Epithelial tissues, or epithelium(from Greek. epi- over and thele- nipple) - border tissues covering the surface of the body and lining its cavities, mucous membranes internal organs. Also, epithelia form glands (glandular epithelium) and receptor cells in the sense organs (sensory epithelium).

1. Lecture: EPITHELIAL TISSUE. COVERING EPITHELIUM 1.

2. Lecture: EPITHELIAL TISSUE. COVERING EPITHELIUM 2.

3. Lecture: EPITHELIAL TISSUES. glandular epithelium

Kinds epithelial tissue: 1. Integumentary epithelium, 2. Glandular epithelium (form glands) and can be distinguished 3) Sensory epithelium.

General morphological features of the epithelium as a tissue:

1) Epithelial cells are located close to each other, forming layers of cells;

2) The epithelium is characterized by the presence of a basement membrane - a special non-cellular formation that creates the basis for the epithelium, provides barrier and trophic functions;

3) Virtually no intercellular substance;

4) There are intercellular contacts between cells;

5) Epitheliocytes are characterized by polarity - the presence of functionally unequal cell surfaces: apical surface (pole), basal (facing the basement membrane) and lateral surfaces.

6) Vertical anisomorphism - unequal morphological properties of cells of different layers of the epithelial layer in stratified epithelium. Horizontal anisomorphism - unequal morphological properties of cells in single-layer epithelium.

7) There are no vessels in the epithelium; nutrition is carried out by diffusion of substances through the basement membrane from the vessels connective tissue;

8) Most epithelia are characterized by a high ability to regenerate - physiological and reparative, which is carried out thanks to cambial cells.

The surfaces of the epitheliocyte (basal, lateral, apical) have a distinct structural and functional specialization, which is especially well detected in the single-layer epithelium, including the glandular epithelium.

Lateral surface of epithelial cells provides cell interaction due to intercellular connections that cause mechanical communication of epitheliocytes with each other - these are tight junctions, desmosomes, interdigitations, and slot-like contacts provide the exchange of chemicals (metabolic, ionic and electrical communication).

Basal surface of epithelial cells attached to the basement membrane, with which it connects with the help of hemidesmosomes. The basal and lateral surfaces of the plasmolemma of the epitheliocyte together form a single complex, the membrane proteins of which are: a) receptors that perceive various signal molecules, b) carriers of nutrients coming from the vessels of the underlying connective tissue, c) ion pumps, etc.

basement membrane(BM) binds epithelial cells and the underlying loose fibrous connective tissue. At the light-optical level, on histological preparations, BM looks like a thin strip, poorly stained with hematoxylin and eosin. At the ultrastructural level, three layers are distinguished in the basement membrane (in the direction from the epithelium): 1) a light plate, which connects to the hemidesmosomes of epitheliocytes, contains glycoproteins (laminin) and proteoglycans (heparan sulfate), 2) a dense plate contains collagen IV, V, VII types , has a fibrillar structure. Thin anchor filaments cross the light and dense plates, passing into 3) the reticular plate, where the anchor filaments bind to collagen (collagen types I and II) connective tissue fibrils.

Under physiological conditions, BM prevents the growth of the epithelium towards the connective tissue, which is disturbed during malignant growth, when cancer cells grow through the basement membrane into the underlying connective tissue (invasive tumor growth).

Apical surface of epithelial cells may be relatively smooth or protrude. Some epithelial cells have special organelles on it - microvilli or cilia. Microvilli are maximally developed in epithelial cells involved in absorption processes (for example, in small intestine or tubules of the proximal nephron), where their combination is called the brush (striated) border.

Microcilia are mobile structures containing complexes of microtubules inside.

Sources of epithelial development. Epithelial tissues develop from three germ layers, starting from 3-4 weeks of human embryonic development. Depending on the embryonic source, the epithelium of ectodermal, mesodermal and endodermal origin is distinguished.

Morphofunctional classification of epithelial tissue

I. Integumentary epithelium

1. Single layer epithelium - all cells lie on the basement membrane:

1.1. Single-row epithelium (cell nuclei at the same level): flat, cubic, prismatic;

1.2. Stratified epithelium(cell nuclei on different levels due to horizontal anisomorphism): prismatic ciliated;

2. Stratified epithelium- only the lower layer of cells is connected with the basement membrane, the overlying layers are located on the underlying layers:

2.1. Flat - keratinizing, non-keratinizing

3. Transitional epithelium - occupies an intermediate position between single-layer multi-row and stratified epithelium

II. Glandular epithelium:

1. With exocrine secretion

2. With endocrine secretion

SINGLE-LAYER EPITHELIUM

Single layered squamous epithelium formed by flattened polygonal cells. Examples of localization: mesothelium covering the lung (visceral pleura); the epithelium lining the inside of the chest cavity (parietal pleura), as well as the parietal and visceral layers of the peritoneum, the pericardial sac. This epithelium allows the organs to come into contact with each other in the cavities.

Single layered cuboidal epithelium formed by cells containing a nucleus of a spherical shape. Localization examples: follicles thyroid gland, small ducts of the pancreas and bile ducts, renal tubules.

Single-layer single-row prismatic (cylindrical) epithelium formed by cells with a pronounced polarity. The elliptical nucleus lies along the long axis of the cell and is shifted to their basal part; the organelles are unevenly distributed throughout the cytoplasm. On the apical surface are microvilli, brush border. Examples of localization: lining the inner surface of the small and large intestines, stomach, gallbladder, a number of large pancreatic ducts and bile ducts liver. This type of epithelium is characterized by the functions of secretion and (or) absorption.

Single-layer multi-row ciliated (ciliated) epithelium airways is formed by cells of several types: 1) low intercalated (basal), 2) high intercalated (intermediate), 3) ciliated (ciliated), 4) goblet. The low intercalary cells are cambial, with their wide base adjacent to the basal membrane, and with their narrow apical part they do not reach the lumen. Goblet cells produce mucus that coats the surface of the epithelium, moving along the surface due to the beating of cilia of ciliated cells. The apical parts of these cells border on the lumen of the organ.

MULTILAYER EPITHELIUM

Stratified squamous keratinized epithelium(MPOE) forms the outer layer of the skin - the epidermis, and covers some areas of the mucous membrane oral cavity. MPOE consists of five layers: basal, spiny, granular, shiny (not present everywhere), and stratum corneum.

Basal layer formed by cells of a cubic or prismatic shape, lying on the basement membrane. Cells divide by mitosis - this is the cambial layer, from which all overlying layers are formed.

Spiny layer formed by large cells of irregular shape. Dividing cells can be found in the deep layers. In the basal and spinous layers, tonofibrils (bundles of tonofilaments) are well developed, and desmosomal, dense, slit-like junctions are between the cells.

Granular layer consists of flattened cells - keratinocytes, in the cytoplasm of which there are grains of keratohyalin - a fibrillar protein, which in the process of keratinization turns into eleidin and keratin.

glitter layer expressed only in the epithelium of thick skin covering the palms and soles. The zona pellucida is the zone of transition from the living cells of the granular layer to the scales of the stratum corneum. On histological preparations, it looks like a narrow oxyphilic homogeneous strip and consists of flattened cells.

stratum corneum consists of horny scales - postcellular structures. The processes of keratinization begin in the prickly layer. The stratum corneum has a maximum thickness in the epidermis of the skin of the palms and soles. The essence of keratinization is to ensure the protective function of the skin from external influences.

Differenton keratinocyte includes cells of all layers of this epithelium: basal, spiny, granular, shiny, horny. In addition to keratinocytes, the stratified keratinizing epithelium contains a small amount of melanocytes, macrophages (Langerhans cells) and Merkel cells (see the topic "Skin").

The epidermis is dominated by keratinocytes organized according to the column principle: cells at different stages of differentiation are located one above the other. At the base of the column are cambial poorly differentiated cells of the basal layer, the top of the column is the stratum corneum. The keratinocyte column includes keratinocyte differon cells. The columnar principle of epidermal organization plays a role in tissue regeneration.

Stratified squamous nonkeratinized epithelium covers the surface of the cornea of ​​the eye, mucous membrane of the oral cavity, esophagus, vagina. It is formed by three layers: basal, spiny and superficial. The basal layer is similar in structure and function to the corresponding layer of the keratinizing epithelium. The spinous layer is formed by large polygonal cells, which flatten as they approach the surface layer. Their cytoplasm is filled with numerous tonofilaments, which are located diffusely. The surface layer consists of polygonal flat cells. Nucleus with poorly distinguishable granules of chromatin (pycnotic). During desquamation, the cells of this layer are constantly removed from the surface of the epithelium.

Due to the availability and ease of obtaining the material, the stratified squamous epithelium of the oral mucosa is a convenient object for cytological studies. Cells are obtained by scraping, smearing or imprinting. Next, they are transferred to a glass slide and a permanent or temporary cytological preparation is prepared. The most widely used diagnostic cytological examination this epithelium in order to reveal the genetic sex of the individual; violations of the normal course of the process of differentiation of the epithelium during the development of inflammatory, precancerous or tumor processes in the oral cavity.

3. transitional epithelium - a special type of stratified epithelium that lines most of the urinary tract. It is formed by three layers: basal, intermediate and superficial. The basal layer is formed by small cells that have a triangular shape on the cut and, with their wide base, are adjacent to the basement membrane. The intermediate layer consists of elongated cells, the narrower part adjacent to the basement membrane. The surface layer is formed by large mononuclear polyploid or binuclear cells, which change their shape to the greatest extent when the epithelium is stretched (from round to flat). This is facilitated by the formation in the apical part of the cytoplasm of these cells at rest of numerous invaginations of the plasmolemma and special disc-shaped vesicles - reserves of the plasmolemma, which are built into it as the organ and cells stretch.

Regeneration of integumentary epithelium. The integumentary epithelium, occupying a borderline position, is constantly affected by the external environment, so the epithelial cells quickly wear out and die. In a single-layer epithelium, most cells are capable of dividing, and in a multilayer epithelium, only cells of the basal and partially spinous layers have this ability. Integumentary epithelium is characterized by a high degree of ability to regenerate, and in connection with this, up to 90% of all tumors in the body develop from this tissue.

Histogenetic classification of integumentary epithelium(according to N.G. Khlopin): there are 5 main types of epithelium that develop in embryogenesis from various tissue primordia:

1) Epidermal - formed from the ectoderm, has a multi-layer or multi-row structure, performs barrier and protective functions. For example, the epithelium of the skin.

2) Enterodermal - develops from the intestinal endoderm, is a single-layer cylindrical structure, carries out the absorption of substances. For example, intestinal epithelium.

3) Whole nephrodermal - has a mesodermal origin (coelomic lining, nephrotome), in structure it is single-layer, flat or prismatic, performs mainly a barrier or excretory function. For example, the epithelium of the kidneys.

4) Angiodermal - includes endothelial cells of mesenchymal origin (angioblast).

5) The ependymoglial type is represented by a special type of tissue of neural origin (neural tube) that lines the cavities of the brain and has a structure similar to the epithelium. For example, ependymal gliocytes.

glandular epithelium

Glandular epithelial cells can be located singly, but more often form glands. Glandular epithelial cells - glandulocytes or glandular cells, the secretion process in them proceeds cyclically, is called the secretory cycle and includes five stages:

1. The phase of absorption of the initial substances (from the blood or intercellular fluid), from which the final product (secret) is formed;

2. The phase of secretion synthesis is associated with the processes of transcription and translation, the activity of grEPS and agrEPS, the Golgi complex.

3. The maturation phase of the secret occurs in the Golgi apparatus: dehydration and addition of additional molecules occur.

4. The accumulation phase of the synthesized product in the cytoplasm of glandular cells is usually manifested by an increase in the content of secretory granules, which can be enclosed in membranes.

5. The secretion removal phase can be carried out in several ways: 1) without violating the integrity of the cell (merocrine type of secretion), 2) with the destruction of the apical part of the cytoplasm (apocrine type of secretion), with a complete violation of the integrity of the cell (holocrine type of secretion).

The glands are divided into two groups: 1) endocrine glands, or endocrine glands, which produce hormones - substances that have a high biological activity. There are no excretory ducts, the secret enters through the capillaries into the blood;

and 2) glands of external secretion, or exocrine, the secret in which is released into the external environment. Exocrine glands consist of terminal (secretory sections) and excretory ducts.

The structure of the exocrine glands

The terminal (secretory) sections consist of glandular cells (glandulocytes), which produce a secret. Cells are located on the basement membrane, they are characterized by pronounced polarity: the plasmolemma has a different structure on the apical (microvilli), basal (interaction with the basement membrane) and lateral (intercellular contacts) surfaces of cells. Secretory granules are present in the apical part of the cells. In cells that produce secrets of a protein nature (for example: digestive enzymes), GREPs is well developed. In cells synthesized non-protein secrets (lipids, steroids), aEPS is expressed.

In some glands formed by epidermal type epithelium (for example, sweat, milk, salivary), in addition to glandular cells, the terminal sections contain myoepithelial cells - modified epitheliocytes with a developed contractile apparatus. Myoepithelial cells, with their processes, cover the glandular cells from the outside and, by contracting, contribute to the secretion from the cells of the terminal section.

The excretory ducts connect the secretory sections with the integumentary epithelium and ensure the release of synthesized substances onto the surface of the body or into the cavity of organs.

The division into terminal sections and excretory ducts is difficult in some glands (for example, the stomach, uterus), since all parts of these simple glands are capable of secretion.

Classification of exocrine glands

I. Morphological classification exocrine glands is based on a structural analysis of their terminal sections and excretory ducts.

Depending on the form of the secretory (terminal) section, alveolar, tubular and mixed (alveolar-tubular) glands are distinguished;

Depending on the branching of the secretory section, branched and unbranched glands are distinguished.

The branching of the excretory ducts determines the division of the glands into simple (the duct does not branch) and complex (the duct branches).

II. By chemical composition produced secret distinguish between serous (protein), mucous, mixed (protein-mucous), lipid and other glands.

III. According to the mechanism (method) of excretion The secretion of exocrine glands is divided into apocrine (mammary gland), holocrine (sebaceous gland) and merocrine (most glands).

Examples of classification of glands. Classification characteristic sebaceous gland skin: 1) simple alveolar gland with branched terminal sections, 2) lipid - according to the chemical composition of the secret, 3) holocrine - according to the method of excretion of the secret.

Characteristic lactating (secret-producing) breast: 1) complex branched alveolar-tubular gland, 2) with a mixed secret, 3) apocrine.

Gland regeneration. Secretory cells of merocrine and apocrine glands are stable (long-lived) cell populations, and therefore they are characterized by intracellular regeneration. In the holocrine glands, restoration is carried out due to the reproduction of cambial (stem) cells, i.e. cellular regeneration is characteristic: newly formed cells differentiate into mature cells.

First of all, epithelial tissues are divided into single-layer and stratified epithelium. A unilayer epithelium is an epithelium in which all cells lie on a basement membrane. In the stratified epithelium, the cells lie in several layers, but only the bottom row of cells touches the basement membrane.

Single layer epithelium.

Single layer epithelium, consisting of cells of the same shape and size, is called single-row. However, in cases where a single-layer epithelium consists of cells of unequal shape and size, such an epithelium is called multi-row. Single-row epithelium may consist of prismatic, cuboidal, or squamous cells. In this regard, there are single-layer squamous epithelium, single-layer cubic epithelium, single-layer columnar epithelium.

Single layered squamous epithelium- mesothelium, lines all the serous membranes (pleura, peritoneum, cardiac membrane), develops from the mesoderm. Cells have a polygonal or somewhat irregular shape. The boundary between the cells is uneven, due to which the protrusions of the cell membrane of one cell protrude into the recesses of another cell. Cell borders are detected only when treated with silver. Each cell contains one, less often several, flattened nuclei. The cytoplasm is granular and contains vacuoles. Electron microscopy reveals small microvilli on the surface of mesothelial cells. The cytoplasm contains all common organelles: mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, etc.

Mesothelium, covering the serous membranes, prevents the formation of connective tissue adhesions that occur during inflammatory diseases. In addition, through the mesothelium, the process of absorption of substances from the serous cavities is carried out. These processes of absorption occur most intensively along the periphery of the cell. During regeneration, mesothelial cells increase their planar dimensions and move to the wound surface. Cell reproduction occurs by mitosis.

Single layered cuboidal epithelium lines the tubules of the kidneys, small bronchi, ducts of the glands, etc. IN various bodies this epithelium performs various functions: in the kidneys - absorption, in the glands - secretory, etc. In embryogenesis, this epithelium develops from the mesoderm and endoderm. Each cell of this epithelium has approximately the same height and width. Sometimes there are microvilli on the apical surface of cuboidal epithelial cells.

Single layered columnar epithelium- is located in the middle section of the digestive tract, in the uterus and oviducts, excretory ducts of the glands (liver and pancreas). This epithelium develops from different germ layers: from the endoderm (intestinal epithelium), from the mesoderm (epithelium of the tubules of the kidneys, vas deferens). The functional significance of this epithelium varies in different organs. So, the epithelium of the stomach secretes mucus, which promotes the digestion of food and protects the mucous membrane from chemicals. The intestinal epithelium takes part in the processes of absorption. In all cells of the prismatic epithelium, polar differentiation is pronounced. Cell nuclei are elliptical in shape and lie in the basal part of the cell. Organelles are located above the nucleus. Special structures can form on the apical surface: microvilli in the intestinal epithelium, cilia in the uterine epithelium.

Single layered epithelium lines the mucous membrane of the airways. This epithelium develops from the endoderm and mesoderm.

In a single layered epithelium, all cells lie on the basement membrane. In this case, the shape and size of the cells are not the same. There are several types of cells in this epithelium. Prismatic cells (ciliated)- the tops of these cells make up the surface of the epithelial layer and often have ciliated cilia. The basal part of the cells is narrowed, and the apical part is expanded. Insertion cells cubic and spindle-shaped, located between the prismatic ones. goblet cells- these are cells that secrete mucus (mucin) on the surface of the epithelium, which protects it from mechanical, chemical and infectious influences. Basal cells- These are low cells, lie on the basement membrane and belong to the cambial cells, which divide and differentiate into ciliated and goblet cells. In addition, this epithelium contains endocrine cells that carry out local regulation muscle tissue bronchi. Due to the fact that these cells have a different shape, their nuclei lie at different levels and form several rows, therefore such an epithelium is called multi-row. The single-layer multi-row ciliated epithelium of the airways, due to the oscillation of the cilia, contributes to the removal of dust particles.

Stratified epithelium- This is an epithelium, which consists of several layers of cells. In this case, only the lower layer of cells lies on the basement membrane. There are stratified squamous keratinized epithelium, stratified squamous non-keratinized epithelium and stratified stratified transitional epithelium.

Stratified squamous nonkeratinized epithelium covers the cornea of ​​the eye, the mucous membrane of the oral cavity, esophagus, etc. The cells of this epithelium are located in several layers. The cells of the lower layer, lying directly on the basement membrane, have a cylindrical shape. These cells are poorly differentiated and divide by mitosis. Due to these cells, all other layers are replenished. Therefore, this layer (basal) is called the germ layer. In the next layers, the cells flatten and acquire processes that wedged between the underlying cells. These cells are called prickly. The closer to the surface, the more flattened the cells become. The surface cells are flat, these cells also contain tonofibrils.

Stratified squamous keratinized epithelium- makes up the outermost layer of the skin (epidermis). In contrast to the non-keratinizing epithelium, in this epithelium, cells are transformed into horny scales, which lie on the surface in the form of a layer. The transition to horny scales is carried out gradually, therefore, many layers are found in the composition of the keratinizing epithelium. The cells of this epithelium are called keratinocytes.

The deepest layer is a layer of high prismatic cells lying on the basement membrane - this basal layer. The cell membrane in the basal part of the cells gives deep finger-like protrusions penetrating into the dermis. Due to this layer, the strength of the bond with the underlying tissues is ensured. Here are the stem cells of differon keratinocytes. In addition, melanocytes are located in this layer, the cytoplasm of which contains a large number of melanin pigment granules concentrated around the nucleus. There is also a small number of intraepidermal macrophages (Langerhans cells. A layer of spiny cells is located above the basal cells. These cells are characterized by the presence of a large number of processes (spines). Keratinosomes appear in the cytoplasm of these cells, which are granules containing lipids. These granules are secreted into macrophages and melanocytes also lie here.Melanocytes, with the help of pigment, create a barrier that prevents the penetration of ultraviolet rays into the body.Langerhans cells (macrophages) are involved in immune reactions and regulate the reproduction of keratinocytes, forming together with them "proliferative units" Then there are 2-3 layers of flat cells (keratinocytes), in the cytoplasm of which keratohyalin protein granules appear, which indicates the beginning of the process of keratinization.In addition to keratohyalin, the cells of the granular layer contain filaggrin proteins (rich in histidine), involucrin, keratolinin, loricrin. These proteins are involved in the processes of keratinization. This layer is called the granular layer. Then comes a shiny layer, represented by flat cells impregnated with the protein ellaidin. The surface layer consists of horny scales, which are air bubbles surrounded by keratin protein. Between the scales there is a cementing substance, a product of keratinosomes, rich in lipids, which gives the layer a waterproofing property. The outermost horny scales lose contact with each other and constantly fall off the surface of the epithelium. They are replaced by new ones - due to reproduction, differentiation and movement of cells from the underlying layers. Due to this, the epidermis is completely renewed every 3-4 weeks. The significance of the keratinization process lies in the fact that the stratum corneum formed in this process is resistant to mechanical and chemical influences, has poor thermal conductivity and is impermeable to water and many water-soluble toxic substances.

Stratified transitional epithelium. This epithelium got its name due to the fact that it can change its structure. Transitional epithelium lines the renal pelvis, ureteral mucosa, Bladder and other organs of the urinary tract. If you take the wall of the bladder filled with urine (stretched), and consider the structure of its epithelium, you can see a two-layer epithelium. At the same time, the basal layer of cells is represented by cells of a cubic shape. The superficial cells are also cuboidal, but much larger. The epithelium of the bladder, which is in a collapsed state, has a different structure. Due to the fact that the surface of the basement membranes, as it were, decreases, some of the cells of the basal layer do not fit on it and are forced out into an additional layer, but retain their connection with the basement membrane with a narrow stalk.

Thus, the transitional epithelium changes its structure depending on the functional state of the organ, i.e. change in its volume.

According to the ability to secrete, epithelial tissues are divided into 2 main types: integumentary (non-glandular) and glandular (secretory).

Glandular or secretory epithelium. This is the epithelium that secretes a secret onto its free surface. For example, the mucous membrane of the stomach, intestines, bronchi, urinary organs is always moistened with a secret produced by epithelial cells. Secretory epitheliocytes are characterized by a high degree of development of the endoplasmic reticulum, mitochondria and the Golgi apparatus, i.e. organelles directly involved in the secretion process. Secretory granules are present at the apical pole of these cells. In addition, glandular cells are characterized by the presence of intracellular capillaries, which are folds of the plasmalemma.

In some cases, glandular cells are concentrated in organs that specialize in secretion - glands. Glands are formed during embryogenesis from epithelial cells growing into the underlying connective tissue. All glands in our body are divided into endocrine and exocrine. Endocrine glands are glands that secrete their secretion directly into the blood or lymph (pituitary, pineal, thyroid and etc.). Exocrine glands are glands that secrete their secret into the cavity or on the surface of the skin (salivary, sweat, sebaceous, prostate, etc.).

exocrine glands. Exocrine glands are unicellular and multicellular. The only example of single-celled glands in the human body are goblet cells. Multicellular glands consist of two main parts: specialized cells that synthesize the secret (secretory or terminal) and a system of tubes (tubules) through which the secret moves (excretory ducts).

Thus, the exocrine glands consist of end sections and excretory ducts. The shape of the end sections distinguish: alveolar, tubular and alveolar-tubular glands. According to the structure of the excretory duct exocrine glands are divided into simple and complex. Simple glands are glands in which the excretory duct does not branch (sweat glands). Complex glands are characterized by the presence of a branching excretory duct (liver, pancreas, salivary glands). According to the structure of the end section distinguish between branched and unbranched glands.

Exocrine glands are different the nature of the secret. In this regard, there are protein (serous) glands (parotid, pancreas), mucous (goblet cells), protein-mucous (submandibular, sublingual) and sebaceous (sebaceous glands of the skin), saline (lacrimal, sweat).

The protein terminal sections consist of secretory cells of a prismatic shape, the cytoplasm of which stains basophilically, which is due to the content of free ribosomes and those associated with the endoplasmic reticulum. The rounded nucleus lies on the basal pole. At the apical pole there are numerous granules of an immature secret - a zymogen, which is a vesicle surrounded by a membrane containing a secret intended for excretion.

The mucous terminal sections consist of large irregularly shaped cells, the nuclei of which are flattened and located at the basal pole closer to the basement membrane. The cytoplasm is light and filled with vesicles containing mucus.

Protein-mucous (mixed) terminal sections consist of mucous cells, on top of which there is an accumulation of a group of protein cells, resembling a crescent moon in shape and called the protein crescent.

Exocrine glands differ from each other not only in the nature of the secretion secreted, but also according to the method (mechanism) of secretion of this secret. Merocrine glands (salivary) secrete their secret through the plasmalemma in the form of bubbles surrounded by a membrane, while the integrity of the plasma membrane is not violated. With the apocrine type of secretion, partial destruction of the apical part of the secretory cells (sweat glands of the axillary region, mammary glands) is possible. However, a number of researchers do not recognize this type of secretion. In the holocrine glands, in the process of secretion, the destruction and death of the entire cell occurs, i.e., the cells die and are destroyed, thus forming a secret that is pushed out through the hair follicles and lubricates the hair. The only example of this type of secretion is the sebaceous glands of the skin. At the same time, the restoration of dead cells is carried out due to poorly differentiated cells located on the basement membrane.

The single-layer epithelium is divided into squamous, cuboidal and prismatic epithelium according to the shape of the cells. Prismatic epithelium is also called columnar or columnar.

Single-layer epithelium can be of two types: single-row and multi-row. In a single-row epithelium, all cells have the same shape - flat, cubic or prismatic, and their nuclei lie on the same level, i.e. in one row. Single-layer epithelium, which has cells of various shapes and heights, the nuclei of which lie at different levels, i.e. in several rows, is called multi-row, or pseudo-multilayer.

Meaning

The epithelium separates the organism (internal environment) from the external environment, but at the same time serves as an intermediary in the interaction of the organism with environment. Epithelial cells are tightly connected to each other and form a mechanical barrier that prevents the penetration of microorganisms and foreign substances into the body. Epithelial tissue cells live for a short time and are quickly replaced by new ones (this process is called regeneration). Epithelial tissue is also involved in many other functions: secretion (external and internal secretion glands), absorption (intestinal epithelium), gas exchange (lung epithelium). The main feature of the epithelium is that it consists of a continuous layer of densely packed cells. The epithelium can be in the form of a layer of cells lining all surfaces of the body, and in the form of large clusters of cells - glands: liver, pancreas, thyroid, salivary glands, etc. In the first case, it lies on the basement membrane, which separates the epithelium from the underlying connective tissue . However, there are exceptions: epithelial cells in the lymphatic tissue alternate with elements of connective tissue, such an epithelium is called atypical.

Structure

1) basal, which, in addition to poorly differentiated stem epithelial cells, contains cells with processes - melanocyte pigment cells, Langerhans cells (dendritic macrophages), as well as Merkel cells (mechanoreceptors) 2) spinous, the structure of which is similar to that of the non-keratinized epithelium described above; the basal and spinous layers together form the sprout zone of the epidermis (Malpighi zone) 3) granular - consists of flattened cells containing grains of the fibrillar protein keratohyalin; 4) shiny - on histological preparations it looks like a homogeneous shiny strip due to the presence of eleidin in its flat cells, which is a complex of keratohyalin with tonofibrils and represents the next stage in the formation of a horny protein - keratin; 5) horny - consists of horny scales filled with keratin and air bubbles; external scales under the influence of lysosomal enzymes lose their connection with each other and constantly peel off from the surface of the epithelium. Transitional epithelium lays out the urinary tract - renal pelvis, calyces, ureters, bladder.

5 Stratified squamous non-keratinized and keratinized epithelium

The stratified squamous non-keratinized epithelium (Fig. 1) consists of three layers of cells, among which there are basal, spinous (spiky), intermediate and superficial: - The basal layer is formed by relatively large prismatic or cylindrical cells that are attached to the basement membrane with numerous napivdesmosomes; - The spinous (spiky) layer is formed by large cells of a polygonal shape, have processes in the form of spikes. These cells are located in several layers, which are interconnected by numerous desmosomes, and in their cytoplasm there are many tonofilaments; - The surface layer is formed by flat dying cells that are exfoliated. The first two layers form the germinal layer. Epitheliocytes divide mitotically and, moving upwards, flatten and gradually replace the cells of the surface layer that have been aggravated. The free surface of many cells is covered with short microvilli and small folds. The epithelium of this type covers the mucous membrane of the oral cavity, the esophagus of the vagina, the vocal folds, the transition zone of otkhodniks, the female urethra, and also forms the anterior epithelium of the cornea of ​​the eye. That is, the stratified squamous non-keratinized epithelium covers the surface, constantly moistened by the secretion of glands located in the subepithelial loose loose connective tissue.

Stratified squamous keratinized epithelium covers the entire surface of the skin, forming its epidermis (Fig. 2). In the epidermis of the skin, 5 layers are distinguished: basal, spinous (spinous), granular, shiny and horny: - In the basal layer there are prismatic cells with numerous small processes surrounded by a basement membrane, and in the cytoplasm above the nucleus there are melanin granules. Between the basal epitheliocytes placed pigment cells - melanocytes; - The spinous (spinous) layer is formed by several rows of large polygonal epithelial cells, which have short processes - spikes. These cells, especially their processes, are interconnected by numerous desmosomes. The cytoplasm is rich in tonofibrilams and tonofilaments. Epidermal macrophages, melanocytes and lymphocytes are also located in this layer. These two layers of epitheliocytes form the sprout layer of the epithelium; - The granular layer consists of flattened epitheliocytes that contain many grains (granules) of keratohyalin; - The shiny layer, on histological preparations, looks like a shiny light strip, formed from squamous epithelial cells containing eleidin; - The stratum corneum is formed from dead flat cells - horny scales, filled with keratin and air bubbles and are regularly exfoliated. The transitional epithelium changes its structure depending on the functional state of the organ. The transitional epithelium covers the mucous membrane of the renal calyces and bowl, ureters, bladder, and the initial part of the urethra. In the transitional epithelium, three cell layers are distinguished - basal, intermediate and integumentary: - The basal layer consists of small, intensely stained irregularly shaped cells that lie on the basement membrane; - The intermediate layer contains cells of various shapes, which are mainly in the form of tennis rackets with narrow legs that are in contact with the basement membrane. These cells have a large nucleus, numerous mitochondria are located in the cytoplasm, a moderate amount of elements of the endoplasmic reticulum, the Golgi complex; - The integumentary layer is formed by large light cells, in which there may be 2-3 nuclei. The shape of these epithelial cells, depending on the functional state of the organ, can be flattened or pear-shaped. When the walls of organs are stretched, these epitheliocytes become flat, and their plasma membrane is stretched. The apical part of these cells contains the Golgi complex, numerous spindle-shaped vesicles, and microfilaments. In particular, when the bladder is full, the epithelial cover is not interrupted. The epithelium remains impermeable to urine and reliably protects the bladder from damage. When the bladder is empty, the epithelial cells are high, the plasma membrane of the surface cells forms folds, up to 8-10 rows of nuclei are visible on the preparation, and when the bladder is full (stretched), the cells are flattened, the number of rows of nuclei does not exceed 2-3, the cytolem of the surface cells is smooth.

6. Glandular epithelium. Microscopic and submicroscopic features of glandular cells. Classification of glands. the epithelium that produces secrets is called glandular and its cells are secretory cells or secretory glandulocytes. Glands are built from them, which can be designed as an independent organ. Or be just a part of it.

Distinguish between endocrine and exocrine glands.

Exocrine, consist of two parts: the end part and the excretory ducts, through which the secretion enters the surface of the body or into the cavity of the internal organ.

Endocrine: devoid of excretory ducts. Their active substances, hormones, enter the bloodstream.

Exocrine glands are diverse in structure and function, they can be unicellular and multicellular.

Exocrine multicellular glands can be single-layered and multi-layered, this is genetically determined (sweat, sebaceous, mammary, salivary glands)

Unicellular glands of the fundus of the stomach of the uterus, pancreas.

According to the structure of the excretory ducts, they are distinguished: simple and complex.

Simple glands have a non-branching excretory duct, while complex glands have a branching one. The terminal sections of simple glands branch and do not branch, in complex ones they branch.

According to the shape of the terminal sections, the exocrine glands are classified into alveolar, tubular and tubular-alveolar. In the olveolar gland, the cells of the terminal sections form vesicles or sacs, in tubular glands they form the appearance of a tube. The tubular olveolar has an intermediate position between the sac and tubule. Terminal cells are glandulocytes.

According to the method of secretion formation, the glands are divided into holocrine, apocrine, merocrine. With holocrine secretion, glandular metamorphosis of glandulocytes begins from the periphery of the terminal section and proceeds in the direction of the excretory duct. Stem cells are small in size. This method ends with the complete destruction of the cell.

During apocrine secretion, the apical part of the secretory cell is destroyed. This type of secretion takes place in the sweat or mammary glands.

With merocrine secretion, the cell is not destroyed (Glands of the stomach, salivary glands and pancreas)

Single layered stratified ciliated epithelium (pseudostratified or anisomorphic)

All cells are in contact with the basement membrane, but have different heights, and therefore the nuclei are located at different levels, i.e. in several rows. Lines the airways. Function: purification and humidification of passing air.

In the composition of this epithelium, 5 types of cells are distinguished:

Top row:

Ciliated (ciliated) cells are tall, prismatic in shape. Their apical surface is covered with cilia.

On the middle row:

• - Goblet cells - have the shape of a glass, do not perceive dyes well (white in the preparation), produce mucus (mucins);
• - Short and long insertion cells (poorly differentiated and among them stem cells; provide regeneration);
• - Endocrine cells, the hormones of which carry out local regulation of the muscle tissue of the airways.

On the bottom row:

Basal cells are low, lie on the basement membrane in the depth of the epithelial layer. They belong to cambial cells.

Stratified epithelium.

1. Multilayered flat non-keratinizing lines the anterior (oral cavity, pharynx, esophagus) and final section (anal rectum) digestive system, cornea. Function: mechanical protection. Source of development: ectoderm. Prechordal plate in the endoderm of the foregut.

Consists of 3 layers:

• a) basal layer - cylindrical epithelial cells with weakly basophilic cytoplasm, often with a mitotic figure; in a small amount of stem cells for regeneration;
• b) spiny (intermediate) layer - consists of a significant number of layers of spiny cells, the cells are actively dividing.

In the basal and spinous layers, tonofibrils (bundles of tonofilaments from keratin protein) are well developed in epitheliocytes, and desmosomes and other types of contacts are between epitheliocytes.

c) integumentary cells (flat), senescent cells, do not divide, gradually exfoliate from the surface.

Stratified squamous epithelium has nuclear polymorphism:

• - the nuclei of the basal layer are elongated, located perpendicular to the basal membrane,
• - the nuclei of the intermediate (prickly) layer are rounded,
• - the nuclei of the surface (granular) layer are elongated and located parallel to the basement membrane.
• 2. Stratified squamous keratinizing - this is the epithelium of the skin. It develops from the ectoderm, performs a protective function - protection from mechanical damage, radiation, bacterial and chemical effects, delimits the body from the environment.
• Ш In thick skin (palm surfaces), which is constantly under stress, the epidermis contains 5 layers:
  • 1. basal layer - consists of prismatic (cylindrical) keratinocytes in the cytoplasm of which keratin protein is synthesized, which forms tonofilaments. Here are the stem cells of diferon keratinocytes. Therefore, the basal layer is called sprout, or rudimentary
  • 2. prickly layer - formed by polygonal keratinocytes, which are firmly interconnected by numerous desmosomes. In place of desmosomes on the surface of the cells there are tiny outgrowths - "spikes" directed towards each other. In the cytoplasm of spiny keratinocytes, tonofilaments form bundles - tonofibrils and keratinosomes appear - granules containing lipids. These granules are released into the intercellular space by exocytosis, where they form a lipid-rich substance that cements keratinocytes. In addition to keratinocytes, in the basal and spinous layers there are process-shaped melanocytes with granules of black pigment - melanin, intraepidermal macrophages (Langerhans cells) and Merkel cells that have small granules and are in contact with afferent nerve fibers.
  • 3. granular layer - the cells acquire a rhomboid shape, the tonofibrils disintegrate and keratohyalin protein is formed inside these cells in the form of grains, this begins the process of keratinization.
  • 4. lustrous layer - a narrow layer, in which cells become flat, they gradually lose their intracellular structure (not nuclei), and keratohyalin turns into eleidin.
  • 5. stratum corneum - contains horny scales that have completely lost their cell structure, are filled with air bubbles, and contain keratin protein. With mechanical stress and with a deterioration in blood supply, the process of keratinization intensifies.
• Ø In thin skin, which is not stressed, there is no granular and shiny layer.

The basal and spiny layers make up the growth layer of the epithelium, since the cells of these layers are capable of dividing.

4. Transitional (urothelium)

There is no polymorphism of the nuclei, the nuclei of all cells have rounded shapes. Sources of development: the epithelium of the pelvis and ureter - from the mesonephric duct (a derivative of the segmental legs), the epithelium of the bladder - from the endoderm of the allantois and the endoderm of the cloaca. The function is protective.

Lines hollow organs, the wall of which is capable of strong stretching (pelvis, ureters, bladder).

• - basal layer - from small dark low-prismatic or cubic cells - poorly differentiated and stem cells, provide regeneration;
• - intermediate layer - from large pear-shaped cells, with a narrow basal part, in contact with the basement membrane (the wall is not stretched, therefore the epithelium is thickened); when the wall of the organ is stretched, pear-shaped cells decrease in height and are located among the basal cells.
• - integumentary cells - large dome-shaped cells; with a stretched wall of an organ, the cells flatten; cells do not divide, gradually exfoliate.

Thus, the structure of the transitional epithelium changes depending on the state of the organ:

• - when the wall is not stretched, the epithelium is thickened due to the "displacement" of some of the cells from the basal layer to the intermediate layer;
• - with a stretched wall, the thickness of the epithelium decreases due to the flattening of the integumentary cells and the transition of some of the cells from the intermediate layer to the basal one.

Histogenetic classification (according to sources of development) ed. N.G. Khlopin:

• 1. Epithelium of the skin type (epidermal type) [skin ectoderm] - protective function
• - stratified squamous non-keratinizing epithelium;
• - keratinized stratified squamous epithelium (skin);
• - single-layer multi-row ciliated epithelium of the airways;
• - transitional epithelium of the urethra (?); (epithelium of the salivary, sebaceous, mammary and sweat glands; alveolar epithelium of the lungs; epithelium of the thyroid and parathyroid glands, thymus and adenohypophysis).
• 2. Epithelium of the intestinal type (enterodermal type) [intestinal endoderm] - carries out the processes of absorption of substances, performs a glandular function
• - single-layer prismatic epithelium of the intestinal tract;
• - epithelium of the liver and pancreas.
• - The epithelium of the renal type (nephrodermal) [nephrotome] - the epithelium of the nephron; in different parts of the channel:
  • - single-layer flat; or - single-layer cubic.
• - Epithelium of the coelomic type (celodermal) [splanchnotome] - a single-layer squamous epithelium of serous integuments (peritoneum, pleura, pericardial sac);
• - epithelium of the gonads; - epithelium of the adrenal cortex.
• 4. Epithelium of the neuroglial type /ependymoglial type/ [neural plate] - brain cavities;
• - retinal pigment epithelium;
• - olfactory epithelium;
• - glial epithelium of the organ of hearing;
• - taste epithelium;
• - epithelium of the anterior chamber of the eye;
• 5. Angiodermal epithelium /endothelium/ (cells lining the blood and lymphatic vessels, cavities of the heart) there is no consensus among histologists: some refer the endothelium to a single-layer squamous epithelium, others to a connective tissue with special properties. Source of development: mesenchyme.

glandular epithelium

The glandular epithelium is specialized for secretion production.

Secretory cells are called glandulocytes (ER and PC are developed).

The glandular epithelium forms glands:

I. Endocrine glands - do not have excretory ducts, the secret is secreted directly into the blood or lymph; plentifully supplied with blood; produce hormones or biologically active substances that have a strong regulatory effect on organs and systems, even in small doses.

II. Exocrine glands - have excretory ducts, secrete a secret onto the surface of the epithelium (on the outer surfaces or in the cavity). They consist of terminal (secretory) sections and excretory ducts.

Principles of classification of exocrine glands:

I. According to the structure of the excretory ducts:

• 1. Simple - the excretory duct does not branch.
• 2. Complex - the excretory duct branches.

II. According to the structure (shape) of the secretory (terminal) sections:

• 1. Alveolar - a secretory section in the form of an alveolus, a vesicle.
• 2. Tubular - secretory section in the form of a tube.
• 3. Alveolar-tubular (mixed form).

III. According to the ratio of excretory ducts and secretory sections:

• 1. Unbranched - one secretory section opens into one excretory duct.
• 2. Branched - several secretory sections open into one excretory duct.

IV. By type of secretion:

• 1. Merocrine - during secretion, the integrity of the cells is not violated. It is characteristic of most glands (salivary glands, pancreas).
• 2. Apocrine (apex - apex, crinio - excretion) - during secretion, the apex of the cells is partially destroyed (torn off):
  • - micro-apocrine - in the process of removing the secret, microvilli (sweat glands) are destroyed;
  • - macro-apocrine - in the process of removing the secret, the apical part of the cytoplasm (mammary gland) is destroyed.
• 3. Holocrine - during secretion, the cell is completely destroyed (eg: sebaceous glands of the skin).

V. By localization:

• 1. Endoepithelial - a unicellular gland in the thickness of the integumentary epithelium. Ex: goblet cells in the intestinal epithelium and airway. ways.
• 2. Exoepithelial glands - the secretory section lies outside the epithelium, in the underlying tissues.

VI. By the nature of the secret:

• - protein (I produce protein / serous / fluid - parotid gland),
• - mucous membranes (oral cavity; goblet cell),
• - mucous-protein /mixed/ - submandibular gland,
• - sweat,
• - greasy,
• - dairy, etc.

Secretion phases:

• 1. Entry into the glandular cells of the starting materials for secretion synthesis (amino acids, lipids, minerals, etc.).
• 2. Synthesis (in EPS) and accumulation (in PC) in the glandular cells of the secret.
• 3. Extraction of a secret.
• 4. Restoration of the cell structure.

The cells of the glandular epithelium are characterized by the presence of organelles: EPS of a granular or agranular type (depending on the nature of the secret), a lamellar complex, mitochondria.

23852 0

Stratified squamous epithelium (SSE)

The MPE is thin, almost colorless, without vessels, as a rule, has a thickness of about 150–200 µm, and consists of 4 layers of cells (basal, parabasal, intermediate, and superficial). The MPE is capable of constant renewal due to the continuous desquamation of the surface layers (its renewal cycle averages 4-5 days).

Its main function is protective. Normally, the MPE joins with the columnar epithelium of the cervical canal in the area of ​​the external os.

The basal layer of the MPE is located on the basement membrane separating it from the stroma. In histological analysis, the basal lower layer is represented by one row of rounded or low-cylindrical cells with a relatively large oval nucleus rich in chromatin. This layer is a reserve, thanks to it there is a constant replenishment of MPE cells. Melanocytes are sometimes found among the cells of the basal layer.

The parabasal layer consists of 2-3 rows of polygonal cells with large nuclei, basophilic cytoplasm and low glycogen content, with high mitotic activity.

Above it is an intermediate layer, which consists of large polygonal cells with small nuclei, light cytoplasm, and a high content of glycogen. The closer the layer is to the surface of the epithelium, the higher the differentiation of cells and the content of glycogen in the cytoplasm.

The topmost layer of the epithelium is called the superficial. It has a cellular structure, and its nuclei are few and pycnotic, the cytoplasm is abundant, eosinophilic due to the high content of keratin microfilaments.

Columnar epithelium (CE)

The cervical canal has a fusiform shape, its mucous membrane is represented by numerous folds and ridges that form crypts with a depth of 4 mm or more. At histological examination they are called cervical glands. There are no true tubular glands in the cervical canal and exocervix. An element of the endocervix are pseudoglands or crypts, the cells of which secrete mucus, therefore, upon examination, the epithelium lining the endocervix always looks juicy, moist.

Normally, the canal is lined with a single-layer columnar epithelium (CE) lying on the basement membrane, with tall cylindrical cells, basally located nuclei and a large number of vacuoles associated with mucus production. The secret of these cells is acidic and neutral mucins, the secretion of which is carried out using apocrine and merocrine types of secretion.

The so-called pluripotent reserve cells are also located on the basement membrane under the CE, which are capable of providing the physiological process of epithelial regeneration. Differentiation of reserve cells can occur in the direction of both cylindrical and squamous epithelium. On colposcopy, CE is usually reddish in color due to its thinness and translucent underlying vessels.

Histological structure of the epithelium of the cervix. MPE (1) and CE (2) are joined. Stained with hematoxylin and eosin

In women of reproductive age, the junction of these two types of epithelium is normally located in the area of ​​the external os, it can be located on the exocervix in young women, and inside the cervical canal in older women. The location of the CE on the exocervix is ​​called ectopia. Ectopia refers to a physiological condition that is not a pathology and therefore is not included in the ICD-10 list of diseases.