wound around the axon). Each oligodendrocyte myelinizes several axons with its processes. Myelin gives white matter its white color.

Satellite cells (mantle cells)envelop the cell bodies of neurons in the spinal, cranial and autonomic ganglia. They have a flattened shape, a small round or oval nucleus. Provide

barrier function

regulate neuronal metabolismocapture neurotransmitters

Lemmocytes (Schwann cells) are analogs of oligodendrocytes.They are part of myelinated and unmyelinated nerve fibers. They participate in the formation of nerve fibers, isolating the processes of neurons. They have the ability to produce a myelin sheath, synthesize proteins P0, P1, P2. Each Schwann cell myelinizes one axon. (marker - S100b)

Astrocytes. Origin, cytology, localization, functions

Astroglia(from the Greek astra — star and glia — glue) is represented by astrocytes — the largest of the glial cells, which are found in all parts of the nervous system. Astrocytes are characterized by a light oval nucleus, cytoplasm with moderately developed major organelles, numerous glycogen granules and intermediate filaments. The latter penetrate from the cell body into the processes and contain a special glial fibrillary acidic protein (GFAP), which serves as a marker of astrocytes. At the ends of the processes there are lamellar extensions ("legs"), which, connecting with each other,

in the form of membranes surround vessels or neurons. Astrocytes form gap junctions between themselves, as well as with oligodendroglia and ependymal glia cells. They have receptors for many neurotransmitters.

Astrocytes are divided into two groups:

Protoplasmic (plasmatic) astrocytesare found predominantly

gray matter of the central nervous system;They are characterized by the presence of numerous branched short, relatively thick processes and a low content of GFCB.

Fibrous astrocytesare located mainly in the white matter of the central nervous system. Long, thin, slightly branching processes extend from their bodies. They are characterized by a high content of GFAP.

Functions of astrocytes:

supporting —formation of the supporting framework of the central nervous system, inside which other cells and fibers are located; during embryonic development they serve as supporting and guiding elements along which the migration of developing neurons occurs. The guiding function is also associated with the development of:

nerve growth factor (NGF)

components of the intercellular matrix - laminin and fibronectin (accelerate

elongation of neuronal processes)

demarcation, transport and barrier(aimed at ensuring an optimal microenvironment for neurons):

A) the formation of perivascular boundary membranes by flattened end portions of processes that envelop the capillaries from the outside, forming the basis of the blood-brain barrier (BBB). The BBB separates the neurons of the central nervous system from the blood and tissues of the internal environment and includes:

1) capillary endothelium, the cells of which are connected by tight junctions (the formation of these junctions is induced by contact with astrocytes),

capillary basement membrane,

perivascular membrane,formed by flattened processes of astrocytes, B) formation (together with other elements of glia) of the superficial border

glial membrane (marginal glia) of the brain,located under the pia mater,

also the border glial membrane under the ependymal layer, which participates in the formation of the neurocerebrospinal fluid barrier, which separates neurons from the cerebrospinal fluid (CSF),

or cerebrospinal fluid,and is formed by ependymal glia and astrocyte processes, B) the formation of perineuronal membranes surrounding the bodies of neurons and areas

synapses (insulating function, in combination with some other functions - ensuring an optimal microenvironment for neurons)

(in short, they protect neurons from all sides)

metabolic and regulatory —is considered one of the most important functions

astrocytes, which is aimed at maintaining certain concentrations of K ions+and mediators in the microenvironment of neurons. Astrocytes, together with oligodendroglia cells, participate in the metabolism of mediators (catecholamines, GABA,

peptides, amino acids), actively capturing them from the synaptic cleft after synaptic transmission has occurred and then transmitting them to the neuron;

protective (phagocytic, immune and reparative) -participation in various protective reactions when nerve tissue is damaged. Astrocytes, like microglial cells (see below), are characterized by pronounced phagocytic activity. Like the latter, they also have the characteristics of APC:

express MHC class II molecules on their surface

capable of capturing, processing and presenting antigens

produce cytokines

In the final stages of inflammatory reactions in the central nervous system, astrocytes grow and form a glial scar at the site of damaged tissue.

Ependymal glia (1) includes ependymal cells (EC), tanycytes (TC), and choroid ependymal cells (CEC).

Astrocytic glia (2) are represented by protoplasmic astrocytes (PA) and fibrous astrocytes (FA). Lamellar extensions of astrocyte processes, connecting with each other, form the superficial limiting glial membrane (SLGM) of the brain, as well as perivascular limiting membranes (PVLM).

Oligodendroglia (3) include satellite cells (SCs) surrounding the cell bodies of neurons

(HP), as well as cells that are part of the nerve fibers - lemmocytes (LC) in the PNS and

oligodendrocytes (ODC) in the central nervous system.

Microglia (4). Actively phagocytic microgliocytes become rounded, lose their processes and become vacuolated.

Ependymal glia (1) includes ependymal cells (EC),tanycytes (TC), choroid ependymocytes (CEC).

Oligodendroglia (3) include satellite cells (SC) surrounding the cell bodies of neurons (HP),

also cells that are part of the nerve fibers - lemmocytes (LC) in the PNS and oligodendrocytes (ODC) in the CNS.

Microglia (4). Actively phagocytic microgliocytes become rounded, lose their processes and become vacuolated.

Formation of the myelin sheath. Structure of myelin. Myelin-forming cells

Myelin-forming cells include oligodendrocytes and Schwann cells.

Myelin -a compact structure of membranes spirally wrapped around axons. 70% of myelin's mass is lipids.

Important components of myelin are myelin proteins: P0 (we know it), P22, basic or alkaline myelin protein, proteolipid and others.

Formation of the myelin sheathoccurs through the interaction of the axial cylinder and oligodendroglia cells with some differences in the PNS and CNS.

Axial cylinder(=axon) contains mitochondria, smooth endoplasmic reticulum elements, vesicles, and cytoskeletal elements - microtubules, neurofilaments, and microfilaments. The diameter of the axon, and therefore the speed of impulse conduction along this axon, is determined by the number of neurofilaments in it.

Formation of the myelin sheath in the PNS:the immersion of the axial cylinder into the lemmocyte is accompanied by the formation of a long mesaxon, which begins to rotate around the axon, forming the first loosely arranged turns of the myelin sheath. As the number of turns (plates) increases during the maturation of myelin, they are located more and more densely and partially merge; the spaces between them, filled with the cytoplasm of the lemmocyte, are preserved only in individual areas that are not stained with osmium - myelin notches (Schmidt-Lanterman). During the formation of the myelin sheath, the cytoplasm and nucleus of the lemmocyte are pushed to the periphery of the fiber, forming a neurolemma. Along the length of the fiber, the myelin sheath has an intermittent course.

Formation of myelinated (1-3) and unmyelinated (4) nerve fibers in the peripheral nervous system. A nerve fiber is formed by immersion of the axon (A) of a nerve cell into the cytoplasm of a lemmocyte (LC). When a myelinated fiber is formed, a duplicate of the LC plasmalemma — the mesaxon (MA) — is wound around A, forming turns of the myelin sheath (MS). In the unmyelinated fiber shown in the figure, several A (a "cable" type fiber) are immersed into the cytoplasm of the LC. I is the LC nucleus.

Nodal interceptions (Ranvier)—areas in the area of the border of neighboring lemmocytes, in which the myelin sheath is absent, and the axon is covered only by the interdigitating processes of neighboring lemmocytes (see Fig. 14-9). Nodal interceptions are repeated along the course

myelinated fiber with an interval equal to, on average, 1-2 mm. In the area of the nodal interception, the axon often expands, and in its plasma membrane there are numerous sodium channels (which are absent outside the interceptions under the myelin sheath).

Formation of the myelin sheath in the central nervous system:the axial cylinder is not immersed in the cytoplasm of the oligodendrocyte, but is embraced by its flat process, which subsequently rotates around it, losing cytoplasm, and its turns are transformed into plates of the myelin sheath (Fig. 14-10). Unlike Schwann cells, one oligodendrocyte of the CNS can participate with its processes in the myelination of many (up to 40-50) nerve fibers. The sections of the axon in the region of the nodes of Ranvier in the CNS are not covered by the cytoplasm of oligodendrocytes.

Formation of myelinated fibers by oligodendrocytes in the central nervous system. 1 — the axon (A) of a neuron is covered by a flat process (FP) of an oligodendrocyte (ODC), the turns of which transform into plates of the myelin sheath (MS). 2 — one ODC with its processes can participate in the myelination of many A. The A sections in the region of nodal interceptions (NI) are not covered by the ODC cytoplasm.

Sensory nerve endings. Classification, structure, examplesNerve endings—terminal apparatus of nerve fibers.

Receptor (sensory) nerve endingsperceive signals from the outside

environment (exteroceptors) and internal organs (interoreceptors). Depending on the nature of the irritation registered by the receptors, they are divided in accordance with physiological classification into mechanoreceptors, chemoreceptors, thermoreceptors and pain receptors (nociceptors). In specialized sensory organs (taste, smell, vision, balance and hearing) there are special receptor cells that perceive the corresponding irritations.

Free sensory nerve endingsconsist only of terminal branches of the dendrite of a sensory neuron. They are found in the epithelium, as well as in connective tissue (in general, the endings in the connective tissue of the branching of the axial cylinder are surrounded by cells similar to Schwann's, and the name is arbitrary). Penetrating the epithelial layer, nerve fibers lose their myelin sheath and neurolemma, and the basement membrane of their lemmocytes merges with the epithelial one. They lie in the basal and spinous layers of the epithelium (highly sensitive areas - in the granular layer). Free nerve endings provide signal perception:

temperature (heat and cold)

mechanical

painful

changes in pH, pO2, pCO2

Non-free encapsulated nerve endings- the basis is formed by the branches of the dendrite, which are directly surrounded by lemmocytes and covered on the outside by a special connective tissue capsule. These are:

plate-shaped bodies (Vater-Pacini)

tactile corpuscles (Meissner's)

Ruffini's bodies

Krause flasks

neuromuscular spindles

nerve tendon spindles (Golgi tendon organs)

Encapsulated receptors. Structure, localization, function

1) Plate bodies (Vater-

Pacini)are found in the connective tissue of internal organs and skin. They look like round formations with a diameter of 1-5 mm, perceive pressure and vibration. The structural components of the body are:

1) inner bulb (bulb),

formed by modified flattened lemmocytes, into which one or more nerve fibers penetrate, having a straight course;

2) outer flask -layered connective tissue capsule,

consisting of fibroblasts and collagen fibers that form 10-

60 concentric plates with liquid between them. Works as a filter, allowing only the dynamic component of the mechanical receptor to pass through.

When the capsule plates are deformed, pressure is transmitted to the nerve ending, which causes depolarization of its membrane.

connective tissue of the skin and various organs

2) Tactile corpuscles (Meissner's)

located mainly in the papillary layer of the dermis, have an ellipsoid shape and small size (about 50-120 microns).

Their inner bulb consists of flat glial cells lying perpendicular to the long axis of the body, between which are located branches of dendrites. Collagen fibrils, connected with the basal layer of the epithelium, penetrate between the glial cells. The capsule is thin, passes into the perineurium.

Ruffini's corpuscleslie in the connective tissue part of the skin and joint capsules; they perceive pressure and have the appearance of spindle-shaped structures up to 1-2 mm long.

The inner bulb is formed by glial cells, between which are numerous branching terminals of dendrites with extensions at the ends. The capsule is well expressed, formed by collagen fibers. They are connected with epithelial cells.

They are characterized by specific osmiophilic granules ranging in size from 80 to 200 nm. They are concentrated mainly in the cytoplasmic areas facing the nerve terminal. Peptides and neuron-specific substances (e.g., methionine-enkephalin, VIP, substance P) have been found in tactile epithelial cells, which indicates the endocrine function of the cells and allows them to be considered a component of the diffuse neuroendocrine system. Tactile epithelial cells participate in recognizing the shape of an object, its edges, and surface texture.

Krause flasks—small (40-150 µm) round bodies that are mechanoreceptors and possibly cold receptors. They are located in

connective tissue of the papillary dermis

lamina propria of the oral mucosa, epiglottis

in the conjunctiva of the eye.

Inner flaskeducated

flattened glial cells, between which thin branches of the dendrite form a plexus in the form of a ball. The capsule consists of flat cells that are a continuation of the perineurium.

5) Neuromuscular spindles -receptors

stretching of striated muscle fibers- complex encapsulated

nerve endings that have both sensory and motor innervation. The number of spindles in a muscle depends on its function and is higher the more precise its movements. The neuromuscular spindle is 0.5-7 mm long and is located parallel to the course of the muscle fibers, called extrafusal.

The spindle is covered with a thin connective tissue capsule (a continuation of the perineurium), inside which are thin striated intrafusal muscle fibers of two types:

fibers with a nuclear bag - in the expanded central part of which there are clusters of nuclei (1-4 fibers/spindle);

nuclear chain fibers - thinner with nuclei arranged in a chain-like pattern in the central part (up to 10 fibers/spindle)

6) Neurotendon spindles (Golgi tendon organs, p.221 in a thick textbook) —stretch receptors— spindle-shaped encapsulated structures about 0.5-1 mm long, located in the area of the junction of striated muscle fibers with collagen fibers of tendons. Each spindle is formed by a capsule of flat fibrocytes (a continuation of the perineurium), which covers a group of tendon bundles, braided with numerous terminal branches of nerve fibers, partially covered with lemmocytes. Excitation of receptors occurs when the tendon is stretched during muscle contraction.

7) Sensitive nerve endings of the joint capsule- an important element of the body's proprioceptive system. The spindle-shaped bodies are located in the peripheral areas of the capsule.

134. Myelin and its structure. Formation of the myelin sheath in the CNS and PNS

-repeat 131

135. Degeneration and regeneration of nerve fibers in the peripheral nerveRegeneration of nerve fibers in the PNS- a sequence of processes during which

the neuron process actively interacts with glial cells.

Degeneration of nerve fibers over a small area of the central segment and over the entire peripheral segment is also called Wallerian.

1) In the perikaryon, Nissl substance is sprayed (tigrolysis), which causes axonal transport to stop.

2) Axial cylinders are destroyed, myelin disintegrates

3) Fragments of cylinders and myelin are captured by macrophages and Schwann cells =>

Büngner's bands are formed - chains of Schwann cells that serve as guide paths for regenerating axons (axons from the central segment of the nerve fiber).

Regeneration of the peripheral departmentgoes as follows:

The axon growth cone moves along Büngner's bands due to axon growth factors and other stimulants released by Schwann cells (see above).

The axon takes all this goodness and carries it to the perikaryon, where these dopings stimulate protein synthesis. Schwann cells, in addition, also proliferate and synthesize components of the basal membrane, and also stimulate the elongation of the axon and control its directed growth. Without them, it is impossible.

Sprouting(collateral branching). Collaterals can form from intact and surrounding fibers, which also restore lost connections. Collaterals most often originate from the nodes of Ranvier.

Spinal ganglion. Structure (connective tissue, neurons, neuroglia)

Spinal (spinal) node

(ganglion)has a spindle-shaped form and is covered with a capsule of dense fibrous connective tissue. Along its periphery are dense clusters of bodies of sensory pseudounipolar neurons; and the central part is occupied by their processes and thin layers of endoneurium located between them, carrying vessels. Pericaryons are surrounded by satellite cells. Glia contains mantle gliocytes.

Neurotransmitters - substance P, somatostatin and cholecystokinin.

- general view: RR - posterior root, AR - anterior root, RN - mixed nerve, K - capsule of the node, PUN - pseudounipolar neurons (bodies), NF - nerve fibers, B - section of the node at higher magnification: MG - mantle gliocytes, FB - fibroblasts.

Characteristics of neurons of the spinal ganglia:

	Small	Intermediate	Large
Function	Painful	Tactile	proprioception
	(high threshold	sensitivity
	mechanoreceptors) and
	temperature
	sensitivity

Cerebellar cortex. Layers, neurons, connections between neurons

Cerebellumis located above the medulla oblongata and the pons and is the center of balance, maintaining muscle tone, coordinating movements and controlling complex and automatically performed motor acts. It is formed by two hemispheres with a large number of grooves and convolutions on the surface and a narrow middle part

(worm) and is connected to other parts of the brain by three pairs of legs. The gray matter forms the cerebellar cortex and nuclei, which lie deep in its white matter.

Ganglionic layer

Form the bodies of Purkinje cells. The perikarya of Purkinje cells are pear-shaped and form a virtually continuous layer. From the body, 2-3 strongly branching dendrites extend into the molecular layer. An axon extends from the body of the Purkinje cell through the granular layer into the white matter. These axons are the only efferent fibers that emerge from the cerebellar cortex. They end in neurons of the cerebellar nuclei. Near the body, many collaterals extend from the axon to other Purkinje cells.

All afferent pathways of the cerebellum terminate in one way or another in these cells.

Molecular layer

Basket cells are multipolarneurons of irregular shape. They form long and sparsely branched dendrites. The axon forms branches along its entire length, ending in the form of baskets on the bodies of Purkinje cells.

Stellate cellsare located closer to the surface of the cortex. Their axons form synaptic contacts with the dendrites of Purkinje cells.

Granular layer

Grain cells.Small body and 3-4 short dendrites. Axons ascend to the molecular layer, where they form T-shaped branches running parallel to the surface of the cerebellum - parallel fibers that form synapses with dendrites:

Purkinje cells

Basket cells

Stellate cells

Golgi cells type 2

Golgi cells type 2.Pericaryons lie under the ganglionic layer, dendrites branch in the molecular layer. Axons are part of the cerebellar glomeruli, ending in synaptic contacts on the rosettes of mossy fibers. Some of the collaterals of the axons of the pear-shaped Purkinje cells end on Golgi cells type 2.

Cerebellar afferents

The cerebellar cortex contains numerous fibers from various parts of the brain.

Bryophytic (mossy) fibers,Having penetrated the granular layer, they branch and form terminal rosettes that come into contact with the dendrites of the granule cells in the cerebellar glomeruli. Mossy fibers also form synapses with the dendrites of type 2 Golgi cells. Consequently, mossy fibers come into contact with both the axons of type 2 Golgi cells and their dendrites.

Climbing (liana-like) fibersapproach the bodies of the Purkinje cells and here they split into several thin branches that encircle the dendrites. There is one climbing fiber per Purkinje cell.

Cerebellar glomeruli -This is a cluster of terminal branches of the processes of various cerebellar neurons and mossy fibers. The glomerulus is surrounded by a capsule of glial cells. Around it are clusters of granule cells.

The glomeruli contain:

Rosettes are the ends of mossy fibers.

Bird's feet are terminals of granule cell dendrites

Axons of Golgi cells type 2 and part of their dendrite branches

Layers and neurons of the cerebral cortex

1)Layers of the bark

I. Molecular. Contains rare perikarya, where axons and dendrites pass.

Just beneath the pia mater.

Horizontal Cajal cells -form a tangential interweaving of fibers of this layer

II. External granularThe dendrites of neurons branch and rise into the molecular layer, axons either go into the white matter or form arcs and also go into the molecular layer.

Pyramidal cells

Stellate cells

External pyramidal. The perikaryon of pyramidal cells increases in size in the deep parts of the layer. The apical dendrites of pyramidal cells are directed to the molecular layer, and the lateral ones form synapses with the cells of this layer. The axons of these cells terminate within the gray matter or are directed to the white matter.

Pyramidal cells

Other small debris

IV. Internal granular. It is wide in the visual and auditory areas of the cortex, and is practically absent in the sensorimotor area. The axons of the cells of this layer form connections

cells of the upper and lower layers of the cortex.

Martinotti cells

Stellate cells

V. Internal pyramidal (ganglionic). The apical dendrites of pyramidal cells reach layer I, forming apical bouquets there, lateral dendrites spread within the same layer. The axons of giant and large pyramidal cells project onto the nuclei of the brain and spinal cord, the longest of them, as part of the pyramidal tracts, reach the caudal segments of the spinal cord.

Pyramidal neurons (Betz cells)

VI. Polymorphic. It is formed by a multitude of neurons of various sizes and shapes, as well as a certain number of pyramidal and granular neurons.

The outer parts of the layer contain larger cells, the inner ones - smaller and more sparsely located. The axons of these cells go into the white matter as part of the efferent pathways, and the dendrites penetrate to the molecular layer. The axons of small Martinotti cells rise to the surface of the cortex and branch in the molecular layer.

Fusiform neurons

Stellate neurons

Martinotti cells

1 - pyramidal neuron, 2 - stellate neuron, 3 - spindle-shaped neuron, 4 - Martinotti cells, 5 - horizontal neurons

2)Neurons of the cortex

The neurons of the cortex are multipolar,of various sizes and shapes, include more than 60 species, among which two main species are distinguished - pyramidal and non-pyramidal.

Pyramidal neurons. The perikaryon is 10-100 µm in size and has a long apical dendrite extending from the top of the pyramid and other dendrites extending from the lateral surfaces of the perikaryon. An axon extends from the base of the pyramid and goes into the white matter. The recurrent collateral branches of the axon end on other

pyramidal neurons or intercalated cortical neurons. The main function of pyramidal cells is the formation of efferent pathways (giant and large cells).

Betz cells (giant pyramidal neurons)located in layer V

motor cortex, these are the largest neurons of the cortex. The size of their perikaryon is more than 100 µm, they give rise to large myelinated axons of the pyramidal tract.

Meynert cellsare also located in layer V of the visual cortex of the occipital lobe. They send axons to the brainstem and participate in the eye movement reflex.

Stellate neurons. Their perikarya are round, polygonal or triangular, 4-8 µm in diameter. The axon and dendrites extend a short distance from the perikarya and participate in the formation of intracortical connections.

Fusiform neuronsare most often found in layer VI. Dendrites extend from opposite ends of the perikaryon. The axon extends deep into the white matter.

Martinotti cells (inverted pyramidal neurons)present in all layers except the first. They have a polygonal perikaryon and short dendrites. The axon is directed vertically to the surface of the cortex, giving off collaterals in all layers.

Horizontal neurons of Ramon y Cajalare located in layer I. From their spindle-shaped perikaryon a long axon extends, which, together with the dendrites, forms horizontal connections within layer I.

To top it all off, there's also:spiny stellate, basket-shaped, axo-axonic cells, cells

"candelabra", cells with a double bouquet of dendrites.

The main function of non-pyramidal cells is the integration of neural circuits within the cortex.

Meninges. Histological characteristics

(Epidural space - between the vertebrae and the spinal cord)

It is filled with loose fibrous connective tissue rich in fat cells and contains numerous blood vessels.

Dura mater (dura mater)

It is formed by dense fibrous connective tissue with a high content of elastic fibers.

The dura mater of the brain is tightly fused with the periosteum of the skull bones, there is no epidural space. It is covered with loose fibrous connective tissue.

The dura mater of the brain forms a series of processes that penetrate between the parts of the brain, separating them from each other. Between its folds there are spaces lined with endothelium, filled with venous blood - the sinuses of the dura mater.

On the side facing the arachnoid membrane, it is covered by a layer of flat glial cells (meningothelium) and is separated from it by the subdural space.

Subdural space

Contains a small amount of tissue fluid other than CSF.

Arachnoid mater (arachnoidea)

It is loosely attached to the dura mater, from which it is separated by a narrow subdural space.

The arachnoid membrane is formed by connective tissue with a high content of fibroblasts. In the area of the grooves it does not adjoin the soft tissue.

On the surfaces facing the subdural and subarachnoid spaces, the arachnoid membrane is lined with a layer of flat glial cells that also cover the trabeculae.

Subarachnoid space

It is crossed by numerous thin, branching connective tissue strands.

(trabeculae) extending from the arachnoid mater and intertwining with the pia mater. Large blood vessels pass through this space, the branches of which feed the brain. Filled with cerebrospinal fluid.

Pia mater

Formed by a thin layer of connective tissue with a high content of small vessels and nerve fibers, it directly covers the surface of the brain, repeating its relief and penetrating into the grooves. On both surfaces (facing the subarachnoid space and adjacent to the brain tissues) it is covered with meningothelium.

The pia mater surrounds the vessels penetrating the brain, forming a perivascular capillary membrane around them, which is subsequently (as the vessel caliber decreases) replaced by a perivascular border glial membrane formed by astrocytes. In the area of the roof of the third and fourth ventricles, and some areas of the wall of the lateral ventricles of the brain, the pia mater, together with the ependyma, participates in the formation of vascular plexuses that produce CSF.

The pia mater is separated from the CNS tissues by the external limiting glial membrane and the basement membrane formed by astrocytes.

Ependyma. Origin, localization, cell morphology, functionsEpendymal glia, or ependymaformed by cubic or cylindrical cells

forms (ependymal cells), single-layered layers of which line the cavities of the ventricles of the brain and the central canal of the spinal cord. Since the cells of the ependymal glia form layers in which their lateral surfaces are connected by intercellular connections, according to its morphofunctional properties it is classified as an epithelia.

Some of the ventricular cells of the neural tube remain in situ (i.e. do not migrate); this is the future ependyma.

The nucleus of ependymocytes contains dense chromatin, organelles are moderately developed, and vesicles are present. The apical surface of some ependymocytes bears cilia, which move CSF with their movements, and a long process extends from the basal pole of some cells, extending to the surface of the brain and being part of the superficial border glial membrane (marginal glia).

Choroid ependymal cells— ependymocytes in the area of the vascular plexuses — the sites of CSF formation. They have a cubic shape and cover the roof of the third and fourth ventricles, parts of the wall of the lateral ventricles. On their convex apical surface there are numerous microvilli, the lateral surfaces are connected by complexes of compounds, and the basal ones form protrusions (legs) that intertwine with each other, forming a basal labyrinth. The layer of ependymocytes is located on the basement membrane, separating it from the underlying loose connective tissue of the pia mater, which contains a network of fenestrated capillaries with high permeability due to numerous pores in the cytoplasm of endothelial cells.

Function:Ependymocytes of the choroid plexus are part of the hemato-cerebrospinal fluid

barrier (barrier between blood and CSF),through which ultrafiltration of blood occurs with the formation of CSF. They secrete cerebrospinal fluid.

Tanicites -specialized ependymal cells in the lateral parts of the wall of the third ventricle, infundibular recess, median eminence. They have a cubic or prismatic shape, their apical surface is covered with microvilli and individual cilia (almost none), and a long process extends from the basal surface, ending in a lamellar expansion on the blood capillary (see Fig. 14-6).

Function:Tanycytes absorb substances from the CSF and transport them in their own way.

process into the lumen of the vessels, thereby ensuring a connection between the CSF in the lumen of the ventricles of the brain and the blood.

The hemato-cerebrospinal fluid barrier includes:

cytoplasm of fenestrated endothelial cells

endothelial basement membrane

loose fibrous connective tissue

ependymal basement membrane

layer of ependymal cells.

Retina of the eye. Photoreceptor cells: structure, connections, functionRetina(retina) - the inner lining of the eye, has a visual

section, along the serrated edge (ora serrata) passing into the blind section, covering the back

ciliary body and the iris. At the posterior edge of the optical axis of the eye, the retina has

a round yellow spot (macula lutea) about 2 mm in diameter. The central pit (fovea

centralis) - a depression in the middle of the yellow spot, the place of the best

perception. The optic nerve (nervus opticus) emerges from the retina medial to the yellow

spots. The optic nerve disc (discus nervi optici) is formed here. In the center of the disc

There is a depression in which the vessels that feed the retina are visible.

Structural components of the retinaare its neurons, pigment epithelium, neuroglia and vessels.

Retinal neuronsform a three-member chain of radially arranged cells connected to each other by synapses: (1) neurosensory (photoreceptor); (2) bipolar (associative) and (3) ganglion. In addition to these cells, there are two more types of neurons that provide communication at the level of connections of neurosensory and bipolar neurons (horizontal cells) and ganglion (amacrine cells).

Layers of the retina. The visual part of the retina is formed by sequentially (from the outer surface of the eyeball) arranged layers (Fig. 8-46): pigment, outer nuclear, outer reticular, inner nuclear, inner reticular and ganglion.

Pigment layer(stratum pigmentosum).Polygonal cells adjacent to the vascular membrane. One pigment epithelial cell interacts

outer segments of dozens of photoreceptor cells - rods and cones. Pigment epithelial cells store vitamin A, participate in its transformations and transfer its derivatives to photoreceptor cells for the formation of visual pigment.

Outer segment -photoreceptor dendrites, layer of cones and rods.

External glial limiting membrane -a dark stripe separating the photosensory layer from the outer nuclear layer. Corresponds to the outer border of the Müller cells, connected by their processes to the photoreceptor cells;

Outer nuclear layer(external nuclear stratum)includes the nucleated portions of the photoreceptor cells. The cones are concentrated in the area of the macula lutea. The eyeball is organized in such a way that the central part falls on the cones.

light spot from the visualized object. Rods are located along the periphery of the yellow spot.

External mesh(stratum plexiforme externum).Here, contacts between the internal segments of rods and cones and the dendrites of bipolar cells are made.

Internal nuclear(stratum nucleare internum). Contains bipolar cells,

connecting rods and cones with ganglion cells, as well as horizontal and amacrine cells. The perikarya of amacrine cells are located in the inner part of the inner nuclear layer.

Internal mesh(stratum plexiforme internum).In it, bipolar cells contact ganglion cells, and amacrine cells act as interneurons. A popular concept is that a limited number of bipolar cells transmit information to 16 types of ganglion cells with the participation of at least 20 types of amacrine cells.

Ganglionic layer(stratum ganglionicum)contains ganglion neurons. The general scheme of information transmission in the retina is as follows: receptor cell → bipolar cell → ganglion cell and simultaneously amacrine cell → ganglion cell.

Nerve fiber layer -axons of neurons that make up the optic nerve.

Inner glial limiting membrane -formed by the bases of the Müller cells and their basement membrane.

Retinal neurons(bipolar, horizontal, amacrine and ganglion cells)

synthesize acetylcholine, dopamine, L-glutamic acid, glycine, γ-aminobutyric acid. Some neurons contain serotonin, its analogs (indolamines) and neuropeptides.

Horizontal cells. Pericaryons are located in the outer part of the inner nuclear layer, and processes enter the area of the synapses between photoreceptor and bipolar cells. Horizontal cells receive information from the cones and transmit it to the cones.

Amacrine cells. Their perikarya are located in the inner part of the inner nuclear layer in the area of synapses between bipolar and ganglion cells. They facilitate the conduction of the signal to the neurons that form the optic nerve.

Bipolar cellsreact to image contrast. Some bipolars react more strongly to color than to black and white contrast. Some receive information primarily from rods, others from cones.

Ganglion cells- large multipolar neurons of many varieties. Their axons form the optic nerve. Ganglion cells respond to many properties of a visual object (for example, light and dark objects, uniformity of illumination, the color of the object, its orientation).

Retinal glia. In addition to neurons, the retina contains large radial glia cells. Their nuclei are located in the inner nuclear layer. The outer processes end in microvilli, forming the outer boundary layer. The inner processes have an expansion (pedicle) in the inner boundary layer at the border with the vitreous body. Glial cells (Müller cells) play an important role in regulating ionic homeostasis of the retina.

Photoreceptor cells- rods and cones. The peripheral processes of photoreceptor cells consist of outer and inner segments connected by a cilium.

A distinction is made between central and peripheral vision, which is associated with the nature of the distribution of rods and cones in the retina.

areas of the central fossaare located mainly cones. Each cone of the central fovea forms a synapse with only one bipolar neuron. Central vision, as well as visual acuity, are realized by cones. Color perception is a function of cones. There are three types of cones, each of which contains only one of three different (red, green and blue) visual pigments.

Rod neurosensory cells- with narrow, elongated peripheral processes (rods). The outer segment of the process has a cylindrical shape and contains a stack of 1000-1600 membrane disks (flattened sacs).

The membranes of the discs contain the visual pigment rhodopsin, which includes protein and vitamin A aldehyde. Rhodopsin decomposes under the influence of light, changing the ionic permeability of the membranes and generating an electrical signal due to hyperpolarization of the receptors. It regenerates in the dark.

• The outer segment has many flattened closed discs containing visual pigments:

rhodopsin - in rods

iodopsin (red, green and blue pigments) - in cones

The disks are constantly updateddue to their formation in the proximal parts of the outer segments and displacement to the distal ones, where they are phagocytized by the pigment epithelium.

• The inner segment of the process contains elongated mitochondria, a centriole, elements of the aER and grER, and the Golgi complex. It provides the outer segment with energy.

substances, necessary for photoreception. The central process ends

spherical thickening (spherule) and forms a synapse with a bipolar cell in the outer plexiform layer.

Cone neurosensory cells- similar in structure to rod cells.

The only differences are -

the outer segments of their peripheral process (cones) are conical in shape (shorter and wider than those of rod cells)

the disc membrane contains the visual pigment iodopsin

there is no constant movement of discs and their phagocytosis by the pigment epithelium

nuclei - larger and lighter than those of rod cells

The visual pigment consists of an apoprotein (opsin) covalently linked to a chromophore (11-cis-retinal or 11-cis-dehydroretinal).

Eye. Choroid and its derivatives. Development, structure, functionsEyeconsists of the eyeball, which contains photoreceptor (neurosensory)

cells, and the auxiliary apparatus, which includes the eyelids, lacrimal apparatus and oculomotor muscles.

Wall of the eyeballformed by three shells:

external - fibrous(consists of the sclera and cornea)

middle - vascular(includes the choroid, ciliary body and iris)

internal - mesh, connected to the brain by the optic nerve Development: The rudiment of the eye appears in the 22-day-old embryo as a pair of shallow

invaginations in the forebrain. After the neuropores close, the invaginations enlarge and form outgrowths - the optic vesicles. Cells migrate here from the neural crest, which will later become:

Scleral cells

Ciliary muscle cells

Endothelial cells

Corneal fibroblasts

The optic vesicles are connected to the embryonic brain by means of optic stalks.

Coming into contact with the ectoderm, they initiate the formation of the lens.

Invagination of the wall of the vesicle leads to the formation of the optic cup. Its outer layer forms the pigment layer of the retina, and the inner layer forms the rest of it.

The optic cup is surrounded by mesenchyme - it forms the vascular tunic of the eye. The vascular tunic includes the vascular tunic itself, the ciliary body and

iris.

a) the choroid properprovides nutrition to the retina, it consists of loose fibrous connective tissue with a high content of pigment cells.

The composition includes four plates (layers):

supravascular- external, lies on the border with the sclera;

vascular- contains arteries and veins that provide blood supply to the choriocapillary plate;

choriocapillary - a flattened dense network of capillariesuneven caliber,

the endothelium of which is fenestrated on the side facing the retina. Capillaries cover 90-95% of the outer surface of the retina;

basal- includes the capillary basement membrane, a network of collagen and elastic fibers and the basement membrane of the retinal pigment epithelium.

b) ciliary body- a thickened anterior portion of the vascular tunic, which looks like a muscular-fibrous ring located between the dentate line and the root of the iris. Its base is formed by the ciliary muscle, and ciliary processes extend from the anterior portion. It is covered by ciliary epithelium, which belongs to the anterior (ciliary) portion of the retina.

ciliary muscleconsist of bundles of smooth muscle cells, lying circularly in the internal sections and meridianally-radially in the external sections. By contracting, it weakens the tension of the fibers of the ciliary belt, increasing the curvature of the lens and focusing the eye on nearby objects.

ciliary processes- folds of the ciliary body, 70-80 in number, protruding into the posterior chamber of the eye. Formed by connective tissue with a high content of pigment cells and fenestrated capillaries. Serve as attachment sites for the fibers of the ciliary belt (zonule of Zinn) - bundles of elastic filaments, interwoven with opposite ends into the lens capsule.

Functionciliary body:

Accommodation of the eye(changing the curvature of the lens)

Production of aqueous humor

Ciliated epithelium covering the processes- two-layer cubic. Consists of:

internal non-pigmented cellswith developed organelles and numerous basal processes forming the basal labyrinth

outer pigmented cells, containing pigment granules and also forming the basal labyrinth.

Each layer of the epithelium is located on its own basement membrane. It produces aqueous humor and participates in the formation of a barrier between blood and moisture.

c) iris- the most anterior part of the vascular membrane, separating the anterior and

backchambers of the eye. It is a ring-shaped plate with an opening of varying diameter (the pupil), connected by its ciliary edge to the ciliary body. The base (stroma) is formed by loose connective tissue with a large number of vessels and pigment cells (which determine the color of the eyes). Contains five layers:

anterior epithelium(single layer flat- a continuation of the posterior corneal epithelium; according to some data, this layer is formed by a discontinuous lining of fibroblasts and pigment cells);

outer border;

vascular(contains numerous vessels);

internal border;

posterior pigment epithelium(bilayered cubic - continuation of the ciliary epithelium of the retina).

Muscles of the irisformed by smooth muscle cells of neural origin:

constrictor pupillae muscle, consists of concentric bundles of cells

(innervated by parasympathetic nerve fibers);

pupillary dilator muscleconsists of bundles of cells running radially along the pigment epithelium (innervated by sympathetic nerve fibers).

143. Development, structure of the outer shell (sclera) of the eye. Structure of the corneaFibrous membrane -external, consists of the sclera - a dense opaque membrane,

covering the back 5/6 of the surface of the eyeball, and the cornea - the transparent anterior part, covering the anterior 1/6.

Scleraformed by dense fibrous connective tissue consisting of flattened bundles (plates) of collagen fibers running in different directions parallel to the surface of the organ, and fibrocytes and elastic fibers lying between them. In the deep layers it may contain melanocytes.

It performs protective and supporting functions; the tendons of the eye muscles are attached to its outer surface.

It passes into the cornea in the limbus area, on the inner surface of which there is a system of endothelium-lined canals (trabecular meshwork) leading to the venous sinus of the sclera (Schlemm's canal) - the outflow path of aqueous humor from the anterior chamber of the eye. When the outflow is disrupted, intraocular pressure increases, which is typical for a common disease - glaucoma.

The thinnest area of the sclera is the cribriform plate area.

Development:

Cornea- part of the fibrous membrane, a transparent plate convex outward, thickening from the center to the periphery. Includes five layers:

anterior epithelium- multilayer flat non-keratinizing, contains numerous nerve endings that provide high sensitivity of the cornea, is constantly moistened by the secretion of the lacrimal glands. Has a high ability to regenerate, being renewed every 7 days. In the limbus area it passes into the conjunctival epithelium. Absolutely transparent.

anterior limiting plate (Bowman's membrane)- the compacted outer layer of the cornea's own substance; located under the basement membrane of the anterior epithelium, consists of a network of collagen fibrils;

proper substance (stroma)- makes up 90% of the cornea's thickness - a special dense fibrous connective tissue consisting of flat bundles (plates) of collagen fibers located at an angle to each other and flattened fibrocytes lying between them. Glycoproteins of the main substance (chondroitin and keratan sulfates) provide transparency of the stroma. Contains numerous nerve endings;

blood and lymphatic vessels are absent;

posterior limiting plate (Descemet's membrane)- a three-dimensional network of collagen filaments; often considered to be the basement membrane of the posterior epithelium;

posterior epithelium (endothelium) - single-layer flat, formed by interdigitating cells with high metabolic activity. Participates in the exchange of fluid and ions in the cornea. Regenerates poorly.

Corneal nutritionis carried out due to aqueous moisture (in its central areas)

diffusion from the vessels of the limbus region(in the peripheral).

Development:

The corneal endothelium is made of mesenchyme, the epithelium is made of ectoderm.

Retinal ganglion neurons. Cytology and relationshipsGanglion cells- large multipolar cells with eccentric

located nucleus and a large nucleolus. The cytoplasm occupies a large volume and contains well-developed organelles. Dendrites form synaptic connections with the axons of bipolar cells and processes of amacrine cells. Axons, gathering together, form the optic nerve.

They react to many properties of a visual object: light/dark, uniformity of illumination, the color of the object and its orientation.

They are divided into several types depending on the area of branching of the dendrites and the number of cells covered by them.

Cornea of the eye. Origin and structure

- repeat 143

Crystalline lens. Development, structure, function

Crystalline lens- a transparent biconvex body that is held by the fibers of the ciliary belt, changing its curvature depending on their tension and thereby providing the ability to focus on the retina objects located at different distances from the eye (accommodation).

a) lens capsule- a thin transparent layer that covers the lens from the outside, is the basement membrane of its epithelium. Contains glycoproteins and consists of a network of microfilaments that have significant elasticity (decreasing with age). Serves as a place for attaching the fibers of the ciliary belt. Impermeable to macrophages and antigens, but ensures the metabolism of the lens.

b) lens epithelium- a layer of cubic cells lying subcapsularly on its anterior surface; in the equatorial region, the cells divide by mitosis (nuclear or germinal zone), lengthen and gradually transform into lens fibers.

c) lens fibers - elongated(up to 7-10 mm) epithelial cells of a hexagonal shape, lying parallel to the surface of the lens in concentric layers (up to 2000 in an adult) and forming its own substance, which consists of a cortex and a nucleus. Their organelles and nucleus are located in the equatorial region, the cytoplasm contains special proteins - crystallins. The fibers are held together by numerous gap junctions and spherical interdigitations. Shifting toward the center of the lens, they lose their nuclei and condense, nesting on each other and forming the nucleus of the lens.

Development: Lens placodeseparates from the ectoderm and forms the lens vesicle, above which the ectoderm closes. As the vesicle develops, the thickness of its walls changes - a thin anterior epithelium and lens fibers appear on the posterior surface. At first, the fibers synthesize alpha- and beta-crystallins, and later begin

synthesize and gamma-crystalins. Nuclei and organelles are lost. During intrauterine development, the lens receives nutrition from the vitreous artery.

Taste buds. Localization, cellular composition, cell structure, functionsThe peripheral part of the taste analyzer is the taste buds. They are found in

epithelium of the mouth, tongue, anterior pharynx, esophagus and larynx (maximum boundary - vocal cords). Their main localization - chemosensitive papillae of the tongue: fungiform, circumvallate and foliate.

Taste bud(gemma gustatoria)has an ellipsoid shape, a height of 27-115 µm and a width of 16-70 µm. In its apical section there is a taste canal filled with an amorphous substance, opening onto the surface of the epithelium with a taste pore. The taste bud is formed by 30-80 elongated cells, closely adjacent to each other. Most of these cells come into contact with nerve fibers penetrating

kidney from the subepithelial nerve plexus. Regeneration is present. Taste bud cells are morphologically heterogeneous. The following are distinguished:

Cells of the type1have up to 40

microvilli, the apical part contains many electrodense granules. There is a Golgi complex, a cytoskeleton in the form of bundles of microfilaments and microtubules. In the basal part - dense mitochondria and grEPS.

Cells of the type2have a lighter cytoplasm, as well as a smooth ER. Microvilli are rare and small. There are lysosomes, multivesicular bodies, etc.

Cells of the type3also contain low microvilli, centrioles and some vesicles. The GREP is developed

weakly, smooth ER - strongly. The peculiarity of the cells is a multitude of granular and light vesicles related to afferent synapses.

Cells of the type4are located in the basal part of the kidney. Contain a large nucleus and microfilaments. They may be the precursors of other cell types - but this is not certain.

Support cells - according to the BBB, it is also in the kidney.

Chemoreceptor cells. Although all cell types form contacts with afferent fibers, the function of chemopreception is associated with type III cells. In the presynaptic region of taste cells, granular vesicles contain serotonin, a neurotransmitter of the afferent synapse. Chemoreceptor cells perceive sweet, sour, bitter, salty, and the taste of glutamate (umami).

Organ of balance. Development, localization, morpho-functional characteristics of the constituent structures

Development

Remember the auditory placodes (paired thickenings of the ectoderm near the neural groove)? Well, after subsequent invagination of the ectoderm, the auditory vesicle is formed, in which the elliptical saccule with semicircular canals and the spherical saccule later appear.

Organ of balanceincludes specialized receptor zones in the sac,

the uterus and ampullae of the semicircular canals.

The sac and the uteruscontain spots (macules) - areas in which the single-layer flat epithelium of the membranous labyrinth is replaced by prismatic, Macules include 7.5-9 thousand sensory epithelial (hair) cells connected by complexes of compounds

supporting cellsand covered by the otolithic membrane. The macula of the utricle occupies a predominantly horizontal position, and the macula of the saccule is vertical.

a) sensory epithelial (hair)

cellscontain numerous mitochondria, a developed aER and a large Golgi complex, at the apical pole there is one long cilium

(kinocilia)and 40-80 rigid stereocilia

(specialized microvilli)

of varying length (the longest are adjacent to the cilium). In the maculae, the hair cells form groups within which the kinocilia are oriented in the same way, and the orientation of the groups themselves is different. The cells are divided into two types:

(1) hair cells type I

(pear-shaped)- with an expanded basal part, almost completely covered by the afferent nerve ending in the form of a cup; lie in the center of the ridges.

hair cells type II (prismatic)- tall, narrow or amphora-shaped;

small afferent and efferent nerve endings are adjacent to the basal part;

lie on the periphery of the scallops.

b) supporting cells- high prismatic cells with numerous microvilli on the apical surface. Participate in the formation of the otolith membrane.

c) otolithic membrane- a layer of a special gelatinous substance covering the macula, in which the stereocylin and kinocilia of the hair cells are immersed. On its surface, calcium carbonate crystals - otoliths (statoconia) - are located in several layers,

shaped like pointed cylinders. The epithelium of the cristae is surrounded by a gelatinous dome.

Function of the organ of balanceconsists of the perception of gravity, linear and angular accelerations, which are converted into nerve signals transmitted to the central nervous system, coordinating the work of muscles, which allows you to maintain balance and navigate in space.

The macula of the saccule and utricle respond to gravity and linear acceleration.In connection

the fact that the specific mass of otoliths is three times greater than that of endolymph, they have inertia when the position of the head changes, displacing the otolith membrane and deforming the stereocilia of the hair cells immersed in it, which causes the emergence of action potentials transmitted to the afferent nerve fibers.

The ampullar ridges perceive angular accelerations: when the body rotates, an endolymph current arises, which deflects the dome, which stimulates the hair cells due to the bending of the stereocilia. The movement of the dome towards the kinocilium causes excitation of the receptors, and in the opposite direction - their inhibition.

Olfactory organ. Development. Structure of olfactory epithelium cells. Mucous glands

Development

The olfactory organs are of ectodermal origin. The main organ develops from placodes - thickenings of the anterior part of the head ectoderm. The olfactory pits are formed from the placodes. In human embryos, in the 4th month of development, supporting epithelial cells and neurosensory olfactory cells are formed from the elements that make up the walls of the olfactory pits. The axons of the olfactory cells unite and go through the unformed ethmoid bone to the olfactory bulb.

The peripheral section of the olfactory analyzer (Fig. 8-49) is represented by the olfactory lining (area olfactoria), which occupies the middle part of the superior nasal concha and the corresponding area of the mucous membrane of the nasal septum.

The olfactory epithelium contains receptor cells, the total number of which reaches 50 million. Their central processes (axons) transmit information to the olfactory bulb.

Olfactory receptor cells are surrounded by supporting cells. These are either tall cylindrical or small cells. The tall ones reach the surface of the receptor layer.

contain microvilli. Olfactory epithelium

It also contains pigment cells, which are responsible for the yellow color of the olfactory lining.

terminal sections are located in the subepithelial connective tissue

Bowman's glands (tubular-alveolar), blood vessels, and bundles of unmyelinated olfactory nerve fibers. Mucus secreted by Bowman's glands covers the surface of the olfactory mucosa with a layer 60 µm thick.

the olfactory senses are involved in the process of chemoperception

cilia, immersed in mucus. The olfactory nerve is a collection of thin olfactory filaments that pass through the openings of the ethmoid bone to the olfactory bulbs and form bundles of 10-100 filaments.

Receptor cell

Morphology.The body of the olfactory cell contains numerous mitochondria, cisterns of the endoplasmic reticulum with ribosomes, elements of the Golgi complex, and lysosomes. In addition to the central (axon), the olfactory cells have a short peripheral process (dendrite) ending on the surface of the olfactory epithelium with a spherical thickening - the olfactory club with a diameter of 1-2 μm. It contains mitochondria, small vacuoles, and basal bodies for 20-80 olfactory hairs extending from the top of the club, 30-200 μm long, having the structure of typical cilia. The membrane of the olfactory cilia contains receptors for odorous substances. Receptor cells are the only neurons in the body capable of regeneration.

Function.The receptor cells of the olfactory mucosa register 25-35 primary odorants, but their combinations form many millions of perceived odors.

cAMP-dependent gate ion channels are embedded in the plasma membrane of olfactory cilia.

Interaction of an odorant with a receptor protein in the plasma membrane => activation of G protein => increased adenylate cyclase activity => increased cAMP levels

There is also the inositol triphosphate system.

Epidermis. General characteristics. Layers. Cell types

The skin is covered by the epidermis - a multilayered flat keratinized epithelium. Depending on the thickness of the epidermis, a distinction is made between skin with high keratinization (thick skin) and skin with low keratinization (thin skin).

Thick skin(on the palms and soles) - formed by thick (400-600 microns) epidermis

a thick stratum corneum, a relatively thin dermis; hair and sebaceous glands are absent.

Thin skin(on other parts of the body) - formed by a thin (75-150 µm) epidermis with a poorly developed stratum corneum, a relatively thick dermis; there is hair and skin glands.

It projects into the underlying dermis in the form of epidermal ridges alternating with its papillae. This increases the mechanical strength of the connection between the epidermis and the dermis and the surface area of mutual exchange between them.

Cell types in the epidermis

Keratinocytes(90% - 95/98%). They are continuously formed in the basal layer and mix into the overlying layers, undergoing differentiation and eventually turning into horny scales that are exfoliated from the surface of the skin. They contain cytokeratin, which is expressed differently depending on the layer and skin type.

Melanocytes

Lanherhans cells(skin macrophages)

Merkel cells+ nerve terminal

Lymphocytes(T-lymphocytes)

The epidermis of thick skin consists of five layers;

basal

prickly

granular

shiny (there is none in the thin one)

horny

Basal layerformed by a single row of basophilic cells of cubic or prismatic shape, lying on a basement membrane with well-developed organelles,

numerous keratin filaments (tonofilaments). These cells:

(a) play the role of cambial elements of the epithelium (among them there are stem cells and mitotic figures are found)

(b) provide a strong connection between the epidermis and dermis (connected to neighboring cells by desmosomes, and to the basement membrane by hemidesmosomes).

Spinous layerconsists of several rows of large irregularly shaped cells connected to each other by desmosomes in the area of numerous processes ("spines") that contain bundles of tonofilaments. Organelles are well developed. In the deep sections, dividing cells are found. Synthesize desmoplakin - a desmosome protein.

Granular layer- thin, formed by several rows of flattened

(spindle-shaped in section) cells. The nucleus is flat, dark, in the cytoplasm there are numerous tonofilaments, as well as granules of two types:

a) keratohyaline- large, basophilic, containing the precursor of the horny substance; tonofilaments penetrate into them;

b) lamellar (keratinosomes)- small (visible only under an electron microscope), with a lamellar structure. Contain a number of enzymes and lipids, which are released into the intercellular space during exocytosis, providing a barrier function and water resistance of the epidermis.

Shiny layer(only present in thick skin) - light, homogeneous, contains the protein eleidin. Consists of 1-2 rows of flattened oxyphilic cells with undefined borders. Organelles and nucleus disappear, keratohyalin granules dissolve, forming a matrix into which tonofilaments are immersed.

Stratum corneumis formed by flat horny scales that do not contain a nucleus or organelles and are filled with tonofilaments lying in a dense matrix. Their plasma membrane is thickened due to the deposition of proteins (mainly involucrin) on the inner surface. The scales have high mechanical strength and resistance to chemicals. In the outer parts of the layer, the desmosomes are destroyed and the horny scales are exfoliated from the surface of the epithelium.

Structure of the skin itself (dermis)

Dermis (the skin itself)- ¾ of the thickness of the entire skin. It is located under the epidermis, provides it with nutrition, gives the skin strength and contains its derivatives. It includes two layers:

papillary- forms conical protrusions (papillae) protruding into the epidermis. Repeats the contours of the basement membrane of the epidermis. Consists of loose fibrous connective tissue with lymphatic and blood capillaries, nerve fibers and endings. Provides connection of the dermis with the basement membrane of the epidermis with the help of reticular, elastic fibers and special anchor fibrils. Contains collagen types 1, 3, 7.

reticulate- deeper, thicker and stronger - formed by dense fibrous irregular connective tissue and contains a three-dimensional network of thick bundles of collagen fibers interacting with a network of elastic fibers. Contains

collagen type 1.

152. Melanocytes. Origin, localization, structure, functioningMelanocytesare of neural origin (from the neural crest). Their body lies in

basal layer, and long processes go into the spinous layer.

Melanin- a black-brown (eumelanin) or yellow-red (pheomelanin) pigment - is synthesized and accumulated in the cell body in granules (melanosomes),

which are transported to its processes. From the latter they enter the keratinocytes, where they protect their nuclear apparatus from damage by ultraviolet rays, and are subsequently destroyed by lysosomes. The synthesis of melanin and its transport to epithelial cells are stimulated

melanocyte-stimulating hormone (MSH) and ACTH, A

also by the action of sunlight (tanning). They are enhanced in dark races compared to light races. Formed from DOPA.

Melanin synthesis is impaired in albinism; the number of melanocytes is not changed. Tyrosinase is a melanocyte enzyme that contains copper and is sensitive to UV. It catalyzes

conversion of tyrosine to DOPA.

Melanocortins- regulate the ratio of melanin types in the skin.

153. Sensory nerve endings of the skin. Structure, localization in skin layers, functions

The most powerful nerve plexuses of the skin are located in the subcutaneous tissue. Free nerve endings in the epidermis form mechanoreceptors,

thermoreceptors and receptors of pain (nociceptive) sensitivity. Thermoreceptors are divided into receptors of cold (25-30 °C) and heat (40-42 °C) sensitivity. Their branched terminals pass between the cells of the deep layers of the epidermis.

Merkel cells (tactile epithelioid cells; tactile complex)- are of neural origin, connected to the afferent nerve fiber and perform a receptor function. Their body lies in the basal layer, and the processes are connected by desmosomes with the epithelial cells of the basal and spinous layers. They are located in the skin of the palms and soles

The organelles are moderately developed; in the basal part of the cell, granules with a dense center and a light rim accumulate, containing a mediator, which, upon mechanical deformation of the processes, is released into the synaptic cleft.

Meissner's corpuscles (tactile corpuscle)- in the papillary layer of the skin. They are located in the most sensitive areas of the body - genitals, lips, nipples of the mammary gland, fingers, toes.

Ruffini bodies (fusiform bodies)- in the skin itself. The plantar surface of the foot.

Krause flasks.In the mesh layerThe skin contains Krause's end flasks - encapsulated mechanoreceptors that have a similar structure to the lamellar body, but are smaller in size.

Pacinian corpuscles (lamellar corpuscles)- the largest encapsulated receptors, located deep in the skin and in the subcutaneous tissue, mainly in the fingers, external genitalia and mammary gland. All of these are afferent fibers.

Vegetative innervation- muscles of the SMC and cells of the glands regulate blood supply and sweating. These are efferent fibers.

Immunological function of the skin. Skin cells involved in immune reactions

The skin is an immunologically active organ.

Keratinocytesnot only ensure the formation of a protective keratin layer on the skin surface, but also produce hormones that regulate the size of the T- population

lymphocytes and their differentiation.

They produce:

interleukin 1

interleukin 7

transforming growth factor-beta (TGF-beta)

Under the influence of an irritating stimulus (hypoxia, trauma, exposure to chemical factors)

interleukin 6

interleukin 8

interleukin 12

transforming growth factor-alpha (TGF-alpha)

granulocyte-macrophage colony-stimulating factor (GM-CSF)

platelet-derived growth factor (PDGF)

fibroblast growth factor-b (FGFb)

tumor necrosis factor-alpha (TNF-alpha)

Immunocompetent cellsIn the epidermis, as you remember, there are T-lymphocytes and antigen-presenting Langerhans cells.

When Ag penetrates the epidermis, an immune response develops. Ag interacts with Langerhans cells, which process and transport it to the lymph nodes and present it to T-lymphocytes programmed to respond to this Ag. Langerhans cells are located in the basal and spinous layers of the epidermis.

endothelial cells participate in the distribution of T-lymphocytes in the integument

blood vessels of the skin itself, which express address markers on their surface, as well as extracellular matrix proteins (fibronectin and laminin).

155. The skin's ability to regenerate. Cells involved in the process of epidermis and dermis restoration

Regeneration (renewal) of the epidermisensures its barrier function due to the constant replacement and removal of outer layers that are damaged and contain microorganisms on their surface.

The renewal period is 20-90 days (depending on the area of the body and age); it is sharply reduced when the skin is exposed to irritating factors and in some diseases (for example, psoriasis).

Epidermal proliferative unit- a clone formed by keratinocytes of different layers of the epidermis with different degrees of differentiation, combining different stages of differon, i.e. cells of different degrees of differentiation and originating from a single stem cell located in the basal layer. In the center of the EPE is the Langerhans cell. As the cells differentiate and multiply, they shift to the surface of the epidermis, forming a proliferative unit of the epidermis, which occupies a certain area of it in the form of a column. Their maximum mitotic activity is observed at night, and their lifespan is 2-4 weeks.

Wound healinggoes as follows:

- At the bottom of the wound, a small amount of fibrin is formed in the skin itself

- Keratinzoites of the basement membrane grow inward, covering the exposed surface

connective tissue part of the skin. When lesions occur at this depth of the skin, hyperpigmentation may form due to the influence of sunlight - this is due to the fact that damage to the capillary loops serves as a stimulus for mast cells to release biologically active substances into the skin (histamine, serotonin), stimulating melanocytes to produce melanin, which is then absorbed by keratinocytes and gives them a specific dark color.

- The continuity of the epithelial layer is restored.

- Fibroblasts also proliferate in the meantime, supported by growth factors. 1) Superficial damage. In this case, recovery occurs due to

keratinocytes of hair follicles and sebaceous glandsfrom the deep layers of the skin itself (stem cells of the outer root sheath and cambial cells of the sebaceous glands)

2) Deep damage.When both the epidermis and the hair follicles with sebaceous glands are destroyed, small defects heal on their own due to the migration and proliferation of keratinocytes from adjacent areas of the epidermis.

Large skin defects.In this case, split grafts are used - fragments of skin from other parts of the body. It consists of the epidermis and the skin itself. Part of the skin itself with follicles and sebaceous glands remains at the site of collection.

156. SKIN. SWEAT GLANDS: CLASSIFICATION, LOCALIZATION, STRUCTURE. HORMONAL REGULATION, INNERVATION.

Leather.

Includes 3 layers:

EPIDERMIS (cutaneous tissue)

It is represented by a multilayered flat keratinized epithelium, among the cells of which the following types of cells are scattered in a mosaic pattern:

Keratinocytes

(make up the lion's share >90%, approximately 95-98%)

keratinocytes of different layers of the epidermis:

- stem cells (basal layer) - the progenitors of proliferative units of the epidermis, high mitotic activity, low probability of entering terminal differentiation and adhesive capacity.

- spiny cells (located closer to the surface of the epidermis) - high mitotic activity, have numerous processes and desmosomes, have granules, are surrounded by a membrane, synthesize desmoplakin - a desmosome protein.

- granular cells - clusters of intermediate filaments connected by proteins rich in histidine and cystine.

- the horny layer - is represented by densely packed horny scales, having the shape of a 14-sided figure, which are peeled off from the surface of the epidermis. The least penetrating layer.

Melanocytes

(pigment cells, originate from the neural crest, are dendritic cells, extend into the basal layer, and the processes extend into the overlying layers)

From tyrosine AK, the pigment melanin is formed through the DOPA stage, which is capable of capturing other cells of the epidermis.

If cells contain melanin, but do not synthesize it, but accumulate it - melanophores.

Skin macrophages - Langerhans cells

(formed from blood monocytes, are antigen-presenting cells)

Merkel cells + nerve terminal

(responsible for tactile sensitivity, located in the basal layer)

Lymphocytes (T-lymphocytes) 2. DERMIS

¾ of the skin's thickness, approximately 75%, consists of two layers:

Papillary

Very thin, repeating the contours of the BM epidermis and formed by loose, unformed connective tissue with a predominance of elastic fibers; this layer contains a dense capillary network

Reticulate

approximately 80% of the thickness of the dermis

Formed by dense, unformed connective tissue with a predominance of collagen fibers. The terminal secretory sections of sweat and sebaceous glands, as well as hair follicles, are located here.

ADIPOSE (SUBCUTANEOUS) TISSUE

Thermoregulation

Depreciation

Sweat glands: classification, localization, structure.

Sweat glands are simple tubular, unbranched glands.

The glands consist of a secretory section, which contains dark, light and myoepithelial cells (basket cells) and an excretory duct formed by a two-layer cubic epithelium, which opens into a sweat pore. Dark and light differ:

-ability to reproduce

-synthetic activity

Basket cells are an obligatory component of all exocrine glands of ectodermal origin, contain an actimyosin complex and, by contracting, with their processes facilitate the removal of secretion.

A distinction is made between:

ECCRENE

The secretory sections are located deep in the reticular layer, on the border with the subcutaneous tissue.

APOCRYNE

Found in the armpits, inguinal, perianal areas, around the nipples. Do not function until puberty. Respond to hormonal effects. (apical parts of cells are rejected)

Hormonal regulation

During sweating, the glands secrete the vasodilator bradykinin. Consequently, the glands participate in thermoregulation, influencing both sweating and the intensity of blood supply to the skin.

Innervation

Eccrine sweat glands are innervated by fibers of the sympathetic division of the ANS.

When they are excited, neurotransmitters are released from the varicose veins.

ACh directly and indirectly (through basket cells) stimulates sweating,

VIP causes vasodilation associated with sweating.

ADRENORECEPTOR AGONISTS reduce the secretory activity of sweat glands

HAIR. STRUCTURE OF THE HAIR FOLLICLE, HAIR BULB. HAIR GROWTH. HAIR PIGMENTATION, INNERVATION OF THE HAIR FOLLICLE.

Hair

Classification:

Long hair (head, armpits, moustache, beard, genital area)

Bristly hair (eyebrows, eyelashes, external auditory canal, vestibule of the nasal cavity)

Downy (other parts of the hair)

Hair is laid down in the 3rd month of development

A distinction is made between the root (located in the thickness of the skin and consists of the medulla, cortex and cuticle) and the rod (no living cells, located above the surface of the skin)

Root structure:

Medulla (shaped like a rouleaux, contains soft keratins that divide at the base of the hair; cells contain trichohyalin granules, vesicles, and pigment)

Cortex (flattened cells adjacent to the medulla, also dividing; near the hair follicle, contain hard keratin and pigment)

Cuticle (in some hairs, has a non-cellular structure, is present in eyelashes; lies close to the cortex, consists of flat cells, perpendicular to its surface)

*HAIR FOLLICLE - consists of the hair root + outer and inner root sheath

-internal epithelial sheath of the hair

2 types of cells: Henle's layer and Huxley's layer (merge into one in the middle and upper sections, contain soft keratin)

in the lower sections it originates from the hair follicle and ends at the level of the sebaceous gland ducts

external epithelial sheath of the hair

It is a continuation of the germ layer of the epidermis, surrounded by a glassy membrane

*HAIR BULB - the thickened base of the hair root where the sheaths unite and constant cell proliferation occurs, which is why it is called the hair matrix (hair growth)

Hair pigmentation

Dependent on the presence of melanin produced by melanocytes in the hair follicle. The relationship between melanocytes and keratinocytes is the same as in the epidermis. As keratinocytes differentiate, they capture melanin, which determines the pigmentation of the medulla and cortex.

Innervation of the hair follicle

Human hair is innervated by 5-9 nerve fibers that go below the mouth of the sebaceous gland, then change direction and circularly embrace the hair. From the circular fibers, fibers branch off, running parallel to the hair shaft as part of the hair follicle above the expansion of the hair bulb, forming a terminal complex - a palisade (picket) apparatus.

Palisade apparatus

The terminals are in contact with the vitreous membrane and have the shape of a flattened cylinder located between the Schwann cells.

Pilo-Ruffini complex

is represented by a large number of afferent fibers, branching in a ring around the hair follicle below the mouth of the sebaceous gland. Among their terminals are bundles of collagen fibers and connective tissue cells analogous to perineurium cells, which do not have their own basement membrane and form a semblance of a capsule of the complex.

Merkel cells

Compact, band-like clusters of cells run circumferentially in the epithelium of the hair follicle near the infundibulum

M, raising hair

Innervated by sympathetic fibers

DIFFERON: CONCEPT NEUROSECRETORY CELLS OF THE HYPOTHALAMUS. LOCALIZATION, HORMONES, HORMONE TRANSPORT ROUTES.

Neurosecretory cells of the hypothalamus, localization, hormones

Typical nerve cells. The releasing hormones synthesized in the perikarya of these neurons

hormones (liberins-somatoliberin, gonadotropin-releasing hormone, etc. and statins-somatostatin), arginine, vasopressin, neurophysinsand oxytocin are transported along the axons of these neurons as part of membrane vesicles to the axo-vasal synapses. These hormone-producing cells are part of many nuclei of the hypothalamus (including the supraoptic, periventricular). Part of the axons of these neurons end in the ependymal

lining of the 3rd ventricle.

Hormone transport pathways

Transport of hormones synthesized in neurosecretory cells occurs along the hypothalamic-pituitary tract formed by the axons of these cells. The final station is the axovasal synapses of the neurohypophysis.

Liberins and statins enter the adenohypophysis through the bloodstream from the primary capillary network in the median eminence, then into the portal veins and into the secondary capillary network of the pituitary gland. The sinusoidal capillaries of this network, surrounding the adenocytes, provide the effect of neurohormones on the cells of the adenohypophysis.

NUCLEI AND NEUROSECRETORY CELLS OF THE HYPOTHALAMUS. HORMONES OF THE HYPOTHALAMUS.

The hypothalamus is divided into anterior, middle, and posterior sections.

FrontContains pairedsupraotic(above the optic chiasm) andparaventricular

(in the wall of the 3rd ventricle) nuclei

Formed by large secretory neurons, in the bodies and processes of these neurons there are secretory granules. Neurites of large secretory neurons form the hypothalamic-pituitary tract, consisting of the supraoptic-pituitary and paraventriculo-pituitary bundles.

They producevasopressin(supraoptic = superooptic nuclei) andoxytocin(paraventricular = periventricular nuclei)

AverageContains a number of nuclei consisting of small secretory neurons (lie on the periphery

nuclei) and adrenergic neurons.

The most important ones arearcuate (infundibular)Andextra-medial(larger) nuclei located in the area of the gray tubercle.

They produceadrenohypophyseal hormones

Neurites of cells in the median eminence form axo-vasal synapses on loops of the primary capillary network.

Hypothalamic hormones are calledreleasing hormones.

Neurohormones that stimulate the release of pituitary tropic hormones are calledliberins.

For neurohormones that inhibit the release of tropic hormones, the designation-statins.

OXYTOCIN. SYNTHESIS, TRANSPORT, SECRETION, TARGETS, EFFECTS.

Synthesis and transport

They are synthesized in neurosecretory neurons of the hypothalamus. Expression occurs in multibranched cells of the epioptic and periventricular nuclei of the hypothalamus. Membrane vesicles containing translation products are transported along the axons of these neurons as part of the hypothalamic-pituitary pathway to the posterior lobe of the pituitary gland, and through axo-vasal synapses the hormones are secreted into the blood.

Secretion

The secretion is regulated by the impulse activity of the axons of neurosecretory neurons. In this case, oxytocin is split off from neurophysins and enters the blood.

Targets and effects

SMC myometry

oxytocin stimulates contraction of the SMC during labor, orgasm, and menstrual break

Myoepithelial cells of the mammary gland

oxytocin is secreted upon stimulation of the nipple and areola and stimulates contraction of the myoepithelial cells of the alveoli of the lactating mammary gland (milk ejection reflex)

VASOPRESSIN. SYNTHESIS. TRANSPORT. TARGETS. EFFECTS

Synthesis and transport

Occurs in some neurosecretory neurons of the periventricular and supraoptic nuclei of the hypothalamus. Extrahypothalamic expression is possible in malignant tumor cells. Membrane vesicles containing translation products are transported along the axons of these neurons as part of the hypothalamic-pituitary pathway to the posterior lobe of the pituitary gland, and hormones are secreted into the blood through axo-vasal synapses.

Targets and effectsAntidiuretic hormone

Kidney tubules Regulates reabsorption, water exchange

Maintaining a constant osmotic pressure of the body's fluids

Vessels Narrows blood vessels (vasoconstriction)

DEVELOPMENT AND STRUCTURE OF THE PITUITARY GLAND

Development

It is formed from two rudiments - ectodermal and neurogenic.

Ra'tke's Pocket

At 4-5 weeks, the ectodermal epithelium of the roof of the oral bay forms the Rathke pouch, an outgrowth directed toward the brain. From this pituitary pouch, the adenohypophysis (anterior, intermediate, and tuberal lobes, which are part of the pituitary stalk) develops.

Infundibular process

Towards Rathke's pouch grows a protrusion of the diencephalon, giving rise to the neurohypophysis (the posterior lobe of the pituitary gland, the neurohypophyseal part of the pituitary stalk and the median eminence)

Structure

Anatomicallyhas a stalk and a body, histologically divided into the adeno- and neurohypophysis

Adenohypophysis

Consists offront(epithelial endocrine gland that synthesizes tropic hormones),intermediate(weakly expressed, sometimes cells with expression of the proopiomelanocortin gene are found) andtubercular(strands of epithelial cells between which are the pituitary portal veins, connecting the primary and secondary capillary networks)share.

Neurohypophysis

neurophysins),neurohypophyseal part of the stalk(contains axons of the hypothalamic-pituitary tract passing into the posterior lobe) andmedian eminence(secretion of releasing hormones, the targets of which are the endocrine cells of the anterior lobe)

LIBERINS. PLACE OF SYNTHESIS. TRANSPORT. FUNCTION

Synthesis

Occurs in the neurosecretory cells of the hypothalamus

Transport

Liberins enter the adenohypophysis through the bloodstream from the primary capillary network in the median eminence, then into the portal veins and into the secondary capillary network of the pituitary gland. The sinusoidal capillaries of this network, surrounding the adenocytes, provide the effect of neurohormones on the cells of the adenohypophysis.

Function

Stimulates the release of pituitary tropic hormones.

GONADOLIBERINS. SYNTHESIS AND SECRETION. TARGETS AND EFFECTS.

Synthesis and secretion

-For women- in the hypothalamus there are 2 centers: tonic (provides background secretion of gonadotropin-releasing hormone, which occurs intermittently, with an interval of 60-90 minutes) and cyclic (provides cyclic release during the ovarian cycle, regulating FSH and LH, the interval is 40-90 minutes, after ovulation it decreases to 90-180 minutes - In men, there is one center - tonic - 8-14 impulses per minute Secretion of gonadotropin-releasing hormone is stimulated by kisspeptin, and inhibited by sex hormones and prolactin Synthesized by neurosecretory cells of the small-cell nuclei of the hypothalamus

Targets and effects

Gonadotrophs of the anterior pituitary gland - stimulates the synthesis and secretion of FSH and LH in gonadotroph-producing cells

ADENOHYPOGYSIS. STRUCTURE. HORMONES. TARGETS. EFFECTS.

Structure

Hormones

Tropic hormones - the anterior lobe synthesizes STH (somatotrophin), TSH

(thyrotrophin), ACTH (adrenocorticotropic), gonadotropins (FSH, LH), prolactin

Targets and effects

The target organs are the endocrine glands. Effects: stimulate the glands, and an increase in the blood level of the hormones they secrete suppresses the secretion of the pituitary hormone by the principle of feedback.

TROPIC HORMONES OF THE ADENOHYPOGYSIS.

Synthesis

in the anterior part of the adenohypophysis

Hormones

Tropic hormones - the anterior lobe synthesizes STH (somatotrophin), TSH

(thyrotrophin), ACTH (adrenocorticotropic), gonadotropins (FSH, LH), prolactin

Targets and effectsThe target organs are the endocrine glands

Effects - stimulate the glands, and the increase in the blood level of hormones secreted by them suppresses the secretion of the pituitary hormone according to the principle of feedback

POSTERIOR LOBE OF THE PITUITARY GLAND. ORIGIN. STRUCTURE. FUNCTIONS.

Structure and functions

Histologically, the neurohypophysis consists of neuroglial cells (pituitary cells), blood vessels, ansones of the hypothalamic-pituitary tract, and axo-vasal synapses. Includesposterior pituitary gland(hormones are not synthesized, but arginine, ADH, oxytocin and neurophysins are synthesized into the blood through the wall of blood capillaries),neurohypophyseal part of the stalk(contains axons of the hypothalamic-pituitary tract passing into the posterior lobe) andmedian eminence(secretion of releasing hormones, the targets of which are the endocrine cells of the anterior lobe)

Origin

It is formed from the infundibular process, which is a protrusion of the diencephalon towards Rathke's pouch

BLOOD SUPPLY SYSTEM OF THE ANTERIOR AND POSTERIOR LOBES OF THE PITUITARY GLANDThe afferent pituitary arteries in the mediobasal hypothalamus (median eminence) form the primary capillary network. The axon terminals of the neurosecretory cells of the hypothalamus terminate on these capillaries. Blood from the primary capillary network is collected in the portal veins, which run along the pituitary stalk (tubercular part) into the anterior lobe. Here, the portal veins pass into the capillaries of the secondary network. Blood from the secondary capillary network, enriched with hormones of the anterior lobe, enters the general circulation through the efferent veins

PINEAL GLAND. STRUCTURE AND FUNCTIONS.

Structure

A conical outgrowth of the diencephalon connected to the wall of the 3rd ventricle. The capsule is formed by connective tissue of the pia mater. Partitions extend from the capsule, containing blood vessels and plexuses of sympathetic nerve fibers. The partitions do not completely divide the body of the gland into lobules. The parenchyma of the organ consists ofpinealocytesAndinterstitial cells.

Functions

Little studied, most likely a link in the implementation of biological rhythms, including circadian rhythms

THYROID GLAND. DEVELOPMENT. STRUCTURE. THYROID FOLLICULAR CELLS: FORMATION OF IODINE-CONTAINING HORMONES, REGULATION OF FORMATION. EFFECTS OF HORMONES.

Development

During embryogenesis, 3-4 pairs of gill pockets are formed from the material, as is the entire branchiogenic group of glands. (lecture)

Endocrine cells of the thyroid gland have a dual origin: from the wall of the pharynx (from the ectoderm of the pharyngeal pockets) and the neural crest.

Structure

Consists of two parts - stroma and parenchyma

Stroma

-capsule-consists of dense fibrous connective tissue

- septa (trabeculae) - strands of dense fibrous connective tissue containing

blood vessels, lymphatic vessels and nerves

-interstitium-space is filled with the supporting element of the parenchyma, a framework of

loose connective tissue with blood and lymphatic vessels.

Parenchyma

a set of histological elements that perform the main function of an organ. A set of cells that secrete thyroid hormones and C-cells that synthesize calcitonin.

Formation of iodine-containing hormones

Follicular cells form the wall of the follicle and form its contents, synthesizing and secreting thyroglobulin into a colloid => iodinated, and then broken down in phagolysosomes before the cell reutilizes amino acids, and T3 and T4 are formed from monoiodotyrosine and diiodotyrosine

Regulation of education

Thyroid stimulating hormone is the main regulator of thyroid function (synthesized by the pituitary gland). Stimulates the synthesis and secretion of T3 and T4

Effects of hormones

T3, T4 participate in early embryogenesis - ensure morphogenesis, increase tissue sensitivity to catecholamines. Increase metabolic processes, accelerate the catabolism of proteins, fats and carbohydrates, are necessary for the normal development of the central nervous system, increase heart rate and cardiac output.

THYROXINE(T4). SYNTHESIS. SECRETION. REGULATION. FUNCTION

Synthesis and secretion

Follicular cells form the wall of the follicle and form its contents, synthesizing and secreting thyroglobulin into a colloid => iodinated, and then broken down in phagolysosomes until the cell reutilizes amino acids, and thyroxine is formed from monoiodotyrosine and diiodotyrosine

Regulation

Thyroid stimulating hormone is the main regulator of thyroid function (synthesized by the pituitary gland). Stimulates the synthesis and secretion of thyroxine

Function

Thyroxine is involved in early embryogenesis - ensures morphogenesis, increases tissue sensitivity to catecholamines. Increases metabolic processes, accelerates the catabolism of proteins, fats and carbohydrates, is necessary for the normal development of the central nervous system, increases heart rate and cardiac output.

PARATHYROID GLANDS. DEVELOPMENT. STRUCTURE. HORMONE. TARGETS. EFFECTS OF THE HORMONE.

Development

I think that the development is the same as that of the thyroid gland, since the parathyroid gland is located under the thyroid capsule, and there is no information in the lecture or in the textbook, so here it is:

During embryogenesis, 3-4 pairs of gill pockets are formed from the material, as is the entire branchiogenic

group of glands. (lecture)

Endocrine cells of the thyroid gland have a dual origin: from the wall of the pharynx (from the ectoderm

pharyngeal pockets) and neural crest

There is another textbook: derivatives of 3-4 pairs of gill pockets, the epithelial lining of which has a prechondral genesis. At 5-6 weeks of embryogenesis, 4 rudiments of glands are formed in the form of epithelial buds. At 7-8 weeks, these buds are pinched off from the walls of the gill pockets, joining the posterior surface of the thyroid gland.

Structure

Each of the 4 glands has its own thin capsule, from which septa extend, containing blood vessels. The parenchyma, formed by strands and islands of epithelial cells, contains 2 types of cells - chief and oxyphilic.

Main

They have basophilic cytoplasm (developed granular EPS), Golgi complex, small mitochondria and serum granules containing PTH.

Oxyphilic

They are evenly distributed in the parenchyma of the gland or form small clusters. They contain large mitochondria, a weakly expressed Golgi complex and a moderately developed ER. Their function is unknown, but their number increases with age.

Fat cells

Always present in the gland, with age the amount increases Hormone. Effects and targets

Parathyroid hormone (parathyrin, parathormone, parathyroid hormone, PTH, thyrocalcitonin)

SUPPORTS CALCIUM HOMEOSTASIS

Increases serum calcium levels, enhancing its leaching from bones and calcium reabsorption in the kidneys

Stimulates the formation of calcitriol in the kidneys, and calcitriol enhances the absorption of calcium and phosphates in the intestines

Reduces the reabsorption of phosphates in the renal tubules and increases their leaching from the bones

THYROCALCITONIN (PARATHYRIN, PTH). HORMONE-PRODUCING CELLS. TARGETS AND EFFECTS OF THE HORMONE.

Hormone-producing cells

Secreted by C-cells (K-cells) of the thyroid gland and parathyroid gland. Also secreted in the thymus, in the lungs, in the cells of the diffuse endocrine system. Secretion is regulated by calcium ions (stimulated by its increase and inhibited by its decrease)

Effects and targets

Parathyroid hormone (parathyrin, parathormone, parathyroid hormone, PTH, thyrocalcitonin)

SUPPORTS CALCIUM HOMEOSTASIS

Increases serum calcium levels, enhancing its leaching from bones and calcium reabsorption in the kidneys

Stimulates the formation of calcitriol in the kidneys, and calcitriol enhances the absorption of calcium and phosphates in the intestines

Reduces the reabsorption of phosphates in the renal tubules and increases their leaching from the bones

DEVELOPMENT OF THE ADRENAL GLAND.

At the 6th week of intrauterine development, large mesodermal cells of the coelomic epithelium form a cluster at the cranial end of the mesonephros. Soon, a vascular pole is formed - the place where future chromaffin cells of the medulla migrate from the neural crest to penetrate into the central part of the gland. At the 8th week, mesodermal cells begin to multiply intensively, and 2 zones of the cortex are formed:external(definitive-small, have basophilic cytoplasm and a dense nucleus. during the first year of life are differentiated into the glomerular, fascicular and reticular zones) andembryonic(fetal - large cells with acidophilic cytoplasm and a large pale nucleus. In the fetal period, the fetal zone accounts for most of the cortex. By the end of the first year of life, it completely disappears), located on the border with the medulla. By the 30th week, the volume of the medulla increases 4 times

ADRENAL CORTEX. DEVELOPMENT. STRUCTURE. BLOOD FLOW. CELL CHARACTERISTICS. CORTEX HORMONES.

Development

At 8 weeks, mesodermal cells begin to multiply intensively and the

zones of the cortex:external(definitive - small, have basophilic cytoplasm and a dense nucleus. During the first year of life, they differentiate into glomerular, fascicular and reticular zones) andembryonic(fetal - large cells with acidophilic cytoplasm and a large pale nucleus. In the fetal period, the fetal zone accounts for the majority of the cortex. By the end of the first year of life, it completely disappears)

Structure and hormones

The gland is surrounded by a capsule of dense fibrous connective tissue, from which connective tissue septa extend in places into the thickness of the organ.

Stroma Consists of loose fibrous connective tissue that supports endocrine cells.

tissue, contains numerous blood capillaries with fenestrated endothelium.

Parenchyma A collection of epithelial strands that have different orientations at different distances

from the capsule of the adrenal gland. Because of this, it is possible to distinguish the glomerular, fascicular and reticular zones.

-BEAM

75% of the bark thickness

The strands of endocrine cells and the blood capillaries between them are located parallel to each other. Glucocorticoids are synthesized

-GLOSS

15% of the bark thickness

Bundles of endocrine cells are folded under the capsule and look like a ball when cut.

Mineralocorticoids are synthesized

-NET

10% of the bark thickness

In the deepest parts of the cortex, strands of endocrine cells intertwine to form a network. Glucocorticoids and androgen-type hormones are synthesized.

Blood flow

It is carried out from 3 sources:

Superior adrenal artery (branch of the inferior phrenic artery)

Middle adrenal artery (arrives from the aorta)

Inferior adrenal artery (branch of renal artery)

Cell features

The cells appear vacuolated, which is why they are calledspongiocytes

They contain round mitochondria with cristae in the form of tubes and vesicles, branched smooth ER, elements of granular ER, lysosomes, numerous lipid inclusions, pigment granules containing lipofuscin.

SOMATROPIN (STH, GROWTH HORMONE). SYNTHESIS AND ITS REGULATION. TARGETS AND EFFECTS.

Synthesis and regulation of secretion

Stimulates secretion of somatoliberin, and inhibits somatostatin. It is secreted by the adenohypophysis, as well as lymphocytes. There is a daily rhythm: at night, during deep sleep, secretion increases 2-5 times. The effect of somatotropin is carried out at a normal level of thyroid and sex hormones.

Targets and effects

Stimulates the growth of epiphyseal cartilage tissue and bone growth in length

Stimulates periosteal bone growth and bone thickness growth

Stimulates muscle tissue growth

Stimulates the growth of all types of connective tissue

Stimulates the growth of internal organs

Affects protein metabolism

ERYTHROPOIETIN. FORMATION. FUNCTIONS.

Erythropoietin. Hemopoietin.

Education

It is synthesized by juxtamedullary cells of the kidneys, as well as hepatocytes, bone marrow macrophages, liver Kupffer cells and neurons of the central nervous system. It is regulated by oxygen saturation and stimulated by hypoxia.

Functions

Stimulates the division of red blood cell precursors

Stimulates differentiation of erythroid cells

Stimulates hemoglobin synthesis in erythroid cells and reticulocytes

Inhibits apoptosis of red blood cell precursor cells

5. Stimulates the release of red bone marrow reticulocytes into the blood

Increases vascular tone

Increases the resistance of neurons of the central nervous system and myocardium to hypoxia

Increases blood flow and enhances metabolism in red bone marrow tissue

ALDOSTERONE. SYNTHESIS AND ITS REGULATION. TARGETS AND EFFECTS.(Mineralcorticoid)

Synthesis and its regulation

Secreted by the zona glomerulosa of the adrenal cortex. Secretion is stimulated by angiotensin 2. It is also regulated by sodium and potassium levels: it is stimulated by a decrease in sodium and an increase in potassium. Secretion is also slightly stimulated by corticotropin and inhibited by atriopeptin. Prostaglandins: E1 and E2 stimulate, F inhibits. Trauma and stress conditions increase secretion.

Targets and effects

Maintenance of electrolyte balance in body fluids is accomplished by influencing the reabsorption of ions in the renal tubules and collecting ducts.

Increases sodium absorption in the gastrointestinal tract and water reabsorption, ensures physiological osmolarity of the internal environment.

ADRENOCORTICOSTROPIC HORMONE (ACTH). SYNTHESIS AND ITS REGULATION. TARGETS AND EFFECTS.

Synthesis and secretion

It is synthesized by the adenohypophysis (basophilic adipocytes-corticotrophs), some neurons of the central nervous system, lymphocytes, placenta and cells of the macrophage system. Secretion occurs with a daily rhythm: maximum secretion in the morning hours, minimum from 18:00 to 2-3 in the morning. The rhythm of corticotropin does not correspond to the rhythm of corticoliberin secretion.

Corticoliberin stimulates the synthesis and secretion of ACTH;

high doses of glucocorticoids inhibit, low concentrations stimulate

Targets and effects

Stimulates the synthesis and secretion of hormones of the adrenal cortex (hypersecretion of ACTH leads to hyperplasia of the adrenal cortex with increased secretion of glucocorticoids and mineralocorticoids, ACTH deficiency causes endocrine insufficiency of the adrenal glands.

GLUCOCORTICOIDS. SITE OF FORMATION, STRUCTURE OF ENDOCRINE CELLS. TARGETS AND EFFECTS OF HORMONES.

(Corticosteroids)

Place of formation

Secreted by the zona fasciculata of the adrenal cortex, regulates corticoliberin and corticotropin

Features of the structure of endocrine cells

The cells appear vacuolated, which is why they are calledspongiocytes

Targets and effects of hormones

Stimulates glucose production in the liver by increasing the rate of gluconeogenesis and stimulating the release of AA in the muscles

ADRENAL MEDULE. DEVELOPMENT, STRUCTURE, HORMONES.

Development

The medulla is formed in the 6th-77th week of embryogenesis from a common rudiment with the sympathetic ganglia - the neural crest. Sympathoblasts migrate to the interrenal body, multiply and differentiate into chromaffinocytes. Connective tissue and vessels develop from the mesenchyme.

Structure

In a delicate supporting framework consisting of loose fibrous connective tissue, there are numerous vascular cavities - venous sinuses - a variant of capillaries of the sinusoid type. Their distinctive feature is a significant lumen diameter, reaching tens and hundreds of microns. They consist of chromaffin cells.

Hormones

When the sympathetic nervous system is activated, the adrenal glands release catechol amines (adrenaline and noradrenaline) into the blood.

PANCREAS. STRUCTURE OF THE EXOCRINE PART, FUNCTION AND ITS REGULATION.

Structure

Consists of endocrine and exocrine parts. Endocrine - islets of Langerhans. Exacrine: lobules are distinguished, consisting of acini and initial sections of excretory ducts. Ducts remove secretory products of the acinus and excrete bicarbonate. Centroacinous cells are located in the center of the acini. Excretory ducts begin from them. Cuboidal or columnar epithelium of intralobular excretory ducts passes into columnar epithelium of interlobular ducts. Enteroendocrine cells are present among the epithelial cells.

-ACINOUS CELLS

characterized by pronounced polar differentiation. The apical part contains granules with digestive enzymes. The nucleus is shifted to the basal part, where the granular EPS is developed

Function and regulation

Participates in the digestion of proteins, lipids and carbohydrates. The bicarbonate secreted by the gland, together with the bicarbonate of the duodenum and the hepatobiliary system, participates in the neutralization of hydrochloric acid coming from the stomach into the duodenum. ACh and neuropeptides enhance the secretory activity of acinar cells. Sympathetic nerve fibers inhibit the secretory function of acinar cells through the adrenergic input.

PANCREATIC ISLE (LANGERHANS). HISTOLOGICAL CHARACTERISTICS, HORMONES, THEIR TARGETS AND EFFECTS.

They consist of epithelial cells - endocrinocytes. The islets are penetrated by blood capillaries, surrounded by pericapillary space. The endothelium of the capillaries has fenestrae, facilitating the flow of hormones from endocrinocytes into the blood through the pericapillary space.

There are 5 types of endocrinocytes:

A cells (glucagonocytes)

Contain acidophilic granules. The cells are located on the periphery. The hormone glucagon breaks down glycogen and increases the sugar content in the blood.

B cells (insulocytes)

Cubic or prismatic shape. Insulin regulates the synthesis of glycogen from glucose.

D-cells (dendritic islet cells)

The shape is stellate with processes. Granules of medium size and density are determined in the cytoplasm. Somatostatin accumulates in the granules, which inhibits the secretion of insulin and glucagon, suppresses the secretion of somatotropic hormone

VIP cells (argyrophilic cells)

Contains vasoactive intestinal polypeptide. It dilates blood vessels,

lowers blood pressure, inhibits the secretion of sodium and chlorine in the stomach, stimulates the release of glucagon and insulin.

PP cells Polygonal endocrinocytes. Contain pancreatic polypeptide-regulation

exocrine secretion inpancreasAndliver.

MAIN CELL TYPES OF THE BLOOD VESSEL WALL.

Endothelial cells

Polygonal flattened cells, mononuclear diploid cells, connected between

intercellular contacts. A sensitive element that enhances changes in hemodynamics and chemical composition of blood. On one side it is washed by blood, and on the other it faces the structures of the vascular wall.

GMK

The lumen of the blood vessels decreases with the contraction of the SMC of the media.

They have processes that form numerous gap junctions with neighboring SMCs.

ARTERIES OF THE ELASTIC TYPE. STRUCTURE OF THE SHELLS.

They include the aorta, pulmonary, common carotid and iliac arteries. The wall contains a large amount of elastic membranes and elastic fibers.

Structure of the shells:

1. Inner shell

-ENDOTHELIUM

The lumen is lined with large polygonal or round endothelial cells connected by tight and gap junctions. The cytoplasm contains electron-dense granules, numerous light pinocytotic vesicles and mitochondria. It is separated from the connective tissue by a basal membrane.

-SUBENDOTHELIAL LAYER

Langerhans layer is a connective tissue with elastic and collagen fibers.

2. Middle shell

-FINISHED ELASTIC MEMBRANES

Elastic fibers, the number and thickness of which increases with age - SMC Between the elastic fibers are SMCs, arranged in a spiral. SMC

arteries are specialized for the synthesis of elastin, collagen and components of the amorphous intercellular substance

-CARDIOMYOCYTES

Present in the media of the aorta and pulmonary artery

3. Outer shell

Contains bundles of collagen and elastic fibers oriented longitudinally or spirally. The adventitia contains small blood and lymphatic vessels, as well as myelinated and unmyelinated fibers.

MUSCLE VEINS, STRUCTURE OF SHELLS.

Internal elastic membrane Located between the inner and middle membranes

The middle layer of the SMC is oriented circularly in relation to the lumen of the vessel, which ensures

regulation of vessel lumen depending on the tone of the SMC

External elastic membrane The middle shell is delimited from the outside by an elastic plate, which is less pronounced,

than the internal elastic membrane is developed only in large vessels. In vessels of smaller caliber this structure may be completely absent.

Outer shell Inner layer - loose connective tissue. The outer shell contains

numerous nerve fibers and endings, vascular vessels and fat cells.

ENDOCARDIUM: ORIGIN, STRUCTURE. HEART VALVES, THEIR STRUCTURE.

Origin

The heart is laid down in the 3rd week of intrauterine development. In the mesenchyme between the endoderm and the visceral layer of the splanchnotome, 2 endocardial tubes lined with endothelium are formed. These tubes are the rudiment of the endocardium. The tubes grow and are surrounded by the visceral layer of the splanchnotome. These areas of the splanchnotome thicken and give rise to the myoepicardial plates. As the intestinal tube closes, both rudiments of the heart come together and grow together. Now the common rudiment of the heart has the appearance of a two-layer tube. The endocardium develops from its endocardial part.

Structure

Endothelium

The interior of the endocardium consists of flat, polygonal endothelial cells located on a basement membrane. The cells contain a small number of mitochondria and a moderately developed Golgi complex, many filaments

Musculoskeletal layer

Outside the endothelium, contains collagen and elastic fibers, SMC

Outer connective tissue layer

Consists of fibrous connective tissue. You can find islands of fatty tissue, small blood vessels, nerve fibers.

Heart valves

Mitral valveBetween LP and LV

Bicuspid - prevents regurgitation (backflow) of blood into the left atrium. The posterior leaflet is wider than the anterior one.

Aortic

LV and aorta

Tricuspid (opens towards the aorta)

Pulmonary (lung)

Right ventricle and pulmonary trunk

prevents regurgitation of blood into the pancreas Tricuspid, semilunar cusps

Tricuspid (tricuspid)

PP and PJ

Prevents regurgitation in the RA

Secretory cardiomyocytes. Localization, structure, hormone, its targets and effects

Secretory cardiomyocytescharacterized by a branched form and weak development contractile apparatus, are found mainly in the right atrium and cardiac auricles. The granular EPS and Golgi complex are well developed. The synthesized substances accumulate in secretory granules. In the cytoplasm of these cells are granules containing a peptide hormone - atrial natriuretic factor (ANF). They also secrete a glycoprotein with an anticoagulant effect. When the atria are stretched, the secretion enters the blood

affects the collecting tubules of the kidney, cells of the glomerular zone of the adrenal cortex, which are involved in regulating the volume of extracellular fluid and blood pressure levels.

PNF causes stimulation of diuresis and natriuresis (in the kidneys), vasodilation, inhibition of the secretion of aldosterone and cortisol (in the adrenal glands), and a decrease in blood pressure.

The hormone causes loss of sodium and water in the urine, vasodilation, decreased blood pressure, and inhibition of the secretion of aldosterone, cortisol, and vasopressin.

Conducting system of the heart. Features of the structure of conducting cardiomyocytes

The cardiac conduction system is formed by atypical cardiomyocytes.

The conduction system includes 2 nodes and bundles extending from them.

Sinus node(sinoatrial node) is located in the upper wall of the right atrium.

From it extends the Kis-Flak bundle, connecting the atria and the sinus node with the second node.

Frequency of generated pulses 60-70 minutes

The node mainly consists of P-cells (pacemaker cells). Small in size, polygonal in shape, no T-tubes, few myofibrils. These cells are the self-oscillating system.They serve as the main source electrical impulses that ensure rhythmic contraction of the heart. The high content of free calcium in the cytoplasm of these cells with weak development of the sarcoplasmic reticulum determines the ability of the sinus node cells to generate impulses for contraction. The supply of the necessary energyAtrioventricular node(Aschoff-Tawara node) is located in the lower wall of the right atrium, near the septum.

The bundle of His departs from it, goes to the interventricular septum, divides into the right and left legs. The bundle connects the ventricles. The branches of the bundle legs are the Purkinje fibers. They are located between the endocardium and the myocardium, penetrate the thickness of the myocardium.The functional significance of transitional cells is the transmission of excitation from P-cells to the cells of the His bundle and the working myocardium.The frequency of generated pulses is 40 per minute.

The basis of the node is made up of transitional cells. Cylindrical shape, short

- tubes, numerous myofibrils. Can both generate excitations and contract.

Functional role: 1) generators of the heart rhythm (pacemakers) - sinus node 2) conduction of excitations (the bundles of His and His-Flach receive excitation from the nodes, transmitting it to the Purkinje fibers)

The muscle cells of the conduction system in the trunk and branches of the trunk legs of the conduction system are located in small bundles, they are surrounded by layers of loose fibrous connective tissue. The legs of the bundle branch under the endocardium, as well as in the thickness of the ventricular myocardium. The cells of the conduction system branch in the myocardium and penetrate the papillary muscles. This causes the tension of the valve flaps (left and right) by the papillary muscles even before the contraction of the ventricular myocardium begins.

Atypical cardiomyocytesprovide rhythmic coordinated contraction of various parts of the heart due to their ability to generate and quickly conduct electrical impulses.

- not capable of contraction (few myofibrils, T-tubes, mitochondria, L-tubules)

have increased excitability

energy is obtained by anaerobic breakdown of glycogen to lactate. There are three types: P-cells, Purkinje cells and transitional cells. Purkinje cells form Purkinje fibers, bundles of Keith-Flach, His.

Few myofibrils, no T-tubes, many glycogen granules. Connected to each other by nexuses and desmosomes. From them, excitation is transmitted to the contractile cardiomyocytes of the ventricular myocardium. These cells predominate in the bundle of His and its branches.

Blood-brain barrier. Structure, functions

is a functional barrier that prevents the penetration of a number of substances such as antibiotics, toxic chemicals and bacterial compounds from the blood into the nervous tissue.

It is a special morphological system that ensures homeostasis of the nervous tissue. The functional mechanisms of the barrier are ambiguous and include both enhancing and inhibiting processes of transport of substances from the blood and brain in opposite directions. BBB types I and II are distinguished.

The first and main structural element of the BBB type I is the endothelial monolayer. The endothelial cells have a thickness in the anuclear zone from 200 to 500 nm, in the region of the nucleus up to 2-3 μm. There are very few organelles and micropinocytotic vesicles inside the endothelial cells. There are no fenestrae in the endothelial cells of capillaries of this type.

The second structural unit of the BBB of this type is the basement membrane, which is continuous and always well defined, its thickness is 40-80 nm.

The next component of the BBB is the astroglial cell process spread over the surface of the basement membrane. This process is often called the "vascular stalk". Together, the vascular stalks of astrocytes, which contact each other through tight junctions, create a single glial membrane that covers the capillary surface in the form of a sleeve. The idea of the BBB would be incomplete if we did not take into account the contact of the astrocytic gliocyte with the oligodendroglia - all substances (98%) enter the neuron only through these cells (these are the 4th and 5th components).

Capillaries of type 1 BBB with continuous endothelium normally reliably protect the brain from temporary changes in blood composition. Substances soluble in lipids, and therefore in the cytolemma of the endothelium, can penetrate through BBB type I. These include primarily: ethyl alcohol, heroin, nicotine. Glucose is transported through the BBB, moreover, the introduction of the latter helps to reduce contact between endothelial cells and increase the permeability of the BBB.

BBB type IIis present in several areas of the central nervous system, primarily in the hypothalamus.

Morphologically, the capillary endothelium in the hypothalamus vessels has a fenestrated cytoplasm, there is no tight contact between the endotheliocytes, pericytes disappear in the wall, and the basement membrane becomes thinner several times compared to the first type barrier. Therefore, the hypothalamic capillaries are highly permeable to large-molecular protein compounds, even to such as nucleoproteins. This explains the high sensitivity of the hypothalamus to neuroviral infections and various humoral substances.

1 - capillary endothelium, there are tight contacts between endothelial cells

2 - basement membrane of the capillary

3 - astrocyte legs, enveloping both capillaries and neurons

4 - capillary lumen

5 - neuron

6 - astrocyte

the essence of the barrier is that

nerve cells do not come into close contact with capillaries, and between them there is a layer formed by astrocytes, that is, one part (leg) of the astrocyte contacts the neuron, and the other - with the capillary, capillaries and neurons are covered on all sides by astrocytes

the endothelium of capillaries contains tight junctions

Microcirculatory bed. Vessels, its components, their morpho-functional characteristics

Microcirculatory bed- a functional complex of blood vessels surrounded by lymphatic vessels and capillaries together with connective tissue, providing regulation of blood filling of organs, transcapillary exchange and drainage-deposit function. Includes: arterioles, capillaries, venules, arteriole-venular anastomoses, lymphatic vessels.

Arteriole- a small arterial vessel of the muscular type, with a diameter of 50-100 microns.

The wall consists of:

Inner shell:

Endothelium is a single-layer, flat epithelium of the angiodermal type. Epithelial cells are polygonal, with micro-outgrowths.

Subendothelium - RNSTk.

The internal elastic membrane, which contains openings through which smooth myocytes penetrate and the vessel functions.

Middle - 1-2 layers of circularly arranged smooth myocytes

The outer shell is formed by loose fibrous connective tissue.

As the diameter decreases, all membranes become thinner, smooth myocytes may be absent at the junction of capillaries, and are found only at the sites of vessel bifurcation. The latter, by their position, arterioles are called precapillary, and at the site of their branching into capillaries there are smooth muscle sphincters.

Arteriole function: transport, exchange, ensuring regulation of blood flow and blood filling of organs and tissues.

Capillarieshave different diameters depending on their functions and location in organs. In capillaries, erythrocytes go "in single file", i.e. in one row.

Endothelial cells on the basement membrane

Pericyte cells in the clefts of the basement membrane and adventitial cells. They do not lie in a continuous layer, they are located only on one side of the capillary, covering only a part of it in the form of a basket.

Therefore, capillary permeability depends on the basement membrane and the structure of the endothelium.

Somatic - located in the skeletal muscle tissue of the lungs, supplying blood to the nervous tissue. diameter 4-7 microns.

They have a continuous endothelium and a continuous basement membrane. Between pericytes and epithelial cells there are tight or slit contacts (nexuses). In epithelial cells there are numerous pitocytic vesicles that transport metabolites and metabolic products in one direction or another. The permeability of this type depends on the basement membrane and the ground substance around the adventitial cells. Under the influence of hyalorunidase, the degree of polymerization of macromolecules decreases, which increases permeability.

Fenestrated - are part of the capillary glomerulus of the kidney (for filtering blood and forming primary urine), intestinal villi (for absorbing digestion products), are part of the endocrine organs (endocrine glands, for the transition of hormones into the blood). The endothelium is thinned in its cytoplasmic part, diffusion is facilitated. The basal membrane is continuous. The capillaries have fenestrae - local thinning.

Perforated type

The endothelium and basement membrane have slit-like pores. The presence of pores facilitates the transition of whole cells. Capillaries of this type in some organs have a large diameter and are called sinusoidal. diameter 20-40 μm. It is located in the liver parenchyma, structures of the hematopoietic organs (red bone marrow). The endothelium is discontinuous, the basement membrane is discontinuous - it contains pores. They can close, the diameter is inconstant, can be excluded from the bloodstream. The presence of pores facilitates the migration of high-molecular cells. The thin wall does not contain pericytes.

Ordinary capillaries of this type are located in the glomeruli of the kidneys and have both fenestrae and pores.

Venules are classified into 3 types:

postcapillary venules (diameter 8-30 µm);

collecting venules (diameter 30-50 µm);

muscular venules (diameter 50-100 µm).

Wall of postcapillary venulesis not much different from the venous end of the capillary. The difference is that there are more pericytes in the wall of postcapillary venules, i.e. there is endothelium and pericytes in postcapillary venules, but no myocytes.

Wall of collecting venulesis distinguished by the appearance of smooth single myocytes in the middle layer and a better expressed adventitial layer. Pericytes form a continuous layer over the endothelium.

Wall of muscular venulescharacterized by the presence of 1-2 layers of smooth myocytes in the middle shell. Myocytes are oriented longitudinally. There is no elastic membrane.

Functions of venules:

drainage (entry of metabolic products from connective tissue into the lumen of the venule);

formed elements of the blood migrate from the venules into the surrounding tissue.

Arteriolovenous anastomoses— these are the connections of the vessels through which blood flows from the arterioles to the venules, bypassing the capillaries. The length of the ABA reaches 4 mm, the diameter is more than 30 microns.

ABAs open and close 4-12 times per minute.

ABA functions:

regulation of blood flow in capillaries;

arteriolization of venous blood;

when capillaries are compressed by a pathological process, blood from the arterioles immediately flows into the venules;

increased intravenous pressure.

I. ATYPICAL (HALF-SHUNTS) - (mixed blood) connection through a short

capillary arteriole with venule. Mixed blood enters the venule through these anastomoses, since when blood moves through the half-shunt, an exchange of substances and gases occurs between the blood and surrounding tissues. The functions of half-shunts are drainage and exchange.

- (pure arterial blood) straight, short, loop-shaped

Shunts are divided into:

1) anastomoses	2) anastomoses with special contractile devices are divided into 2
without special	type:
contractile
	A)	ABA type			b)	ABA epithelioid type	, the myocytes of which,
devices, in their
arterial	closing		located longitudinally in the middle shell,
there is at the end	arteries	,	approaching the venous end, they turn into cells
circularly	are characterized by	E, resembling epithelial. When absorbing water
located	presence in them	These cells thicken and close the anastomosis.
smooth	subendothelial	Epithelioid type anastomoses are divided into simple and
myocytes; as in	layer longitudinally	complex.
arterioles, these	located
			 Simple- V	 Complex- bringing
myocytes,	one or
contracting,	several bunches		average		the arteriole divides into
are closing	smooth myocytes,		shell		2-4 branches that lie in
clearance and,	which at		arterioles		one connecting
relaxing,	reduction		there are		woven shell, in this
open it;	thicken and		special		there are places and arterioles
	close the gap		epithelioid		epithelioid cells, and
	anastomosis (ABA		cells,		behind these cells
	locking		capable of		venous begins
	type);		swelling and		anastomosis segment, from
							swelling, from	arteriole to venule
							arterioles to	several depart
							the venule departs	trunks covered with a common
							1 barrel	shell.

Immunocompetent cells: their types, functions and interactions in the immune response

Cells capable of specifically recognizing an antigen and responding to it with an immune reaction. Such cells are T- and B-lymphocytes (thymus-dependent and bone marrow lymphocytes), which, under the influence of foreign agents, differentiate into a sensitized lymphocyte and a plasma cell.

LYMPHOCYTES ARE NOT CAPABLE OF PHAGOCYTOSIS.

T-lymphocytesconsist of functional subtypes CD4 and CD8. They recognize antigen that has been pre-processed and presented on the surface of antigen-presenting cells. They are responsible for cellular immunity and also help B lymphocytes react to antigen during the humoral immune response.

T-helpers(CD4) - synthesize and secrete cytokines - peptide molecules that transmit a signal from one cell to another located nearby. Cytokines include INTERLEUKINS-2, 4, 5, 6, as well as gamma interferon. During the immune response, T-helpers recognize MHC-II molecules. They are the only target of the AIDS virus;

They enhance both humoral (formation of immunoglobulins) and cellular immunity by synthesizing lymphokines - hormones that cause lymphocyte proliferation,

the main one is interleukin 2, i.e. these lymphocytes maintain the number of the entire range of lymphocytes in the body.

Cytotoxic (T8) T lymphocytes, or T killers, or T effectors(CD-8)

destroy virus-infected and foreign cells using perforin. Perforins are cytotoxic proteins that have a lytic region, with the help of which they penetrate the plasma membrane of the target cell, where they combine with each other to form a pore, thereby destroying the target cell. In addition, cytotoxic E-lymphocytes interact with the MHC-I molecule in the plasma membrane of the target cell;

T-suppressors(CD-8) regulate the intensity of the immune response by suppressing the activity of T-helpers, prevent the development of autoimmune reactions, and ensure the mother’s immunity to paternal antigens present on the cells of the fetus;

Memory T-lymphocytes(CD-8) ensure the development of cellular immunity upon repeated exposure to antigens.

B-lymphocytesare responsible for the humoral immune response. Their membrane contains IgM molecules, which are antigen receptors. B-lymphocytes migrate from the red bone marrow to the thymus-independent zones of the lymphoid organs. Their life span is less than 10 days unless they are activated by antigens. Memory B-lymphocytes ensure the development of humoral immunity upon repeated exposure to antigens.

Mature B lymphocytes, or plasma cells, are the only cells in the body capable of synthesizing and secreting antibodies (Ig).

NK cells(5-15%) kill auto-, allo- and xenogenic tumor cells, as well as some cells infected with viruses and bacteria. They do not have a surface determinant. They express differentiation antigens CD2, CD56, CD16 (Fc-fragment receptor).

destroy the target cell using perforin after establishing direct contact with it, and not by phagocytosis, since they have neither MHC-I nor MHC-II. The activity of NK cells is regulated by cytokines, and is enhanced by interleukin-2 and gamma interferon.

participate in antibody-dependent cell-mediated cytolysis by expressing on their surface the receptor for the Fc fragment of IgG, with which the Fc fragment of antibodies bound to the target cell will interact.

Antigen presenting cells(macrophages, follicular dendritic cells of the lymph nodes and spleen, Langerhans cells of the skin, M cells in the lymphatic follicles of the digestive tract, dendritic epithelial cells of the thymus) CAPTURE, PROCESS AND PRESENT antigens (epitopes) on their surface to other immunocompetent cells, produce cytokines (IL-1, etc.). They secrete prostaglandin E2, which suppresses the immune response, and gamma interferon, which enhances the phagocytic and cytolytic activity of macrophages.

Antigen presenting cells in various tissues. Receptors, function.

cells that expose foreignantigenin complex with moleculesmain histocompatibility complexon its surface. T lymphocytes can recognize such complexes with the help ofT-cell receptors. Antigen presenting cellsare being processed antigen andrepresenthis T cells.

Antigen-presenting cells are located on the main pathways of antigen entry into the body.(in the skin and mucous membranes), from where, having captured antigens, they migrate to the peripheral organs of the immune system, where they present antigens to lymphocytes.

Types of antigen-presenting cellsThe ability to present antigens is possessed by dendritic APCs, monocytes and macrophages, as well as B-lymphocytes.

Antigen-presenting cells: macrophages, follicular dendritic cells of the lymph nodes and spleen, Langerhans cells of the skin, M cells in the lymphatic follicles of the digestive tract, dendritic epithelial cells of the thymus, B lymphocytes. Antigen-presenting cells are characterized by the presence of mitochondria, granular ER, Golgi complex and lysosomes. MHC-II molecules are expressed on their surface.

FunctionsAPC includes:

capturenative (unchanged) antigenic material by phagocytosis, pinocytosis, or receptor-mediated endocytosis;

partial proteolysis(processing) of antigen material in endosomes (or lysosomes) for 30-60 minutes at low pH with the release of antigen epitopes (antigenic determinants) - linear peptide chains 8-11 amino acids long that determine the specificity of the reaction of the antigen with the antibody;

synthesis of glycoprotein molecules of the major histocompatibility complex,

or MHC (from English Major Histocompatibility Complex), also called the HLA system in humans (from English Human Leuko-cyte Antigens - human leukocyte antigens);

binding of synthesized MHC molecules to antigen epitopes;

transport of MHC molecule/antigen epitope complexes to the surface of APCs, where they are presented to lymphocytes that recognize them;

expression on the cell surface(along with the MHC/antigen molecule complex) a number of additional (costimulatory) molecules that enhance the process of interaction with lymphocytes; the most important of these is B7;

secretion of soluble mediators(mainly IL-1), which cause activation of lymphocytes.

I'M SO FUCKED UP WITH EVERYTHING OH MY FUCKING GOD!!!!!!

Thymus gland: development, structure, functions

1. Capsule.

2. Interlobular connective tissue.

3. Slices.

4. Cortex.

5. Lymphocytes.

6. Brain matter.

7. Hassal's bodies.

This thing is to the cortex.

Development. The epithelium of the branchiogenic group of glands, which, in addition to the thyroid and parathyroid glands, also includes the thymus, develops from the endoderm of the pharyngeal pouches: the thymus gland develops from the THIRD and FOURTH pair of PHARYNGEAL POUCHES. The rudiment grows in the caudal-ventral direction, maintaining contact with the pharynx, after which it separates from it and shifts caudally and medially with subsequent fusion along the midline with the rudiment of the other side. Soon, lymphoid cells migrating from the bone marrow appear in the thymus rudiment and begin to intensively multiply. Most of the epithelial cells of the thymus originate from epithelial (endodermal) stem cells, but they can also form from the ectoderm.

Structure. The thymus capsule and the septa extending from it into the organ are constructed of dense fibrous connective tissue. The volume of the thymus is filled with an epithelial framework in which thymocytes are located. In a lobule of a mature thymus, the cortex and medulla are distinguished:

The cortex contains dividing cells - lymphoblasts(predecessors of T-

lymphocytes) that interact with dendritic epithelial cells. Dendritic epithelial cells have long processes that are connected to each other by desmosomes, and their cytoplasm contains granules containing thymus hormones: thymosins and thymopoietin. In addition, these cells express a large number of MHC-II molecules. The inner part of the cortex, which contains the descendants of lymphoblasts, non-dividing small thymocytes and dendritic epithelial cells, is functionally important. As they mature, which occurs precisely in the inner part of the thymus cortex, prothymocytes lose the differentiation antigen CD1, but acquire CD3, CD4 and CD8. Their further differentiation occurs in the medulla of the thymus.

2. The medulla receives thymocytes coming from the cortex of the thymus, where they differentiate into CD4+ and CD8+ lymphocytes. Mature T cells (during the learning process, 3-5% of the total number of T-lymphocyte precursor cells that entered the thymus from the red bone marrow remain) leave the medulla through the venules and

efferent lymphatic vessels. The remaining cells are phagocytized by macrophages located in the medulla of the thymus.

The hematothymic barrier makes the cortical part of the thymus inaccessible to antigens from the internal environment of the body and protects the T-lymphocytes maturing here from their action. It is formed by endothelial cells and the basement membrane of the capillaries of the cortex, perivascular connective tissue and its cells (pericytes and macrophages), as well as dendritic epithelial cells with their basement membrane.

Functions of the thymus:

destruction of lymphocytes capable of recognizing the body's own antigen. Receptor molecules in the thymocyte membrane interact with the MHC-autoantigen complex in the epithelial cell membrane. Clones of those thymocytes whose receptors recognize the [MHC-autoantigen] complex are destroyed.

production of humoral factors of the immune system: thymosin and thymopoietin. Thymosins promote differentiation of T-lymphocytes and the appearance of specific receptors in their membrane; they stimulate the production of lymphokines and the production of immunoglobulins. Thymopoietin is a stimulator of differentiation of T-lymphocyte precursors and also affects the differentiation of T-lymphocytes.

Cytotoxic T-lymphocytes and NK-cells. Structure, features of functioning

T-kíllers, cytotoxicśical T-lymphocyteśyou, CTL (killer)— a type of T-lymphocyte that lyses damaged cells of its own body. The targets of T-killers are cells affected by intracellular parasites (which include viruses and some types of bacteria), tumor cells. T-killers are the main component of antiviral immunity.

T-killers directly contact damaged cells and destroy them. Unlike NK cells, T-killers specifically recognize a certain antigen and kill only cells with this antigen. There are tens of millions of T-killer clones, each of which is “tuned” to a certain antigen. (The T-lymphocyte receptor is structurally different from the membrane immunoglobulin molecule - the B-lymphocyte receptor). The clone cells begin to multiply when the corresponding antigen enters the internal environment of the body after the T-killers are activated by T-helpers. T-lymphocytes can recognize a foreign antigen only if it is expressed on the cell surface. They recognize the antigen on the cell surface in combination with a cellular marker: MHC class I molecules. In the process of recognizing the surface antigen, the cytotoxic T lymphocyte comes into contact with the target cell and, if a foreign antigen is detected, destroys it before replication begins. In addition, it produces gamma interferon, which limits the penetration of the virus into neighboring cells. Tumor cells lacking MHC I are not recognized by T killers.

Activated killer T cells kill cells with a foreign antigen for which they have a receptor by inserting perforins (proteins that form a wide, non-closing hole in the membrane) into their membranes and injecting toxins (granzymes) inside. In some cases, killer T cells trigger apoptosis of the infected cell through

interaction with membrane receptors. Cytotoxic T-lymphocytes

develop in the thymus. The formation of a unique T-cell receptor involves

complex mechanisms involving controlled mutagenesis and recombination

certain regions of the genome. Like T-helpers, T-killers undergo a positive

(cells that recognize MHC well survive) and negative (cells that recognize MHC are destroyed)

activated by the body's own antigens) selection. Predecessors

cytotoxic cells are activated by a complex of antigen and MHC class I molecules,

multiply and mature under the influence of interleukin-2, and are also poorly

identified differentiation factors. During the selection of bóMost of the clones

T-lymphocyte precursors die through induced apoptosis.

The formed T-killers circulate through the blood and lymphatic systems,

periodically returning (homing lymphocytes) to the lymphoid organs (spleen,

lymph nodes, etc.). Upon receiving an activation signal from T-helpers

a certain clone of T-killers begins to proliferate (reproduce).

T lymphocytes consist of functional subtypes CD4 and CD8. They recognize antigen that has been pre-processed and presented on the surface of antigen-presenting cells. They are responsible for cellular immunity and also help B lymphocytes react to antigen in the humoral immune response.

T-helpers (CD4) - synthesize and secrete cytokines - peptide molecules that transmit a signal from one cell to another located nearby. Cytokines include INTERLEUKINS-2, 4, 5, 6, as well as gamma-INTERFERON. During the immune response, T-helpers recognize MHC-II molecules. They are the only target of the AIDS virus;

Cytotoxic T lymphocytes, or T killers, or T effectors (CD-8) destroy virus-infected and foreign cells with the help of perforin.

Perforins are cytotoxic proteins that have a lytic region, through which they penetrate the plasma membrane of the target cell, where they combine with each other to form a pore, thereby destroying the target cell. In addition, cytotoxic E-lymphocytes interact with the MHC-I molecule in the plasma membrane of the target cell;

T-suppressors (CD-8) regulate the intensity of the immune response by suppressing the activity of T-helpers, prevent the development of autoimmune reactions, and ensure the mother’s immunity to paternal antigens present on the cells of the fetus;

Memory T-lymphocytes (CD-8) ensure the development of cellular immunity upon repeated exposure to antigens.

Antigen-independent differentiation (training) of lymphocytes in the thymus occurs in the cortex, and lymphocytes are released into the bloodstream in the medulla of the thymus. The precursor cell of T-lymphocytes enters the thymus from the bone marrow during the fetal period. It expresses the differentiation antigen CD7 on its surface, after which it synthesizes the cytoplasmic form of CD3 (cCD3), and later displays CD1 and CD2 on the surface.

Lymphocyte precursors that come to the thymus to learn form several populations: most thymocytes are not capable of learning, a significant part is capable of learning, but remains poorly trained in the learning process. Both populations are destroyed in the thymus by apoptosis. Only a small part of thymocytes

differentiates normally, extends beyond the thymus and ensures the normal functioning of the immune system.

As the cell matures, the CD1 molecule disappears and cCD3 transitions (from the cytoplasmic form) to the membrane form. Thymocytes then begin to express CD4 and CD8, giving rise to thymocytes with a phenotype that can differentiate in two directions, with both subtypes having the membrane marker CD3 and the T-lymphocyte receptor. Such cells leave the thymus and appear in the peripheral blood and lymphoid organs.

In the process of learning, thymocytes receive information about the structure of MHC-I of a normal cell of their own body, after which they change some epitope in their receptor region, which makes it impossible to attack a normal cell of their own body, but allows them to identify altered and foreign cells. When training T-helper lymphocytes, they receive information about the structure of MHC-II.

NK cells make up 5-15% of all lymphocytes circulating in the blood.

EducationNK cells. NK cells do not undergo differentiation in the thymus; they leave the bone marrow into the blood and then migrate to tissues where they provide innate immune protection, which is especially important for protecting the body from viruses and tumors.

StructureNK cells. NK cells are large granular lymphocytes, the bulk of whose abundant cytoplasm contains several mitochondria, free ribosomes with individual elements of rough ER, the Golgi apparatus, and characteristic cytolytic granules with perforin. They lack the surface determinants characteristic of T and B lymphocytes. One of the characteristics of NK cells is the presence of the Fc receptor.

Functions of NK cells.

identify and destroy the body's own cells in which something has gone wrong: they kill tumor cells and cells infected with viruses or other foreign agents.

destroy the target cell using perforin after establishing direct contact with it. The activity of NK cells is regulated by cytokines and is enhanced by interleukin-2 and gamma interferon.

Hematothymic barrier. Localization, structure, functions

there is a hematothymic barrier in the cortex; the structure of its wall is: 1. (blood -->) capillary endothelium --> 2. capillary basement membrane, there may be pericytes and adventitial cells --> 3. pericapillary space --

4.basement membrane of reticuloepithelial cells --

5.reticuloepithelial cells -->(parenchyma)

I don’t know where it is, I don’t understand a thing, it needs to be anatomically or histologically.

Spleen: development, structure, functions. Blood vessels of the spleen

Development.The spleen is laid down in the 5th week of embryogenesis by forming a dense accumulation of mesenchyme. The latter differentiates into reticular tissue, grows with blood vessels, and is populated by stem hematopoietic cells. In the 5th month of embryogenesis, myelopoiesis processes are observed in the spleen, which are replaced by lymphocytopoiesis by the time of birth.

Structure. The spleen is covered externally by a connective tissue capsule containing SMC and a lot of elastin. Trabeculae extend from the capsule into the organ, containing an artery and trabecular veins stretched with blood. Between the trabeculae is the organ parenchyma, which includes:

red pulp surrounding the lymphatic follicles. Erythrocytes predominate here, there are many macrophages that destroy the old erythrocytes; the ellipsoids and venous sinuses are stretched by the blood filling them. The follicular tissue is located around the central artery.

Lymphatic follicles- thymus-independent zone. It is divided into 2 zones:

germinal center - the central part of the follicle, where macrophages, follicular dendritic cells and B-lymphocytes are present;

marginal zone - the boundary between the follicle and the red pulp, where actively phagocytic macrophages are present. In the inner part of this zone are sinuses, where blood flows from the arterial vessels of the follicle. The blood comes into contact with the parenchyma of the organ, from which T- and B-lymphocytes emerge into the tissue, distributing themselves in zones of the spleen that are specific for each cell type.

white pulp - a collection of lymphoid tissue of the spleen, represented by a cluster of T-lymphocytes around the arteries emerging from the trabeculae (thymus-dependent zone).

Functions of the spleen:

production of immunoglobulins, which are necessary for the rapid and effective removal of bacteria from the bloodstream. The spleen is involved in the removal of poorly opsonized bacteria (well opsonized bacteria are removed from the bloodstream in the liver);

phagocytosis of damaged and old erythrocytes;

humoral function: the spleen is the site of formation of humoral factors that influence the mononuclear phagocyte system.

Hormones of the spleen:

Tuftsin stimulates phagocyte activity;

Splenin is a functional analogue of thymopoietin, which is a stimulator of differentiation of T-lymphocyte precursors and also affects the differentiation of T-lymphocytes.

Blood circulation in the spleen:

Trabecular arteries - pulp arteries - arterioles and capillaries of the follicle - sinuses of the marginal zone - exit of T- and B-lymphocytes from the vascular bed. Arterioles of the follicle - brush arterioles of the red pulp - capillaries - sinusoids.

The arteries entering the splenic gate branch into smaller trabecular arteries, which, leaving the trabeculae, enter the pulp, becoming pulp arteries;

From the pulp arteries, arterioles called

CENTRAL ARTERIES, which branch into capillaries within the follicles of the white pulp;

The central arteries exit the follicle into the red pulp and divide into brush arterioles - diverging branches that are part of the ellipsoids containing clusters of macrophages surrounding the vessels. Within the ellipsoids, the arterioles become capillaries:

open circulation theory: blood from the capillaries goes into the reticular tissue of the red pulp, and then into the sinusoids;

closed circulation theory: capillaries open directly into sinusoids.

Between the endothelial cells of the sinusoids there are longitudinal slits through which the formed elements of the blood pass;

From the sinusoids, blood sequentially enters the pulpal and trabecular veins to the splenic gate.

Lymph node. Structure of the cortex and medulla, cellular composition, sinuses. T- and B-zones

Development. The rudiments of lymph nodes appear at the end of the 2nd - beginning of the 3rd month of embryogenesis in the form of accumulations of mesenchyme along the lymphatic vessels. Soon, reticular tissue is formed from the mesenchyme, which makes up the stroma of the organ. By the end of the 4th month, lymphocytes move into the rudiments of the nodes and clusters are formed - primary nodules without a center of reproduction. At the same time, the organ is divided into cortex and medulla.

Structure. The lymph node is covered externally by a connective tissue capsule, from which trabeculae extend into the organ. It is divided into cortical and cerebral parts, between which is located the thymus-dependent paracortical zone, as well as sinuses.

Cortex. Here are located clusters of lymphoid tissue in the form of secondary nodules. These are rounded formations up to 1 mm in diameter. The central part of the nodule is called the center of reproduction, or reactive center. Here, antigen-dependent proliferation of B-lymphocytes and their differentiation into precursors of plasma cells occurs. In addition, in the center of reproduction are dendritic cells of bone marrow origin, which on their processes retain antigens that activate B-lymphocytes, macrophages of monocytic genesis, phagocytizing autoimmune B-lymphocytes that die by apoptosis, antigens and foreign particles. Along the periphery of the secondary nodule is a crescent-shaped crown consisting of small lymphocytes (recirculating B-lymphocytes, memory B-cells, immature plasma cells). At the border of the crown's multiplication center, T-lymphocytes (helpers) are found, which promote the development of B-lymphocytes into immunoblasts. The latter migrate into the brain cords extending from the paracortical zone and nodules into the brain substance. Lymphatic nodules are dynamic structures. They are formed and then disappear.

Paracortical zoneThe lymph node is located on the border between the cortex and medulla. It is called the thymus-dependent zone, or T-zone, because it disappears when the thymus is removed. In the paracortical zone, blast transformation of T-lymphocytes, their proliferation and transformation into specialized cells of the immune system occur. There are many dendritic cells here. They appear as a result of migration from the integumentary tissues of intraepidermal macrophages. On their surface, they carry antigens and present them to T-lymphocytes (helpers). In addition, in this zone there are special venules lined with cubic endotheliocytes. Through the wall of these venules, T- and B-lymphocytes pass from the blood into the stroma of the lymph node.

Medullalymph nodes is the site of maturation of plasma cells. Together with the secondary nodules of the cortex, the medullary cords make up the thymus-independent zone, or B-zone, of the lymph nodes. In addition to B-lymphocytes and plasma cells, the medullary cords contain T-lymphocytes and macrophages.

Sinuses.The marginal sinus is located under the capsule, where lymph flows from the afferent lymphatic vessels. The marginal sinus passes through the intermediate sinuses into the sinuses of the medulla, and from there the lymph leaves the organ through the efferent lymphatic vessels in the gate area.

Development of the tooth

A tooth is divided into a crown and a root. The roots of the teeth are fixed in the dental alveoli. The narrow area between the crown and the root is the neck of the tooth. The cavity of the tooth contains the pulp (vascular-nerve bundle)

Blood vessels and nerves enter the pulp through the root canal. Dentin is covered with enamel in the crown area, and another type of mineralized tissue, cementum, in the root area. Between the cementum and the alveolar septa is the periodontal ligament (periodontium), formed by bundles of collagen fibers that connect the cementum of the tooth root and the bone tissue of the alveolar septa. In the neck area, the periodontal ligament borders on the mucous membrane of the gums. The periodontium is a broader concept. It includes the periodontium, as well as the tissues that are connected

structures: adjacent areas of the mucous membrane of the gum, areas of bone of the dental sockets. Parts of the tooth and periodontium are divided into hard (mineralized) and soft (non-mineralized) according to their physical properties. Hard components: enamel, dentin, cement, alveolar. Soft parts: dental pulp, mucous membrane of the adjacent gum, periosteum of the alveolar processes and periodontium.

The main volume of the tooth is occupied by dentin, a type of bone tissue. The root of the tooth is fixed in the dental alveolus of the bone, surrounded by the periodontium, which is attached to the dentin of the root with cement. The crown is covered with enamel. The dentin located underneath it continues into the root of the tooth. In the central part of the tooth, in the pulp cavity, is the pulp of the tooth. The pulp cavity at the top of the root opens with one or more dental openings. In the dentin, there are thin tubules directed from the pulp cavity to the surface of the tooth. In these tubules in a living tooth, there are processes of odontoblasts. Their bodies are located in the pulp on the border with dentin.

I REMINDED YOU, GUYS, WHAT'S IN THE TOOTH

Tooth enamel develops from the ectoderm of the oral cavity; other tissues are of mesenchymal origin.

Development of teeth. The formation of milk teeth begins at the end of the 2nd month of intrauterine development. The following structures participate in the formation of the tooth germ: the dental plate, the enamel organ, the dental papilla and the dental sac.

The dental plate appears in the 7th week of intrauterine development as a thickening of the epithelium of the upper and lower jaws. In the 8th week, the dental plate grows into the underlying mesenchyme.

The enamel organ is a localized cluster of cells of the dental plate, corresponding to the position of the tooth, and determines the shape of the crown of the future tooth. The cells of the organ form the outer and inner enamel epithelium. Between them is a loose mass of cells — the enamel pulp. The cells of the inner enamel epithelium differentiate into cylindrical cells that form enamel — ameloblasts (enameloblasts). The enamel organ is connected to the dental plate, and then (in the 3rd-5th month of intrauterine development) completely separates from it.

The dental papilla is a collection of mesenchymal cells originating from the neural crest and located within the enamel goblet organ. The cells form a dense mass that takes the shape of the crown of the tooth. The peripheral cells differentiate into odontoblasts.

Dental bag— mesenchyme surrounding the tooth germ. Cells that come into contact with the root dentin differentiate into cementoblasts and deposit cementum. The outer cells of the dental sac form the connective tissue of the periodontium.

Development of a milk tooth. (I don't give a shit whether it's necessary or not) In a two-month fetus, the rudiment of a tooth is represented only by a formed dental plate in the form of an epithelial outgrowth into the underlying mesenchyme. The end of the dental plate is expanded. From it, the enamel organ will develop in the future. In a three-month fetus, the formed enamel organ is connected to the dental plate by a thin epithelial strand - the neck of the enamel organ. Inner enamel cells of a cylindrical shape (ameloblasts) are visible in the enamel organ. Along the edge of the enamel organ, the inner enamel cells pass

external, lying on the surface of the enamel organ and having a flattened shape. The cells of the central part of the enamel organ (pulp) acquire a stellate shape. Part of the pulp cells, adjacent directly to the layer of enameloblasts, form an intermediate layer of the enamel organ, consisting of 2-3 rows of cubic cells. The dental sac surrounds the enamel organ and then merges at the base of the tooth germ with the mesenchyme of the dental papilla. The dental papilla increases in size and grows even deeper into the enamel organ. Blood vessels penetrate into it.

On the surface of the dental papilla, cells with dark basophilic cytoplasm, located in several rows, differentiate from mesenchymal cells. This layer is separated from the ameloblasts by a thin basal membrane. The crossbars of the bone tissue of the dental alveoli are formed in the circumference of the dental rudiment. In the 6th month of development, the nuclei of the ameloblasts move in the direction opposite to their initial position. Now the nucleus is located in the former apical part of the cell, bordering the pulp of the enamel organ. In the dental papilla, a peripheral layer of regularly located pear-shaped odontoblasts is determined, the long process of which is directed toward the enamel organ. These cells form a narrow strip

unmineralized predentin, outside of which is some mature mineralized dentin. On the side facing the dentin layer, a strip of organic matrix of enamel prisms is formed. The formation of dentin and enamel extends from the apex of the crown to the root, which is fully formed after the crown has erupted.

Formation of permanent teeth. Permanent teeth are laid at the end of the 4th month of intrauterine development. From the common dental plate behind each rudiment of the milk tooth, the rudiment of the permanent tooth is formed. At first, the milk and permanent teeth are in a common alveolus. Later, they are separated by a bone partition. By the age of 6-7, osteoclasts destroy this partition and the root of the falling milk tooth.

The main stages of tooth development.

There are two main stages in tooth development.

Stage I — FORMATION OF THE ENAMEL ORGAN AND DENTAL PAPILLA

At the end of the 2nd month of intrauterine development, the ectodermal epithelium of the oral cavity on the surface of the gum forms an invagination, which is called the dental plate. Later, in the projection of each future tooth, the ectoderm begins to immerse itself in the underlying mesenchyme, and ectodermal clusters are formed - dental buds. The cells of the ectodermal dental buds continue to divide, which leads to a gradual increase in their size and even greater immersion in the mesenchyme. Under the bottom of such a dental bud, the cells of the mesenchyme begin to divide. The mesenchyme lying under the bottom of the dental bud is called the dental papilla. As a result of the division of the mesenchyme cells of the dental papilla, the bottom of the ectodermal dental bud rises and it takes the form of an inverted double-walled goblet. Such an inverted double-walled goblet receives a new name - the enamel organ. Three groups of cells are distinguished in it: internal cells (bottom cells), external cells (roof cells) and intermediate cells. Further differentiation of cells of the ectodermal enamel organ and cells of the mesenchymal dental papilla occurs:

The internal cells of the enamel organ transform into enameloblasts, which subsequently form enamel.

The outer cells of the enamel organ gradually atrophy.

The intermediate cells of the enamel organ subsequently form the enamel cuticle.

The mesenchymal cells located at the apex of the dental papilla differentiate into odontoblasts (dentinoblasts), which form the dentin of the tooth.

Stage I ends with the differentiation of cells of the enamel organ and dental papilla.

The enamel organ is surrounded on the outside by mesenchyme, which forms the dental sac.

stage - FORMATION OF DENTAL TISSUE

Dentin formation: odontoblasts on their apical surface, which is adjacent

enameloblasts, begin to produce the substance of dentin. First, predentin is formed, and then it is impregnated with calcium salts and turns into dentin.

During the process of dentin formation, odontoblasts are constantly pushed back into the dental papilla, eventually ending up in the peripheral part of the dental pulp.

Formation of enamel: enameloblasts on their basal surface, which is adjacent to the odontoblasts, begin to produce enamel substance. During the process of enamel formation, enameloblasts constantly shift outward, eventually their cytoplasm is saturated with enamel substance and they disappear.

Pulp formationoriginates from the remaining mesenchymal cells of the dental papilla.

The formation of cementum occurs from the mesenchymal cells of the dental sac.

stage of histogenesis of dental tissues.

Stage of the dental plate. Formation, stages of development, structure, derivatives of the enamel organ.

Tooth rudiments appear in the 6th-8th week of embryogenesis as a thickening of the multilayered flat epithelium of the oral cavity of the embryo. At the same time, the so-called dental plate is formed. The dental bud stage is characterized by intensive proliferation of cells on the edge of the dental plate, the rounded mass of which actively grows into the adjacent mesenchyme. This epithelial cell mass, separated from the surrounding mesenchyme by the basal membrane, is called the dental bud.

At the end of the proliferative processes in the dental plate, there are 10 dental buds in the rudiments of the upper and lower jaws.

The dental cup stage covers the interval between the 9th and 10th weeks. At this stage, cellular proliferation continues, but the volume of the dental bud does not increase significantly. The dental bud, which forms the enamel organ, takes the shape of a cup, which maintains a connection with the rest of the dental plate with the help of a thin epithelial strand - the neck of the enamel organ. The mesenchyme inside the dental bud condenses into a dense cellular mass that repeats the curvature of the enamel organ cup and takes the shape of the crown of the tooth. Here, the dental papilla is formed - a cluster of mesenchymal cells located inside the enamel organ cup, which is subsequently transformed into the dental pulp. The enamel organ and the dental papilla are separated by a basal membrane, in place of which the dentinoenamel junction will subsequently pass. The mesenchyme surrounding the dental rudiment forms a dental sac. Later, the supporting and retaining apparatus of the tooth - the periodontium - will develop from this rudiment.

The dental bell stage occurs between the 11th and 12th weeks. The enamel organ stretches and takes on the shape of a bell. The dental papilla increases in size and grows deeper into the enamel organ.

Tooth germ. The tooth rudiment is connected to the oral epithelium by the dental plate. The enamel organ is formed by the outer and inner enamel epithelia, separated by a loose mass of cells - the enamel pulp. The cells of the inner enamel epithelium differentiate into enameloblasts, which form enamel. The dental papilla is located inside the goblet-shaped enamel organ as a cluster of mesenchymal cells. The peripheral cells of the dental papilla differentiate into odontoblasts and form dentin.

Enamel organ. The cells of the enamel organ form the outer and inner enamel epithelium. Between them is a loose mass of cells - the enamel pulp. Along the edge of the enamel organ, the inner enamel cells pass into the outer ones, lying on the surface of the enamel organ. The enamel organ is connected to the dental plate, and then (3-5th month) completely separates from it.

The outer enamel epithelium is composed of cuboidal cells and serves as a protective barrier during amelogenesis.

Cells of the inner enamel epithelium are the precursors of ameloblasts

(enameloblasts), which form enamel, contain a large round nucleus. The Golgi complex is located in the part of the cell that faces the enamel pulp. In the cytoplasm of the opposite pole of the cell, facing the dental papilla, there are numerous vesicles, including pinocytotic vesicles, components of the granular endoplasmic reticulum, and free ribosomes. Small mitochondria are located in close proximity to the nucleus. Gap junctions between the cells ensure their communication. The basal membrane is preserved between the internal enamel epithelium and the dental papilla. The epithelium of the enamel organ contains

cytokeratins 5, 14 and 17, characteristic of epithelial cells of the basal layer of multilayered epithelium, in smaller quantities cytokeratins 7, 8, 19 and very little cytokeratin 18, a marker of single-layer epithelia. At the early stage of the dental bell, cytokeratin 14 is predominantly detected in the cells of the inner enamel epithelium, which by the late stage of the dental bell, when the ameloblasts are finally differentiated, is replaced by cytokeratin 19.

Enamel pulp. The outer and inner enamel epithelia are separated by the pulp of the enamel organ. It is represented by a network of dendritic (stellate) cells that form a stellate reticulum (stellate network). In the outer part of the enamel organ, an intermediate layer (stratum intermedium) is distinguished. It is adjacent to the ameloblast layer and consists of 3-4 rows of flat or cubic cells.

Stage of opposition and maturation. The final stages of odontogenesis include the apposition stage (Latin appositio addition, overlay), at which the formation of the enamel, dentin and cement matrix begins. In the subsequent stage of maturation, complete calcification of the matrix of these parts of the tooth occurs. In different teeth, the beginning of these stages

their duration varies. For the formation of enamel, dentin and cementum, inductive interactions between the ectodermal structures of the enamel organ and the mesenchymal structures of the dental papilla and dental sac are important. The basal membrane, which separates tissues of different genesis, participates in these interactions.

Formation of the dental papilla. Derivatives of the dental papilla.

Dental papilla. The superficial mesenchymal cells, arranged in several rows, with dark basophilic cytoplasm differentiate into odontoblasts, the cells that produce the dentin matrix. This layer is separated from the ameloblast precursors by a thin basement membrane. The internal cells of the dental papilla participate in the formation of the pulp.

Formation of the dental sac. Derivatives of the dental sac.

The dental sac surrounds the enamel organ and then merges at the base of the tooth germ

mesenchyme of the dental papilla. Cells that come into contact with the dentin of the root differentiate into cementoblasts and deposit cementum. The outer cells of the dental sac form the connective tissue of the periodontium and the bone of the alveoli. Around the tooth rudiment is the mesenchyme that forms the dental sac. The dental sac surrounds the enamel organ and then merges at the base of the tooth rudiment with the mesenchyme of the dental papilla. From it the cementum of the tooth will develop. Cells that come into contact with the dentin of the root differentiate into cementoblasts and deposit cementum. The outer cells of the dental sac form the connective tissue of the periodontium and the bone of the alveoli.

Changing teeth

The first set of teeth (baby teeth) consists of 10 in the upper and 10 in the lower jaw. The eruption of baby teeth in a child begins at the 6th-7th month of life. The first to erupt on either side of the midline in the upper and lower jaws are the central (medial) and lateral incisors. Laterally to the incisors appear the canines, followed by two molars. A full set of baby teeth is formed at approximately the age of two. Baby teeth serve for the next 4 years. Baby teeth are replaced between the ages of 6 and 12. The permanent front teeth (canines, premolars) replace the corresponding baby teeth and are called replacement permanent teeth. Premolars (permanent premolars) replace baby molars (large molars). The rudiment of the second large molar is formed in the first year of life, and the third molar (wisdom tooth) - by the fifth year. The eruption of permanent teeth begins at the age of 6-7 years. The first to erupt is the large molar (first molar), then the central and lateral incisors. At 9-14 years, premolars, canines and the second molar erupt. Wisdom teeth erupt last of all - at the age of 18-25 years.

Development of the tooth root. Tooth eruption. Change of teeth..

Formation of the tooth root. When the tooth crown is fully formed and the tooth is ready for eruption, the formation of the tooth root begins. The neck loop (epithelial diaphragm) is responsible for the development of the root - the edge of the enamel organ, where the inner and outer enamel epithelia come into contact and form a two-layer structure. The neck loop begins to grow into the surrounding mesenchyme of the dental sac, lengthens and shifts from the area of the formed crown, embracing the tissue masses of the dental papilla. As a result of the growth of the edges of the enamel organ, the root epithelial sheath is formed, determining the shape of the root of the developing tooth. In addition, the root epithelial sheath induces the formation of dentin in the root area as a continuation of the dentin of the tooth crown.

The stage of loss of baby teeth and their replacement with permanent ones. The rudiments of permanent teeth are formed in the 5th month of embryogenesis as a result of the growth of epithelial strands from the dental plates. Permanent teeth develop very slowly, located next to the baby teeth, separated from them by a bone partition. By the time the baby teeth are replaced (6-7 years), osteoclasts begin to destroy the bone partitions and roots of the baby teeth. As a result, the baby teeth fall out and are replaced by the permanent teeth, which are growing rapidly at that time.

Tooth enamel. Formation, structure, organization, properties

Enamelis the upper shell and covers the crowns of the teeth. The thickness of the enamel is 2.5 mm along the cutting edge or in the area of the chewing tubercles of the molars and decreases as it approaches the neck.

Under the enamel there is a characteristically striated dentin on the crown, which continues as a solid mass into the root of the tooth. Cells that are absent in mature enamel and the erupted tooth, called enameloblasts (ameloblasts), participate in the formation of enamel (synthesis and secretion of components of its organic matrix).

Enamel is the hardest tissue in the body. However, enamel is fragile. Its permeability is limited, although enamel has pores through which water and alcohol solutions of low-molecular substances can penetrate. Comparatively small water molecules, ions, vitamins, monosaccharides, amino acids can slowly diffuse in the enamel substance. Fluorides (drinking water, toothpaste) are included

crystals of enamel prisms, increasing the resistance of enamel to caries. The permeability of enamel increases under the influence of acids, alcohol, with a deficiency of calcium, phosphorus, fluorine.

Enamel is formed by organic substances, inorganic substances, and water. Their relative content in weight percent: 1:96:3. By volume: organic substances 2%, water - 9%, inorganic substances - up to 90%. Calcium phosphate, included

the composition of hydroxyapatite crystals, is 3/4 of all inorganic substances. In addition to phosphate, calcium carbonate and fluoride are present in small quantities - 4%. Of the organic compounds, there is a small amount of protein - two fractions (soluble in water and insoluble in water and weak acids), a small amount of carbohydrates and lipids was found in the enamel.

Structural unit of enamel— a prism with a diameter of about 5 µm. The orientation of the enamel prisms is almost perpendicular to the boundary between the enamel and dentin. Adjacent prisms form parallel bundles. On sections parallel to the enamel surface, the prisms have the shape of a keyhole: the elongated part of the prism of one row lies in another row between two bodies of adjacent prisms. Due to this shape, there are almost no spaces between the prisms in the enamel. There are prisms of other (in section) shapes: oval, irregular, etc. The course of the prisms perpendicular to the enamel surface and the enamel-dentin boundary has s-shaped bends. We can say that the prisms are helically curved.

There are no prisms on the border with dentin or on the enamel surface.

(non-prism enamel). The material surrounding the prisms also has different characteristics

is called the “prism shell” (the so-called adhesive (or fusion) substance), the thickness of such a shell is about 0.5 microns, in some places the shell is absent.

Enamel is an exceptionally hard tissue, which is explained not only by its high content

calcium salts, but also the fact that calcium phosphate is found in enamel in the form of hydroxyapatite crystals. The ratio of calcium to phosphorus in crystals normally varies from 1.3 to 2.0. With an increase in this ratio, the resistance of enamel increases. In addition to hydroxyapatite, other crystals are also present. The ratio of different types of crystals: hydroxyapatite - 75%, carbonate apatite - 12%, chlorine apatite - 4.4%, fluorapatite - 0.7%.

Between the crystals there are microscopic spaces - micropores, the totality of which is the environment in which the diffusion of substances is possible.

In addition to micropores, enamel contains spaces between prisms - pores. Micropores and pores are the material substrate of enamel permeability.

There are three types of lines in the enamel, reflecting the uneven nature of enamel formation over time: transverse striation of enamel prisms, Retzius lines and the so-called neonatal line.

The transverse striation of the enamel prisms has a period of about 5 µm and corresponds to the daily periodicity of prism growth.

Due to differences in optical density due to lower mineralization, the lines of Retzius are formed at the border between the elementary units of enamel. They look like arches located in parallel at a distance of 20-80 μm. The lines of Retzius can be interrupted, they are especially numerous in the neck area. These lines do not reach the surface of the enamel in the area of the chewing tubercles and along the cutting edge of the tooth. The elementary units of enamel are rectangular spaces delimited from each other by vertical lines - the boundaries between the prisms and horizontal lines (transverse striation of the prisms). Due to the different rate of enamel formation at the beginning and end of amelogenesis, the size of the elementary units is also important, differing between the superficial and deep layers of enamel. Where the lines of Retzius reach the surface of the enamel, there are grooves - perichymes, running in parallel rows along the surface of the tooth enamel.

The surface areas of enamel are denser than the underlying parts, the concentration of fluoride is higher here, there are grooves, pits, elevations, non-prismatic areas, pores, micro-holes. Various layers may appear on the surface of the enamel, including colonies of microorganisms in combination with amorphous organic matter (dental plaque). When inorganic substances are deposited in the plaque area, tartar is formed.

Hunter-Schreger bands in enamel are clearly visible in polarized light as alternating bands of varying optical density, directed from the border between dentin almost perpendicular to the enamel surface. The bands reflect the fact of deviation of prisms from the perpendicular arrangement in relation to the enamel surface or to the enamel-dentin border. In some areas, enamel prisms are dissected longitudinally (light bands), in others - transversely (dark bands).

Dentin. Formation, structure

Dentin is denser than bone tissue and cement, but much softer than enamel. Dentin permeability is significantly greater than enamel permeability, which is associated not so much with the permeability of the dentin substance itself, but with the presence of tubules in the mineralized dentin substance.

Compound

Organic substances - 18%, inorganic substances - 70%, water - 12%. By volume: organic substances - 30%, inorganic substances - 45%, water - 25%. Of the organic substances, the main component is collagen type I, significantly less chondroitin sulfate and phospholipids. Dentin is highly mineralized, the main inorganic component is hydroxyapatite crystals Ca10(PO4)6(OH)2. In addition

calcium phosphate, calcium carbonate is present in dentin. Crystals of mature dentin are flatter and smaller than crystals of enamel prisms.

Mineralization proteinsDentin mineralization involves phosphorin, dentin sialophosphoprotein, bone sialoprotein, osteocalcin, osteonectin, and dentin matrix protein 1. Osteocalcin and collagen type I are expressed in polarizing odontoblasts. Amelogenin and dentin sialophosphoprotein come from ameloblasts. Later, when dentin mineralization begins, osteoblasts produce more dentin sialophosphoprotein and less osteocalcin. Osteocalcin acts as an inhibitor of mineralization, while phosphorin and dentin sialophosphoprotein are involved in later mineralization processes. Bone sialoprotein, produced and secreted by odontoblasts, serves as a nucleator for hydroxyapatite crystal formation. Osteonectin is predominantly present in the unmineralized predentin.

Enzymes. Odontoblasts produce and secrete enzymes from the matrix metalloproteinase (MMP) family into the dentin matrix, such as MMP-2 (gelatinase A) and MMP-9 (gelatinase B), which break down matrix proteins during dentinogenesis. Thus, in the dentin of a developing tooth, amelogenin is broken down by gelatinase A into several fragments with different molecular weights. Gelatinase A also breaks down dentin matrix protein 1 (DMP1).

Dentin is a heterogeneous structure. Its morphological organization varies depending on its location in the anatomical parts of the tooth, and also depends on its proximity to specific structures, such as tubules. The section parallel to the dentinoenamel junction shows heterogeneities in dentin mineralization.

Primary dentin. It is formed during mass dentinogenesis. In the mantle

(superficial) and peripulpal dentin, the orientation of collagen fibers is different.

Mantle dentin (dentinum vestiens) is located at the border with enamel. It is the first to appear and mineralize in the tooth. Mantle dentin is characterized by the radial arrangement of collagen fibers in relation to the long axis of the tooth, i.e. they are oriented perpendicular to the dentinoenamel junction.

Peripulpar dentin is the main mass of dentin adjacent to the dental pulp. It is formed after the mantle dentin and is more mineralized than it. Peripulpar dentin is characterized by the tangential arrangement of collagen fibers that run parallel to the dentinoenamel junction.

Secondary dentinIt is deposited between the main mass of dentin (primary dentin) and predentin in the formed tooth after its eruption (after the formation of the opening of the apex of the tooth). It is formed slowly and is less mineralized than primary.

Regular dentin (organized dentin) is located in the root area of the tooth.

Irregular irritation dentin (disorganized dentin) is located in the apical part of the tooth cavity.

Tertiary dentin. Substitute (reparative, reactive, tertiary) dentin is formed quickly in places of damage to hard dental tissues, for example, with caries, increased abrasion, etc. Odontoblasts in the area of damage may die, and new ones take their place, differentiating from precursor cells located in the pulp. The course of the tubules in substitutive dentin is less regular than in secondary dentin. A variety of substitutive dentin is sclerotic dentin, which occurs in chronic caries. In this case, the odontoblast processes die, and the dentinal tubules remain free. These tubules can be filled with a matrix that mineralizes and resembles peritubular dentin. Clinically, dentin in the caries focus is dark, smooth and transparent.

Predentin or unmineralized dentinis located between the odontoblast layer and dentin. Predentin is newly formed and unmineralized dentin. Between the predentin and peripulpal dentin there is a thin plate of mineralizing predentin - intermediate dentin - the calcification front. Mineralization of predentin occurs soon after its formation. The process occurs in two stages. At the early stage, hydroxyapatite crystals are concentrated among the collagen fibers of the predentin in the form of dentin balls. They gradually increase in size and merge. At the second stage, new areas of mineralization are formed in the form of similar globules, but already in partially mineralized predentin. These new areas of crystal formation become ordered, organized into layers, but initially do not merge. Incomplete fusion at this stage of dentin mineralization leads to differences in the microscopic organization of the crystals. In areas where primary and secondary mineralization and fusion of dentin spheres have occurred, rounded areas of enlightenment begin to be visible on dentin sections. Such dentin is called globular. Dark areas of dentin located between globular dentin are called interglobular dentin. In these areas, only primary mineralization occurs, and here the dentin spheres do not completely merge. Interglobular dentin is less mineralized than globular. Interglobular dentin is predominantly localized within the dentin of the crown, and is also located near the dentinoenamel junction. Its content increases with some anomalies, such as dentin dysplasia.

Granular dentin. In the root of the tooth, between the main mass of dentin and the acellular cement, there is a granular layer of dentin, which consists of alternating areas of hypo- or completely non-mineralized dentin (interglobular spaces) and fully mineralized dentin in the form of spherical formations (dentin balls or calcospherites).

Lines

There are several types of structural lines in dentin. The lines are usually perpendicular to the dentinal tubules. The following main types of lines are distinguished: contour lines associated with the bends of the dentinal tubules and lines associated with uneven mineralization.

Contour lines are visible in polarized light and are formed by the superposition of secondary folds of dentinal tubules. Contour lines are quite rare in primary dentin, they are more often located at the border between primary and secondary dentin.

Lines of increment are dark bands that cross the dentinal tubules at right angles, analogous to the lines of periodicity of mineralization in enamel. Lines of increment are formed due to the uneven rate of calcification during dentinogenesis. Since the mineralization front is not necessarily strictly parallel to the predentin, the course of the lines can be tortuous.

The newborn lines, as in enamel, reflect the fact of the change in the dentinogenesis regime at birth. These lines are expressed in the baby teeth and in the first permanent molar.

Dental pulp: origin, structure, functions

Pulp— the soft part of the tooth, represented by loose connective tissue, contains collagen and a moderate amount of reticulin fibers, fibronectin, tenascin. Among the cellular elements of the pulp there are poorly differentiated mesenchymal cells, which are considered as a source for restoring the populations of odontoblasts and fibroblasts in the event of their death due to tissue damage. The pulp also contains macrophages, lymphocytes, plasma cells, mast cells, eosinophils. The pulp is intensively supplied with blood and contains numerous sensitive nerve endings. The pulp provides dentinogenesis, trophic, sensory (trigeminal nerve) and protective functions. The pulp is divided into peripheral, intermediate and central layers.

Peripheral layer of pulpcontains - analogs of bone osteoblasts. Odontoblasts

secrete collagen, glycosaminoglycans (chondroitin sulfate) and lipids, which are part of

composition of the organic matrix of dentin. As predentin mineralizes

(non-calcified matrix) odontoblast processes are found to be embedded in

dentinal tubules.

Growth hormone. Of all the cell types that form hard tissues in the body (osteoblasts, cementoblasts, odontoblasts, ameloblasts) and are capable of synthesizing bone morphogenetic proteins (BMP), alkaline phosphatase, osteocalcin and osteontine, odontoblasts are the ones that respond most to the action of growth hormone. Under the influence of growth hormone, odontoblasts increase the production of a number of growth factors and proteins for the dentin matrix.

Intermediate layer of pulpcontains numerous stellate cells, the thin and long processes of which form a network, precursors of odontoblasts and forming collagen fibers.

Central layer of pulp— loose fibrous connective tissue with numerous anastomosing capillaries and nerve fibers, the terminals of which branch in the intermediate and peripheral layers. In elderly people, irregularly shaped calcified formations called denticles are often found in the pulp. True denticles consist of dentin surrounded on the outside by odontoblasts. False denticles are concentric deposits of calcified material around necrotic cells.

TOOTH INNERVATION

A distinction is made between the innervation of the tooth itself and the innervation of the periodontium. The dental pulp is innervated by the sensory fibers of the trigeminal nerve, which enter the pulp together with

blood vessels through a canal in the root of the tooth. In the dental pulp, nerve fibers terminate on blood vessels and form a plexus near the inner surface of the dentin. Thin unmyelinated fibers penetrate some distance into the dentinal tubules. Nerve fibers in the dentinal tubules can form varicose expansions. These fibers form free nerve endings and conduct pain impulses. In the peripheral part of the pulp, branches of unmyelinated fibers pass between the bodies of odontoblasts. Here, the fibers are surrounded by Schwann cells. Most of the nerve endings in the predentin and dentin interact with the processes of odontoblasts. These are believed to be mechanoreceptors that play a central role in the afferent innervation of dentin.

Esophagus. Esophagus membranes and their structure

StructureThe esophagus is made up of the mucous membrane, submucosa, muscular and adventitial membranes.

Mucous membraneforms longitudinal folds and consists of three layers: epithelial, lamina propria and muscularis. The epithelial layer is a multilayered flat nonkeratinizing epithelium formed by the basal, spinous and flat cell layers. Epithelial regeneration occurs very quickly due to the division of basal cells. The main type of epithelial cells are epithelial cells, Langerhans cells, intraepithelial lymphocytes and endocrine cells are also found. The lamina propria of the mucous membrane is formed by loose fibrous connective tissue. Its main structures are blood and lymphatic vessels, nerve fibers, single lymphoid follicles, excretory ducts of the esophageal glands and the terminal sections of the cardiac glands of the esophagus, which are found only in two places: at the level of the cricoid cartilage of the larynx and the fifth cartilage of the trachea or in the lower part of the esophagus near its entrance to the stomach. These are simple, branched tubular glands similar to the cardiac glands of the stomach, hence their name. The terminal sections consist of cubic or cylindrical mucocytes that produce mucus. The muscularis mucosae are formed

longitudinal bundles of smooth muscle tissue. It participates in the formation of folds and facilitates the passage of rough lumps of food.

SubmucosaIt is formed by loose fibrous connective tissue and participates in the formation of folds of the mucous membrane, providing its nutrition and mobility.

Muscular membraneformed by an internal circular and external longitudinal layer. In the upper third it is transversely striated, in the middle third it is transversely striated,

smooth, in the lower third - only smooth muscle tissue. The circular layer of the muscular membrane forms the upper and lower sphincters of the esophagus. The function of the membrane is to move food to the stomach. Between the layers of the muscular membrane is the intermuscular nerve plexus of Auerbach.

Serous membraneis part of the esophagus wall only in its subdiaphragmatic section. It is formed by two layers: the inner one is loose fibrous connective tissue, the outer one is mesothelium. The rest of the outer shell is represented by adventitia, which contains many vessels and a nerve plexus.

Stomach. The membranes and their structure

The stomach is a layered organ.. Consists of four membranes: mucous, submucous, muscular and serous. The mucous membrane has a complex relief, represented by gastric pits, folds and fields. Pits are depressions of the epithelium in the proper plate of the mucous membrane. Folds are protrusions of the mucous and submucous membranes into the lumen of the stomach. Fields are areas of the mucous membrane that include a group of glands, delimited from other such groups by a pronounced layer of loose fibrous connective tissue with translucent blood vessels. Pits and folds significantly increase the working surface of the mucous membrane.

The mucous membrane consists of three layers: epithelial, proper and muscular plates.

Epithelial layeris represented by a single-layer cylindrical glandular epithelium. It is formed by glandular epithelial cells - mucocytes that secrete alkaline mucus. This mucus consists mainly of water (95%), lipids and glycoproteins, which in combination form a hydrophobic protective gel. Bicarbonate secreted by the surface epithelial cells into the mucous gel creates a pH gradient: from 1 - on the surface of the stomach facing the lumen, to 7 - at the surface of the epithelial cells. Mucus forms a continuous layer up to 0.5 μm thick. Mucus tightly adjoining the surface of the epithelium very effectively performs a protective function, while the more soluble superficial mucous layer adjacent to the lumen is partially digested by pepsin and mixes with the contents of the stomach. The epithelial cells also form an important defense mechanism through their mucus-producing capacity, intercellular tight junctions, and ion pumps that maintain intracellular pH levels, as well as bicarbonate production necessary for gel alkalinization.

Lamina propria of the mucous membraneformed by loose fibrous connective tissue. It contains small blood and lymphatic vessels, nerve trunks, lymphoid nodules. The main structures of the lamina propria

are glands. All gastric glands are simple tubular branched. They open into the gastric pits and consist of three parts: the fundus, body and neck. Depending on their location, the glands are divided into cardiac, main or fundic and pyloric. The structure and cellular composition of these glands are not the same. In quantitative terms, the main glands predominate. They are the most weakly branched of all the gastric glands. Their cellular composition is as follows:

chief cells;

parietal cells;

accessory or mucous cells;

endocrinocytes;

cervical mucocili.

Submucosa- is represented by loose fibrous unformed connective tissue. Contains submucous nerve plexus, lymphatic follicles, vascular collectors. Forms folds.

Muscular membraneformed by 3 layers of smooth muscle tissue. The inner layer is longitudinal, the middle layer is circular, and the outer layer is obliquely directed smooth myocytes. The circular layer is strongly developed in the pyloric section, where it participates in the formation of the circular fold - the involuntary sphincter. In the cardiac section, a similar sphincter in humans is poorly developed.

The outer shell is serous.The inner plate is connective tissue, the outer one is epithelial (single-layer flat epithelium - mesothelium).

Physiological regeneration is provided by mitotic division of precursor cells. Reparative regeneration - the epithelial defect is also eliminated by cell proliferation, or - in the case of severe damage to the mucosa - is replaced by a connective tissue scar.

Stomach. Mucosal epithelium and muco-bicarbonate barrier

Epithelial layeris represented by a single-layer cylindrical glandular epithelium. It is formed by glandular epithelial cells - mucocytes that secrete alkaline mucus. This mucus consists mainly of water (95%), lipids and glycoproteins, which in combination form a hydrophobic protective gel. Bicarbonate secreted by the surface epithelial cells into the mucous gel creates a pH gradient: from 1 - on the surface of the stomach facing the lumen, to 7 - at the surface of the epithelial cells. Mucus forms a continuous layer up to 0.5 μm thick. Mucus tightly adjoining the surface of the epithelium very effectively performs a protective function, while the more soluble superficial mucous layer adjacent to the lumen is partially digested by pepsin and mixes with the contents of the stomach. Integumentary epithelial cells also form an important defense mechanism through their mucus-producing capacity, intercellular tight junctions, and ion pumps that maintain levels

HCO3—

intracellular pH, as well as the production of bicarbonate, which is necessary for alkalization of the gel.

The mucobicarbonate barrier protects the mucous membrane from the action of acid, pepsin and other potential damaging agents.

Mucusis constantly secreted onto the inner surface of the stomach wall. Bicarbonate (HCO ions3-), secreted by superficial mucous cells, has a neutralizing effect. pH. The mucus layer has a pH gradient. On the surface of the mucus layer, the pH is 2, and in the near-membrane part it is more than 7. H+. Permeability of the plasma membrane of gastric mucosal cells for H+varies. It is insignificant in the membrane facing the lumen of the organ (apical), and is quite high in the basal part. With mechanical damage to the mucous membrane, when exposed to oxidation products, alcohol, weak acids or bile, the concentration of H+in cells increases, which leads to their death and destruction of the barrier.

Rice. 22-7. GASTRIC SECRETION. I —. Mechanism secretions

epithelial cells of the gastric and duodenal mucosa: A - HCO output3- in exchange for Cl- stimulate some hormones (eg, glucagon) and inhibit Cl transport blocker-furosemide. B - active transport of HCO3-, independent of Cl transport-; B and G - transport of HCO3-through the membrane of the basal part of the cell into the cell and through the intercellular spaces (depends on the hydrostatic pressure in the subepithelial connective tissue of the mucous membrane). II - Parietal cell. The system of intracellular canals significantly increases the surface area of the plasma membrane. Numerous mitochondria produce ATP to ensure the operation of the ion pumps of the plasma membrane. III - Parietal cell: ion transport and secretion of HCl. Na+,TO+-ATPase is involved in the transport of K+ into the cell. Cl- enters the cell in exchange for HCO3-through the lateral surface membrane (1), and exits through the apical membrane; 2 - Na exchange+on H+. One of the most important links is the output of H+through the apical membrane over the entire surface of the intracellular tubules

exchange on K+at help H+,TO+-ATPase.. IV - Regulations activities

parietal cellsThe stimulating effect of histamine is mediated through cAMP, whereas the effects of acetylcholine and gastrin are mediated through an increase in Ca influx.2+into the cell. Prostaglandins reduce the secretion of HCl by inhibiting adenylate cyclase, which leads to a decrease in the level of intracellular cAMP. H blocker+,K+-ATPase (eg, omeprazole) reduces HCl production. PC - protein kinase activated by cAMP; phosphorylates membrane proteins, enhancing the work of ion pumps.

Regulation. Secretion of bicarbonate and mucus is enhanced by glucagon, prostaglandin E, gastrin, and epidermal growth factor. To prevent damage and restore the damaged barrier, antisecretory agents (e.g., histamine receptor blockers), prostaglandins, gastrin, and sugar analogs (e.g., sucralfate) are used.

Breaking the barrier. Under unfavorable conditions, the barrier is destroyed within a few minutes, epithelial cells die, and edema and hemorrhage occur in the proper layer of the mucous membrane. Factors that are unfavorable for maintaining the barrier are known: Ú non-steroidal anti-inflammatory drugs (eg, aspirin, indomethacin); Ú ethanol, Ú bile salts, Ú Helicobacter pylori is a gram-negative bacterium that survives in the acidic environment of the stomach. H. pylori affects the surface epithelium of the stomach and destroys the barrier, contributing to the development of gastritis and ulcerative defects of the stomach wall. This microorganism is isolated from 70% of patients with gastric ulcer and 90% of patients with duodenal ulcer or antral gastritis.

Regenerationepithelium, forming a layer of bicarbonate mucus, occurs due to stem cells located at the bottom of the gastric pits; cell renewal time

— about 3 days. Regeneration stimulants: Ú gastrin from endocrine cells of the stomach, Ú gastrin-releasing hormone from endocrine cells and endings of vagus nerve fibers, Ú epidermal growth factor coming from the salivary, pyloric glands, duodenal glands and other sources. Mucus. In addition to the superficial cells of the gastric mucosa, mucus is secreted by cells of almost all gastric glands. Pepsinogen. The chief cells of the fundic glands synthesize and secrete pepsin precursors (pepsinogen), as well as a small amount of lipase and amylase. Pepsinogen has no digestive activity. Under the influence of hydrochloric acid and especially previously formed pepsin, pepsinogen is converted into active pepsin. Pepsin is a proteolytic enzyme active in an acidic environment (optimum pH from 1.8 to 3.5). At a pH of about 5, it has virtually no proteolytic activity and is completely inactivated within a short time. Intrinsic factor. For the absorption of vitamin B12The intestine requires (intrinsic) Castle factor, synthesized by the parietal cells of the stomach. The factor binds vitamin B12and protects it from destruction by enzymes. Complex of intrinsic factor with vitamin B12in the presence of Ca ions2+interacts with receptors of the epithelial cell of the distal ileum. In this case, vitamin B12enters the cell, and the intrinsic factor is released. The absence of the intrinsic factor leads to the development of anemia. Hydrochloric acid Hydrochloric acid (HCl) is produced by parietal cells, which have a powerful system of intracellular canals (Fig. 22-7, II), significantly increasing the secretory surface. The cell membrane facing the lumen of the canals contains a proton pump (H+,K+-ATPase),

pumping out of the cell+in exchangeTO+. Chlorine-bicarbonate

anion exchangerembedded in the membrane of the lateral and basal surfaces of cells: Cl-enters the cell in exchange for HCO3-through this anion exchanger and enters the lumen of the tubules. Thus, both components of hydrochloric acid appear in the lumen of the tubules: and Cl-, and H+. All other molecular components (enzymes, ionic

pumps, transmembrane carriers) are aimed at maintaining the ionic balance inside the cell, primarily at maintaining intracellular pH.

mechanism of hydrochloric acid formation

Chloride ions are actively transported from the cytoplasm of parietal cells into the lumen of intracellular tubules, and sodium ions are transported outward. These two effects create a potential in the tubules (from -40 to -70 mV), leading to the diffusion of large quantities of potassium ions and some sodium ions into the tubules.

In the cell cytoplasm, water dissociates into hydrogen and hydroxyl ions. Hydrogen ions are secreted into the tubules by active transport in exchange for potassium ions. This process is catalyzed by H+, K+-ATPase. As a result, potassium and sodium ions that diffused into the tubules are reabsorbed into the cytoplasm of the cells, and hydrogen ions take their place in the tubules, creating a solution of concentrated hydrochloric acid there, which goes out through the secretory tubules, i.e. onto the surface of the gastric epithelium.

Water passes into the tubules by osmosis. As a result, the tubular secretion contains hydrochloric acid at a concentration of 150-160 mmol/l, potassium chloride at a concentration of 15 mmol/l and a small amount of sodium chloride.

In the final stage, carbon dioxide formed during cell metabolism combines with hydroxyl ions under the influence of carbonic anhydrase to form bicarbonate ions. Bicarbonate ions diffuse from the cytoplasm into the extracellular fluid in exchange for chloride ions entering the cell and subsequently secreted into the tubules of the parietal cells.

At peacethe cell secretes chlorine.

When stimulatedN's work is intensified+,TO+-ATPase, resulting in increased H2O transport.+from the cell. At the same time, the transport of Cl increases by 2-3 times.-in exchange for HCO3-. As a result, the intracellular pH remains unchanged. Stimulation of the parietal cells causes the release of an acidic solution, isotonic with the extracellular fluid, containing 160 mmol/l of hydrochloric acid with a pH of about 0.8. The content of hydrogen ions in this solution is 3 million times higher than in arterial blood.

Regulation of hydrochloric acid secretionis shown in Fig. 22-7,IV. The parietal cell is activated through m-cholinergic receptors (blocker - atropine), H2-histamine receptors (blocker - cimetidine) and gastrin receptors (blocker - proglumide). The indicated blockers or their analogs, as well as vagotomy, are used to suppress the secretion of hydrochloric acid. There is another way to reduce the production of hydrochloric acid - blockade of H+,TO+-ATPase.

Fundal part of the stomach. Features of the structure of the mucous membrane. Fundal glands

The proper (fundal) glands of the stomach are located in the area of the bottom and body of the stomach. Their terminal sections are practically unbranched. The proper gland consists of a secretory part (bottom and body) and an excretory duct (neck and its mouth - isthmus).

Contains three types of exocrine cells:

Principal cells: are located in groups - in the area of the bottom and body of the glands. They have a small size, a round nucleus, basophilic cytoplasm, protein granules

secretion in the apical part of the cell. They form inactive forms of digestive enzymes - pepsin (breaks down proteins) and chymosin (breaks down milk proteins).

Parietal cells: are located singly, outside of other cells, adjacent to their basal sections. These are large cells of irregular shape with a round nucleus, oxyphilic cytoplasm, having intracellular canals that pass into intercellular canals and then into the lumen of the gland.

Mucous (accessory) cells: located in the body of the glands (one type of cells) and in the neck of the glands (cervical cells). These are relatively small cells with a flattened nucleus and light (weakly stained) cytoplasm. They form

mucus-like secretion. Cervical cells are poorly differentiated cells - a source of regeneration of other glandular cells and epithelium.

In the glands themselves, there are endocrinocytes (flattened cells containing granules throughout their entire volume) of several types:

EC cells: produce serotonin, which stimulates the secretory and motor activity of the stomach and intestines, and melatonin, which determines the daily periodicity of secretion and motility of the gastrointestinal tract.

ECL cells: produce histamine, which affects gastrointestinal motility and vascular health and stimulates the secretion of HCl by parietal cells.

P-cells: produce bombesin, which stimulates the secretion of HCl, pancreatic juice and stimulates gallbladder motility.

Pyloric part of the stomach. Features of the structure of the mucous membrane. Pyloric glands

The mucous membrane of the cardiac part of the stomach contains simple or branched tubular cardiac glands and branched pyloric glands. The cardiac glands are located in the cardiac part of the stomach. The pyloric glands are located in the transition zone of the stomach into the duodenum. The pyloric and cardiac glands contain three types of exocrine cells (among them, mucous cells predominate):

Principal cells: are located in groups - in the area of the bottom and body of the glands. They are small in size, have a round nucleus, basophilic cytoplasm, granules of protein secretion in the apical part of the cell. They form inactive forms of digestive enzymes - pepsin (breaks down proteins) and chymosin (breaks down milk proteins).

mucus-like secretion. Cervical cells are poorly differentiated cells - a source of regeneration of other glandular cells and epithelium.

Endocrinocytes of the pyloric glands and cardiac glands:

G-cells (found in both the cardiac and pyloric glands): produce gastrin, which stimulates the secretory and motor activity of the stomach; enkephalin, which is one of the endogenous morphines, i.e. has an analgesic effect.

D-cells (found only in the pyloric): produce somatostatin,

which inhibits exocrine and endocrine functions of the gastrointestinal tract.

D1 cells (found only in the pyloric cells): produce VIP

(vasointestinal peptide), which is an antagonist of somatostatin in its effect on the pancreas: it stimulates its exocrine and endocrine activity. In addition, by dilating blood vessels, it reduces blood pressure.

Glands of the stomach. Structure, cellular composition of cardiac, fundic, pyloric glands

Glands of the stomachin its various sections have different structures. There are three types of gastric glands: proper glands of the stomach, pyloric and cardiac. Proper, or fundic, glands of the stomach predominate quantitatively. They are located in the area of the body and bottom of the stomach. Cardiac and pyloric glands are located in the parts of the stomach with the same names.

The stomach's own glands— the most numerous. In humans, there are about 35 million of them. The area of each gland is approximately 100 mm2. The total secretory surface of the fundic glands reaches enormous sizes — about 3...4 m2. In structure, these glands are simple unbranched tubular glands. The length of one gland is about 0.65 mm, its diameter varies from 30 to 50 µm. The glands open in groups into the gastric pits. In each gland, there is an isthmus (isthmus), a neck (cervix) and a main part (pars principalis), represented by the body (corpus) and the bottom (fundus). The body and the bottom of the gland make up its secretory section, and the neck and isthmus of the gland are its excretory duct. The lumen in the glands is very narrow and almost invisible on preparations.

The stomach's own glands contain 5 main types of glandular cells:

chief exocrine cells,

parietal exocrine cells,

mucous, cervical mucocytes,

endocrine (argyrophilic) cells,

undifferentiated epithelial cells.

Chief exocrine cellsare located mainly in the area of the bottom and body of the gland. The nuclei of these cells are rounded and lie in the center of the cell. The cell is divided into basal and apical parts. The basal part has pronounced basophilia. Granules of protein secretion are found in the apical part. The basal part contains a well-developed synthetic apparatus of the cell. There are short microvilli on the apical surface. Secretory granules have a diameter of 0.9-1 μm. The chief cells secrete pepsinogen, a proenzyme (zymogen), which in the presence of hydrochloric acid is converted into an active form, pepsin. It is assumed that chymosin, which breaks down milk proteins, is also produced by the chief cells. When studying the various phases of secretion of the chief cells, it was revealed that in

In the active phase of secretion production and accumulation, these cells are large, and pepsinogen granules are clearly visible in them. After secretion, the size of the cells and the number of granules in their cytoplasm decrease significantly. It has been experimentally proven that when the vagus nerve is irritated, the cells quickly release pepsinogen granules.

Parietal exocrine cellsare located outside the main and mucous cells, adjacent to their basal ends. They are larger than the main cells, irregularly rounded in shape. Parietal cells lie singly and are concentrated mainly in the area of the body and neck of the gland. The cytoplasm of these cells is sharply oxyphilic. Each cell contains one or two round nuclei lying in the central part of the cytoplasm. Inside the cells there are special systems of intracellular canals with numerous microvilli and small vesicles and tubes that form the tubulovesicular system, which plays an important role in the transport of Cl-ions. Intracellular canals pass into intercellular canals located between the main and mucous cells and opening into the lumen of the gland. Microvilli extend from the apical surface of the cells. The parietal cells are characterized by the presence of numerous mitochondria. The role of the parietal cells of the stomach's own glands is to produce H+ ions and chlorides, from which hydrochloric acid (HCl) is formed.

Mucous cells, mucocytesare represented by two types. Some are located in the body of the proper glands and have a compacted nucleus in the basal part of the cells. In the apical part of these cells, many round or oval granules, a small number of mitochondria and the Golgi apparatus are found. Other mucous cells are located only in the neck of the proper glands (the so-called cervical mucocytes). Their nuclei are flattened, sometimes of an irregular triangular shape, usually located at the base of the cells. In the apical part of these cells are secretory granules. The mucus secreted by the cervical cells is weakly stained with basic dyes, but is well revealed by mucicarmine. Compared to the superficial cells of the stomach, the cervical cells are smaller in size and contain significantly fewer mucus droplets. Their secretion differs in composition from the mucoid secretion secreted by the glandular epithelium of the stomach. In contrast to other cells of the fundic glands, mitotic figures are often found in the cervical cells. It is believed that these cells are undifferentiated epithelial cells (epitheliocyti nondifferentiati) - the source of regeneration of both the secretory epithelium of the glands and the epithelium of the gastric pits.

Among the epithelial cells of the stomach's own glands there are also single endocrine cells belonging to the APUD system.

Pyloric glandsare located in the transition zone of the stomach into the duodenum. Their number is about 3.5 million. The pyloric glands differ from the glands proper in several ways: they are located more rarely, are branched, have wide lumens; most pyloric glands lack parietal cells.

The terminal sections of the pyloric glands are built mainly from cells resembling the mucous cells of the glands themselves. Their nuclei are flattened and lie at the base of the cells. Mucus is detected in the cytoplasm using special staining methods. The cells of the pyloric glands are rich in dipeptidases. The secretion produced by the pyloric glands already has an alkaline reaction. Intermediate cervical cells are also located in the neck of the glands.

The structure of the mucous membrane in the pyloric part has some peculiarities: the gastric pits here are deeper than in the body of the stomach, and occupy about half of the entire thickness of the mucous membrane. Near the exit from the stomach, this membrane has a well-defined annular fold. Its appearance is associated with the presence of a powerful circular layer in the muscular membrane, forming the pyloric sphincter. The latter regulates the flow of food from the stomach into the intestine.

Cardiac glands— simple tubular glands with highly branched terminal sections. The excretory ducts (necks) of these glands are short, lined with prismatic cells. The nuclei of the cells are flattened, lying at the base of the cells. Their cytoplasm is light. When specially stained with mucicarmine, mucus is revealed in it. Apparently, the secretory cells of these glands are identical to the cells lining the pyloric glands of the stomach and the cardiac glands of the esophagus. Dipeptidases are also found in them. Sometimes

In the cardiac glands, chief and parietal cells are found in small numbers.

Gastrointestinal endocrinocytesIn the stomach, several types of endocrine cells have been identified based on morphological, biochemical and functional characteristics.

EC cells(enterochromaffin) - the most numerous, located in the area

body and bottom of the glands between the principal cells. These cells secrete serotonin and

melatonin. Serotonin stimulates the secretion of digestive enzymes, the release

mucus, motor activity. Melatonin regulates photoperiodicity

functional activity (i.e. depends on the action of the light cycle). G-

cells(gastrin-producing) are also numerous and are found mainly in

pyloric glands, as well as in the cardiac glands, located in the area of their body and bottom,

sometimes cervix. The gastrin they secrete stimulates the secretion of pepsinogen by the main

cells, hydrochloric acid - parietal cells, and also stimulates motility

stomach. With hypersecretion of gastric juice, a person experiences an increase in the number

G cells. In addition to gastrin, these cells secrete enkephalin, which is one of the

endogenous morphines. It is credited with the role of pain mediation. Less numerous

are P-, ECL-, D-, D1-, A- and X-cells. P-cells secrete bombesin,

stimulating the secretion of hydrochloric acid and pancreatic juice, rich in

enzymes, and also enhance the contraction of the smooth muscles of the gallbladder.ECL-

cells(enterochromaffin-like) are characterized by a variety of shapes and

are located mainly in the body and bottom of the fundic glands. These cells

produce histamine, which regulates the secretory activity of the parietal

chloride-secreting cells. D- and D1-cells are found mainly in

pyloric glands. They are producers of active polypeptides D-

cellssecrete somatostatin, which inhibits protein synthesis. D1 cells secrete

vasointestinal peptide (VIP), which dilates blood vessels and reduces

blood pressure, and also stimulates the release of pancreatic hormones

glands. A-cells synthesize glucagon, i.e. have a similar function to endocrine

A-cells of the pancreatic islets.

The submucosa of the stomach consists of loose fibrous irregular connective tissue containing a large number of elastic fibers. It contains the arterial and venous plexuses, a network of lymphatic vessels, and the submucous nerve plexus.

The muscular membrane of the stomach is relatively poorly developed in the area of its fundus, is well expressed in the body and reaches its greatest development in the pylorus. In the muscular membrane

Three layers are distinguished, formed by smooth muscle cells. The outer, longitudinal layer is a continuation of the longitudinal muscular layer of the esophagus. The middle - circular, also representing a continuation of the circular layer of the esophagus, reaches its greatest development in the pyloric region, where it forms the pyloric sphincter with a thickness of about 3-5 cm. The inner layer is represented by bundles of smooth muscle cells, having an oblique direction. Between the layers of the muscular membrane are the intermuscular nerve plexus and plexuses of lymphatic vessels.

The serous membrane of the stomach forms the outer part of its wall.

Vascularization. The arteries that feed the wall of the stomach pass through the serous and muscular membranes, giving them the corresponding branches, and then pass into a powerful plexus in the submucosa. The branches from this plexus penetrate through the muscular plate of the mucous membrane into its proper plate and form a second plexus there. Small arteries branch off from this plexus, continuing into blood capillaries that envelop the glands and provide nutrition to the epithelium of the stomach. From the blood capillaries lying in the mucous membrane, blood collects in small veins. Relatively large postcapillary veins of a star-shaped form (w. stellatae) pass directly under the epithelium. Damage to the epithelium of the stomach is usually accompanied by rupture of these veins and significant bleeding. The veins of the mucous membrane, gathering together, form a plexus located in the proper plate near the arterial plexus. The second venous plexus is located in the submucosa. All the veins of the stomach, starting with the veins lying in the mucous membrane, are equipped with valves. The lymphatic network of the stomach originates from the lymphatic capillaries, the blind ends of which are located directly under the epithelium of the gastric pits and glands in the proper plate of the mucous membrane. This network communicates with a wide-meshed network of lymphatic vessels located in the submucosa. Individual vessels extend from the lymphatic network, penetrating the muscular membrane. Lymphatic vessels from the plexuses lying between the muscular layers flow into them.

InnervationThe stomach has two sources of efferent

innervations: parasympathetic (from the vagus nerve) and sympathetic (from the border sympathetic trunk). Three nerve plexuses are located in the wall of the stomach: intermuscular, submucous and subserous. Nerve ganglia are few in number in the cardiac region, increasing in number and size in the direction of the pylorus.

The ganglia of the most powerful intermuscular plexus are built mainly from type I cells (Dogel's motor cells) and a small number of type II cells. The greatest number of type II cells is observed in the pyloric region of the stomach. The submucous plexus is poorly developed. Excitation of the vagus nerve leads to acceleration of stomach contraction and increased secretion of gastric juice by the glands. Excitation of the sympathetic nerves, on the contrary, causes a slowdown in the contractile activity of the stomach and a weakening of gastric secretion.

Afferent fibers form a sensory plexus located in the muscular membrane, the fibers of which provide receptor innervation of nerve nodes, smooth muscles, and connective tissue. Polyvalent receptors have been found in the stomach.

General characteristics of the glands of the gastric mucosa. Structure and functions of the pyloric and cardiac glands

The gastric mucosa contains many glands that open in groups into the gastric pits. Up to 4-5 glands open into each pit. These groups of glands are surrounded by layers of connective tissue with vessels that outline another of the relief formations of the mucous membrane - the gastric fields, which have a polygonal shape and a diameter of 1 to 16 mm

The surface of the mucous membrane is lined with a single-layer cylindrical epithelium. Each cell in the apical part contains a drop of mucus (mucin granules). In the basal part lies an oval nucleus and organelles. The main role of these cells is to produce mucus, which covers the mucous membrane with a thick layer and protects

from mechanical impact of coarse food particles and from chemical impact of gastric juice. The amount of mucus in the stomach increases sharply when irritants enter it: alcohol, mustard, acid. The rate of renewal of the superficial epithelium of the stomach is 3-4 days. The superficial epithelium reaches maximum differentiation and completes its life cycle in the apex area, where it is rejected into the lumen of the stomach. In addition, epithelial cells can be utilized without leaving the epithelial layer, by the mechanism of apoptosis. In recent years, it has been established that the superficial pit epithelium is capable of secreting prostaglandins under the influence of hydrochloric acid and under the action of damaging factors. Prostaglandins provide protection of the gastric mucosa from damaging factors by stimulating mucus formation, enhancing blood circulation, secretion of bicarbonates by epithelial cells, increasing the hydrophobicity of mucus, and also cytoprotective action. Mucus together with bicarbonates forms a mucous-bicarbonate barrier that protects the mucous membrane from the action of hydrochloric acid, pepsin and other chemical compounds. This barrier is easily destroyed under the influence of alcohol, aspirin and other drugs. Regeneration stimulants are gastrin of endocrine cells and epidermal growth factor coming from the salivary and pyloric glands.

Proper layer of the mucous membraneis represented by loose fibrous irregular connective tissue. It often contains clusters of lymphoid elements or solitary follicles, as well as numerous blood vessels.

The gastric glands are located in the proper layer of the mucous membrane. They are very closely spaced and the connective tissue between them is visible as thin layers. Three types of glands are located in the proper layer, corresponding to the zones of the stomach: cardiac, fundic and pyloric glands.

The structure of the mucous membrane in the pyloric part has some features:

The gastric pits here are deeper than in the body of the stomach and occupy about

half of the entire thickness of the mucous membrane. Near the exit from the stomach, this membrane has a well-defined annular fold. Its appearance is associated with the presence of a powerful circular layer in the muscular membrane, forming the pyloric sphincter. The latter regulates the flow of food from the stomach into the intestine.

Cardiac glands— simple tubular glands with highly branched terminal sections. The excretory ducts (necks) of these glands are short, lined with prismatic cells. The nuclei of the cells are flattened and lie at the base of the cells. Their cytoplasm is light. Mucus is revealed in it when specially stained with mucicarmine. Apparently, the secretory cells of these glands are identical to the cells lining the pyloric glands of the stomach and the cardiac glands of the esophagus. Dipeptidases have also been found in them. Sometimes, chief and parietal cells are found in small quantities in the cardiac glands.

Parietal cell. Localization, structure. Functions and their hormonal regulation

lining cell- a cell of the stomach that secretes hydrochloric acid andinterior Castle factor.Also called a parietal cell or parietal glandulocyte, parietal cells are located on the outer portion of the major (also called fundic) glands of the stomach, which make up the bulk of the glands lining the fundus, body, and intermedia of the stomach. No other cell in the human body ever comes into contact with such a strong acid (pH about 1).

Number of parietal cells (in millions): in men - from 960 to 1,260, on average - 1,090; in women - from 690 to 910, on average - 820.

The structure of the parietal cell is polarized: its opposite membranes differ sharply. Secretion of HCl by parietal cells occurs on their apical membrane, it is based on transmembrane transfer of hydrogen ions (protons) and is performedproton pump - N+/TO+-ATPase. After activation, the proton pump molecules are embedded in the membrane of the secretory canals of the parietal cell and transfer hydrogen ions from the cell to the lumen of the gland, exchanging them for potassium ions from the extracellular space. Ion transfer occurs due to the energy of ATP (34% of the parietal cell volume is occupied by ATP-synthesizing mitochondria). This process precedes the release of chlorine ions Cl from the cytosol of the parietal cell.-. Thus, hydrochloric acid is formed in the lumen of the secretory canal of the parietal cell. Due to the functioning of the proton pump, a significant concentration gradient of hydrogen ions is created and a significant difference is establishedpH between the cytosol of the parietal cell (pH 7.4) and the lumen of the secretory canalicle (pH about 1). The basolateral membrane contains a number of receptors for both stimulating and inhibitory ligands that regulate secretory activity. The parietal cell is closely associated withenterochromaffin-likecells,G-cells,gastrin-producing cells and D-cells producingsomatostatin.The proton pump is activated by stimulation of its receptors: gastrin G-receptors, acetylcholine M3-receptors, histamine H2-receptors. Receptors for somatostatin, prostaglandins, epidermal growth factor participate in the reverse process - inhibition of HCl secretion, including that stimulated by histamine(T.L.

Lapina).

Functional diagram of the parietal cell (Dubinskaya T.K. and others.) A) resting phase: 1 - secretory canals; 2 - tubulovesicles B) phase of hydrochloric acid secretion, formation of ion-exchange transport systems: 1

— secretory canals; 2 — ion channels; 3 —proton pump

The secretory activity of the parietal cell is provided by three main effector systems capable of synergism:

histamine activates N2-receptors, adenylate cyclase related

gastrin it works through G-receptors, associated with phospholipase C, phosphatidylinositol-splitting

acetylcholine, a neurotransmitter of the parasympathetic division of the autonomic nervous system, also acts through activation of the inositol cycle

Each of the three main stimulants (histamine, gastrin and acetylcholine) is capable of

independent effect.

Acetylcholine and gastrin enhance

the action of histamine. This effect,

most likely related to the influence

both mediators on

admissioncalcium.

Anticholinergic agents

reduce the effects of gastrin and

histamine.Blockers

N2-receptors slow down the action

gastrin and acetylcholine. Thus

Thus, the maximum secretory

parietal cell activity

is possible only under normal conditions

the functioning of all

stimulating receptors

mechanisms of regulation of secretion of hydrochloric acid in the stomach. The parietal cell is shown in blue, G is the gastrin receptor, H2— histamine receptor, M3- acetylcholine receptor.

Mechanisms of reduction

stomach acidity

Since acid is the most important factor in the formationulcers,erosion, developmentgastritis,then when treating such (acid-dependent) diseases it is important to achieve a decrease in acidity in the organs of the gastrointestinal tract. This can be achieved with the help of surgeryvagotomy,which consists of cutting the vagus nerve or its branches that stimulate the secretion of acid in the stomach, but most often various pharmacological agents are used for this. With the exception ofantacids,chemically neutralizing the already secreted acid, the remaining drugs act at the level of the parietal cells, inhibiting the secretion process in one way or another. The figure below schematically depicts a parietal cell, the mechanism of its regulation and the sites of application of the action of various secretion blockers and antacids:

Regulation of hydrochloric acid secretion and the site of action of secretion blockers

antacids Designations: M1R and M2R - acetylcholine receptors, GR - gastrin receptors, H2R — histamine receptors, PP — proton pump, BCC —antagonist calcium (Ca blocker2+-receptors)

Enteroendocrine cells of the stomach and intestine. Types and localization of endocrine cells, their hormones, targets and effects

Enteroendocrine cells are found in the neck and base of the gastric glands.

Endocrinocytes of the pyloric glands and cardiac glands:

D-cells (found only in the pyloric): produce somatostatin,

which inhibits exocrine and endocrine functions of the gastrointestinal tract.

D1 cells (found only in the pyloric cells): produce VIP

Endocrinocytes of the stomach's own glands:

ECL cells: produce histamine, which affects gastrointestinal motility and vascular health and stimulates the secretion of HCl by parietal cells.

P-cells: produce bombesin, which stimulates the secretion of HCl, pancreatic juice and stimulates gallbladder motility.

Muscular membrane of the stomach. Structure, innervation, regulation of motility

The muscular coat of the stomach consists of three layers. The outer longitudinal layer is a continuation of the same layer of the esophagus. At the lesser curvature it reaches its greatest thickness, and at the greater curvature and the fundus of the stomach it becomes thinner, but occupies a larger surface. The middle circular layer is also a continuation of the same layer of the esophagus and completely covers the stomach. At the exit from the stomach (at the level of the pylorus) it forms a thickening, which is called the compressor, or sphincter, of the pylorus (m. sphincter pylori). The deep layer consists of oblique fibers (fibrae obliquae), the bundles of which form separate groups. In the area of the entrance to the stomach, the bundles cover it in a loop, passing to the anterior and posterior surfaces of the body of the stomach. Contraction of the muscular loop causes the presence of the cardiac notch.

Regulation of peristalsis

Nervous regulation of the stomach is carried out by parasympathetic and sympathetic innervation. The vagus nerve carries excitatory stimuli to the stomach, while the sympathetic nerve carries mainly inhibitory stimuli. The celiac and vagus nerves carrycentral nervous systemafferent fibers from numerous receptorsdigestive tract.The centers of stomach movements are located in the medulla oblongata and midbrain.

Regulation of gastric peristalsis is also carried out by the overlyingdepartments brain,right up to the cerebral cortex. This is evident from the fact that conditioned reflex stimuli (the sight and smell of food) influence the contraction of the stomach muscles.

It should be noted that the stomach is capable of contracting even after all the nerves leading to it have been cut, since it has automatism, i.e. the ability to contract under the influence of impulses arising within it.

Regulation of gastric secretion

The vagus nerve, which stimulates the secretion of the gastric glands, occupies a dominant position in the regulation of gastric secretion. If the experiment of imaginary feeding is carried out on an animal whose vagus nerves are cut below the place where the branches of theto the heartand light, then the secretion of the gastric glands ceases. Irritation by electric current of the peripheral end of the cut nerve stimulates secretion. The sympathetic fibers running in the trunk of the vagus nerve can be attributed to an inhibitory effect on the secretion of the stomach. It has now been proven that the splanchnic nerve is also of great importance in secretory activity. It has also been proven that the centripetal fibers, which are of great importance for information, also pass through the vagus and splanchnic nerves.cerebral cortexabout the processes in the stomach.

An empty stomach is in a uniformly tense tonic contraction and its walls are in a collapsed state. The first portions of food entering the stomach push its walls apart and come into close contact with the mucous membrane. The next portions of food are placed on the first and the stomach is filled with food layer by layer. With eachthe act of swallowingthe walls of the stomach relax somewhat and allow a new portion of food to pass through.

Slow tonic contractions of the stomach muscles sometimes compress its contents, sometimes release this pressure and gradually mix it. In the pyloric part of the stomach, these contractions reach great strength and mix the food gruel well.

The oblique muscles of the stomach, when contracted, bring the entrance and exit of the stomach closer together, forming a fold of the mucous membrane from one opening to the other in the form of a short and semi-closed tube, which is called the "gastric track." It can be seen with fluoroscopy. Liquid and semi-liquid food can pass through this tube directly from the esophagus to the intestine. There is also a constriction of the stomach along the line between the fundus and the pylorus, which gives the stomach an hourglass shape. The physiological significance of this spasm of the circular muscle of the stomach remains unknown, but clinically it is known as a symptom of gastric disease.

Stomach. Nervous plexuses, sympathetic and parasympathetic innervation, regulation of function

InnervationThe stomach has two sources of efferent innervation: parasympathetic (from the vagus nerve) and sympathetic (from the border sympathetic trunk).

There are three nerve plexuses located in the wall of the stomach: intermuscular, submucosal and subserous.

The endocrine system of the stomach includes endocrine (enteroendocrine) cells of the gastric mucosa and glands (see question 33).

The influence of hormones on the main processes in the stomach:

Secretion of mucus and bicarbonate in the stomach. Stimulated by: gastrin, gastrin-releasing hormone, glucagon, prostaglandin E, epidermal growth factor. Suppresses somatostatin.

Secretion of pepsin and hydrochloric acid in the stomach. Stimulate acetylcholine, histamine, gastrin. Suppress somatostatin and gastric inhibitory peptide.

Gastric motility. Stimulates acetylcholine, motilin, VIP. Suppresses somatostatin, cholecystokinin, adrenaline, noradrenaline, gastric inhibitory peptide.

Features of the structure of the mucous membrane of the small and large intestine

Small intestineIt is conventionally divided into 3 sections: the duodenum, the jejunum and the ileum. The length of the small intestine is 6 meters, and in people who eat mainly plant foods, it can reach 12 meters.

The wall of the small intestine consists of 4 membranes: mucous, submucosa, muscular and serous.

The mucous membrane of the small intestine has its own relief, which includes intestinal folds, intestinal villi and intestinal crypts.

Intestinal foldsare formed by the mucous and submucous membranes and are

circular character. Circular folds are highest in the duodenum.

the course of the small intestine, the height of the circular folds decreases. Intestinal

villiare finger-shaped outgrowths of the mucous membrane. In the duodenum

In the intestine, the intestinal villi are short and wide, and then along the small intestine they

become tall and thin. The height of the villi in different parts of the intestine reaches

0.2 - 1.5 mm. Between the villi, 3-4 intestinal crypts open. Intestinal

cryptsare depressions of the epithelium into the proper layer of the mucous membrane, which increase in size as they move through the small intestine.

The surface of the small intestine mucosa (including the surface of the villi and crypts) is covered with a single-layer prismatic epithelium. The lifespan of the intestinal epithelium is from 24 to 72 hours. Solid food accelerates the death of cells that produce chalons, which causes an increase in the proliferative activity of the epithelial cells of the crypts. According to modern concepts, the generative zone of the intestinal epithelium is the bottom of the crypts, where 12-14% of all epithelial cells are in the synthetic period. In the process of life, epithelial cells gradually move from the depth of the crypt to the top of the villus and, at the same time, perform numerous functions: they multiply, absorb substances digested in the intestine, secrete mucus and enzymes into the intestinal lumen. The release of enzymes in the intestine occurs mainly along with the death of glandular cells. The cells, rising to the top of the villus, are rejected and disintegrate in the intestinal lumen, where they release their enzymes into the digestive chyme.

Among intestinal enterocytes, there are always intraepithelial lymphocytes, which penetrate here from the proper plate and belong to T-lymphocytes (cytotoxic, memory T-cells and natural killers). The content of intraepithelial lymphocytes increases with various diseases and immune disorders.

Intestinal epitheliumincludes several types of cellular elements

(enterocytes): bordered, goblet, non-bordered, tufted, endocrine, M-cells, Paneth cells.

Border cells(columnar) make up the main population of intestinal epithelial cells. These cells are prismatic, with numerous microvilli on the apical surface that have the ability to contract slowly. The fact is that microvilli contain thin filaments and microtubules. Each microvilli has a bundle of actin microfilaments in the center that are connected on one side to the plasma membrane of the apex of the villus, and at the base they are connected to the terminal network - horizontally oriented microfilaments. This complex ensures the contraction of microvilli during absorption. There are 800 to 1800 microvilli on the surface of the border cells of the villi, and only 225 microvilli on the surface of the border cells of the crypts. These microvilli form a striated border. The microvilli are covered with a thick layer of glycocalyx on the surface. Polar arrangement of organelles is characteristic of border cells. The nucleus is located in the basal part, above it is the Golgi apparatus. Mitochondria are also localized at the apical pole. They have a well-developed granular and agranular endoplasmic reticulum. Between the cells are endplates that close the intercellular space. In the apical part of the cell is a well-defined terminal layer, which consists of a network of filaments located parallel to the cell surface. The terminal network contains actin

myosin microfilaments and is connected to intercellular contacts on the lateral surfaces of the apical parts of enterocytes. With the participation of microfilaments in the terminal network, the closure of intercellular gaps between enterocytes is ensured, which prevents the entry of various substances into them during digestion. The presence of microvilli increases the surface of cells by 40 times, due to which the total surface of the small intestine increases and reaches 500 m. On the surface

Microvilli contain numerous enzymes that provide hydrolytic breakdown of molecules that are not destroyed by enzymes of gastric and intestinal juice (phosphatases, nucleoside diphosphatases, aminopeptidases, etc.). This mechanism is called membrane or parietal digestion.

Membrane digestion not only a very effective mechanism for breaking down small molecules, but also the most advanced mechanism combining hydrolysis and transport processes. The enzymes located on the membranes of the microvilli have a dual origin: they are partly adsorbed from the chyme, and partly synthesized in the granular endoplasmic reticulum of the limbic cells. During membrane digestion, 80-90% of peptide and glucosidic bonds and 55-60% of triglycerides are broken down. The presence of microvilli turns the intestinal surface into a kind of porous catalyst. It is believed that microvilli are capable of contracting and relaxing, which affects the processes of membrane digestion. The presence of glycocalyx and very small spaces between the microvilli (15-20 μm) ensures the sterility of digestion.

After cleavage, the hydrolysis products penetrate the membrane of microvilli, which has the ability of active and passive transport.

When fats are absorbed, they are first broken down into low-molecular compounds, and then fats are resynthesized inside the Golgi apparatus and in the canals of the granular endoplasmic reticulum. This entire complex is transported to the lateral surface of the cell. Fats are removed into the intercellular space by exocytosis.

The breakdown of polypeptide and polysaccharide chains occurs under the action of hydrolytic enzymes localized in the plasma membrane of microvilli. Amino acids and carbohydrates penetrate the cell using active transport mechanisms, i.e. using energy. They are then excreted into the intercellular space.

The main functions of the border cells, which are located on the villi and crypts, are parietal digestion, which occurs several times more intensively than intracavitary digestion, and is accompanied by the breakdown of organic compounds to final products and the absorption of hydrolysis products.

Goblet cellsare located singly between the bordered enterocytes. Their content increases in the direction from the duodenum to the large intestine. In the crypt epithelium, there are slightly more goblet cells than in the villus epithelium. These are typical mucous cells. They exhibit cyclic changes associated with the accumulation and secretion of mucus. In the mucus accumulation phase, the nuclei of these cells are located at the base of the cells and have an irregular or even triangular shape. Organelles (Golgi apparatus, mitochondria) are located near the nucleus and are well developed. At the same time, the cytoplasm is filled with mucus droplets. After the secretion is released, the cell decreases in size, the nucleus decreases, and the cytoplasm is freed from mucus. These cells produce mucus, which is necessary for moisturizing the surface of the mucous membrane, which, on the one hand, protects the mucous membrane from mechanical damage, and on the other, facilitates the movement of food particles. In addition, mucus protects against infectious damage and regulates the bacterial flora of the intestine.

M-cellsare located in the epithelium in the area of localization of lymphoid follicles (both group and single). These cells have a flattened shape, a small number of microvilli. At the apical end of these cells there are numerous microfolds, so they are called "cells with microfolds". With the help of microfolds, they are able to capture macromolecules from the intestinal lumen and form endocytic vesicles that are transported to the plasma membrane and released into the intercellular space, and then into the proper plate of the mucous membrane. After that, t. propria lymphocytes, stimulated by the antigen, migrate to the lymph nodes, where they proliferate and enter the blood. After circulation in the peripheral blood, they again populate the proper plate of the mucous membrane, where B-lymphocytes turn into plasma cells that secrete IgA. Thus, antigens coming from the intestinal cavity attract lymphocytes, which stimulates the immune response in the intestinal lymphoid tissue. The cytoskeleton is very poorly developed in M-cells, so they are easily deformed under the influence of interepithelial lymphocytes. These cells do not have lysosomes, so they transport various antigens using vesicles without changing. They are devoid of glycocalyx. Lymphocytes are located in the pockets formed by the folds.

Tufted cellshave long microvilli protruding into the intestinal lumen on their surface. The cytoplasm of these cells contains many mitochondria and tubules of the smooth endoplasmic reticulum. Their apical part is very narrow. It is assumed that these cells function as chemoreceptors and, possibly, carry out selective absorption.

Paneth cells(exocrinocytes with acidophilic granularity) lie at the bottom of the crypts in groups or singly. In their apical part are dense oxyphilic-stained granules. These granules are easily stained with eosin in a bright red color, dissolve in acids, but are resistant to alkalis. These cells contain a large amount of zinc, as well as enzymes (acid phosphatase, dehydrogenases and dipeptidases. Organelles are moderately developed (the Golgi apparatus is best developed). Paneth cells perform an antibacterial function, which is associated with the production of lysozyme by these cells, which destroys the cell walls of bacteria and protozoa. These cells are capable of active phagocytosis of microorganisms. Due to these properties, Paneth cells regulate the intestinal microflora. In a number of diseases, the number of these cells decreases. In recent years, IgA and IgG have been identified in these cells. In addition, these cells produce dipeptidases that break down dipeptides into amino acids. It is assumed that their secret neutralizes hydrochloric acid contained in the chyme.

Endocrine cellsbelong to the diffuse endocrine system. All endocrine cells are characterized by

the presence of secretory granules in the basal part under the nucleus, which is why they are called basal-granular. On the apical surface there are microvilli, which apparently contain receptors that react to changes in pH or to the absence of amino acids in the chyme of the stomach. Endocrine cells are primarily paracrine. They secrete their secretion through the basal and basal-lateral surface of the cells into the intercellular space, directly influencing neighboring cells, nerve endings, smooth muscle cells, and vascular walls. Some of the hormones of these cells are secreted into the blood.

The most common endocrine cells in the small intestine are the following: EC cells (secreting serotonin, motilin and substance P), A cells

(producing enteroglucagon), S cells (producing secretin), I cells (producing cholecystokinin), G cells (producing gastrin), D cells (producing somatostatin), D1 cells (secreting vasoactive intestinal polypeptide). The cells of the diffuse endocrine system are distributed unevenly in the small intestine: the greatest number of them is contained in the wall of the duodenum. Thus, in the duodenum there are 150 endocrine cells per 100 crypts, and in the jejunum and ileum - only 60 cells.

Borderless or borderless cellsare located in the lower parts of the crypts. Mitoses are often found in them. According to modern concepts, borderless cells are poorly differentiated cells and act as stem cells for the intestinal epithelium.

Proper layer of the mucous membraneis made of loose, unformed connective tissue. This layer makes up the bulk of the villi, and lies in the form of thin layers between the crypts. The connective tissue here contains many reticular fibers and reticular cells and is distinguished by its great looseness. In this layer, in the villi under the epithelium, there is a plexus of blood vessels, and in the center of the villi there is a lymphatic capillary. These vessels receive substances that are absorbed in the intestine and transported through the epithelium and connective tissue t.propria and through the capillary wall. The products of protein and carbohydrate hydrolysis are absorbed into the blood capillaries, and fats - into the lymphatic capillaries.

Numerous lymphocytes are located in the proper layer of the mucous membrane,

which lie either singly or form clusters in the form of single solitary or grouped lymphoid follicles. Large lymphoid clusters are called Peyrov's patches. Lymphoid follicles can even penetrate the submucosa. Peyrov's patches are mainly located in the ileum, less often in other parts of the small intestine. The highest content of Peyrov's patches is found during puberty (about 250), in adults their number stabilizes and decreases sharply in old age (50-100). All lymphocytes lying in t.propria (singly and grouped) form the intestinal-associated lymphoid system, containing up to 40% of immune cells (effectors). In addition, at present, the lymphoid tissue of the small intestinal wall is equated with the bursa of Fabricius. Eosinophils, neutrophils, plasma cells and other cellular elements are constantly found in the lamina propria.

Muscular plate (muscular layer) of the mucous membraneconsists of two layers of smooth muscle cells: an internal circular layer and an external longitudinal layer. From the internal layer, individual muscle cells penetrate into the thickness of the villi and facilitate the contraction of the villi and the extrusion of blood and lymph, rich in absorbed products from the intestine. Such contractions occur several times a minute.

The mucous membrane of the large intestine has a characteristic relief, represented by intestinal crypts and intestinal folds. Intestinal villi exist only until the 4th month of uterine life.

Intestinal foldsThe large intestine is formed by the mucous and submucous membranes and is crescent-shaped.

Intestinal cryptsThe crypts of the large intestine are depressions of the intestinal epithelium into the proper layer of the mucous membrane (Luberkin's glands). The crypts of the large intestine are more developed than in the small intestine, are located more often, they are longer and wider.

Intestinal crypts and intestinal folds significantly increase the total surface area of the large intestine.

The surface of the mucous membrane of the large intestine is covered with a single-layer cylindrical epithelium, which includes several types of cellular elements: columnar (bordered) exocrine cells, goblet exocrine cells and endocrine cells.

Bordered (columnar) exocrine cellsresemble in their structure the bordered cells of the small intestine, but contain fewer microvilli, and the striated border is thinner. Bordered cells are formed at the bottom of the crypts, from where they migrate and in the process produce glycoproteins, initially accumulating in the apical part of the cell, providing for absorption processes.

Goblet cellsare the main population of intestinal epithelial cells. Their number increases along the large intestine. These cells secrete mucus, which protects the mucous membrane from mechanical damage and promotes the formation of feces. They are also formed at the bottom of the crypts.

Endocrine cellsbelong to the diffuse endocrine system. Their main mass is located at the bottom of the crypts. Their number is significantly less than in the small intestine. The main population is EC cells and ECL cells.

Borderless cellsare poorly differentiated cells and are located at the bottom of the crypts. Mitoses are often found in them. These cells are considered to be stem cells, due to which the remaining cells of the epithelium of the large intestine are formed.

Cells with acidophilic granularity (Paneth cells)are found in small quantities.

The rate of epithelial renewal is 4-6 days.

Proper lamina of the mucous membrane (t.propria mucosae)is made of loose, unformed connective tissue containing a large number of reticular fibers that form a dense network. It is located between the crypts. In this layer lie more than 20,000 solitary lymphatic follicles, which often even enter the submucosa.

Muscular plate of the mucous membrane (t.muscularis mucosae)is made of smooth muscle tissue and forms 2 layers: an internal circular layer and an external longitudinal layer. This layer is more pronounced than in the small intestine.

Intestinal crypt epithelium. Cellular composition, cell functions

The intestinal crypts of the small intestine are tubular depressions of the epithelium lying in the proper plate of its mucous membrane, and the mouth opens into

lumen between the villi. The epithelial lining of the intestinal crypts contains the following types of cells: border cells (or M cells), goblet cells, endocrine cells,

intestinal cells with acidophilic granularity (Paneth cells) and undifferentiated epithelial cells.

Bordered:Intestinal enterocytes with a striated border make up the bulk of the epithelial lining of the crypts. Question #39. And their variety is M-cells (in

ileal), - there are few villi on the apical surface - chemoreceptors, register pH, are located in those places where there are lymph nodes in the proper plate of the mucous membrane. The cytolemma has microfolds, with the help of which these cells capture antigens from the intestinal lumen, form endocytic vesicles that enter the proper plate of the mucous membrane, where they come into contact with lymphocytes and stimulate them to differentiate.

Goblet cells (mucocytes):secrete mucin, on the cell surface they interact with water, forming mucus.

Enteroendocrine:synthesis of hormones that regulate motility, secretion, and peristalsis.

Cl. Paneta(exocrinocytes with acidophilic granules): only at the bottom of the crypts, they break down dipeptidases to a\k, neutralize HCl, synthesize antibiotic-like compounds that prevent putrefaction processes at the bottom of the crypts. (They secrete a bactericidal substance - lysozyme, which destroys the bacterial membrane; a polypeptide antibiotic - depheisin - increases the permeability of the membrane of bacteria, parasites; tumor necrosis factor α).

Undifferentiated epithelial cells(stem, borderless) only in crypts - source of physiological regeneration of crypt epithelial cells and villi, life span 3 days.

218. Villi of the small intestine, structure. Cellular composition and renewal of the epithelium

The wall of the small intestine includes the mucous membrane, submucosa, muscular and serous membranes. The mucous membrane consists of epithelium, connective tissue and smooth muscle plates. The relief of the mucous membrane is uneven due to the presence of folds, villi and crypts. Intestinal villi are outgrowths of the mucous membrane into the lumen of the small intestine. Intestinal crypts are tubular depressions of the epithelium in the proper plate of the mucous membrane. The number of intestinal villi in the human small intestine is estimated at several million.

The surface of the villi is formed by a single-layer prismatic bordered epithelium, and the base is loose fibrous connective tissue containing blood capillaries and one lymphatic capillary. The stroma of the villi contains smooth muscle cells, which provide up to 4-6 contractions of the villus per minute, as well as plasma and mast cells, B- and T-lymphocytes, macrophages. Shortening of the villi, compression of the lumen of their capillaries and rhythmic pushing of blood in the capillaries of the stroma of the villi are of significant importance in the processes of absorption and transport of nutrients. In the processes of absorption, an active role belongs, first of all, to the epithelium covering the villi, which forms a single system with the epithelium of the crypt. The absorption of nutrients occurs only after the enzymatic breakdown of proteins into amino acids, fats into monoglycerides, fatty acids, glycerol and carbohydrates into glucose. Amino acids and glucose, having passed through the epithelial cells of the villi and undergoing further transformations, enter the blood capillaries of the villi. The absorption of fats is also accompanied by complex transformations in the epithelial cells with the subsequent entry of lipids into the lymphatic

capillaries. The intestinal crypts contain cambial and stem cells, which are responsible for the renewal of the cellular composition of the crypt and villi epithelium. Mitotic figures are found mainly in the middle part of the crypts. In the intestinal epithelium, the locations of poorly differentiated proliferating and specialized functionally active cells are clearly delineated. During development, as a result of divergent differentiation, several cellular differentiates with different structural and functional properties are formed from a stem cell, which is common to all cells: columnar epithelial cells (bordered, absorptive), goblet exocrine cells (mucous), Paneth cells, and endocrine cells. These cells migrate from the site of proliferation in two directions. The first two types shift to the epithelium covering the villi. Paneth cells and endocrine cells migrate to the bottom of the crypts.

The small intestine consists of three sections: the duodenum, jejunum, and ileum. In the small intestine, all types of nutrients - proteins, fats, and carbohydrates - undergo chemical processing.

The digestion of proteins involves enzymes of pancreatic juice (trypsin, chymotrypsin, collagenase, elastase, carboxylase) and intestinal juice (aminopeptidase, leucine aminopeptidase, alanine aminopeptidase, tripeptidases, dipeptidases, enterokinase).

Enterokinase is produced by the cells of the intestinal mucosa in an inactive form (kinazogen), provides for the conversion of the inactive enzyme trypsinogen into active trypsin. Peptidases provide further sequential hydrolysis of peptides, which began in the stomach, to free amino acids, which are absorbed by intestinal epithelial cells and enter the blood.

The digestion of carbohydrates also involves enzymes of the pancreas and intestinal juice: β-amylase, amylo-1,6-glucosidase, oligo-1,6-glucosidase, maltase (α-glucosidase), lactase, which break down polysaccharides and disaccharides into simple sugars (monosaccharides) - glucose, fructose, galactose, absorbed by intestinal epithelial cells and entering the blood.

Digestion of fats is carried out by pancreatic lipases, which break down triglycerides, and intestinal lipase, which ensures hydrolytic breakdown of monoglycerides. The products of fat breakdown in the intestine are fatty acids, glycerol, monoglycerides, which enter the blood and, for the most part, the lymphatic capillaries.

In the small intestine, the process of absorption of the breakdown products of proteins, fats and carbohydrates into the blood and lymphatic vessels occurs. In addition, the intestine performs a mechanical function: it pushes the chyme in the caudal direction. This function is carried out due to peristaltic contractions of the muscular membrane of the intestine. The endocrine function, performed by special secretory cells, consists of the production of biologically active substances - serotonin, histamine, motilin, secretin, enteroglucagon, cholecystokinin, pancreozymin, gastrin and gastrin inhibitor.

Structure.The wall of the small intestine is made up of the mucous membrane, submucosa, muscular and serous membranes.

The inner surface of the small intestine has a characteristic relief due to the presence of a number of formations - circular folds, villi and crypts (intestinal glands of Lieberkühn). These structures increase the overall surface of the small intestine, which helps to perform its main functions of digestion. Intestinal villi and crypts are the main structural and functional units of the mucous membrane of the small intestine.

Circular foldsformed by the mucous membrane and submucosa.

Intestinal villiare finger- or leaf-shaped protrusions of the mucous membrane that freely protrude into the lumen of the small intestine.

The shape of the villi in newborns and in the early postnatal period is finger-shaped, and in adults it is flattened - leaf-shaped. Flattened villi have two surfaces - cranial and caudal - and two edges (ridges).

The number of villi in the small intestine is very large. Most of them are in the duodenum and jejunum (22-40 villi per 1 mm2), somewhat less - in the ileum (18-31 villi per 1 mm2). In the duodenum, the villi are wide and short (their height is 0.2-0.5 mm), in the jejunum and ileum they are somewhat thinner, but higher (up to 0.5-1.5 mm). Structural elements of all layers of the mucous membrane participate in the formation of each villus.

Intestinal crypts(glands of Lieberkühn) are epithelial depressions in the form of numerous tubes lying in the proper plate of the mucous membrane. Their mouths open into the lumen between the villi. There are up to 100 crypts per 1 mm2 of intestinal surface, and in total there are more than 150 million crypts in the small intestine. Each crypt is about 0.25-0.5 mm long and up to 0.07 mm in diameter. The total area of crypts in the small intestine is about 14 m2.

Mucous membraneThe small intestine consists of a single-layer columnar bordered epithelium, a proper layer of the mucous membrane and a muscular layer of the mucous membrane

The epithelial layer of the small intestine contains four main cell populations:

columnar epithelial cells,

goblet exocrine cells,

Paneth cells, or exocrine cells with acidophilic granules,

endocrinocytes or K-cells (Kulchitsky cells),

as well as M-cells (with microfolds), which are a modification of columnar epithelial cells.

The source of development of these populations are stem cells located at the bottom of the crypts, from which committed progenitor cells are initially formed, which divide by mitosis and differentiate into a specific type of epithelial cells. Progenitor cells are also located in the crypts, and in the process of differentiation they move towards the top of the villus, where differentiated cells incapable of division are located. Here they finish their life cycle and are exfoliated. The entire cycle of epithelial cell renewal in humans is 5-6 days.

The epithelium of the crypts and villi is a single system in which several cell compartments at different stages of differentiation can be distinguished, and each compartment consists of about 7-10 cell layers. All cells of the intestinal crypt represent a single clone, i.e. they are descendants of a single stem cell. The first compartment is represented by 1-5 rows of cells in the basal part of the crypts - committed progenitor cells of all four types of cells - columnar, goblet, Paneth and endocrine. Paneth cells, differentiating from stem cells and progenitor cells, do not move, but remain at the bottom of the crypts. The remaining cells after 3-4 divisions of the progenitor cells in the crypts (the dividing transit population, constituting the 5th-15th rows of cells) move to the villus, where they make up the transit non-dividing population and the population of differentiated cells.

Physiological regeneration(renewal) of the epithelium in the crypt-villus complex is provided by mitotic division of precursor cells. A similar mechanism underlies reparative regeneration, and the epithelial defect is eliminated by cell proliferation.

In addition to epithelial cells, the epithelial layer may contain lymphocytes located in the intercellular spaces and then migrating to l. propria and from there to the lymph capillaries. Lymphocytes are stimulated by antigens entering the intestine and play an important role in the immune defense of the intestine.

Bordered cells of the intestinal epithelium. Structure, functioning

The bordered cells (enterocytes) are prismatic in shape and have a large number of microvilli on the apical surface, forming a striated (brush, or absorption) border. The microvilli are covered with a glycocalyx on the outside, with microtubules and actin contractile microfilaments located longitudinally in the center, providing contraction during absorption. The glycocalyx and cytolemma of the microvilli contain enzymes for the breakdown and transport of nutrients into the cell cytoplasm: aminopeptidases; glycosidases (maltase, lactase), completing the breakdown of proteins and carbohydrates; enterokinase, which converts trypsinogen into trypsin; lipase - digestion of fats. In the apical part of the cells on the lateral surfaces there are tight contacts with neighboring cells, which ensures the tightness of the epithelium. Closer to the basal part of the cells there are desmosomes and intermediate contacts between the cells. The cytoplasm contains smooth and granular ER, Golgi apparatus, mitochondria and lysosomes.

Functions:

1) produce digestive enzymes that participate in parietal digestion;

participation in parietal digestion;

selective absorption of breakdown products of proteins, fats and carbohydrates, vitamins and chemical elements (Ca, Fe) into the blood and lymph.

During parietal digestion, lumps of dense gel called flocculi are formed from the parietal mucus, which adsorb digestive enzymes in large quantities. The concentration of digestive enzymes on the surface of the flocculi significantly increases the efficiency of parietal digestion compared to cavity digestion, in which enzymes work

the intestinal lumen in a solution called chyme.

Nervous system of the digestive tract. Localization of plexuses. Sympathetic and parasympathetic innervation.

Plexus:

Intermuscular plexus (Auerbach's) - located in the muscular membrane of the digestive tract; necessary for controlling the motility of the digestive tract.

Submucous nerve plexus (Meissner's) - in the submucosa; controls the smooth muscle cells of the muscular layer of the mucosa and the secretion of glands of the mucous and submucosa.

Parasympathetic innervation:

The pathway consists of two neurons, both cholinergic, muscarinic receptors:

The body of the first neuron in the autonomic nucleus of the vagus nerve (for the esophagus, stomach, duodenum, pancreas, gallbladder); in the parasympathetic nucleus of the sacral region (for the caudal region); form synapses with the second neuron of the motor pathway.

The cell body of the second neuron is a Dogel cell of type 1. Their axons form endings on SMCs and glandular cells.

Sympathetic innervation:

A neural chain contains either 2 or 3 neurons:

The first neuron is cholinergic, located in the autonomic nucleus of the lateral horn of the spinal cord.

The second neuron is located in the ganglia of the sympathetic trunk and has an adrenergic nature (norepinephrine). Its axons enter the organs of the digestive tract and innervate glandular cells and SMC (two-neuron chain).

The axons of the second neuron form synapses with intramural neurons (a three-neuron chain); synapses are formed with Dogel cells of the 1st type.

Sensory innervation of their two neurons: sensory - Dogel cell type 2.

Immune defense in the digestive system. Structures, its components.

Tonsils. Localization, structure, meaning.

Tonsils are a cluster of lymphoid tissue in the folds of the mucous membrane. Pirogov's lymphoepithelial pharyngeal ring is part of the lymphoid apparatus of the digestive tract on the border of the oral cavity and pharynx. Includes:

Palatine tonsils- located between the palatine arches; enclosed in a connective tissue capsule.

a) epithelium - multilayered flat nonkeratinizing, covers the surface of the tonsil and projects into the lamina propria, forming 10-20 deep branching crypts. Sharply infiltrated (especially in the crypts) by lymphocytes, macrophages and plasma cells, contains dendritic antigen-presenting cells.

b) the proper plate contains:

-lymphatic nodules with large germinal centers.

- internodal diffuse lymphoid tissue with postcapillary venules (with high endothelium), which carry out hemato-tissue exchange of lymphocytes.

supranodular (subepithelial) connective tissue,

infiltrated by lymphocytes and plasma cells.

Lingual tonsilis located in the mucous membrane of the root of the tongue. It is covered with a multilayered flat nonkeratinizing epithelium, forming 35-100 short and weakly branching crypts, into the lumen of which the ducts of the mucous salivary glands open. Each crypt is surrounded by lymphoid tissue (diffuse and nodules), together with which it forms a structural and functional unit of the tonsil - the lingual follicle, delimited from the neighboring ones by a thin connective tissue capsule. The epithelium of the crypts is infiltrated with lymphocytes.

Pharyngeal tonsilis located on the back surface of the nasopharynx. It is covered with a single-layer multi-row prismatic ciliated epithelium, which is infiltrated with lymphocytes and macrophages and forms folds. In its own plate - lymphoid tissue (diffuse and nodules). The tonsil is surrounded by a capsule of dense connective tissue, behind which lie numerous terminal sections of mixed protein-mucous glands, the secretion of which is excreted into the space between the folds.

Tubal tonsils- small accumulations of lymphoid tissue in the area of the pharyngeal opening of the auditory tube. Covered with a single-layer multi-row prismatic ciliated epithelium and are very similar in structure to the pharyngeal.

Liver. Cell types: localization, structure, function.

Main cell types:

Hepatocytes-Polyploidy is typical for cells, the nucleus has 1-2 nucleoli, usually located in the center of the cell. Granular and smooth ER is well developed, there are many mitochondria, elements of the Golgi complex are present in various parts of the cell. Cells contain lysiosomes and peroxisomes. Oxidative enzymes peroxisomes-aminooxidase, catalase, urate oxidase. Oxygen is utilized in peroxisomes and mitochondria. Numerous inclusions are present in the cytoplasm of the cell, mainly glycogen. Two poles are distinguished in the cell: sinusoidal and biliary. The sinusoidal pole faces the Disse space, it has microvilli that participate in the transport of substances from the blood to hepatocytes and back. The biliary pole also has microvilli, this facilitates the excretion of bile components. Bile capillaries are formed at the points of contact of the biliary poles of two hepatocytes.

Cholangiocytes-epithelial cells of the intrahepatic bile ducts. They participate in the transport of proteins and actively secrete water and electrolytes.

Stem cells-Cholangiocytes and hepatocytes are growing cell populations. Their stem cells are oval cells located in the bile ducts.

Sinusoidal cells of the liver:

Endothelial cells-Distinguishing features: absence of a typical basement membrane, presence of fenestrae, ability to endocytosis. Cells contact with the help of numerous processes, separating the lumen of the sinusoid from the Disse space. The nucleus is located along the cell membrane from the Disse space, the Golgi complex is between the nucleus and the lumen of the sinusoid. There are many pinocytotic vesicles and lysosomes in the cytoplasm. Endocytosis of all types of molecules with a diameter of no more than 0.1 μm.

Von Kupffer cells-belong to the mononuclear phagocyte system, are located in the sinusoid, processes between endothelial cells. The main place of localization is the periportal region of the liver. In their cytoplasm there are lysosomes with high

peroxidase activity, phagosomes, pigments, hemoglobin inclusions. The cells remove foreign material, fibrin, excess activated coagulation factors from the blood, participate in the phagocytosis of aging and damaged erythrocytes, and the exchange of iron and hemoglobin. Iron from destroyed erythrocytes in the form of hemosiderin accumulates for subsequent use in the synthesis of hemoglobin.

Pit cells -lymphocytes, located on or between endothelial cells. NK cells, act against tumor and virus-infected cells.

Ito cells (lipocytes, fat-storing cells)-have a branched shape,

are located in the Disse space or between hepatocytes. In hepatocytes, retinol esters are converted to retinol and a complex of vitamin A with retinol-binding protein is formed. The complex is secreted into the Disse space, from where it is deposited by Ito cells.

Liver. Structural organization. Hepatic and portal lobules, hepatic acinus.

Classic liver slice- hexanal form, in the center - the central vein, the basis is the blood flow. Between the strands of hepatocytes lie sinusoids. In the area of the junctions of several classical lobules is the portal zone.

Portal lobule- triangular shape, based on the outflow of blood. In the center is a triad (tetrad) - interlobular artery, interlobular vein, interlobular lymphatic capillary, cholangiolum. The vertices of the triangle are the central zone. The portal lobule more fully reflects the exocrine function of the liver associated with the outflow of bile.

Acinus- a rhombus, its two vertices are the central vein, the other two are the portal zone.

Liver. Structure of the classical lobule. Portal zone. (see above)

226. Features of the structure of intralobular capillaries of the liver (hepatic sinusoids).

Presinusoidal space of Disse.

Liver sinusoids-anastomosing voids between anastomosing strands of hepatocytes. In the sinusoids, mixed blood comes from the hepatic artery and portal vein (for cellular composition, see 223)

Disse Space- the space between hepatocytes and endothelial cells of the sinusoids. The microvilli of the hepatocytes face the space. The reticulin fibers that support the structure of the sinusoids are located here.

Hepatocytes. Structure. Functions.

Features:

Secretion of bile-Hepatocytes capture free bilirubin from the blood, conjugate it with glucuronic acid and secrete non-toxic conjugated bilirubin into the bile capillaries.

Protein synthesis-Hepatocytes secrete albumin, fibrinogen, prothrombin, factor 3, angiotensinogen, etc. into the Disse space.

Carbohydrate metabolism-Excess carbohydrates from food are absorbed by hepatocytes with the help of insulin and stored as glycogen.

Lipid metabolism-Chylomicrons from the Disse space enter hepatocytes, where they are stored as triglycerides or secreted back into the blood as lipoproteins.

Detoxification-A non-toxic form of biliubin is formed in hepatocytes.

Hematopoietic-In the postnatal period, thrombopoietin is synthesized.

Liver. Organization of bile outflow. Functions of bile.

Bile ducts:

Bile capillaries (hepatocytes) - cholancioles - small bile ducts - interlobular bile

ducts (cuboidal epithelium) - large septal and trabecular bile ducts

(columnar epithelium)-right and left intrahepatic ducts-hepatic ducts-

common hepatic duct-common bile duct-duodenum.

Physiologically active substances (for example, conjugated glucocorticoids) are removed from the body through bile; as part of the bile, IgA enters the intestinal lumen from the Disse space.

Functions of the liver.

Secretion of bile-Hepatocytes capture bilirubin from the blood, conjugate it with glucuronic acid and secrete non-toxic conjugated bilirubin into the bile capillaries.

Protein synthesis-Hepatocytes synthesize almost all blood plasma proteins: albumins, angiotensinogen, prothrombin, factor 3, thrombopoietin, etc.

Carbohydrate metabolism-Excess glucose in the blood that occurs after eating is stored in the form of glycogen with the help of insulin.

Lipid metabolism-Chylomicrons from the Disse space enter hepatocytes, where they are stored as triglycerides or secreted back into the blood as lipoproteins.

Stocking up -glycogen depot, triglycerides, carbohydrates, iron, copper are stored. Itoh cells accumulate lipids and retinoids.

Detoxification-inactivation of the products of hemoglobin metabolism, proteins, and xenobiotics using enzymes during oxidation, methylation, and binding reactions.

Body protection-von Kupffer cells remove microorganisms and their waste products from the blood; pit cells are active against tumor and virus-infected cells; hepatocytes transport IgA from the Disse space into the bile.

Hematopoietic-embryonic hematopoiesis; in the postnatal period, thrombopoietin is synthesized.

Pancreas. Structure, functions of the exocrine part.

Acinus of the pancreas.In the center of the acinus are located the centroacinous cells, from which the excretory ducts begin. The cubic or cylindrical epithelium of the intralobular ducts passes into the cylindrical epithelium of the interlobular ducts. The branching interlobular ducts open into the main (Wirsung) duct, surrounded by connective tissue, which acts as the axial skeleton of the gland.

Structure.Secretory cells are characterized by pronounced polar differentiation. In the apical part there are numerous zymogen granules with digestive enzymes - the zymogen zone. In the apical part there are actin microfilaments and microtubules that participate in the intracellular transport of zymogen granules and the release of their contents into the extracellular space. The area between the zymogen granules and the nucleus is occupied by the Golgi complex. The nucleus is shifted to the basal part. In the basal part there is a well-defined granular eps, mitochondria, and free ribosomes.

The membranes of adjacent acinar cells in the apical part are connected by tight junctions, intermediate junctions, and desmosomes, which provide a barrier for large molecules, but are permeable to water and ions. Acinar cells are also connected by gap junctions, which provide electrical coupling and the transfer of ions and low-molecular substances between cells.

Functions:The pancreas produces pancreatic juice and enzymes that enter the lumen of the duodenum:

Pancreatic juice-isotonic to blood plasma, pH=8-8.5 due to the high content of bicarbonate, which neutralizes the acidic reaction of the chyme

Proteases -protein-digesting enzymes, trypsin, chymotrypsin, elastase, etc.

Nucleases-enzymes that break down nucleic acids.

Enzymes that break down fats-lipase, phospholipases, lecithinase.

Alpha-amylase-a pancreatic enzyme that breaks down carbohydrates.

The optimum pH for enzyme action is 7-8; enzyme precursors are produced and are activated in the intestinal lumen.

Organization, structural features, functions of the excretory ducts of the salivary glands.

Insert section.Lined with flat or cuboidal epithelium, surrounded on the outside by a layer of myoepithelial cells.

Striated duct (salivary tube).Lined with cylindrical epithelium, in the basal part finger-like outgrowths with chains of mitochondria, increasing the area of the cell membrane for ion transport. Epithelial cells of the striated duct convert isotonic secretion into hypotonic.

Interlobular duct.It passes through the connective tissue partitions of the gland. The epithelium of small ducts is single-row prismatic, while that of larger ducts is multi-row prismatic.

Common excretory duct.Lined with stratified cuboidal epithelium, at the mouth the epithelium becomes stratified squamous.

Parotid salivary gland. Development, blood supply, innervation. Structure of secretory sections, excretory ducts (see 231). Composition of secretion.

The development of the gland begins with the formation of strands formed by the epithelium of the oral cavity at 8-

week of embryogenesis from the ectoderm. It is a complex branched protein alveolar gland. The gland is covered with a connective tissue capsule on the outside and has a lobular structure. The lobules consist of terminal (secretory) sections and intralobular ducts (intercalated and striated).

The secretory sections consist of conical cells, their nucleus is in the middle or closer to the base of the cell, the cytoplasm is filled with small granules of secretion. The secretory section is surrounded by myoepithelial cells on the outside.

The interlobular excretory ducts lined with multilayered epithelium and blood vessels pass through the connective tissue layers between the lobules. The common duct (stenon's) opens into the vestibule of the oral cavity at the level of the second upper molar.

Parasympathetic innervation increases salivation. Saliva is hypotonic in relation to blood plasma, lysozyme, lactoferrin, immunoglobulin A are present in saliva, the protein gland secretes amylase and glycoproteins. Endocrine cells secrete nerve growth factor and epidermal growth factor into the salivary glands.

Submandibular salivary gland. Development, blood supply, innervation. Structure of secretory sections, excretory ducts (see 231). Composition of secretion.

The rudiment of the gland is formed in the 6th week of intrauterine development from the ectoderm. The gland is covered with a connective tissue capsule. The lobules of the gland are heterogeneous due to the presence of different cells that form the secretory sections.

Mucous cellslarge, conical in shape with a flattened nucleus located at the base of the cell. The cytoplasm is light and transparent, filled with granules containing mucin.

Protein cellsdarker, surround the mucous membranes in the form of crescents of Januzzi. At the basement membrane are myoepithelial cells.

The interlobular excretory ducts lined with multilayered epithelium and blood vessels pass through the connective tissue layers between the lobules. The common duct (Wharton's) opens at the bottom of the oral cavity behind the incisors.

Parasympathetic innervation increases salivation. Saliva is hypotonic in relation to blood plasma, saliva contains lysozyme, lactoferrin, immunoglobulin A, the submandibular gland secretes mucin and glycoproteins. Endocrine cells secrete nerve growth factor and epidermal growth factor into the salivary glands.

Trachea. Membranes and their structure. Cellular composition of the mucous epithelium.

Mucous membrane:

Single-layer multi-row columnar polar differentiated ciliated epithelium.Cellular types of epithelium, 4 main: high ciliated, large intercalated, small intercalated, goblet (produces mucus). In addition to them, there are also: non-ciliated (chemoreceptor - registers pH), neuroendocrine, poorly differentiated goblet (capable of synthesis, but do not do this, Langerhans cells.

Own record-loose connective tissue with a large number of macrophages, mast cells; dense capillary network.

Submucosa -loose connective tissue, large vessels. Here are located the terminal secretory sections of the mucous glands, the excretory ducts of which open into the lumen of the organ.

Fibrocartilaginous membrane-half rings of hyaline cartilage, the open ends are connected by bundles of SMC.

Adventitia

Mucous membrane of the airways. Structural features in different sections.

As the caliber of the airways decreases, the composition of the mucous membrane changes:

The muscular layer of the mucous membrane is absent in the upper sections, but appears in the lower ones (already present in the bronchi)

After the 2-row stage (small caliber bronchi), the multi-row epithelium disappears (in the bronchioles it is already single-row)

The height of the epithelium decreases to cubic (bronchioles)

The number of goblet cells decreases

The number of neuroendocrine hormones (bombesin, calcitonin, serotonin, etc.) increases.

In the distal portions of the terminal bronchioles, ciliated cells are absent, but Clara cells appear.

Glands of the airways. Localization, structure. Nervous and humoral regulation of secretion. Effects of adrenaline, acetylcholine, histamine (nothing in textbooks no, please look for it)

The mucous and protein-mucous glands are located in the submucosa.

Acetylcholine and histamine are bronchoconstrictors, adrenaline is a bronchodilator.

Structure of the bronchial wall. Changes in the structure of the bronchial wall as their caliber decreases.

Reduction in the height of the epithelium

After the stage of two-row (small-caliber bronchi), the multi-row (bronchioles) disappears.

Decreased number of goblet cells

Increase in the number of neuroendocrine cells

A decrease in the number of mucous glands, up to their complete disappearance in the bronchioles

Clara cells appear in the bronchioles, synthesizing the protein component of surfactant

Thinning and disappearance of adventitia

The semicircles of hyaline cartilage of the trachea are replaced first by plates, then by islands, and then completely disappear into the small-caliber bronchi.

As the fibrocartilaginous membrane decreases, the amount of SMC increases and a muscular layer appears.

Lung acinus. Structure and functions.

Before the terminal bronchiole, the preterminal

239. Structure of the wall of the alveoli of the lung. Pneumocytes: types, structure, functions.

Pneumocyte type 1 (flat alveolar cell, respiratory alveolocyte) - there are many pinocytic vesicles on the periphery, the cells are not capable of dividing, ensures the diffusion of gases.

Pneumocytes type 2 (high alveolar cell, secretory alveolocyte, surfactant-producing cell) - on the apical surface of the microvilli, a feature of the cells - the presence of lamellar bodies in the cytoplasm, the substances of these bodies are secreted by the cell into the alveolar space(at the lecture he said about them: layered bodies, containing lipids that will be part of the surfactant; In Bykov the bodies are also plate-like and nothing no about lipids).

Air-blood barrier. Structure, functions (see Figure 239)

Structure:

Surfactant

Anuclear portion of type 1 pneumocytes

Common basement membrane with the endothelium

Anuclear portion of endothelium

Functions-Transfer of O2 from the alveolar air to the blood and CO2 gas from the blood to the alveolar air is carried out through the pulmonary membrane, or the aerohematic barrier; in the capillaries of the lungs, HCO3- leaves the erythrocytes in exchange for Cl- in the plasma with the help of a special anion exchanger.

Alveolar macrophage. Origin, localization, structure, functions.

Alveolar macrophages are of bone marrow origin: their population is maintained both by their proliferation in the lung and by their transformation from monocytes.

They are located in the alveoli (alveolar septa).

There are many microfolds on the surface of macrophages, the cells form long cytoplasmic processes that allow them to migrate through interalveolar pores. With the help of processes, they can attach to the surface of the alveoli and capture particles.

Functions:

Phagocytosis of microorganisms and dust particles entering with inhaled air

Antimicrobial and antitumor activity mediated by oxygen radicals, proteases, cytokines

Secrete alpha 1-antitrypsin, a glycoprotein that protects alveolar elastin from degradation by leukocyte elastase

They produce factors that inhibit the function of T-lymphocytes, which reduces the immune response.

Surfactant. Formation, chemical composition, functions.

The main amount of surfactant is produced after the 32nd week of intrauterine development, reaching the maximum amount by the 35th week. Before birth, an excess of surfactant is formed, which is removed after birth by alveolar macrophages. Production occurs in the presence of corticosteroids.

Surfactant-emulsion of phospholipids, proteins and carbohydrates (according to the lecture phosphoglycoprotein). The main surface-active component is DIPALMITOYLPHOSPHATIDYLCHOLINE (phospholipid).

Functions:

Reduction of the surface tension of the tissue fluid film covering the alveolar cells, which promotes the straightening of the alveoli and prevents their walls from sticking together during respiratory movements

Formation of an anti-edematous barrier that prevents the release of fluid from the interstitium into the lumen of the alveoli

Bactericidal

Immunomodulatory

Stimulation of alveolar macrophage activity

It is part of the aerohematic barrier and is permeable to gases.

Urinary tract. Structure of the ureter.

Mucous membranecollected in longitudinal folds: transitional epithelium; proper layer is represented by connective tissue, in which lymphatic follicles are occasionally found; the muscular layer of the mucosa is absent.

Submucosa-small alveolar-tubular glands.

Muscular membrane-in the upper two-thirds of two layers of the SMC: internal longitudinal, external circular; in the lower third on the outside there is another longitudinal layer

Adventitia-fibrous connective tissue with many elastic septa.

Development of the kidney. Pronephros. Mesonephros. Metanephros.

Develops from the intermediate mesoderm (nephrotome).

Pronephrosrudimentary and non-functional. Nephrotomes give rise to nephric tubules, nephric tubules of paired adjacent segments unite and form paired longitudinal ducts - the primary renal duct. Small branches separate from the dorsal aorta: one penetrates the wall of the nephric tubule, the other - into the wall of the coelomic cavity, forming the internal and external glomeruli. The glomeruli consist of a spherical plexus of capillaries and, together with the tubules, form nephrons. As new nephrotomes appear, the previous ones degenerate; by the end of the 4th week, all signs of nephrotomes are absent.

Mesonephrosacts in the early stages of intrauterine development. The glomerulus is embedded in the wall of the tubule, where the tubule forms an epithelial capsule. The capsule and glomerulus form the renal corpuscle. The lateral end of the tubule flows into the primary renal duct, which is now called the Wolffian (mesonephric duct). By the middle of the 2nd month, the mesonephros reaches its maximum size; a large ovoid organ on either side of the midline. Part of the caudal tubules and the mesonephric duct are retained in the male fetus. A number of structures of the male reproductive system are formed from the tubules of the mesonephros. In the metanephros, urine is weakly concentrated due to the absence of medulla structures.

Metanephros-permanent kidney. Formation begins with the onset of mesonephros degeneration. Develops from the metanephrogenic blastema (the source of the nephron tubules) and the metanephric diverticulum (the source of the collecting ducts and large urinary tract). When entering the cloaca, the mesonephric duct forms a metanephric diverticulum, which is introduced into the caudal part of the intermediate mesoderm. The mesoderm thickens around the diverticulum, forming a metanephrogenic blastema. A derivative of the diverticulum, the collecting duct, is covered at the distal end with a cap of the metanephrogenic blastema. Under the inductive influence of the tubules, vesicles are formed from the tissue, giving rise to tubules. The tubules, uniting with the capillary glomeruli, form nephrons.

Kidney. Structure of the cortex and medulla.

Cortexis represented by a granular layer located under the capsule. The granular appearance is given by the renal corpuscles and convoluted tubules of the nephron.

Medullahas a radially striated appearance, contains the ascending and descending parts of the nephron loop, collecting tubules, blood vessels. The outer part is located under the cortex, the inner part is the tops of the pyramids. Collecting

the tubules and straight sections of the nephrons form the pyramids of the medulla, their apices

facing the renal pelvis. The caliber of the tubes increases and forms a collecting duct

(papillary canal) opening at the apex of the papilla into the cavity of the minor renal calyces.

Kidney. Juxtaglomerular complex. Cellular composition, localization and function of cells.

Together, all components regulate the function of this nephron.

Cells of the macula densa -belong to the distal tubule in its part between the afferent and efferent arterioles; are chemosensitive, register the content of chlorine cations, urine flowing through the distal tubule. They contact juxtaglomerular and juxtavascular cells, since in this part of the tubule there is no basement membrane.

Juxtaglomerular cells-are located in the wall of the afferent arteriole; modified SMC. They synthesize the hormone-enzyme renin.

Juxtavascular cells (Gurmagtig cells)-are located under the distal tubule. In case of pathology, they synthesize renin.

Mesangial cells-between the capillary endothelium and the podocyte legs. They gnaw the basement membrane of the filtration barrier, thereby participating in its renewal; have phagocytic activity, act as supporting cells, and produce the mesangial matrix.

Mesangial cells of the renal corpuscle. Localization, morphology, function.

Mesangial cells are branched, with a dense nucleus, well-developed organelles, and a large number of filaments (including contractile ones)

peripheral areas of the cytoplasm. They have receptors for angiotensin 2, vasopressin and atrioceptin.

Functions:

They act as supporting elements

Can regulate blood flow in the glomerulus (due to contractile properties)

They have phagocytic properties (absorb macromolecules that accumulate during filtration and participate in the renewal of the basement membrane)

They produce the mesangial matrix (contains glucosaminoglycans, fibronectin, laminin).

Renal corpuscle. Localization, structure, function.

The renal corpuscles are located in the cortex of the kidney, giving it a granular appearance. The renal corpuscle is represented by the Bowman-Shumlyansky capsule, inside which the vascular glomerulus is stratified, formed by capillaries with fenestrated endothelium. The outer leaflet of the capsule is flat epithelial cells, the inner leaflet is podocytes. The lumen of the capsule is the space between the podocytes and flat epithelial cells. Two poles are distinguished in the corpuscle: vascular (the site of the afferent and efferent arterioles) and urinary (the site of the departure of the renal tubule).

Functions:In the renal corpuscle, plasma filtration and primary urine formation occur

249. Nephron. Thin tubule (loop of Henle): structure, functions.

Thin section of the loop-flat epithelium, irregularly shaped cells, the nucleus protrudes into the lumen, the presence of rare microvilli and one cilium is characteristic. In this section, active reabsorption of sodium and water occurs (the presence of aquaporin proteins). The difference in osmolarity is the main reason for water reabsorption. In the deep sections of the renal medulla, osmolarity is several times higher than the osmolarity of the cortex.

Nephron. Distal straight and distal convoluted tubule. Structure, functions.

Thick section of Henle's loop- distal straight tubule - cubic epithelium with striation (finger-shaped outgrowths with chains of mitochondria), but without a border. Mainly sodium and chlorine are reabsorbed, impermeable to water.

Distal convoluted canal- structurally, this is the same section of the Henle loop, where urine acidification occurs. Sodium ions are absorbed in exchange for a hydrogen proton, and potassium and ammonium ions also enter the tubule. The cells of the distal convoluted tubule are the target of aldosterone, resulting in increased blood pressure due to increased sodium reabsorption.

Proximal tubules of the nephron (straight and convoluted). Structure and functions of cells.

Epithelium-cubic bordered. Dense spaces are formed between the cells in the apical part.

contacts. In the basal part of the cell there are finger-like outgrowths with chains of mitochondria

(mitochondria are everywhere except the apical part). The cell contains many lysosomes, vacuoles, pinocytosis

bubbles. The core is round.

The straight section has the same structure, but the number of microvilli decreases as it approaches the thin section.

Functions:

Reabsorption of high molecular weight compounds: the main site of phosphate reabsorption; glucose is reabsorbed by combined transport with sodium ions using membrane glycoproteins; water is reabsorbed through channels formed by aquaporin (according to the lecture, reabsorption of only high-molecular compounds, without water and electrolytes).

Synthesis of D3 (ensures the absorption of calcium in the small intestine, regulation of the excretion of calcium and phosphates in the urine).

Filtration barrier. Structure, functions. Regulation of filtration

Filtration barrierin the renal corpuscle is a set of structures through which substances are filtered from the blood into the primary urine. It consists of:

Endothelium of glomerular capillaries(more specifically, the cytoplasm of fenestrated endothelial cells)

Three-layer basement membrane(common to endothelium and podocytes)

Filtration slotsbetween the small legs of the podocytes

Permeabilitythe filtration barrier for a given substance is determined by its mass, charge

configuration of its molecules. Substances with a molecular weight over 69,000 normally do not enter the urine. The endothelium retains the formed elements of the blood and the largest protein molecules; the least permeable part of the barrier is considered to be the dense layer of the basement membrane or filtration gaps. If the barrier is damaged, a significant amount of protein and even formed elements enter the urine from the blood.

Efficiencyfiltration in the renal corpuscle is ensured by an unusually high (50-70 mm Hg) pressure in the glomerular capillaries (created due to the smaller diameter of the efferent arteriole compared to the afferent one), as well as a significant volume of blood passing through them (1800 l/day), 10 times greater than the volume of glomerular filtrate (primary urine) - 180 l/day.

Through the FB, the components of blood plasma are filtered from the blood into the cavity of the capsule, forming primary urine.

1,25-Dihydroxycholecalciferol (calcitriol). Formation, targets, effects

A steroid hormone, a derivative of vitamin D3.

Education

It occurs in different places in three stages. First, in the epidermal cells, under the influence of ultraviolet rays, vitamin D3 (cholecalciferol) is formed from provitamin. Then in the liver, calcidiol is formed from it. Then in the kidneys (in the epithelium of the proximal convoluted tubules), under the influence of parathyroid hormone, calcidiol is converted into calcitriol.

Effects

Regulation of calcium metabolism:

Stimulates the absorption of Ca in the small intestine

Stimulates Ca reabsorption in the nephron tubules

Stimulates the deposition of Ca in bone tissue

Inhibits the secretion of parathyroid hormone

Increases calcium transport into cells

Regulation of phosphorus metabolism:

Stimulates the absorption of phosphorus in the small intestine

Stimulates the reabsorption of phosphorus in the nephron tubules

Renin. Place of formation, regulation of secretion. Targets and effects

Renin- an enzyme that cleaves angiotensin I from the plasma protein angiothesinogen in response to a drop in blood pressure or a decrease in blood volume (renin-angiotensin system).

Place of formation- produced by juxtaglomerular (epithelioid, granular) cells of the kidney apparatus of the same name.

These are modified smooth muscle cells of the middle coat of the afferent (to a lesser extent, efferent) arteriole at the vascular pole of the glomerulus. They have baroreceptor properties and, when the pressure drops, they release renin, which they synthesize and which is contained in large dense granules. The organelles are moderately developed; due to their processes, they form contacts with the intima of the arterioles and the dense spot.

(Renin accumulates in secretory granules and, when the appropriate signal is received, is secreted into the lumen of the afferent arteriole. According to the baroreceptor theory, renin-synthesizing cells function as baroreceptors. An increase in the pressure in the lumen of the afferent arteriole decreases the secretion of renin. When the pressure decreases, the stretching of the arteriole wall decreases, which causes an increase in the secretion of renin by the juxtaglomerular cells. The release of norepinephrine from numerous endings of the axons of sympathetic neurons in the periglomerular complex increases the secretion of renin. The cells of the macula densa register the content of Na+ ions in the lumen of the distal tubule. With an excess of Na+ ions (in this case, the osmotic pressure in the tubule increases), the secretion of renin by the juxtaglomerular cells is inhibited.)

Kidney. Organization of blood flow

Blood flows to the kidneys through the renal arteries, which, upon entering the kidneys, split into interlobar arteries running between the medullary pyramids. At the border between the cortex and medulla, they branch into arcuate arteries. From them, interlobular arteries branch off into the cortex. From the interlobular arteries, intralobular arteries diverge to the sides, from which afferent arterioles begin. From the upper intralobular arteries, afferent arterioles are directed to the short and intermediate nephrons, from the lower ones - to the juxtamedullary nephrons. In this regard, cortical circulation and juxtamedullary circulation are conventionally distinguished in the kidneys.

cortical circulatory systemafferent arterioles break up into capillaries that form the vascular glomeruli of the renal corpuscles of the nephrons. The capillaries of the glomeruli gather into efferent arterioles, which are somewhat smaller in diameter than the afferent arterioles. In the capillaries of the glomeruli of the cortical nephrons, the blood pressure is unusually high - over 50 mm Hg. This is an important condition for the first phase of urine formation - the process of filtering fluid and substances from the blood plasma into the nephron.

The efferent arterioles, having traveled a short distance, again disintegrate into capillaries that encircle the nephron tubules and form the peritubular capillary network. In these “secondary” capillaries, the blood pressure, on the contrary, is relatively low – about 10-12 mm Hg, which contributes to the second phase of urine formation – the process of reabsorption of part of the fluid and substances from the nephron into the blood.

From the capillaries, the blood of the peritubular network is collected in the upper sections of the cortex first into the stellate veins, and then into the interlobular veins, in the middle sections of the cortex - directly into the interlobular veins. The latter flow into the arcuate veins, which pass into the interlobular veins, which form the renal veins, emerging from the renal hilum.

Thus, nephrons, due to the peculiarities of cortical circulation (high blood pressure in the capillaries of the glomeruli and the presence of a peritubular network of capillaries with low blood pressure), actively participate in urine formation.

juxtamedullary circulatory system afferent and efferent arterioles of the glomeruli of the renal corpuscles of the pericerebral nephrons are approximately the same diameter or efferent

arterioles are even somewhat wider. Therefore, the blood pressure in the capillaries of these glomeruli is lower than in the glomeruli of the cortical nephrons.

Efferent glomerular arteriolesjuxtamedullary nephrons go into the medulla, breaking up into bundles of thin-walled vessels, somewhat larger than normal capillaries, called vasa recta. In the medulla, both the efferent arterioles and the vasa recta give off branches to form the cerebral capillary network.

The vasa recta form loops at different levels of the medulla, turning back. The descending and ascending parts of these loops form a countercurrent system of vessels called the vascular bundle. The capillaries of the medulla collect into the vena straight, which flow into the arcuate veins.

Due to these features, the pericerebral nephrons participate less actively in urine formation. At the same time, the juxtamedullary circulation plays the role of a shunt, i.e. a shorter and easier path along which part of the blood passes through the kidneys under conditions of strong blood filling, for example, when a person performs heavy physical work.

Development of the gonads. Indifferent gonads. Sexual differentiation

The development of the reproductive system in the initial stages of embryogenesis occurs in both sexes in the same way (indifferent stage), and in close contact with the development of the excretory system.

The rudiment of the gonads becomes noticeable in the 4-week embryo in the form of genital ridges - thickenings of the coelomic epithelium on the surfaces of both primary kidneys. However, the primary germ cells in embryos of both sexes - gonocytes in the presomitic stages of embryogenesis appear earlier (in the 3rd week) and are characterized by large cell nuclei, increased glycogen content and high activity of alkaline phosphatase in the cytoplasm. At first, they are found in the wall of the yolk sac, where they quickly multiply, then in the wall of the hindgut;

blood flowing through its vessels, are moved into the thickness of the genital ridges. From the epithelium of the genital ridges, follicular cells are formed in the ovaries or supporting epithelial cells (sustentocytes) in the testes, which provide nutrition to the maturing germ cells. Epithelial cells, with the participation of interstitial (mesenchymal) cells, or endocrinocytes, produce sex hormones. Interstitial (mesenchymal) cells proliferate intensively in the 9th-10th week of intrauterine development. After the 22nd week, their number decreases.

From the genital ridges, the genital cords grow into the stroma of the primary kidney, the basis of which is formed by mesenchyme. These are strands of epithelium in which gonocytes are located. At the same time, the paramesonephric duct, which runs parallel to the mesonephric duct, splits off from the mesonephric duct of the primary kidney, which extends from its body to the cloaca. Differentiation of the indifferent gonad by sex in the human embryo begins in the 6th week of embryogenesis.

IN BRIEF =The sources of the sex glands are the urogenital ridges and primary sex cells. The urogenital (gonadal) ridges are indifferent gonads - the rudiments of the future sex glands (testicles and ovaries). In the 4th week of embryogenesis, gonadal ridges are formed in the thoracolumbar region of the nephrotome (on the medial side of the mesonephros), which are not identified as either male or female sex glands. Indifferent gonads consist of cortex and medulla populated by primary sex cells.

Primary germ cells arise in the 2nd week of embryonic development from cells of the head region of the epiblast. During gastrulation, primary germ cells through the primitive streak

endoderm of the yolk sac and further into the gonadal ridges.During the fetal period, the primary germ cells differentiate into oogonia in the developing ovaries or into spermatogonia in the testes..On the way from oogonia or spermatogonia to mature gametes, several stages are distinguished:reproduction,growth,maturation and formation.

SEXUAL DIFFERENTIATION

Chromosomal sex determination occurs at fertilization, Y‑chromosome—potential determinant of genetic male sex

Factor,determining the development of male gonads(TDF) —one of the inducers of development of the male reproductive gland.Regulatory factorTDF,gene encodedY-chromosomesSRY (Sex-determining Region Y),responsible for the differentiation of the testes from initially bipotent rudiments gonads.

Indifferent gonads

Critical stagedevelopment of indifferent gonads— 8th week of intrauterine development. To45-50day rudiments of the gonads do not have sexual differentiation.Under the influence of transcription factorTDFgonadal ridges develop as testicles;in the absence of the effects of this factor, the ovaries develop.Differentiation of other structures is determined by male sex hormones and Müllerian inhibitory factor.(MIF ¾ Mullerian Inhibiting Factor),produced in the fetal testicles.

Differentiation by male type.With karyotype46XY interstitial endocrine cells of the fetal testes differentiate from the mesenchyme cells of the gonadal ridge.Under the control of gonadotropins(chorionic and pituitary)interstitial endocrine cells of the fetal testes secrete testosterone.Gene expressionSRYin supporting epithelial cells initiates gene transcription,codingMIF.

Differentiation by female typewith karyotype46XX occurs in the absence of a factor that determines testicular developmentY-chromosomes,androgens andMIF.The gonadal ridges develop autonomously as ovaries,under the influence of placental hormones

Ovary and testicle

In the female body, in the indifferent gonads, predominantly the cortex develops and the medulla atrophies.In the male body, the medulla of the indifferent gonad receives preferential development.On8-th week of embryogenesis, the testicles are located at the level of the upper lumbar vertebrae.The suspensory ligament extends downward from the lower pole of the testicle,acting as a conductor of the testicle from the abdominal cavity through the inguinal canal into the scrotum.The descent of the testicles into the scrotum is completed in approximately1month before birth and does not occur with cryptorchidism.

Hematotesticular barrier. Localization, structure, functions

Hematotesticular barrieris called a set of structures, located between the lumens of capillaries and seminiferous tubules.During puberty, supporting cells form tight junctions near the basement membrane,forming the hematotesticular barrier.Thanks to such a barrier,a specific hormonal environment with high levels of testosterone is created in the adluminal space.The barrier isolates maturing germ cells from toxic substances and prevents the development of an autoimmune response against surface Ags.,expressed on the membrane of maturing spermatozoa.

Structure:

capillary endothelium

myoid cells

basement membrane

basal part

Sertoli cell processes

Barrier functions:

prevents autoimmune diseases

maintaining the hormonal environment: estrogen on top, testosterone on the bottom

reduction of toxic substance concentration

Spermiogenesis is the final phase of spermatogenesis.

The formation of male germ cells (spermatogenesis) occurs in the convoluted seminiferous tubules and includes four successive stages or phases: reproduction, growth, maturation and formation (spermiogenesis).

Occurs in Sertoli cells. During the formation stage, the spermatid turns into a spermatozoon, and:

the nucleus is packed super tightly, resulting in it being in a super-packed state in the sperm

from the Golgi complex of the spermatid through the acroblast stage, the acrosome is formed - an organelle containing 12-15 enzymes that destroy the components of the transparent membrane (70% hyaluronidase)

the spermatid's cell center is transformed into 2 centrioles and a tail thread along which mitochondria are aligned

Golgi phase:

1An acrosomal vesicle with an acrosomal granule appears as part of the Golgi complex.

2Centrioles migrate to the opposite side of the cell and initiate axoneme assembly

Head cap phase:

The acrosomal vesicle flattens, covering 2/3 of the surface of the nucleus. Acrosome phase:

1.Acrosomal granule fills acrosomal vesicle → acrosome

2.Chromatin condenses, the nucleus elongates

3.Microtubules form a cylindrical cuff

4.Mitochondria migrate and spiral around the axoneme

5.The spermatid turns its tail into the lumen of the tubule

Ripening phase:

1.The core takes on its final shape

2.The spermatid gets rid of excess cytoplasm, the cuff is destroyed

3.Cytoplasmic bridges are broken.

Convoluted seminiferous tubules. Localization, development, structure

Convoluted seminiferous tubulesare lined with spermatogenic epithelium containing two types of cells - gametes with their precursors at various stages of differentiation (spermatogonia, first-order spermatocytes, second-order spermatocytes, spermatids, spermatozoa) and supporting epithelial cells (sustentocytes). The tubules are surrounded on the outside by a thin connective tissue membrane. The convoluted seminiferous tubules open into straight ones, through which spermatozoa enter the rete testis.

The tubules are lined with spermatogenic epithelium. Large interstitial endocrine cells are visible between the tubules. Spermatozoa are located in the lumen of the tubules.

Sustentocytes.The broad base of the sustentocytes (sustentocytus, supporting epithelial cells) is located on the basement membrane, and the narrowed folded apical part reaches the lumen of the tubule. With the help of tight junctions, the sustentocytes divide the spermatogenic epithelium into basal and adluminal spaces.

basalOnly spermatogonia are located in the supraluminal space. First and second order spermatocytes, spermatids and spermatozoa are located in the adluminal space. Adhesive and gap junctions are established between sustentocytes and gametes. Sustentocytes provide physical support to developing gametes, provide them with nutrients (trophic function), absorb metabolic products, phagocytize the remains of the cytoplasm of developing spermatozoa (residual bodies) and degenerating germ cells, and secrete fluid for transporting spermatozoa in the seminiferous tubules.

Hematotesticular barrier.During puberty, supporting cells near the basement membrane form tight junctions that form the hematotesticular barrier. Due to this barrier, a specific hormonal environment with a high level of testosterone is created in the adluminal space. The barrier isolates maturing germ cells from toxic substances and prevents the development of an autoimmune response against surface Ags expressed on the membrane of maturing spermatozoa.

Sustentocytes are connected by tight, adhesive and gap junctions. Tight junctions responsible for the formation of the hematotesticular barrier are localized between the supporting epithelial cells in their basal part. In the apical part, the cells are connected by gap junctions. In tight junctions, the adhesion junction molecules JAM, occludins and claudins interact with actin through ZO-1 and ZO-2. Adhesive and gap junctions are established between sustentocytes and gametes.

Secretion products.Sustentocytes secrete estrogens, inhibin, and Müllerian inhibitory factor MIF (in the fetal period) into the blood. In the adluminal space, supporting epithelial cells accumulate androgen-binding protein, stem cell factor, transferrin, and plasminogen activators.

Androgen binding protein— a factor that ensures the maintenance of a high concentration of testosterone in the spermatogenic epithelium by accumulating the hormone in the lumen of the seminiferous tubules.

Stem cell factor (SCF)necessary for maintaining the spermatogonial population.

Transferrin, in addition to transporting iron into the spermatogenic epithelium, is a powerful mitogenic factor.

Proteases(cathepsins, plasminogen activators) and protease inhibitors (serpins, cystatins) affect proteolytic reactions, which is important for the migration of maturing germ cells from the basal space to the adluminal space.

Follicle-stimulating hormone (follitropin)— the main stimulating factor of sustentocytes. Follicle-stimulating hormone receptors are related to G-protein, activating adenylate cyclase. An increase in cytosolic cAMP increases the secretory function of supporting epithelial cells.

Endocrine function of the testicle. Male sex hormones and the glandulocytes (Leydig cells) that synthesize them

Endocrine function (synthesis of male sex hormones)- in interstitial endocrine cells.

Hypothalamic-pituitary systemwith the help of gonadotropin-releasing hormone activates the synthesis and secretion of gonadotropic hormones of the pituitary gland, which affect the activity of supporting epithelial and interstitial endocrine cells. In turn, the hormones produced in the testicle correct the endocrine activity of the hypothalamic-pituitary system.

Gonadotropin-releasing hormoneenters the blood from the axons of neurosecretory cells in a pulsating mode with peak intervals of about two hours.

Gonadotropic hormones

Secretion of gonadotropic hormones is maintained by GnRH and inhibited by testicular hormones. The inhibitory effect of testosterone on luteinizing hormone secretion is mainly manifested at the hypothalamus level (through GnRH synthesis), whereas estrogens reduce the sensitivity of gonadotropic cells to GnRH. Sex steroids have little effect on follicle-stimulating hormone secretion, whereas the peptide hormone inhibin has a pronounced inhibitory effect on follicle-stimulating hormone synthesis. The targets of gonadotropic hormones are the testicles. Sustentocytes have follicle-stimulating hormone receptors, and interstitial endocrine cells have luteinizing hormone receptors.

Follitropinactivates the synthesis and secretion of inhibin and estrogens in supporting epithelial cells.

Lutropinstimulates the synthesis and secretion of testosterone in interstitial endocrine cells.

Prolactin.The mechanisms of prolactin's involvement in testicular function regulation are not very clear, although adequate prolactin secretion seems to be necessary for testosterone synthesis. Increased prolactin levels in the blood lead to suppression of testosterone synthesis. Impotence develops in patients with severe hyperprolactinemia as a result of decreased testosterone secretion.

Testicular hormones

Testosteroneenters the sustentocytes, binds to the ASP in the cytosol and is then secreted into the adluminal space to support spermatogenesis. Part of the testosterone is converted into

estrogens. Testosterone and blood estrogens have an inhibitory effect on the secretion of luteinizing hormone by gonadotrophs of the adenohypophysis.

Estradiol.In the smooth endoplasmic reticulum of sustentocytes, testosterone synthesized in interstitial endocrine cells is converted by aromatization.

estrogens. Estrogens bind to receptors in interstitial endocrine cells and suppress testosterone synthesis via a paracrine mechanism.

Inhibin.In response to stimulation by follitropin, sustentocytes secrete inhibin, which blocks the synthesis of follitropin by gonadotropic cells of the adenohypophysis. The structure of inhibin is homologous to MIF, secreted by fetal sustentocytes.

Endocrine interstitial cells (Leydig)

1.They are located between the convoluted seminiferous tubules

2.Developed endoplasmic reticulum, numerous mitochondria, lipid inclusions, rod-shaped Reinke crystals

3.G-protein-coupled luteinizing hormone receptors are embedded in the membrane.

Testosterone

1.5α-reductase → dihydrotestosterone

2.3α-reductase → androstenediol

3.Circulates in the blood in complex with steroid-binding globulin or albumin

4.In the fetal period, it determines the development of the fetus according to the male type

5.In the postnatal period, it ensures the development of secondary sexual characteristics, spermatogenesis, prostate function, seminal vesicles, bulbourethral glands, growth of muscle mass, cartilage, ossification of the epiphyseal plate, an increase in LDL content and a decrease in HDL

6.Aromatization of testosterone in the liver, adipose and nervous tissues by the enzyme P450 aromatase leads to the formation of estradiol and estrone

7.Degradation in the liver, excretion in urine

Epididymis: structure of tubules, functions

The epididymis is divided into a head, body and tail. The head of the epididymis is represented by 10-12 efferent ducts (ductuli efferentes). The body and tail of the epididymis are formed by the epididymal duct

(ductus epididymis), into which the ductuli efferentes open.

Efferent tubules of the appendage

The efferent tubules of the epididymis pierce the tunica albuginea and connect the rete testis with

duct of the epididymis. They are lined with epithelium, the cells of which have different heights

(garland epithelium). Tall cylindrical cells are provided with cilia, which facilitate

movement of sperm through the tubules. Low cuboidal cells have a folded

surface with microvilli. Numerous cells are present in the apical part of the cells.

pinocytic vesicles and lysosomes. The function of these cells is to reabsorb fluid,

formed in the convoluted tubules of the testicle. Outside the epithelial lining is located

its own layer with circularly oriented GMCs, which also contribute to the promotion

spermatozoa through the efferent ducts.

Epididymal duct

Epididymal duct— a single and highly convoluted tubule 4-6 m long. It is lined with multi-row columnar epithelium. Two types of cells are distinguished in the epithelium: basal intercalated and high columnar. The columnar cells are provided with stereocilia glued together in the form of a cone (flame epithelium). Between the bases of the columnar cells are small intercalated cells, which are the precursors of the columnar cells. Under the epithelium is its own layer, surrounded by circularly oriented SMCs. The muscular layer of the duct of the epididymis, as it approaches the ductus deferens, becomes more pronounced and is represented by three layers: internal and external longitudinal and middle circular. Contractions of the SMCs facilitate the movement of spermatozoa into the vas deferens.

Efferent ducts (ductuli efferentes).

Lined with epithelium, the cells of which have different heights (garland epithelium)

The tall cylindrical cells have cilia that help move the sperm. The short cuboidal cells have microvilli and contain lysosomes. The function of these cells is to reabsorb the fluid that forms in the testicles.

Epididymal duct (ductus epididymis).

A single, highly convoluted tubule, 6 meters long.

The site of functional maturation and storage of spermatozoa.

In the epithelium, basal and cylindrical cells with stereocilia (flame epithelium) are distinguished.

Fluid reabsorption, phagocytosis of dead spermatozoa, secretion of sialic acid and glycerophosphocholine, which inhibit capacitation

The prostate gland. Structure, function and its hormonal regulation

The prostate gland, or prostate,— a muscular-glandular organ that covers the upper part of the urethra, into which the ducts of numerous prostatic glands open.

Structure

Prostate— a lobular gland covered with a thin connective tissue capsule. Its parenchyma consists of numerous individual mucous glands, the excretory ducts of which open into the urethra. The glands are located around the urethra in three groups: central, peripheral and transitional.

Briefly:Structure. Consists of 30-50 branched tubular-alveolar glands, separated by connective tissue partitions containing a significant amount of SMC. Each gland has its own excretory duct, opening into the lumen of the urethra.

The secretion enters the urethra due to the contraction of the gland's SMC, participates in the liquefaction of the semen and facilitates its passage through the urethra during ejaculation. Lipids, fibrinolysin, prostate-specific Ag (serine protease), and acid phosphatase are found in normal prostate secretion.

Uterus. Structure of membranes

Uterusis a hollow organ with a thick muscular wall in which the development of the fetus occurs. The fallopian tubes open into its expanded upper part (body), and the narrowed lower part (cervix) protrudes into the vagina, communicating with it through the cervical canal (neck).

Wall (body) of the uterusconsists of three shells:

mucous membrane (endometrium), function: to take out

muscular (myometrium), function: get rid of

serous (perimetry),function: trophic - feeding the fetus.

Endometriumundergoes cyclical restructuring during the reproductive period

(menstrual cycle) in response to rhythmic changes in the secretion of hormones by the ovary (ovarian cycle); its thickness varies from 1 to 7 mm. Each cycle ends with the destruction and removal of part of the endometrium, accompanied by the release of blood (menstrual bleeding).

It consists of an integumentary epithelium, onto the surface of which the uterine glands open, immersed in their own plate (stroma).

a) integumentary epithelium- single-layer prismatic, contains secretory and ciliated cells. The first has a well-developed synthetic apparatus; the apical part, protruding into the lumen, is covered with microvilli and contains secretory granules. The cells of the second type are covered with cilia that flicker in the direction of the vagina. The height of the cells of the integumentary epithelium changes during the cycle.

b) uterine glands (endometrial glands)- simple tubular, in places dichotomously branching near the myometrium, and sometimes penetrating into it to a shallow depth; deep penetration is considered a pathology - adenomyosis.

They are formed by cylindrical epithelium (similar to the integumentary epithelium, but with a smaller number of ciliated cells), the functional activity and morphological features of which change significantly during the menstrual cycle.

c) endometrial stromacontains fibroblast-like cells (capable of a number of transformations), lymphocytes, histiocytes and mast cells. Between the cells there is a network of collagen and reticular fibers; elastic fibers are found only in the wall of the arteries.

The endometrium has two layers that differ in structure and function: basal and functional.

Basal layeris attached to the myometrium and in some areas can penetrate it. Contains the distal sections (bottoms) of the uterine glands, surrounded by stroma with a dense arrangement of cellular elements. It is slightly sensitive to hormones. Serves as a source of restoration of the functional layer, in the menstrual cycle, as well as in case of violation of its integrity after abortion, childbirth. Receives nutrition from the direct arteries, departing from the radial ones, which penetrate the endometrium from the myometrium. Contains the proximal sections of the spiral arteries, which serve as a continuation of the radial ones into the functional layer.

Functional layer(when fully developed) is much thicker than the basal layer; contains a superficial (compact) layer with tightly packed stromal cells and a deep (spongy) layer with numerous glands and vessels. It is highly sensitive to hormones, under the influence of which its structure and function change: at the end of each cycle it is destroyed, being restored again in

next. It is supplied with blood by spiral arteries, which divide into a number of arterioles associated with capillary networks.

Myometrium- the thickest layer of the uterine wall - includes three indistinctly demarcated muscle layers:

subvascular (submucous)- internal, with an oblique arrangement of bundles of smooth muscle cells;

vascular - medium, the widest, containing large vessels (compressed due to powerful contraction of the myometrium during labor after separation of the placenta, helping to stop bleeding). Bundles of smooth muscle cells lie circularly or spirally;

supravascular (subserosal)- external, with oblique or longitudinal arrangement of bundles of smooth muscle cells;

Spontaneous contractile activity of the myometrium, which is characteristic of it in the absence of nervous or hormonal stimulation, is coordinated by multiple gap junctions between smooth muscle cells.

Myometrial stromaformed by layers of connective tissue between bundles of smooth myocytes; elastic fibers are present in small quantities in the peripheral parts of the myometrium of the body of the uterus.

Perimetryhas a typical structure of the serous membrane (mesothelium with underlying connective tissue); it does not completely cover the uterus - in those areas where it is absent, there is an adventitia. The perimetry contains sympathetic nodes and plexuses.

Endometrium. Structure. Characteristics in different phases of the menstrual cycle

See question above

Fallopian tube. The membranes and their structure. Cyclic changes in the mucous membrane

shells

Fallopian tubeis a tubular organ that performs a number of functions:

captures the oocyte,secreted from the ovary during ovulation;

carries out its transfertowards the uterus;

creates conditions for sperm transportin the direction from the uterus;

provides an environment, necessary for fertilization and initial development of the embryo;

carries out the transport of the embryo into the uterus.

AnatomicallyIt is divided into four sections - a funnel with a fringe, opening in the area of the ovary, an expanded part - an ampulla (forms 2/3 of the length of the organ), a narrow part - an isthmus and a short intramural (interstitial) segment located in the wall of the uterus.

Wall of the fallopian tubeconsists of three membranes: mucous, muscular and serous.

Mucous membraneforms numerous branching folds, strongly developed in the funnel and ampulla, where they almost completely fill the lumen of the organ. In the isthmus, these folds are shortened, and in the interstitial segment they turn into short ridges.

a) epitheliummucous membrane - single-layer prismatic, formed by two types of cells - ciliated and secretory. Its height and relative content of ciliated cells in it decrease from the ampulla to the uterus. Lymphocytes are constantly present in the epithelium (they are often mistaken for basal cells).

Ciliated cells- with light cytoplasm and poorly developed organelles. On their apical surface are cilia that flicker in the direction of the uterus.

Secretory cells- with developed organelles, a nucleus with invaginations and a large nucleolus, produce substances necessary for the nutrition of the egg and capacitation of sperm. Secretory granules covered with a membrane accumulate in the convex apical part covered with microvilli.

b) lamina propria of the mucous membrane- thin, contains fibroblasts, lymphocytes, macrophages and mast cells, as well as cells capable of transforming into decidual cells (in case of tubal pregnancy). In the mucous membrane of the fringe there are large veins that overflow with blood before ovulation, which increases its turgor and promotes tight coverage of the ovary by the funnel.

Muscular membranethickens from the ampulla to the intramural segment: consists of a thick internal circular layer and a thin external longitudinal layer, which are not sharply demarcated. Its contractile activity is enhanced by estrogens and inhibited by progesterone.

Serous membraneis distinguished by the presence of a thick layer of connective tissue under the mesothelium, containing vessels and nerves. In the ampullar section, individual bundles of smooth muscle tissue are found, the contraction of which changes the position of the tube in relation to the surface of the ovary.

Menstrual cycle. Characteristics of the uterine endometrium in different phases of the cycle, hormonal regulation of the cycle

Menstrual cyclemanifests itself in regular changes in the endometrium, which occur continuously, repeating every 21-35 (on average, 28) days. It is conventionally divided into three phases: 1) menstrual (bleeding), 2) proliferation, 3) secretion; the starting point of the time count is the onset of menstrual bleeding, which corresponds to the 1st day of the cycle.

menstrual phase, occurring on days 1-4 (all periods are given for an average 28-day cycle), in the first two days (the desquamation period) is characterized by the removal of the destroyed functional layer (formed in the previous cycle) along with a small (50-150 ml) amount of blood. The surface of the endometrium, not covered by epithelium ("physiological wound"), in

the following two days (the regeneration period) undergoes epithelialization due to the migration of epithelium from the bottoms of the glands to the surface of the stroma in the form of layers of flattened cells. This process begins even before the end of menstrual bleeding and is completed by the 4th day, apparently proceeding independently of hormones (at very low estrogen levels).

proliferative phase (postmenstrual)corresponds to days 5-14 of the cycle.

Characterized by increased growth of the endometrium (under the influence of estrogens secreted by the growing follicle) with the formation of structurally formed, but functionally inactive glands. Formation and growth of spiral arteries occurs, slightly convoluted in this phase. The integumentary epithelium is transformed from low prismatic to highly prismatic, the glands, initially having the appearance of straight narrow tubes, acquire a corkscrew-shaped course by the end of the phase, their lumen somewhat widens. The cells of the glands increase in size, often dividing. The number of mitoses in the stroma also increases; its cells become larger.

secretory phase (premenstrual)corresponds to the 15th-28th days of the cycle and is characterized by active activity of the uterine glands and changes in the stromal elements and vessels (under the influence of progesterone secreted by the corpus luteum). In the middle of the phase, the functional layer is clearly divided into compact and spongy layers, and at the end of it it undergoes necrosis due to vascular spasm.

Lutropin. Secretion and its regulation. Targets, effects

Luteinizing hormone (LH).

It is secreted by the adenohypophysis, as well as by some immunocompetent cells.

Development of follicles in the ovary and its hormonal regulation

In the fetal period, the primary germ cells differentiate into oogonia in the developing ovaries. Oogonia enter the reproduction stage. By seven months of intrauterine development, the reproduction stage ceases. Oocytes enter the growth stage. After this, oocytes acquire a membrane of one layer of follicular cells, oogenesis stops in the prophase of the first mitotic division of the maturation phase - a primordial follicle is formed.

At the onset of puberty, the secretion of gonadotropin-releasing hormone increases. Under conditions of low estrogen levels, gonadotropin-releasing hormone is secreted in high doses for 3-5 minutes at 1-hour intervals. In response to this, the anterior pituitary gland begins to secrete FSH. Under the influence of FSH, 3-30 primordial follicles enter the stage of large growth, forming primary follicles (pre-antral). Under the influence of FSH, follicular cells begin to proliferate and secrete the enzyme aromatase, which catalyzes the conversion of androgens

estradiol. Estrogen synthesis by follicular cells increases. Estrogens stimulate an increase in the number of receptors on the membranes of follicular cells.

Secondary follicles (antral).Characterized by further growth. One of the follicles, outpacing all the others in growth, becomes the dominant follicle. Theca is formed around the follicles. In theca, 2 layers are distinguished: theca externa (represented by connective tissue) and theca interna (represented by theca - luteal cells). Theca interna cells secrete androgens, which, penetrating the basal membrane, enter into an aromatization reaction catalyzed by aromatase. The products of this reaction are estrogens. Theca interna cells also have receptors for LH. LH stimulates the synthesis of androgens by theca interna cells.

At this point, the estrogen level becomes so high that the hypothalamus begins to secrete gonadotropin-releasing hormone in small doses for 3-5 minutes, but with an interval of 3 hours. In response to this, the pituitary gland stops secreting FSH and begins active secretion of LH.

Tertiary follicle (Graafian follicle).At low concentrations of FSH, follicular cells stop dividing. But FSH continues to stimulate fluid transport into the follicle cavity, due to which the follicle quickly increases in size from 200 µm to 2.5 cm. In the follicle, individual cavities between follicular cells merge, the oocyte is displaced to the wall of the follicle - an oviparous tubercle is formed. Under the influence of LH, ovulation occurs and follicular and theca - luteal cells are luteinized - a yellow body is formed.

Ovulation occurs: According to Valliulin - the period between the maximum concentrations of FSH and LH - this period is approximately 12 hours.

Oogenesis

Oogenesis(except for the final stages) occurs in the ovarian cortex and includes three phases: 1) reproduction, 2) growth and 3) maturation (meiosis).

Primary germ cells migrate to the ovarian rudiments and differentiate into oogonia, which immediately enter the stage of reproduction (mitosis).

Having completed a series of mitotic divisions, oogonia enter the growth stage. During this period, yolk inclusions accumulate in the cytoplasm.

Following the growth stage, the maturation stage (meiosis) begins. The first division of meiosis remains

incomplete: the first-order oocytes formed in the prophase of the first division of meiosis enter

a long period of rest, continuing until puberty. A primordial follicle is formed.

with the onset of puberty and the establishment of the ovarian-menstrual cycle, the first meiotic division is completed during ovulation and the second division begins, stopping in metaphase. In this case, a large second-order oocyte and a small abortive cell are formed - the first polar (director, or reduction) body. The second meiotic division is completed at

fertilization; the second-order oocyte divides to form a mature egg and a second polar body. The first polar body also undergoes a second meiotic division. Thus

Thus, during oogenesis, one complete egg cell is formed from one ovogonium, under the transparent shell of which three polar bodies are localized.

Oocyte. The structure of the ovulated oocyte and its membranes, the importance of membranes

Structure of a mature (preovulatory) follicle

Tertiary follicle (Graafian follicle).At low concentrations of FSH, follicular cells stop dividing. But FSH continues to stimulate fluid transport into the follicle cavity, due to which the follicle quickly increases in size from 200 µm to 2.5 cm. In the follicle, individual cavities between follicular cells merge, the oocyte is displaced to the wall of the follicle - an oviparous tubercle is formed. Under the influence of LH, ovulation occurs and follicular and theca - luteal cells are luteinized - a yellow body is formed.

Estrogens. Localization and cytology of hormone-producing cells. Regulation of estrogen secretion, their targets and effects

This is a group of steroid hormones. The main estrogen is estradiol, which has the greatest physiological activity; the second most important is estriol; there is also estrone, but its activity is insignificant.

Place of production

Outside of pregnancy:In the follicular phase of the cycle, estrogens are secreted by the follicular cells (granulosa cells) of the growing follicle. In the luteal phase, they are secreted by the cells of the corpus luteum.

During pregnancy:secreted by the placenta (trophoblast) and the corpus luteum. In the first trimester, the main source is the corpus luteum and, to a lesser extent, the placenta. With the beginning of the second trimester, when the corpus luteum ceases to function, the placenta remains the main source of estrogen.

menEstrogens are secreted by Sertoli cells.

Estrogens are also secreted in the brain (?).

Regulation of secretion

Main regulation:During follicle growth, estrogen secretion is stimulated by the estrogens themselves via positive feedback. This is because the estrogens secreted by the follicular cells stimulate the proliferation of the follicular cells themselves, which leads to even greater estrogen secretion.

FSH, which stimulates follicle growth, has a weak stimulating effect on the formation of estrogens. But FSH stimulates the synthesis of androgens, from which estrogens are synthesized.

Additional regulation:estrogen secretion decreases with heavy physical exertion (which in girls can lead to delayed puberty). But with good training, the decrease in estrogen is insignificant or does not occur at all.

Estriol secretion increases especially strongly during multiple pregnancies and sharply increases with impending labor.

Progesterone. Localization and cytology of hormone-producing cells. Regulation of secretion. Targets and effects of progesterone

Follitropin (follicle-stimulating hormone). Synthesis, secretion, targets,

effects

Menstrual corpus luteum. Formation and its regulation, structure, functions

Corpus luteum- temporary endocrine gland, synthesizes progesterone (70%-80%) and estrogen

(20%-30%). It is formed from follicular cells and theca cells remaining in the ovary after ovulation.

Structure.Inside the corpus luteum there is a connective tissue scar surrounded by luteal cells, between which sinusoidal capillaries are located.

Functions.The corpus luteum functions in the luteal phase of the ovarian cycle. Under the influence of LH, luteal cells synthesize and secrete progesterone. Luteal cells also secrete estrogens (but more progesterone: progesterone 2/3, and estrogens 1/3).

The menstrual corpus luteum functions until the end of the cycle (no implantation). Progesterone levels peak 8-9 days after ovulation, which is approximately the time of implantation (if the egg is fertilized).

There are 2 types:

menstrual - 2 weeks

pregnant women - 2-3 months, until the placenta is fully formed.

The life cycle of the corpus luteum has four stages:

Vascularization and proliferation

Characterized by active proliferation of granulosa and theca cells. Capillaries grow into the granulosa from the inner layer of theca, and the basal membrane separating them is destroyed.

Iron metamorphosis

Granulosa and theca cells transform into large polygonal light-colored cells - luteocytes - with a powerfully developed aER, a large number of mitochondria with tubular cristae and lipid droplets. Luteocytes are divided into two types:

a) granular luteocytes- develop from granulosa cells, are large in size, make up the bulk of the yellow body and are located in its center;

b) theca-luteocytes- originate from the internal theca, are relatively small and dark, and lie on the periphery of the corpus luteum.

Blooming stage

Characterized by the active function of luteocytes, which produce progesterone - a female sex hormone that prepares the uterus to accept the embryo and promotes pregnancy. They also produce estrogens and, in small quantities, androgens and oxytocin

during pregnancy - the polypeptide hormone relaxin, which prepares the birth canal for childbirth.

Stage of involution (reverse development)

Includes a sequence of degenerative changes in luteocytes with their destruction and replacement by a dense connective tissue scar - a whitish (white) body, which, decreasing in size, very slowly (over months) sinks into the ovarian stroma.

Regulation of the corpus luteum functionLH is carried out, the receptors of which are present on the luteocytes (and first appear on the granulosa cells of the preovulatory follicles). Progesterone produced by the corpus luteum inhibits the secretion of FSH by the pituitary gland, as a result of which the beginning of the next cycle of follicle growth is inhibited, which is automatically resumed with the extinction of the corpus luteum.

Placenta development. Syncytiotrophoblast, cytotrophoblast. Primary, secondary, tertiary villi

Placenta (baby's place)- is an important temporary organ with multiple functions (see p. 101) that provide the connection between the fetus and the mother's body. At the same time, the placenta creates a barrier between the blood of the mother and the fetus.

The main functions of the placenta:

respiratory

Fetal respiration is provided by oxygen bound to maternal hemoglobin, which diffuses through the placenta into fetal blood, where it combines with fetal hemoglobin (HbF). Fetal hemoglobin-bound CO2 in fetal blood also diffuses through the placenta, enters the mother's blood, where it combines with maternal hemoglobin.

transport of nutrients, water, electrolytes and immunoglobulins

Transport of all nutrients necessary for fetal development (glucose, amino acids, fatty acids, nucleotides, vitamins, minerals) occurs from the mother's blood through the placenta into the fetal blood, and vice versa, metabolic products excreted from the fetus's body enter the mother's blood (excretory function). Electrolytes and water pass through the placenta by diffusion and by pinocytosis.

The transport of immunoglobulins (Ig) involves pinocytotic vesicles of the symplastotrophoblast. Ig that enters the fetus's blood passively immunizes it from the possible action of bacterial antigens that may enter during maternal illnesses. After birth, maternal Ig is destroyed and replaced by newly synthesized Ig in the child's body when exposed to bacterial antigens. Ig class G and A (IgG, IgA) penetrates into the amniotic fluid through the placenta.

excretory -see above

4) endocrine

The endocrine function is one of the important ones, since the placenta has the ability to synthesize and secrete a number of hormones that ensure the interaction of the embryo and the mother's body throughout pregnancy. The place of production of placental hormones is the cytotrophoblast and especially the symplastotrophoblast, as well as decidual cells.

The placenta is one of the first to synthesize human chorionic gonadotropin, the concentration of which rapidly increases in the 2nd-3rd week of pregnancy, reaching a maximum in the 8th-10th week, and in the fetus's blood it is 10-20 times higher than in the mother's blood. The hormone stimulates the formation of adrenocorticotropic hormone (ACTH) in the pituitary gland, and increases the secretion of corticosteroids.

Placental lactogen, which has the activity of prolactin and luteotropic hormone of the pituitary gland, is of great importance in the development of pregnancy. It supports steroidogenesis in the corpus luteum of the ovary in the first 3 months of pregnancy, and also participates in the metabolism of carbohydrates and proteins. This hormone, together with prolactin of the pituitary gland of the mother and fetus, plays a certain role in the production of pulmonary surfactant and fetoplacental osmoregulation. Its high concentration is found in amniotic fluid.

participation in the regulation of myometrial contraction

Progesterone(produced first by the corpus luteum in the ovary, and from the 5th-6th week in the placenta) suppresses uterine contractions, stimulates its growth, has an immunosuppressive effect, suppressing the reaction of fetal rejection. About 3/4 of progesterone in the mother's body is metabolized and transformed into estrogens, and some is excreted in the urine.

Estrogens (estradiol, estrone, estriol)are produced in the symplastotrophoblast of the placental villi (chorion) in the middle of pregnancy, and by the end of pregnancy their activity increases 10 times. They cause hyperplasia and hypertrophy of the uterus. In addition, melanocyte-stimulating and adrenocorticotropic hormones, somatostatin, etc. are synthesized in the placenta.

The placenta contains polyamines (spermine, spermidine), which affect the increase in RNA synthesis

smooth muscle cells of the myometrium, as well as the oxidases that destroy them. An important role is played by amine oxidases (histamine, monoamine oxidase), which destroy biogenic amines - histamine,

serotonin, tyramine. During pregnancy, their activity increases, which contributes to the destruction of biogenic amines and a decrease in the concentration of the latter in the placenta, myometrium and maternal blood.

The placenta consists of two parts: the embryonic, or fetal, and the maternal. The fetal part is represented by the branched chorion and the amniotic membrane attached to it from the inside, and the maternal part is the modified mucous membrane of the uterus, which is rejected during childbirth.

Chorion. Formation, structure, functions

Chorion, or villous membrane, appears for the first time in mammals, develops from the trophoblast and extraembryonic mesoderm. Initially, the trophoblast is represented by a layer of cells,

forming primary villi. They secrete proteolytic enzymes, with the help of which the mucous membrane of the uterus is destroyed and implantation is carried out. In the 2nd week, the trophoblast acquires a two-layer structure due to the formation of an inner cellular layer (cytotrophoblast) and a symplastic outer layer (symplastotrophoblast or syncytiotrophoblast), which is a derivative of the cellular layer. The extraembryonic mesoderm appearing in the embryoblast (in humans, in the 2nd-3rd week of development) grows towards the trophoblast and together with it forms secondary epitheliomesenchymal villi. From this time on, the trophoblast turns into the chorion, or villous membrane (Fig. 47).

At the beginning of the 3rd week, blood capillaries grow into the chorion villi and tertiary villi are formed. This coincides with the beginning of hematotrophic nutrition of the embryo. Further development of the chorion is associated with two processes - the destruction of the uterine mucosa due to the proteolytic activity of the outer (symplastic) layer and the development of the placenta.

Formation of the chorion.During implantation, villi are formed from the cytotrophoblast and syncytotrophoblast, which penetrate the decidual membrane, creating the possibility of transporting substances from the mother's bloodstream to the fetus's bloodstream and back. Three periods are distinguished: previllous, the period of villus formation, and the period of cotyledons.

Previllous period.

Cytotrophoblast and syncytotrophoblast are formed, the blastocyst penetrates the decidual membrane of the uterus. In the early stages of implantation, trophoblast cells do not have cytolytic activity: the cells penetrate the decidual membrane without destruction. Later, as they penetrate the endometrium (decidual membrane), the cells increase their cytolytic activity, as a result of which the endometrial tissues are destroyed and lacunae filled with the mother's blood are formed.

The period of villus formation.

During this period, primary, secondary and tertiary villi are formed sequentially.

Primary villi.They are clusters of cytotrophoblast cells surrounded by syncytotrophoblast. Primary villi are partitions in the lacunae.

Secondary villi. On the 11th day after the formation of the zygote, the inner layer of the extraembryonic mesoderm begins to line the chorion from the inside. On the 12th-13th day, this mesoderm grows into the primary villi, which leads to the formation of secondary villi on the entire surface of the chorion. The secondary villi are also covered with syncytotrophoblast. At this stage, the division of trophoblast cells slows down and vascularization of the future chorion begins.

Tertiary villi. Vessels grow into the secondary villi, and they become tertiary villi. The villi immersed in the basal part of the decidua are supplied with blood not only from the vessels originating from the chorionic mesoderm, but also from the vessels of the allantois. The period of connection of the branches of the umbilical vessels with the local circulatory network coincides with the onset of the fetal heartbeat (21 days) and the circulation of embryonic blood begins in the villi. Vascularization of the villi usually ends at the 10th week of pregnancy. By this time, the placental barrier is formed. From the top of the villi towards the decidual tissue, cellular columns (columns) consisting of cytotrophoblast cells contacting the superficial compact zone of the decidua extend. Cellular columns connect the tops of adjacent villi. A zone of coagulation necrosis (Nitabuch's layer) is formed in the contact area. Next, cytotrophoblast cells penetrate the spongy zone of the endometrium, the myometrium and the wall of the uterine vessels. In the 6th week, the cytotrophoblast grows into the wall of the spiral arteries, which leads to

opening the lumen of these vessels and establishing the circulation of maternal blood among the chorionic villi.

The villi in the area of the chorion facing the uterine cavity (formerly the parietal part of the trophoblast) are weakly expressed and subsequently disappear, therefore this part of the chorion is called the smooth chorion. And the part of the chorion adjacent to the wall of the uterus is the villous chorion.

Cotyledon period.

Cotyledon (quaternary villus)- a structural and functional unit of the formed placenta. It is formed by the stem villus and its branches containing the vessels of the fetus. By the 140th day of pregnancy, 10-12 large, 40-50 small and up to 150 rudimentary cotyledons have formed in the placenta.

Amnion. Formation, structure, function

Amnion— a temporary organ that provides an aquatic environment for the development of the embryo. It arose

evolution in connection with the exit of vertebrates from water to land. In human embryogenesis, it appears at the second stage of gastrulation first as a small bubble, the bottom of which is the primary ectoderm (epiblast) of the embryo. The wall of the bubble forms the extraembryonic ectoderm, which connects with the extraembryonic mesoderm, grows and surrounds the embryo with a thin translucent amniotic membrane (the source of development of its epithelium).

The wall of the amniotic vesicle consists of a layer of cells of the extraembryonic ectoderm and extraembryonic mesenchyme, forming its connective tissue.

The amnion enlarges rapidly, and by the end of the 7th week its connective tissue comes into contact

connective tissue of the chorion. Later, in the umbilical cord, and in the area of the umbilical ring, it closes with the epithelial covering of the embryo's skin.

The amniotic sac forms the wall of a reservoir filled with amniotic fluid,

which the fetus is located. The main function of the amniotic membrane is the production of amniotic fluid, which provides an environment for the developing organism and protects it from mechanical damage. The epithelium of the amnion, facing its cavity, not only secretes amniotic fluid, but also takes part in its reabsorption.

amniotic fluidThe necessary composition and concentration of salts are maintained until the end of pregnancy. The amnion also performs a protective function, preventing harmful agents from entering the fetus.

Placental hormones: human chorionic gonadotropin. Synthesis, secretion, targets,

effects

Human chorionic gonadotropin (hCG).

Secreted by the trophoblast(including as part of the placenta) from 10-12 days of development, and reaches its maximum from the 9th to the 19th week, then decreases slightly, reaches a plateau and remains there for the rest of the pregnancy.

Regulation of secretion

The secretion of hCG is stimulated by gonadotropin-releasing hormone secreted by the trophoblast and somatotropin.

Effects:

Supports the function of the corpus luteum (secretion of progesterone).

Stimulates the endocrine function of Leydig cells in the testes of the male fetus (testosterone secretion)

Endocrine function of the placenta. Placental hormones, their targets and effects

Human chorionic gonadotropin (hCG)- see above

2.Human chorionic somatomammotropin - stimulates the development of mammary glands.

Progesterone- by affecting the myometrium, it reduces the excitability threshold of the SMC. By affecting the SMC of the cervix, it maintains their tone.

Relaxin- during pregnancy it has a relaxing effect on the myometrium, before childbirth it leads to expansion of the cervical os and a decrease in the density of the pubic symphysis.

Prolactin -prepares the mammary glands for lactation. Prolactin of the amniotic fluid is involved in the regulation of water-salt metabolism in the fetus.

Corticoliberin- the level of this hormone can be used to determine the onset of labor.

Estrogens

Placental barrier. Structure, functions

The hematoplacental barrier is formed only by the structures of the fetus!!!

Compound:

(fetal blood)

Endothelium of fetal vessels (in chorionic villi)

Connective tissue of vessels and stroma of villi

Villous epithelium - cytotrophoblast, symplastotrophoblast

Langhans fibrinoid (in places)

(mother's blood)

But in many areas of the placenta, the barrier is reduced to only two components - the endothelium of the fetal vessels and a thinned layer of symplastotrophoblast.

It performs a barrier function - it ensures the selectivity of transport of substances and, in particular, prevents many (but not all!) immunological reactions between the corresponding components of the fetus and mother (e.g. Rhesus conflict).

Mammary gland. Origin. Development. Structure at different stages of development: hormonal regulation of development

Breast— a derivative of the epidermis and is related to the glands of the skin. However, the development of the gland and its functional activity depend on the hormones of the reproductive system.

During embryogenesis, the mammary glands are laid down as milk lines - epidermal ridges located on both sides of the body from the armpit to the groin. In the mid-thoracic region, the epithelial strands of the ridges grow into the skin proper and subsequently differentiate into complex tubular-alveolar glands.

Juvenile glandIt is represented by excretory interlobular and intralobular ducts separated by connective tissue septa; secretory sections are absent.

At the onset of puberty, the mammary gland begins to increase in volume under the influence of estrogens, STH, prolactin and glucocorticoids secreted in the body. Under the influence of estrogens, the mass of the mammary glands increases due to adipose tissue. There are NO secretory sections in the mature non-lactating mammary gland, as well as in the juvenile one.

Lactating gland.Under the influence of progesterone in combination with estrogens, prolactin and chorionic somatomammotropic hormone, differentiation of the secretory sections of the mammary gland is induced. Already in the third month of pregnancy, buds are formed from the growing terminal sections of the intralobular ducts, differentiating into secretory sections - alveoli. The alveoli are lined with cuboidal secretory cells (alveolar cells). From the outside, the wall of the alveoli and excretory ducts is surrounded by myoepithelial cells. The intralobular ducts are lined with a single-layer cubic epithelium, which in the excretory ducts turns into a multilayer flat one. The connective tissue partitions separating the lobules of the mammary gland become less pronounced.

Lactating mammary glandconsists of 15-20 separate complex tubular-alveolar glands, each of which opens with its own excretory duct (milk duct) at the apex of the nipple. The nipple consists of dense connective tissue with a high content of elastic fibers and SMC, located circularly at the base of the nipple and parallel to the milk ducts. The skin around the nipple contains large sebaceous glands that form elevations (areolar tubercles). Milk ducts under the areola form milk sinuses, reservoirs for milk. Pigmentation of the epidermis of the nipple occurs during puberty, the skin of the areola is pigmented during pregnancy.

Milk secretion occurs by the apocrine type. Fats are released together with fragments of the cell membrane, the remaining components of milk are released by exocytosis.

Prolactin (what else to write????)

Lactotropic hormone (LTH)

Place of production

They are secreted by the adenohypophysis and also by lymphocytes.

During pregnancysecreted by the placenta (trophoblast). At the zygote stage, it is secreted by the remaining ovarian follicular cells.

menIn addition to the adenohypophysis, it is secreted by Sertoli cells.

Physiological action

Prepares the mammary glands for lactation. Prolactin of the amniotic fluid is involved in the regulation of water-salt metabolism of the fetus.

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