Epithelial tissues. Glands. Integumentary epithelia

The doctrine of tissues

Tissue is a historically developed system of cells and their derivatives (non-cellular structures), which are similar in structure, sometimes in origin, and specialized to perform certain functions.

Classification of fabrics (according to Leydig and Kölliker, 1853):

Epithelial;

Connecting (internal environment);

Muscular;

Nervous.

The concept of tissue regeneration.

Regeneration is the replacement and renewal of tissue components.

Regeneration is distinguished:

Physiological (constant renewal of worn-out tissue parts)

Reparative (tissue restoration in case of damage).

Sources of regeneration:

Poorly differentiated (cambial) cells within tissues;

Stem cells. These are self-sustaining, rarely dividing cells. Cell populations are maintained by the division of their descendants.

Epithelial tissue

Features of epithelial tissues.

Distinctive:

1. Superficial (borderline) location; one side faces the external environment and the other faces the internal environment. There are exceptions to this rule - the epithelium of serous integuments and endocrine glands.

2. Layer of cells, i.e. has a purely cellular structure (not counting the thinnest intercellular gaps containing a small amount of tissue fluid).

3. Polarity. Cells have two parts (surfaces) that differ in structure: apical and basal. The apical part faces the external environment. Special organelles and closer to it the Golgi apparatus are located here. The basal part faces the internal environment; here, most often, the nucleus and endoplasmic reticulum are located.

Characteristic:

1.Location on the basement membrane.

The basement membrane is a product of the activity of the epithelium and underlying connective tissue.

Has two layers:

Basal lamina (homogeneous part, main chemical component - glycoproteins)

Layer of reticulin fibers.

Functions of basement membranes:

Connects two tissues (epithelium and connective tissue)

Selective diffusion of various substances occurs through the basement membrane.

2. Lack of blood vessels.

Nutrition of the epithelium occurs through the diffusion of substances from the underlying connective tissue.

3.High regenerative ability.

Regeneration of epithelial tissues occurs either:

– by multiplying all cells (solid cambium)

– due to special poorly differentiated (cambial) cells.

However, the regeneration ability of the epithelium is not limitless. If the wound surface is small, then the epithelium covers it completely, and if it is large, it is filled with connective tissue (scar), which has the highest regenerative ability.

Types of cellular contacts (not only epithelial):

1. Simple - the cytolemmas of neighboring cells are brought closer together, but do not merge; thin gaps filled with tissue fluid remain between them. This is the main type of cellular contacts.

2. Dense - the cytolemmas of neighboring cells merge, which prevents the leakage of substances between them. This contact connects: intestinal epithelial cells, endothelial cells of brain capillaries, thymic cortex, etc.

3. Adhesive (adhesive) with the participation of desmosomes. The plasma membranes of neighboring cells do not merge but are held together by a special intercellular binding substance. On the cytoplasmic side there are electron-dense plates from which tonofilaments extend. The cells of the spinous layer of the skin epithelium are connected by this very strong type of contact.

4. Slit - the cytolemmas of neighboring cells are brought together but do not merge and are connected by tiny transverse tubes through which the passage of ions and various molecules from one cell to another is possible. This type of contact connects the muscle cells of the heart.

Special organelles of epithelial cells:

Microvilli (cytoplasmic projections on the apical part of cells, together forming a brush border)

Tonofibrils (thread-like structures that strengthen the cytoplasm of cells)

Cilia

Morphofunctional classification of epithelial tissues.

According to this classification, epithelium is distinguished:

Pokrovny

Glandular

Classification of the integumentary epithelium.

It is also divided into two groups:

Single layer

Multilayer

The epithelium is single-layered if all cells are connected to the basement membrane. In multilayered epithelium, only the lower layer of cells has a connection with the basement membrane, and the overlying layers do not have this connection. They are connected.

Types of single-layer epithelium.

There are epithelium

Single row

Multi-row

The epithelium is single-row if all cells have the same shape and size and therefore the nuclei are arranged in one row. In multirow epithelium, cells have different shapes and sizes and therefore the nuclei form several rows.

Based on the shape of the cells, the following types of single-layer single-row epithelium are distinguished:

Flat

Cubic

Cylindrical (prismatic)

Single layer squamous epithelium(cambium is solid). The epithelium is flat if the height of the cells is less than the width. Let us look at the example of the serous epithelium - mesothelium. It develops from the internal lining of the splanchnotoma and covers the peritoneum, pleura and pericardial sac. The main organs covered with mesothelium: stomach, intestines, lungs, heart, i.e. it covers organs that are constantly in motion. The main purpose of the mesothelium is to create a smooth surface, which facilitates the sliding of contacting organs.

Properties of mesothelium:

1. Very sensitive to the effects of irritants, in which the cells contract strongly and ruptures between them are possible, exposing the underlying loose connective tissue. The consequence of this may be the formation of adhesions.

2. In the presence of an irritant in the abdominal cavity (example), a massive migration of neutrophils through the epithelium occurs, followed by their death and the formation of pus (peritonitis).

3. Various substances are easily absorbed through the epithelium. This property is used by surgeons during interventions in the abdominal cavity; At the end of the operation, various antibiotics are injected into the cavity, with the expectation that they will then quickly enter the circulation.

SINGLE LAYER CUBIC EPITHELIA

Epithelium cubic - if the height of the cells is equal to the width. The cambium is solid. The origin and functions performed depend on the organ in which it is located. Examples where there is a single-layer cubic epithelium: kidney tubules, excretory ducts of glands, etc.

Single layer columnar epithelium.

Has varieties;

Simple

Glandular

Kaemchaty

Ciliated.

Single-layer cylindrical simple. The cells do not have special organelles on the apical part; they form the lining of the excretory ducts of the glands.

Single-layer cylindrical ferrous. The epithelium is called glandular if it produces some kind of secretion. This group includes the epithelium of the gastric mucosa (example), which produces mucous secretion.

Single layer cylindrical bordered. On the apical part of the cells there are microvilli, which together form a brush border. The purpose of microvilli is to dramatically increase the total surface area of ​​the epithelium, which is important for performing the absorption function. This is the epithelium of the intestinal mucosa.

Single layer cylindrical ciliated. On the apical part of the cells there are cilia, which perform a motor function. This group includes the epithelium of the oviducts. In this case, the vibrations of the cilia move the fertilized egg towards the uterine cavity. It must be remembered that if the integrity of the epithelium is violated (inflammatory diseases of the oviduct), the fertilized egg “gets stuck” in the lumen of the oviduct and here the development of the embryo continues for a certain time. It ends with a rupture of the wall of the oviduct (ectopic pregnancy).

Multirow epithelium.

Multirow cylindrical ciliated epithelium of the airways (Fig. 1).

Types of cells in the epithelium:

Cylindrical ciliated

Goblet

Insert

Cylindrical ciliated cells with their narrow base are connected to the basement membrane; cilia are located on the wide apical part.

Goblet cells have cleared cytoplasm. The cells are also connected to the basement membrane. Functionally, these are unicellular mucous glands.

2. Goblet cells

3. Ciliated cells

5. Intercalary cells

7. Loose connective tissue

Insert the cells, with their wide base, are connected to the basement membrane, and the narrow apical part does not reach the surface of the epithelium. There are short and long intercalary cells. Short intercalary cells are the cambium (source of regeneration) of multirow epithelium. From these, cylindrical ciliated and goblet cells are subsequently formed.

Multirow cylindrical ciliated epithelium performs a protective function. On the surface of the epithelium there is a thin film of mucus, where microbes and foreign particles from the inhaled air settle. Vibrations of the cilia of the epithelium constantly move the mucus outward and are removed by coughing or coughing.

Stratified epithelium.

Types of stratified epithelium:

Multilayer flat keratinizing

Multilayer flat non-keratinizing

Transition.

Stratified squamous keratinizing epithelium is the epithelium of the skin (Fig. 2.).

1(a) Basal layer

1(b) Layer spinosum

1(c) Granular layer

1(d) Shiny layer

1(e) Stratum corneum

Layers of the epithelium:

Basal

Spiny

Grainy

Brilliant

Horny

Basal layer- This is one layer of cylindrical cells. All cells of the layer are connected to the basement membrane. The cells of the basal layer are constantly dividing, i.e. are the cambium (source of regeneration) of multilayer epithelium. This layer contains other types of cells, which will be discussed in the “Particular histology” section.

Layer spinosum consists of several layers of polygonal cells. The cells have processes (thorns) with which they are firmly connected to each other. In addition, the cells are connected by contacts such as desmasomes. Tonofibrils (a special organelle) are located in the cytoplasm of the cells, which further strengthens the cytoplasm of the cells.

Cells of the spinous layer are also capable of division. For this reason, the cells of these layers are united under the general name - germ layer.

Granular layer- These are several layers of diamond-shaped cells. There are many large protein granules in the cytoplasm of cells - keratohyalina. The cells of this layer are not capable of division.

Shiny layer consists of cells that are at the stage of degeneration and death. Cells are poorly contoured, they are saturated with protein eleidine. On colored preparations the layer looks like a shiny strip.

Stratum corneum- this is a layer of horny scales layered on top of each other, i.e. the cells died and turned into horny scales. They consist of a strong fibrillar protein - keratin.

The function of the epithelium is protective (mechanical protection against penetration of microbes, toxins, etc. into the internal environment)

Stratified squamous non-keratinizing epithelium covers moist surfaces (oral cavity, esophagus, cornea, vagina, etc.) (Fig. 3).

1. Layer of flat cells

1. Cells of the thyroid layer
2. Cells of the basal layer

1. Proprietary substance of the cornea

The epithelium consists of layers:

Basal

Spiky

The basal and spinous layers have a structure similar to the previous epithelium. The layer of flat cells consists of flattened cells layered on top of each other.

Transitional epithelium(epithelium of the urinary tract). Transitional epithelium is called because the number of layers varies depending on the functional state of the organ, i.e. whether the wall of the organ is stretched or not (Fig. 4). If the wall of the organ is not stretched, three layers are distinguished within the epithelium:

Basal

Piriform cells and

Pokrovny.

Basal layer consists of small cells (compared to cells of other layers) that are connected to the basement membrane. This is a layer of dividing cells (epithelial cambium).

Pyriform cell layer(intermediate) consists of large pear-shaped cells. With their narrow base (looks like a stalk), they are also connected to the basement membrane.

Cover layer form large polygonal cells. On the surface of the cells there is a border (cuticle), apparently protecting the epithelium from the destructive effects of urine.

A(B) Cover layer

A(a) Layer of piriform cells

B(a) Basal layer

If the organ is in an unstretched state, then the epithelium has two layers: basal and integumentary, i.e. pyriform cells are found in the basal layer. Thus, the transitional epithelium is essentially two-layered.

Genetic classification of the integumentary epithelium(according to N.G. Khlopin). It takes into account the source of epithelial development. According to this classification, epithelium is distinguished:

1. Ectodermal type. This group includes: epithelium of the skin, oral cavity (and its derivatives), esophagus, cornea, urinary tract.

This epithelium is characterized by:

– multi-layered

– ability to keratinize

– vertical anisotropy (different vertically)

They develop from the outer germ layer - the ectoderm.

2. Endodermal type. This is the epithelium of the stomach, intestines, liver and pancreas. They develop from the inner germ layer of the endoderm.

3. Renal-coelomic (coelonephrodermal) type. This group includes the epithelium of the kidneys, adrenal glands, gonads, oviducts, uterus and serous integument (mesothelium). They develop from parts of the middle germ layer - mesoderm.

4. Ependymoglial type. This is the epithelium of the retina, spinal canal and ventricles of the brain.

Glandular epithelium.

Cells of this type of epithelium produce secretions or hormones and are the main component of the glands. In this regard, we will analyze the general plan of the structure of the exocrine glands. They have stroma and parenchyma. The stroma (non-working part) is formed by connective tissue (capsule and connective tissue cords extending from it). The parenchyma (working part) consists of epithelial cells.

There are two parts of glands formed by epithelial parenchyma cells:

Secretory (terminal) department

Excretory ducts.

The secretory compartment consists of secretory epithelial cells, sometimes surrounded by myoepithelial cells that promote secretion. The excretory ducts of the glands are lined with varieties of epithelial tissue.

The process of secretion formation (secretory cycle) has the following stages (stages):

Receipt of starting products for synthesis

Secretion synthesis (in the structures of the endoplasmic reticulum)

Maturation and accumulation of secretions

Removing the secret

The last two stages take place in the structures of the Golgi apparatus (complex).

You should know the classification of exocrine glands according to:

building

The nature of the secret and

Type of secretion.

Classification of glands by structure.

Based on the structure of the excretory ducts, the glands are divided into:

Simple and

More difficult

The gland is simple if the excretory duct does not branch. The gland is complex if the excretory duct has branches.

Based on the structure of the terminal sections, the glands are distinguished:

Alveolar;

Tubular

Mixed (alveolar-tubular).

The gland is alveolar, if the end section has a spherical shape; tubular, if it has a tubular shape and mixed, when there are end sections of both spherical and tubular shape.

Simple and complex glands can be: unbranched and branched.

The gland is unbranched if one excretory duct is connected to one terminal section. Branched if it is connected with several terminal sections. The glands are classified according to the nature of their secretions.;

Protein;

Mucous;

Mixed (protein-mucous).

Protein gland, if the secretion is rich in protein (enzymes);

The mucous gland produces a mucous secretion. And the mixed gland produces protein and mucous secretions.

The glands are classified according to the type of secretion:

Merocrine;

Apocrine

Holocrine

Gland merocrine if the secretory cells are not destroyed during secretion;

Apocrine, if during the process of secretion, the apical part of the cells is destroyed and holocrine, if the secretory cells are completely destroyed and turn into secretion.

Most glands secrete according to the merocrine type: salivary glands, liver, pancreas, etc. The mammary glands and some sweat glands secrete according to the apocrine type. An example of holocrine secretion is the sebaceous glands.

CONNECTIVE TISSUE

(tissues of the internal environment).

These tissues hold and connect cells of other tissues (hence the name). All connective tissues have a single source of development - mesenchyme. It is formed by the eviction of cells, mainly from the composition mesoderm. Mesenchyme cells are branched, have poorly developed cytoplasm and relatively large nuclei. The cells are connected only by processes, between which there is free space filled with intercellular fluid. Mesenchyme exists only in the embryonic period; have a wide potential for transformation and, by the time of birth, differentiate into other types of tissue (connective tissue, smooth muscle tissue, reticular tissue).

One of the derivatives of mesenchyme is reticular tissue. It is limited in distribution and is closest in structure to mesenchyme. Consists of reticular cells and fibers. Reticular cells are stellate in shape and are also connected to each other only by processes. The processes are longer and have more cytoplasm than those of mesenchymal cells; the spaces between cells are larger. Tissue fluid circulates in them.

Functionally, reticular cells are divided into:

poorly differentiated, being the cambium of a number of cellular elements of connective tissues and

Differentiated, which can leave the reticular tissue and become macrophages, performing a phagocytic function.

Integumentary epithelia

In accordance with the morphological classification, there are several main types of integumentary epithelium, both multilayer and single-layer. Moreover, multilayer epithelium is characterized by the presence of several layers, of which only the deepest - the basal layer - is located on the basement membrane. The remaining layers are not connected to the basement membrane. In multilayered epithelia, the shape of the cells of the surface layer is decisive in the name (for example, multilayered squamous non-keratinizing epithelium).

As for single-layer epithelium, all cells in it are located on the basement membrane and their nuclei are located either at different levels (in several rows) in a multirow epithelium, or at the same level (in one row) in a single row.

The word uniseriate is often omitted from the name of these epithelia. In the international histological nomenclature of 1987, these single-row epithelia are called simple, single-layer cubic and simple single-layer prismatic (columnar) epithelia. Stratified squamous non-keratinizing epithelium lines the oral cavity, esophagus and cornea of ​​the eye. There are three layers in it - basal, spinous and superficial. The basal layer of cylindrical cells is located on the basement membrane. Due to the mitotic division of these cells, the overlying layers of the epithelium change. In the basal and spinous layers, the cells have well-developed bundles of tonofilaments, and there are desmosomes between the cells. The spinous layer is represented by polygonal-shaped cells, and the superficial layer is represented by flat cells.

Stratified squamous keratinizing epithelium consists of many cells combined into 4-5 main layers -.ba hally, prickly, granular, shiny(not always expressed) and horny. This epithelium forms the epidermis of the skin. Its basal and spinous layers consist, respectively, of cylindrical and polygonal spinous cells capable of reproduction. The flattened cells of the granular layer contain grains of fibrillar protein - keratohyalin. The cells of the stratum lucidum contain the protein eleidin, which strongly refracts light. The stratum corneum is formed by flattened horny scales that do not have nuclei.

Transitional epithelium (cuboidal) typical for urinary drainage organs - renal pelvis, ureters and bladder. This two-layer epithelium consists of basal and integumentary cells, approximately cubic in shape. In an unstretched form, with a contracted organ, the basal cells show signs of enlargement. In this case, the epithelium is divided into three layers: basal, intermediate and superficial. During stretching of the organ wall, the epithelium becomes thinner, and the basal cells in contact with the basement membrane lie in only 2-3 rows.

Single-layer (pseudo-stratified) multirow prismatic ciliated epithelium, lines the airways from the nasal cavity to the bronchi, as well as the fallopian tubes, etc. It contains prismatic ciliated, short and long intercalary cells, as well as goblet glandular cells. All these cells lie on the basement membrane, but have different heights. Their nuclei form 3-4 rows. The tallest cells are the ciliated cells. Thanks to the coordinated movement of their cilia, mucus and foreign dust particles are removed. Mucous cells secrete mucin onto the surface of the epithelial layer.

Single layer single-row (simple) prismatic bordered epithelium present in the middle section of the digestive tract. It lines the inner surface of the small and large intestines and is formed by prismatic cells, the microvilli of which ensure absorption processes. Among these cells located on the basement membrane, there are goblet cells (single-cell glands) that secrete mucus onto the surface of the epithelial layer. The nuclei of all cells of a given epithelium form one row.

Single-layer squamous epithelium, called mesothelium. covers the serous membranes - pleura, peritoneum and pericardium. Flat, polygonal mesothelial cells lie on the basement membrane. The processes of secretion and absorption of serous fluid are carried out through the mesothelium, it promotes the sliding of the serous cover and prevents the formation of adhesions.

Physiological regeneration of epithelia

Physiological regeneration is the renewal of cells in epithelial tissues during their normal functioning. This is a dynamic process that includes both cell destruction and reproduction. Epithelial cells wear out relatively quickly, since they are significantly influenced by external factors due to the fact that most of these tissues occupy a borderline position. Epithelia, as a rule, have a well-defined regenerative ability, developed in the process of evolution, and are classified as renewing tissues. In epithelia, cellular renewal occurs due to the mitotic division of cambial cells.

However, it should be emphasized that each type of epithelium is characterized by specific features of proliferation, localization of cambial cells and patterns of cell differentiation and integration.

The concept of “tissues of the internal environment” unites tissues of various structures and functions that do not border the external environment and the cavities of internal organs. This term cannot be considered entirely apt, since the internal environment of the body is formed not only by blood, connective and skeletal tissues, but also by various epithelia within the internal organs, muscle tissue, and tissues of the nervous system. Therefore, it is advisable to include in this group only those tissues that, by their basic physiological properties, create an internal environment for metabolic reactions, ensure the constancy of the composition of the internal environment of the body, and perform the protective functions of the body.

This primarily applies to the blood system and some types of connective tissue. All of these tissues are derivatives of mesenchyme. Other derivatives of mesenchyme - connective tissues with a pronounced musculoskeletal function and smooth muscle tissue, along with muscle tissues of other origins, will be discussed in the next chapter.

Most mesenchyme derivatives are characterized by the following general characteristics: cell apolarity, richness in intercellular substance, and performance of protective and trophic functions. In addition, the structural elements of the tissue are in close interaction with the blood vessels

End of work -

This topic belongs to the section:

Histology

Histology from the Greek histos tissue logos is the study of the structure, development and vital activity of tissues of living organisms.. The formation of histology is closely related to the development of microscopic technology and.. In the history of the study of tissues and the microscopic structure of organs, two periods are distinguished: pre-croscopic and..

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Details

Epithelial tissues.
Functions: delimiting, barrier, protective, transport, suction, secretory, sensory, excretory.

Morphological characteristics: always borderline position, cell polarity, closeness of cell layers, basement membrane (BM), little intercellular substance, highly pronounced intercellular contacts, rapid renewal and regeneration, no vessels.

Surface epithelia- integumentary (on the surface of the body, mucous membranes of internal organs (stomach, intestines, bladder) and lining (secondary body cavities). They perform the function of absorption and excretion of metabolic products.
Glandular epithelium– secretory function, excretory function (hormones, etc.)

Sources of development of epithelial tissues:
They develop from three germ layers at 3-4 weeks of embryonic development.
Related types of epithelium (from 1 germ layer), in pathological conditions - metaplasia, i.e. pass from one type to another (for example, in the respiratory tract, the epithelium in chronic bronchitis changes from single-layer ciliated to multilayer squamous)

1. Surface epithelia.

Structure.

Epithelia are layers of epithelial cells. There is almost no intercellular substance between them; they are interconnected desmosomes(attachment plates contain plakoglobins, desmoplakin, and desmocalmin) in the cleft, SA-binding desmogleins), intermediate(AFs are attached to E-cadherin through actin and vinculin, the connection of the cytoskeleton with the μl substance), slotted(tubular connexons) and tight contacts(occludin, SA, mg).

Are located on basement membranes 1 micron thick (plates): light 20-40 nm and dark 20-60 nm plates. Light includes an amorphous substance with calcium ions. Dark - an amorphous matrix with proteins (fibrillar structures - collagen type 4), provides mechanical strength. In an amorphous substance - glycoproteins– fibronectin and laminin (induce proliferation and differentiation during regeneration), calcium ions– connection between adhesive molecules of glycoproteins of the basement membrane and hemidesmosomes of epithelioites. Protein glycans and glycosaminoglycans - membrane elasticity and negative charge provide selective permeability and the ability to accumulate toxic substances in pathology.
Epithelial cells are especially tightly connected to the basement membrane in the region of hemidesmosomes. Here, anchor filaments (type 7 collagen) approach the dark plate through the light plate.
Membrane functions: mechanical (attachment), trophic and barrier, morphogenetic (regeneration) and limiting the possibility of invasive epithelial growth, proliferative.

Features of epithelial tissues:
1) does not contain blood vessels (nutrition is diffuse through the membrane from the side of the connecting tissue.
2) has polarity (basal and apical parts have different structures).
3) Capable of regeneration (mitotic division and differentiation of stem cells). Cytokeratins form tonofilaments, exception: endothelium (vimentin)

Classification.

Morphogenetic– the relationship of cells to the basement membrane and their shape.
Single layer epithelium– all cells are connected to the basement membrane. A) single-row (isomorphic) - all cells have the same shape (flat, cubic or prismatic, nuclei lie on the same level). B) multi-row (anisomorphic)
Multilayer– flat keratinizing and many others. Pl. non-keratinizing. Prismatic – mammary gland, pharynx, larynx. Cubic – st. ovarian follicle, ducts of sweat and sebaceous glands.
Transition– lines organs subject to strong stretching – bladder, ureters.

Single layer epithelia. Mononuclear epithelia.

1. Single-layer squamous epithelium:
A) mesothelium– serous membranes (leaves of the pleura, visceral and parietal peritoneum); cells – mesotheliocytes, flat, polygonal in shape and with uneven edges. 1-3 cores. On the free surface there are microvilli. F: secretion and absorption of serous fluid, sliding of internal organs, prevents the formation of adhesions between the organs of the abdominal and thoracic cavities as a result of damage)
B) Endothelium– blood and lymphatic vessels, chambers of the heart. A layer of flat cells - edothelial cells, in 1 layer. Feature: poverty of organelles and the presence of pinocytotic vesicles in the cytoplasm. F – metabolism of substances and gases. Blood clots.

2. Single layer cubic– lines part of the renal tubules (proximal and distal). The cells have a brush border (microvilli) and basal striations (deep folds of the plasmalemma and mitochondria between them). F reverse suction.

3. Single layer prismatic– middle section of the digestive system: the inner surface of the stomach, small and large intestines, gall bladder, ducts of the liver and pancreas. Connected by desmosomes and gap junctions. (in the stomach - glandular cells produce mucus. Due to the gastric dimples - renewal of the epithelium).
In the small intestine there is a single-layer prismatic bordered one. Forms the walls of intestinal crypt glands. Borderless crypt epithelial cells – reproduction and differentiation, renewal 5-6 days. Goblet - secretion of mucus (parietal digestion, protection against infections, mechanical and chemical, endocrine (basal-sulfur) - hormones, Paneth cells (apical-granular) - bactericidal substance - lysozyme.

Multinuclear epithelia.

They line the airways (nasal cavity, trachea, bronchi). Ciliated.
1. Basal cells are low. On BM. deep in the epithelial layer. Cambial. Divide and differentiate into ciliated and goblet - regeneration.
2. Ciliated (ciliated) – tall, prismatic in shape. The apical surface is covered with cilia. Purify the air.
3. Goblet cells – mucus (mucins)
4. Endocrine cells - regulation of muscle tissue.
In the top row - ciliated. Lower – basal, middle – intercalary, goblet and endocrine.

Multilayer epithelia.

1) Stratified squamous non-keratinizing epithelium- cornea of ​​the eye. Oral cavity and esophagus. Basal layer - prismatic epithelial cells at the base. among them are stem cells (mitotic division). Stratum spinosum – cells have an irregular polyangular shape. In these layers, tonofibrils (bundles of tonofilaments made of keratin) are developed, between epithelial cells - desmosomes, etc. The upper layers are flat cells.
2) Keratinizing– covers the surface of the skin. Arr. its epidermis (keratinization, keratinization) with differentiation of keratinoids into horny scales. In connection with the synthesis and accumulation of special proteins in the cytoplasm - cytokeratins (acidic and alkaline), fillagrin, keratolin. The main part of the cells are keratinocytes; as they differentiate, they move from the base layers to the outer layers. Melanocytes (pigment), intraepidermal macrophages (Largenhans cells), lymphocytes, Meckel cells.

1. Basal layer – prismatic keratiocytes, synthesize tonofilaments, SKK, in the cytoplasm
2. Layer spinosum - keratinocytes are connected by desmosomes. in the cytoplasm tonofilaments arr. bundles - tonofibrils, keratinosomes - granules containing lipids - appear by exocytosis in the interstitial space-arrangement. cementing keratin substance.
In the basal and spinous layers there are melanocytes, intraepidermal macrophages (Largenhans cells) - together with keratins, proliferative units) Meckel cells.
3. Granular - flattened keratinocytes, in the cytoplasm there are keratinoglian granules (keratin + filaggrin + keratolinin - strengthens the plasmalemma of cells) granules: keratohyalin (profilagrin - form of keratin, keratinosomes - enzymes and lipids (water resistance and barrier)
4. Shiny - in heavily keratinized areas of the epidermis (palms, soles) - flat keratinocytes (no nuclei or organelles). Under the plasmalemma is keratolinin (the granules merge, the inner part of the cells is filled with a light-refracting mass of keratin fibrils, bound by an amorphous matrix containing filaggrin.
5. The stratum corneum - flat polygonal keratonocytes - thick shells covered with seratolinin and keratin fibrills. Filaggrin breaks down into amino acids, which are part of the keratin fibrils. Between the scales there is cement, a product of keratinosomes, rich in lipids, waterproofing. 3-4 weeks – regeneration.

keratinization:
1. Flattening the shape
2. Assembly of CPF by fillagrin into macrofilaments
3. Sample of the horny scale shell
4. Destruction of organelles and nucleus
5. dehydration

3) Transitional epithelium– urinary drainage organs – renal pelvis, ureters, bladder. Cell layers:
1. Basal - small round cambial cells
2. Transitional
3. Superficial - large, 2-3 nuclear, dome-shaped or flattened, depending on the filling of the organ. Plates of the cobblestone plasmalemma, embedding of disc-shaped vesicles.
Regeneration: source - stem cells in the basal layer in multi-row epithelia - basal cells, in single-layer epithelia - the small intestine - crypts, stomach - pits.
The epithelium is well innervated and has receptors.

Now that we've sorted it out, it's time to move on to the next large group - epithelial ones. There are different types of epithelial tissues To make it easier to navigate through them, we present below diagram 2. This diagram has already been given in the general characteristics of epithelial tissues.

Single layer epithelium are divided into two groups: not all epithelial cells are of the same “growth”, that is, their nuclei are located in a row (single-row single-layer), or there are “undergrowths” and “overgrowths”, the nuclei of which are not at the same level, but on different ones (multi-row single-layer ).

Single row epithelium(Fig. 17), depending on the shape, can be flat (vessels and heart are lined with endothelium, serous membranes have a mesothelial lining, part of the renal nephron is built by flat epithelial cells, and so on), cubic (renal tubules) and cylindrical, or prismatic.

Multirow epithelium(Fig. 18) lines the respiratory tract. All epithelial cells are in contact with the basement membrane. To make it easier for you to understand, imagine a very crowded street. People scurry past each other: some to work, some from work, some on a date, some - wherever they look. You are standing on the steps at the entrance to a large supermarket and looking down at the crowd a little from above. Do you see everyone passing by? Hardly. Teenagers 12-14 years old may not be noticed by you, and little children, led by their mothers, will probably remain out of your sight, although everyone, regardless of age, steps on the same asphalt. So it is with multirow epithelium. The longest epithelial cells are visible on the outside, while the short and medium ones are obscured. The nuclei of all cells form 3 rows (hence the name). Those cells that, like pine trees in the forest, “reached the sun” and look into the lumen of the cavity (bronchus, for example), have special cilia that constantly perform oscillatory movements. Therefore, multirow single-layer epithelium is also called ciliated epithelium.

Another feature that is present when comparing ciliated and columnar epithelial cells is the location of the so-called goblet cells. They secrete mucus that coats the cells, thereby protecting them from chemical and mechanical damage. Actually, it is to the goblet cells (along with small glands) that the mucous membranes owe their name.

IN stratified epithelium not all cells border the basement membrane. Continuing the proposed analogy, let us assume that some mothers, out of fear that the child would be run over by passers-by, took the babies in their arms, and some exemplary fathers, demonstrating to mothers their involvement in caring for their offspring, placed their only-begotten children on their shoulders. In other words, the connection between children's sandals, shoes, sneakers and the asphalt skin of the earth was severed.

As can be seen from Diagram 2, there are three type of stratified epithelium. There are so many layers of cells in each of them that you can lose count. The keratinizing epithelium (Fig. 19) forms the most superficial layer of the skin - the epidermis (the same one that slides off an overzealous tanner). Note that the upper layer of this type of epithelium, having successively gone through all stages of aging, is represented by dead cells that gradually exfoliate. The non-keratinizing epithelium (Fig. 20), located on the mucous membranes of the esophagus, mouth and cornea of ​​the eye, in all its layers, including the most superficial, contains cells that may differ from each other in shape, size and ability to divide (picture I).

Picture I. stratified non-keratinizing epithelium

Transitional epithelium(Fig. 21) stands apart. It is the only one that is not static and is capable of changing the thickness of its own layer; a similar property is manifested in the transitional epithelium, depending on the circumstances. When the bladder is empty, the layer of transitional epithelium lining it from the inside is quite thick (A), but when urine stretches the bladder, the epithelial lining thins (B). This type of epithelium (picture II) also occurs in the renal pelvis and ureters.

Picture II. Transitional epithelium

Glandular epithelium, as already indicated, plays the role of bricks for building glands. Its main function is the production of certain substances. Production, or rather separation, is translated into Latin as secretion (secretio), but what is “separated” is therefore a secret. Glands located in the skin and walls of hollow organs, as a rule, have excretory ducts that carry secretions either outside (sweat, earwax, milk) or into the organ cavity (tracheal mucus, saliva, gastrointestinal enzymes) and are called exocrine glands. If the gland does not have ducts for removing secretions and what it produces goes directly into the blood of the capillaries surrounding it and is carried by the bloodstream, then they speak of an endocrine gland. When the secretion of such a gland affects the functioning of individual systems of the body or the entire body, it is called a hormone (oxytocin, thyroxine, adrenaline, insulin and many others). When it can “intervene” only in the environment and do things within a radius of a few millimeters to 2-4 cm, it is called a mediator (heparin, histamine, as well as serotonin, prostaglandins, quinines, etc., already known to you). However, in cases where the mediator is secreted not by one glandular cell, not by three, but by hundreds of glands, then its effect will no longer be local at all.

Glands can be multicellular, for example, mucous or sweat, and even form entire organs (pituitary gland, adrenal gland, pancreas). But they can be represented by only one cell, because what is a goblet cell if not a unicellular gland. The principle of secretion is the same for any gland. First, they accumulate the necessary substances that enter through the basement membrane from the blood. Then they form their own secret from the resulting components. Next, the elimination stage begins, and not in all glands it is “painless”. For example, the cells that “produce” saliva do not suffer from this at all, while the cells of the mammary glands, along with their tasty secretion, lose part of the cytoplasm, and the epithelial cells that synthesize sebum are completely destroyed. Finally, the fourth phase of secretion involves “licking the wounds” and restoring the original state of the glandular cells.

Exocrine glands may have some structural features that serve as the basis for their simple classification. They are divided into simple (Fig. 22) and complex (Fig. 23) according to the way their excretory duct branches. And the terminal sections can have a tubular or sac-like (alveolar) shape, and they can also branch. Ultimately, there are many variations. Exocrine glands can be distinguished as simple tubular unbranched (1) and branched (3), simple alveolar unbranched (2) and branched (4), and can be complex tubular and/or complex alveolar (5).

Chapter 6. EPITHELIAL TISSUE

Chapter 6. EPITHELIAL TISSUE

Epithelial tissues (from Greek. epi- above and thele- skin) are the oldest histological structures that appear first in phylo- and ontogenesis. They are a system of differentials of polarly differentiated cells, closely located in the form of a layer on the basement membrane (plate), on the border with the external or internal environment, and also form the majority of the glands of the body. There are superficial (integumentary and lining) and glandular epithelia.

6.1. GENERAL MORPHOLOGICAL CHARACTERISTICS AND CLASSIFICATIONS

Surface epithelia- these are border tissues located on the surface of the body (integumentary), the mucous membranes of internal organs (stomach, intestines, bladder, etc.) and secondary body cavities (lining). They separate the body and its organs from their environment and participate in the metabolism between them, performing the functions of absorbing substances (absorption) and releasing metabolic products (excretion). For example, through the intestinal epithelium, food digestion products are absorbed into the blood and lymph, which serve as a source of energy and building material for the body, and through the renal epithelium, a number of nitrogen metabolism products, which are waste products, are released. In addition to these functions, the integumentary epithelium performs an important protective function, protecting the underlying tissues of the body from various external influences - chemical, mechanical, infectious, etc. For example, the skin epithelium is a powerful barrier to microorganisms and many poisons. Finally, the epithelium covering the internal organs creates conditions for their mobility, for example, for heart contraction, lung excursion, etc.

glandular epithelium, forming many glands, performs a secretory function, i.e. synthesizes and secretes specific products -

Rice. 6.1. The structure of single-layer epithelium (according to E. F. Kotovsky): 1 - core; 2 - mitochondria; 2a- Golgi complex; 3 - tonofibrils; 4 - structures of the apical surface of cells: 4a - microvilli; 4b - microvillous (brush) border; 4v- eyelashes; 5 - structures of the intercellular surface: 5a - tight junctions; 5b - desmosomes; 6 - structures of the basal surface of cells: 6a - invaginations of the plasmalemma; 6b - hemidesmosomes; 7 - basement membrane (plate); 8 - connective tissue; 9 - blood capillaries

secrets that are used in processes occurring in the body. For example, the secretion of the pancreas is involved in the digestion of proteins, fats and carbohydrates in the small intestine, the secretions of the endocrine glands - hormones - regulate many processes (growth, metabolism, etc.).

Epithelia are involved in the construction of many organs, and therefore exhibit a wide variety of morphophysiological properties. Some of them are general, allowing one to distinguish epithelia from other tissues of the body. There are the following main features of epithelia.

Epithelia are layers of cells - epithelial cells(Fig. 6.1), which have different shapes and structures in different types of epithelium. There is little intercellular substance between the cells that make up the epithelial layer, and the cells are closely connected to each other through various contacts - desmosomes, intermediate, gap and tight junctions.

Epithelia are located on basement membranes, which are formed as a result of the activity of both epithelial cells and underlying connective tissue. The basement membrane is about 1 µm thick and consists of a subepithelial, electron-transparent, clear lamina

Rice. 6.2. Structure of the basement membrane (diagram according to E. F. Kotovsky): C - light lamina (lamina lucida); T - dark plate (lamina densa); BM - basement membrane. 1 - cytoplasm of epithelial cells; 2 - core; 3 - attachment plate of hemidesmosome (hemidesmosome); 4 - keratin tonofilaments; 5 - anchor filaments; 6 - plasmalemma of epithelial cells; 7 - anchoring fibrils; 8 - subepithelial loose connective tissue; 9 - blood capillary

(lamina lucida) 20-40 nm thick and dark plate (lamina densa) thickness 20-60 nm (Fig. 6.2). The light plate includes an amorphous substance, relatively poor in proteins, but rich in calcium ions. The dark plate has an amorphous matrix rich in proteins, into which fibrillar structures are soldered, providing mechanical strength to the membrane. Its amorphous substance contains complex proteins - glycoproteins, proteoglycans and carbohydrates (polysaccharides) - glycosaminoglycans. Glycoproteins - fibronectin and laminin - act as an adhesive substrate, with the help of which epithelial cells are attached to the membrane. An important role is played by calcium ions, which provide a connection between the adhesive molecules of glycoproteins of the basement membrane and hemidesmosomes of epithelial cells. In addition, glycoproteins induce proliferation and differentiation of epithelial cells during epithelial regeneration. Proteoglycans and glycosaminoglycans create the elasticity of the membrane and its characteristic negative charge, on which its selective permeability to substances depends, as well as the ability to accumulate many toxic substances (toxins), vasoactive amines and complexes of antigens and antibodies under pathological conditions.

Epithelial cells are especially tightly connected to the basement membrane in the region of hemidesmosomes (hemidesmosomes). Here, from the plasma membrane of the basal epithelial cells through the light plate to the dark plate of the basement membrane, “anchors” pass

ny" filaments. In the same area, but from the side of the underlying connective tissue, bundles of “anchoring” fibrils (containing type VII collagen) are woven into the dark lamina of the basement membrane, ensuring strong attachment of the epithelial layer to the underlying tissue.

Thus, the basement membrane performs a number of functions: mechanical (attachment), trophic and barrier (selective transport of substances), morphogenetic (organizing during regeneration) and limiting the possibility of invasive epithelial growth.

Due to the fact that blood vessels do not penetrate into the layers of epithelial cells, nutrition of the epithelial cells is carried out diffusely through the basement membrane from the underlying connective tissue, with which the epithelium is in close interaction.

The epithelium has polarity, i.e., the basal and apical sections of epithelial cells have different structures. In single-layer epithelia, cell polarity is most clearly expressed, manifested by morphological and functional differences in the apical and basal parts of epitheliocytes. Thus, epithelial cells of the small intestine have many microvilli on their apical surface, which ensure the absorption of digestive products. There are no microvilli in the basal part of the epithelial cell; absorption and release of metabolic products into the blood or lymph occurs through it. In multilayered epithelia, in addition, the polarity of the cell layer is noted - a difference in the structure of the epithelial cells of the basal, intermediate and superficial layers (see Fig. 6.1).

Epithelial tissues are usually classified as renewing tissues. Therefore, they have a high ability to regenerate. Restoration of the epithelium occurs due to mitotic division and differentiation of cambial cells. Depending on the location of cambial cells in epithelial tissues, diffuse and localized cambium are distinguished.

Sources of development and classification of epithelial tissues. Epithelia develop from all three germ layers, starting from the 3rd-4th week of human embryonic development. Depending on the embryonic source, epithelia of ectodermal, mesodermal and endodermal origin are distinguished. Epithelial cells form cell layers and are leading cellular differon in this fabric. During histogenesis, the composition of the epithelium (except for epithelial cells) may include histological elements of differons of a different origin (accompanying differons in polydifferent epithelia). There are also epithelia, where, along with border epithelial cells, as a result of divergent differentiation of the stem cell, cellular differentiates of epithelial cells of secretory and endocrine specialization arise, integrated into the composition of the epithelial layer. Only related types of epithelium, developing from the same germ layer, can be subject to pathological conditions. metaplasia, i.e., transition from one type to another, for example, in the respiratory tract, the ectodermal epithelium in chronic bronchitis from a single-layer ciliated one can turn into a multilayered squamous one,

which is normally characteristic of the oral cavity and is also of ectodermal origin.

The cytochemical marker of epithelial cells is the protein cytokeratin, which forms intermediate filaments. In different types of epithelia it has different molecular forms. More than 20 forms of this protein are known. Immunohistochemical detection of these forms of cytokeratin makes it possible to determine whether the material under study belongs to a particular type of epithelium, which is of great importance in the diagnosis of tumors.

Classifications. There are several classifications of epithelia, which are based on various characteristics: origin, structure, function. When constructing classifications, histological features characterizing the leading cellular differentiation are taken into account. The most widely used morphological classification takes into account mainly the relationship of cells to the basement membrane and their shape (Scheme 6.1).

According to this classification, among the integumentary and lining epithelia that make up the skin, serous and mucous membranes of internal organs (oral cavity, esophagus, digestive tract, respiratory organs, uterus, urinary tract, etc.), two main groups of epithelia are distinguished : single-layer And multilayer. In single-layer epithelia, all cells are connected to the basement membrane, but in multilayer epithelia, only one lower layer of cells is directly connected to it, and the remaining overlying layers do not have such a connection. In accordance with the shape of the cells that make up single-layer epithelia, the latter are divided into flat(squamous), cubic And columnar(prismatic). In the definition of multilayer epithelium, only the shape of the cells of the outer layers is taken into account. For example, the epithelium of the cornea of ​​the eye is multilayered squamous, although its lower layers consist of columnar and winged cells.

Single layer epithelium can be single-row or multi-row. In single-row epithelium, all cells have the same shape - flat, cubic or columnar, their nuclei are located at the same level, i.e. in one row. Such epithelium is also called isomorphic (from the Greek. isos- equal). 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(anisomorphic).

Stratified epithelium It can be keratinizing, non-keratinizing and transitional. The epithelium in which keratinization processes occur, associated with the differentiation of cells of the upper layers into flat horny scales, is called multilayer flat keratinizing. In the absence of keratinization, the epithelium is multilayer flat non-keratinizing.

Transitional epithelium lines organs subject to strong stretching - the bladder, ureters, etc. When the volume of an organ changes, the thickness and structure of the epithelium also changes.

Along with morphological classification, it is used ontophylogenetic classification, created by Russian histologist N. G. Khlopin. Depending on the embryonic rudiment, which serves as a source of development

Scheme 6.1. Morphological classification of types of surface epithelium

leading cellular differential, epithelia are divided into types: epidermal (skin), enterodermal (intestinal), coelonephrodermal, ependymoglial and angiodermal types of epithelia.

Epidermal type The epithelium is formed from the ectoderm, has a multilayer or multirow structure, and is adapted to perform primarily a protective function (for example, stratified squamous epithelium of the skin).

Enterodermal type The epithelium develops from the endoderm, is single-layered prismatic in structure, carries out the processes of absorption of substances (for example, single-layered marginal epithelium of the small intestine), and performs a glandular function (for example, single-layer epithelium of the stomach).

Coelonephrodermal type epithelium develops from mesoderm, single-layer, flat, cubic or prismatic in structure; performs mainly a barrier or excretory function (for example, the flat epithelium of the serous membranes - mesothelium, cubic and prismatic epithelium in the urinary tubules of the kidneys).

Ependymoglial type represented by a special epithelium lining, for example, the cavities of the brain. The source of its formation is the neural tube.

TO angiodermal type epithelium refers to the endothelial lining of blood vessels. The structure of the endothelium is similar to single-layer squamous epithelium. Its belonging to epithelial tissues is

Xia controversial. Many researchers classify the endothelium as connective tissue, with which it is connected by a common embryonic source of development - mesenchyme.

6.1.1. Single layer epithelia

Single row epithelia

Single layer squamous epithelium(epithelium simplex squamosum) is represented in the body by mesothelium and, according to some data, by endothelium.

Mesothelium covers the serous membranes (leaves of the pleura, visceral and parietal peritoneum, pericardial sac). Mesothelial cells - mesotheliocytes- flat, have a polygonal shape and uneven edges (Fig. 6.3, A). In the part where the nucleus is located in them, the cells are thicker. Some of them contain not one, but two or even three nuclei, i.e. polyploid. There are microvilli on the free surface of the cell. Serous fluid is released and absorbed through the mesothelium. Thanks to its smooth surface, internal organs can glide easily. The mesothelium prevents the formation of connective tissue adhesions between the organs of the abdominal and thoracic cavities, the development of which is possible if its integrity is violated. Among mesotheliocytes there are poorly differentiated (cambial) forms capable of reproduction.

Endothelium lines blood and lymphatic vessels, as well as the chambers of the heart. It is a layer of flat cells - endotheliocytes, lying in one layer on the basement membrane. Endotheliocytes are relatively poor in organelles; pinocytotic vesicles are present in their cytoplasm. The endothelium, located in the vessels at the border with lymph and blood, participates in the exchange of substances and gases (O 2, CO 2) between them and other tissues. Endotheliocytes synthesize a variety of growth factors, vasoactive substances, etc. If the endothelium is damaged, blood flow in the vessels may change and blood clots may form in their lumen - thrombi. In different parts of the vascular system, endothelial cells differ in size, shape and orientation relative to the axis of the vessel. These properties of endothelial cells are designated as heteromorphy, or polymorphy(N. A. Shevchenko). Endotheliocytes capable of reproduction are located diffusely, with a predominance in the dichotomous division zones of the vessel.

Single layer cuboidal epithelium(epithelium simplex cuboideum) lines part of the renal tubules (proximal and distal). Proximal tubule cells have a microvillous (brush) border and basal striations. The brush border consists of a large number of microvilli. The striation is due to the presence in the basal sections of the cells of deep folds of the plasmalemma and mitochondria located between them. The epithelium of the renal tubules performs the function of reverse absorption (reabsorption) of a number of substances from the primary urine flowing through the tubules into the blood of the intertubular vessels. Cambial cells

Rice. 6.3. The structure of single-layer epithelium:

A- flat epithelium (mesothelium); b- columnar microvillous epithelium: 1 - microvilli (edge); 2 - epithelial cell nucleus; 3 - basement membrane; 4 - connective tissue; V- microphotograph: 1 - border; 2 - microvillous epithelial cells; 3 - goblet cell; 4 - connective tissue

located diffusely among epithelial cells. However, the proliferative activity of cells is extremely low.

Single-layer columnar (prismatic) epithelium(epithelium simplex columnare). This type of epithelium is characteristic of the middle section of the digestive system (see Fig. 6.3, b, c). It lines the inner surface of the stomach, small and large intestines, gallbladder, a number of ducts of the liver and pancreas. Epithelial cells are connected to each other using desmosomes, gap communication junctions, lock-type junctions, and tight junctions (see Chapter 4). Thanks to the latter, the contents of the stomach, intestines and other hollow organs cannot penetrate into the intercellular gaps of the epithelium.

In the stomach, in the single-layer columnar epithelium, all cells are glandular (surface mucocytes) that produce mucus. The secretion of mucocytes protects the wall of the stomach from the harsh influence of lumps of food and the digestive action of gastric juice, which has an acidic reaction, and enzymes that break down proteins. A minority of the epithelial cells located in the gastric pits - small depressions in the wall of the stomach - are cambial epithelial cells capable of dividing and differentiating into glandular epithelial cells. Due to pit cells, every 5 days the gastric epithelium is completely renewed - its physiological regeneration.

In the small intestine, the epithelium is single-layer columnar, actively participating in digestion, that is, in the breakdown of food into final products and their absorption into the blood and lymph. It covers the surface of the villi in the intestine and forms the wall of the intestinal glands - the crypts. The villous epithelium mainly consists of microvillous epithelial cells. The microvilli of the apical surface of the epithelial cell are covered with glycocalyx. Membrane digestion occurs here - the breakdown (hydrolysis) of food substances into final products and their absorption (transport through the membrane and cytoplasm of epithelial cells) into the blood and lymphatic capillaries of the underlying connective tissue. In the part of the epithelium that lines the intestinal crypts, there are borderless columnar epithelial cells, goblet cells, as well as endocrine cells and exocrinocytes with acidophilic granules (Paneth cells). Borderless crypt epithelial cells are cambial cells of the intestinal epithelium, capable of proliferation (reproduction) and divergent differentiation into microvillous, goblet, endocrine and Paneth cells. Thanks to cambial cells, microvillous epithelial cells are completely renewed (regenerated) within 5-6 days. Goblet cells secrete mucus onto the surface of the epithelium. Mucus protects it and the underlying tissues from mechanical, chemical and infectious influences, and also participates in parietal digestion, i.e. in the breakdown of proteins, fats and carbohydrates of food with the help of enzymes adsorbed in it to intermediate products. Endocrine (basal granular) cells of several types (EC, D, S, etc.) secrete hormones into the blood that locally regulate the function of the digestive apparatus. Paneth cells produce lysozyme, a bactericidal substance.

Single-layer epithelia are also represented by derivatives of the neuroectoderm - epithelium of the ependymoglial type. The cell structure varies from flat to columnar. Thus, the ependymal epithelium lining the central canal of the spinal cord and the ventricles of the brain is single-layer columnar. The retinal pigment epithelium is a single-layer epithelium consisting of polygonal cells. The perineural epithelium surrounding the nerve trunks and lining the perineural space is single-layer squamous. As derivatives of the neuroectoderm, epithelia have limited regeneration capabilities, predominantly in an intracellular manner.

Multirow epithelia

Multirow (pseudostratified) epithelia (epithelium pseudostrati-ficatum) line the airways - the nasal cavity, trachea, bronchi, and a number of other organs. In the airways, the multirow columnar epithelium is ciliated. Diversity of cell types

Rice. 6.4. Structure of multirow columnar ciliated epithelium: A- diagram: 1 - flickering cilia; 2 - goblet cells; 3 - ciliated cells; 4 - intercalary cells; 5 - basal cells; 6 - basement membrane; 7 - connective tissue; b- microphotograph: 1 - cilia; 2 - nuclei of ciliated and intercalary cells; 3 - basal cells; 4 - goblet cells; 5 - connective tissue

the composition of the epithelium (ciliated, intercalated, basal, goblet, Clara cells and endocrine cells) is the result of divergent differentiation of cambial (basal) epithelial cells (Fig. 6.4).

Basal epithelial cells low, located on the basement membrane deep in the epithelial layer, participate in the regeneration of the epithelium. Ciliated (ciliated) epithelial cells tall, columnar (prismatic) shape. These cells constitute the leading cellular differential. Their apical surface is covered with cilia. The movement of cilia ensures the transport of mucus and foreign particles towards the pharynx (mucociliary transport). Goblet epithelial cells secrete mucus (mucins) onto the surface of the epithelium, which protects it from mechanical, infectious and other influences. The epithelium also contains several types endocrinocytes(EC, D, P), hormones of which carry out local regulation of the muscle tissue of the airways. All these types of cells have different shapes and sizes, so their nuclei are located at different levels of the epithelial layer: in the upper row - the nuclei of ciliated cells, in the lower row - the nuclei of basal cells, and in the middle - the nuclei of intercalary, goblet and endocrine cells. In addition to epithelial differentials, the multirow columnar epithelium contains histological elements hematogenous differential(specialized macrophages, lymphocytes).

6.1.2. Stratified epithelia

Stratified squamous non-keratinizing epithelium(epithelium stiatificatum squamosum noncornificatum) covers the outside of the cornea of ​​the eye, lining

Rice. 6.5. The structure of the multilayered squamous non-keratinizing epithelium of the cornea (micrograph): 1 - layer of flat cells; 2 - spinous layer; 3 - basal layer; 4 - basement membrane; 5 - connective tissue

oral cavity and esophagus. There are three layers in it: basal, spinous (intermediate) and superficial (Fig. 6.5). Basal layer consists of columnar epithelial cells located on the basement membrane. Among them there are cambial cells capable of mitotic division. Due to the newly formed cells entering differentiation, the epithelial cells of the overlying layers of the epithelium are replaced. Layer spinosum consists of cells of irregular polygonal shape. In the epithelial cells of the basal and spinous layers, tonofibrils (bundles of tonofilaments made from keratin protein) are well developed, and between epithelial cells there are desmosomes and other types of contacts. Surface layers epithelium is formed by flat cells. Having completed their life cycle, the latter die off and disappear.

Stratified squamous keratinizing epithelium(epithelium stratificatum squamosum comificatum)(Fig. 6.6) covers the surface of the skin, forming its epidermis, in which the process of keratinization (keratinization) occurs, associated with the differentiation of epithelial cells - keratinocytes into the horny scales of the outer layer of the epidermis. The differentiation of keratinocytes is manifested by their structural changes in connection with the synthesis and accumulation of specific proteins in the cytoplasm - cytokeratins (acidic and alkaline), filaggrin, keratolinin, etc. There are several layers of cells in the epidermis: basal, spinous, granular, shiny And horny. The last three layers are especially pronounced in the skin of the palms and soles.

The leading cellular differentiation in the epidermis is represented by keratinocytes, which, as they differentiate, move from the basal layer to the overlying layers. In addition to keratinocytes, the epidermis contains histological elements of accompanying cellular differentials - melanocytes(pigment cells), intraepidermal macrophages(Langerhans cells), lymphocytes And Merkel cells.

Basal layer consists of columnar-shaped keratinocytes, in the cytoplasm of which keratin protein is synthesized, forming tonofilaments. The cambial cells of the differon of keratinocytes are also located here. Layer spinosum formed by polygonal keratinocytes, which are tightly connected to each other by numerous desmosomes. In place of desmosomes on the surface of cells there are tiny projections -

Rice. 6.6. Stratified squamous keratinizing epithelium:

A- diagram: 1 - stratum corneum; 2 - shiny layer; 3 - granular layer; 4 - spinous layer; 5 - basal layer; 6 - basement membrane; 7 - connective tissue; 8 - pigmentocyte; b- microphotography

“spines” in adjacent cells directed towards each other. They are clearly visible when the intercellular spaces expand or when cells shrink, as well as during maceration. In the cytoplasm of spinous keratinocytes, tonofilaments form bundles - tonofibrils, and keratinosomes - granules containing lipids appear. These granules are released into the intercellular space by exocytosis, where they form a lipid-rich substance that cements keratinocytes.

Processed forms are also present in the basal and spinous layers melanocytes with granules of black pigment - melanin, Langerhans cells(dendritic cells) and Merkel cells(tactile epithelial cells), which have small granules and are in contact with afferent nerve fibers (Fig. 6.7). Melanocytes use pigment to create a barrier that prevents ultraviolet rays from penetrating the body. Langerhans cells are a type of macrophage, participate in protective immune reactions and regulate the reproduction (division) of keratinocytes, forming together with them “epidermal-proliferative units”. Merkel cells are sensory (tactile) and endocrine (apudocytes) that influence epidermal regeneration (see Chapter 15).

Granular layer consists of flattened keratinocytes, the cytoplasm of which contains large basophilic granules, called keratohyaline. They include intermediate filaments (keratin) and the protein synthesized in the keratinocytes of this layer - filaggrin, and

Rice. 6.7. Structure and cellular-differential composition of multilayered squamous epithelium (epidermis) (according to E. F. Kotovsky):

I - basal layer; II - spinous layer; III - granular layer; IV, V - shiny and stratum corneum. K - keratinocytes; P - corneocytes (horny scales); M - macrophage (Langerhans cell); L - lymphocyte; O - Merkel cell; P - melanocyte; C - stem cell. 1 - mitotically dividing keratinocyte; 2 - keratin tonofilaments; 3 - desmosomes; 4 - keratinosomes; 5 - keratohyaline granules; 6 - keratolinin layer; 7 - core; 8 - intercellular substance; 9, 10 - keratin fibrils; 11 - cementing intercellular substance; 12 - falling scale; 13 - granules in the shape of tennis rackets; 14 - basement membrane; 15 - papillary layer of dermis; 16 - hemocapillary; 17 - nerve fiber

also substances formed as a result of the disintegration of organelles and nuclei that begins here under the influence of hydrolytic enzymes. In addition, another specific protein is synthesized in granular keratinocytes - keratolinin, which strengthens the plasma membrane of the cells.

Shiny layer detected only in heavily keratinized areas of the epidermis (on the palms and soles). It is formed by postcellular structures. They lack nuclei and organelles. Under the plasmalemma there is an electron-dense layer of the protein keratolinin, which gives it strength and protects it from the destructive effects of hydrolytic enzymes. Keratohyalin granules fuse, and the interior of the cells is filled with a light-refracting mass of keratin fibrils glued together by an amorphous matrix containing filaggrin.

Stratum corneum very powerful in the skin of the fingers, palms, soles and relatively thin in other areas of the skin. It consists of flat polygonal-shaped (tetradecahedron) horny scales, which have a thick shell with keratolinin and filled with keratin fibrils located in an amorphous matrix consisting of another type of keratin. In this case, filaggrin breaks down into amino acids, which are part of the keratin fibrils. Between the scales there is a cementing substance - a product of keratinosomes, rich in lipids (ceramides, etc.) and therefore has 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 the reproduction, differentiation and movement of cells from the underlying layers. Thanks to these processes, which make up physiological regeneration, in the epidermis the composition of keratinocytes is completely renewed every 3-4 weeks. The significance of the process of keratinization (keratinization) in the epidermis lies in the fact that the resulting stratum corneum is resistant to mechanical and chemical influences, has poor thermal conductivity and is impermeable to water and many water-soluble toxic substances.

Transitional epithelium(epithelium transitionale). This type of multilayer epithelium is typical of urinary drainage organs - renal pelvis, ureters, bladder, the walls of which are subject to significant stretching when filled with urine. It contains several layers of cells - basal, intermediate, superficial (Fig. 6.8, a, b).

Rice. 6.8. Structure of the transitional epithelium (diagram):

A- with an unstretched organ wall; b- with a stretched wall of the organ. 1 - transitional epithelium; 2 - connective tissue

Basal layer formed by small, almost round (dark) cambial cells. IN intermediate layer The cells are polygonal in shape. Surface layer consists of very large, often bi- and trinuclear cells, having a dome-shaped or flattened shape, depending on the condition of the organ wall. When the wall is stretched due to the filling of the organ with urine, the epithelium becomes thinner and its surface 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 out” upward and take on a pear-shaped shape, while the surface cells located above them take on a dome-shaped shape. Tight junctions are found between superficial cells, which are important for preventing the penetration of fluid through the wall of an organ (for example, the bladder).

Regeneration. The integumentary epithelium, occupying a border position, is constantly influenced by the external environment, so the epithelial cells wear out and die relatively quickly. The source of their restoration is cambial cells epithelium, which provide a cellular form of regeneration, as they retain the ability to divide throughout the life of the organism. As they multiply, some of the newly formed cells begin to differentiate and turn into epithelial cells similar to the lost ones. Cambial cells in multilayer epithelia are located in the basal (primordial) layer; in multilayer epithelia these include basal cells; in single-layer epithelia they are located in certain areas: for example, in the small intestine - in the epithelium of the crypts, in the stomach - in the epithelium of the pits, and also necks of their own glands, in the mesothelium - among mesotheliocytes, etc. The high ability of most epithelia for physiological regeneration serves as the basis for its rapid restoration in pathological conditions (reparative regeneration). In contrast, neuroectoderm derivatives are repaired primarily in an intracellular manner.

With age, a weakening of cell renewal processes is observed in the integumentary epithelium.

Innervation. The epithelium is well innervated. It contains numerous sensory nerve endings - receptors.

6.2. Glandular epithelia

These epithelia are characterized by secretory function. Glandular epithelium (epithelium glandulare) consists of glandular, or secretory, epithelial cells (glandulocytes). They carry out the synthesis, as well as the release of specific products - secretions onto the surface of the skin, mucous membranes and in the cavities of a number of internal organs (external - exocrine secretion) or into the blood and lymph (internal - endocrine secretion).

Through secretion, many important functions are performed in the body: the formation of milk, saliva, gastric and intestinal juice, bile, endo-

crine (humoral) regulation, etc. Most cells are distinguished by the presence of secretory inclusions in the cytoplasm, well-developed endoplasmic reticulum and Golgi complex, polar arrangement of organelles and secretory granules.

Secretory epithelial cells lie on the basement membrane. Their shape is very diverse and varies depending on the phase of secretion. The kernels are usually large, often irregular in shape. In the cytoplasm of cells that produce protein secretions (for example, digestive enzymes), a granular endoplasmic reticulum is well developed. In cells that synthesize non-protein secretions (lipids, steroids), an agranular endoplasmic reticulum is expressed. The Golgi complex is extensive. Its shape and location in the cell change depending on the phase of the secretory process. Mitochondria are usually numerous. They accumulate in places of greatest cell activity, i.e. where secretions are formed. The cytoplasm of cells usually contains secretory granules, the size and structure of which depend on the chemical composition of the secretion. Their number fluctuates depending on the phases of the secretory process. In the cytoplasm of some glandulocytes (for example, those involved in the formation of hydrochloric acid in the stomach), intracellular secretory tubules are found - deep invaginations of the plasmalemma, covered with microvilli. The plasmalemma has a different structure on the lateral, basal and apical surfaces of cells. At the first, it forms desmosomes and tight locking junctions. The latter surround the apical (apical) parts of the cells, thus separating the intercellular gaps from the lumen of the gland. On the basal surfaces of cells, the plasmalemma forms a small number of narrow folds that penetrate the cytoplasm. Such folds are especially well developed in the cells of glands that secrete secretions rich in salts, for example in the cells of the excretory ducts of the salivary glands. The apical surface of the cells is covered with microvilli.

Polar differentiation is clearly visible in glandular cells. It is due to the direction of secretory processes, for example, during external secretion from the basal to the apical part of the cell.

Periodic changes in the glandular cell associated with the formation, accumulation, release of secretion and its restoration for further secretion are called secretory cycle.

To form secretions from the blood and lymph, various inorganic compounds, water and low-molecular organic substances enter the glandular cells from the basal surface: amino acids, monosaccharides, fatty acids, etc. Sometimes larger molecules of organic substances, such as proteins, penetrate into the cell by pinocytosis . Secrets are synthesized from these products in the endoplasmic reticulum. They move through the endoplasmic reticulum to the Golgi complex zone, where they gradually accumulate, undergo chemical rearrangement and form into granules that are released from epithelial cells. An important role in the movement of secretory products in epithelial cells and their secretion is played by cytoskeletal elements - microtubules and microfilaments.

Rice. 6.9. Different types of secretion (diagram):

A- merocrine; b- apocrine; V- holocrine. 1 - poorly differentiated cells; 2 - degenerating cells; 3 - collapsing cells

However, the division of the secretory cycle into phases is essentially arbitrary, since they overlap each other. Thus, the synthesis of secretion and its release proceed almost continuously, but the intensity of secretion may either increase or decrease. In this case, the release of secretion (extrusion) can be different: in the form of granules or by diffusion without forming into granules or by converting the entire cytoplasm into a mass of secretion. For example, in cases of stimulation of the glandular cells of the pancreas, all secretory granules are quickly released from them, and after that, within 2 hours or more, the secretion is synthesized in the cells without forming into granules and is released diffusely.

The mechanism of secretion in different glands is not the same, and therefore three types of secretion are distinguished: merocrine (eccrine), apocrine and holocrine (Fig. 6.9). At merocrine type secretion, glandular cells completely retain their structure (for example, cells of the salivary glands). At apocrine type secretion, partial destruction of glandular cells (for example, mammary gland cells) occurs, i.e., along with secretory products, either the apical part of the cytoplasm of glandular cells (macroapocrine secretion) or the tips of microvilli (microapocrine secretion) are separated.

Holocrine type secretion is accompanied by the accumulation of secretion (fat) in the cytoplasm and the complete destruction of glandular cells (for example, cells of the sebaceous glands of the skin). Restoration of the structure of glandular cells occurs either through intracellular regeneration (with mero- and apocrine secretion), or with the help of cellular regeneration, i.e., division and differentiation of cambial cells (with holocrine secretion).

Secretion is regulated using neural and humoral mechanisms: the former act through the release of cellular calcium, and the latter primarily through the accumulation of cAMP. At the same time, enzyme systems and metabolism, the assembly of microtubules and the reduction of microfilaments involved in intracellular transport and excretion of secretions are activated in glandular cells.

Glands

Glands are organs that produce specific substances of various chemical natures and secrete them into the excretory ducts or into the blood and lymph. The secretions produced by the glands are important for the processes of digestion, growth, development, interaction with the external environment, etc. Many glands are independent, anatomically designed organs (for example, the pancreas, large salivary glands, the thyroid gland), some are only part of the organs (for example , stomach glands).

The glands are divided into two groups: endocrine glands, or endocrine, And exocrine glands, or exocrine(Fig. 6.10, a, b).

Endocrine glands produce highly active substances - hormones, entering directly into the blood. Therefore, they consist only of glandular cells and do not have excretory ducts. All of them are part of the body's endocrine system, which, together with the nervous system, performs a regulatory function (see Chapter 15).

Exocrine glands produce secrets, released into the external environment, i.e. on the surface of the skin or in the cavities of organs lined with epithelium. They can be unicellular (for example, goblet cells) or multicellular. Multicellular glands consist of two parts: secretory or terminal sections (portiones terminalae) and excretory ducts (ductus excretorii). The terminal sections are formed secretory epithelial cells, lying on the basement membrane. The excretory ducts are lined with various

Rice. 6.10. The structure of exocrine and endocrine glands (according to E. F. Kotovsky): A- exocrine gland; b- endocrine gland. 1 - end section; 2 - secretory granules; 3 - excretory duct of the exocrine gland; 4 - integumentary epithelium; 5 - connective tissue; 6 - blood vessel

Scheme 6.2. Morphological classification of exocrine glands

types of epithelium depending on the origin of the glands. In glands formed from endodermal type epithelium (for example, in the pancreas), they are lined with single-layer cubic or columnar epithelium, and in glands developing from ectoderm (for example, in the sebaceous glands of the skin), they are lined with stratified epithelium. Exocrine glands are extremely diverse, differing from each other in structure, type of secretion, i.e., the method of secretion and its composition. The listed characteristics form the basis for the classification of glands. According to their structure, exocrine glands are divided into the following types (see Fig. 6.10, a, b; diagram 6.2).

Simple tubular glands have a non-branching excretory duct, complex glands have a branching one. In unbranched glands one at a time, and in branched glands several terminal sections open into it, the shape of which can be in the form of a tube or a sac (alveolus) or an intermediate type between them.

In some glands derived from ectodermal (stratified) epithelium, for example in salivary glands, in addition to secretory cells, there are epithelial cells that have the ability to contract - myoepithelial cells. These cells, which have a process form, cover the terminal sections. Their cytoplasm contains microfilaments containing contractile proteins. Myoepithelial cells, when contracting, compress the end sections and, therefore, facilitate the release of secretions from them.

The chemical composition of the secretion may be different; therefore, the exocrine glands are divided into protein(serous), mucous membranes(mucosal), protein-mucosal(see Fig. 6.11), greasy, salty(sweat, tears, etc.).

Two types of secretory cells may be present in the mixed salivary glands - protein(serocytes) and mucous membranes(mucocytes). They form

There are protein, mucous and mixed (protein-mucous) terminal sections. Most often, the composition of the secretory product includes protein and mucous components with only one of them predominant.

Regeneration. In the glands, in connection with their secretory activity, processes of physiological regeneration constantly occur. In merocrine and apocrine glands, which contain long-lived cells, restoration of the original state of secretory epithelial cells after secretion from them occurs through intracellular regeneration, and sometimes through reproduction. In holocrine glands, restoration is carried out due to the proliferation of cambial cells. The newly formed cells are then transformed into glandular cells through differentiation (cellular regeneration).

Rice. 6.11. Types of exocrine glands:

1 - simple tubular glands with unbranched end sections;

2 - simple alveolar gland with an unbranched end section;

3 - simple tubular glands with branched end sections;

4 - simple alveolar glands with branched terminal sections; 5 - complex alveolar-tubular gland with branched end sections; 6 - complex alveolar gland with branched end sections

In old age, changes in the glands can be manifested by a decrease in the secretory activity of glandular cells and changes in the composition

secretions produced, as well as weakening of regeneration processes and proliferation of connective tissue (gland stroma).

Control questions

1. Sources of development, classification, topography in the body, basic morphological properties of epithelial tissues.

2. Multilayer epithelia and their derivatives: topography in the body, structure, cellular differential composition, functions, patterns of regeneration.

3. Single-layer epithelia and their derivatives, topography in the body, cellular differential composition, structure, functions, regeneration.

Histology, embryology, cytology: textbook / Yu. I. Afanasyev, N. A. Yurina, E. F. Kotovsky, etc. - 6th ed., revised. and additional - 2012. - 800 p. : ill.