epithelial tissue
Epithelial tissue (epithelium) covers the surface of the body, lines the walls of hollow internal organs, forming a mucous membrane, glandular (working) tissue of the glands of external and internal secretion. The epithelium is a layer of cells lying on the basement membrane, the intercellular substance is almost absent. The epithelium does not contain blood vessels. Nutrition of epitheliocytes is carried out diffusely through the basement membrane.
Epithelial cells are tightly connected to each other and form a mechanical barrier that prevents the penetration of microorganisms and foreign substances inside 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.
The main function of the epithelium is to protect the relevant authorities from mechanical damage and infections. In those places where the body tissue is subjected to constant stress and friction and "wears out", epithelial cells multiply with high speed. Often, in places of heavy loads, the epithelium is compacted or keratinized.
epithelial cells are held together by a cementing agent containing hyaluronic acid. Since blood vessels do not fit the epithelium, the supply of oxygen and nutrients occurs by diffusion through lymphatic system. Nerve endings can penetrate the epithelium.
Signs of epithelial tissue
The cells are arranged in layers
Ш Has a basement membrane
The cells are closely related to each other
Ø Cells have polarity (apical and basal parts)
Ø Absence of blood vessels
Ш Absence of intercellular substance
Ш High ability to regenerate
Morphological classification
Epithelial cells located in a layer can lie in many layers ( stratified epithelium) or in one layer ( single layer epithelium ). According to the cell height epithelium flat, cubic, prismatic, cylindrical.
Single layer epithelium
Single layered cuboidal epithelium formed by cells of a cubic shape, is a derivative of three germ layers (external, middle and internal), located in the tubules of the kidneys, excretory ducts of the glands, bronchi of the lungs. The single-layer cubic epithelium performs absorption, secretory (in the tubules of the kidneys) and delimitation (in the ducts of the glands and bronchi) functions.
Rice.
Single layered squamous epithelium mesothelium, is of mesodermal origin, lines the surfaces of the pericardial sac, pleura, peritoneum, omentum, performing delimiting and secretory functions. The smooth surface of the mesatelia promotes the sliding of the heart, lungs, and intestines in their cavities. Through the mesothelium, the exchange of substances takes place between the fluid that fills the secondary cavities of the body and the blood vessels embedded in the layer of loose connective tissue.
Rice.
Single layer columnar (or prismatic) epithelium ectodermal origin, lining inner surface gastrointestinal tract, gallbladder, excretory ducts of the liver and pancreas. The epithelium is formed by prismatic cells. in the intestines and gallbladder this epithelium is called bordered, as it forms numerous outgrowths of the cytoplasm - microvilli, which increase the surface of the cells and promote absorption. The cylindrical epithelium of mesodermal origin, lining the inner surface of the fallopian tube and uterus, has microvilli and ciliated cilia, the vibrations of which contribute to the advancement of the egg.
Rice.
Single layered ciliated epithelium - cells of this epithelium various shapes and heights have ciliated cilia, the fluctuations of which contribute to the removal of foreign particles that have settled on the mucous membrane. This epithelium lines the airways and is of ectodermal origin. The functions of a single-layer multi-row ciliated epithelium are protective and delimiting.
Rice.
Stratified epithelium
The epithelium, according to the nature of the structure, is divided into integumentary and glandular.
Integumentary (surface) epithelium- these are border tissues located on the surface of the body, mucous membranes of internal organs and secondary cavities body. They separate the body and its organs from their environment and participate in the metabolism between them, carrying out the functions of absorption of substances and excretion of metabolic products. For example, through the intestinal epithelium, the products of digestion of food are absorbed into the blood and lymph, and through the renal epithelium, a number of products of nitrogen metabolism, which are slags, are excreted. 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 and others. For example, the skin epithelium is a powerful barrier to microorganisms and many poisons. Finally, the epithelium covering the internal organs creates the conditions for their mobility, for example, for the movement of the heart during its contraction, the movement of the lungs during inhalation and exhalation.
glandular epithelium- a kind of epithelial tissue, which consists of epithelial glandular cells, which in the process of evolution have acquired the leading property to produce and secrete secrets. Such cells are called secretory (glandular) - glandulocytes. They have exactly the same general characteristics like a covering epithelium. Located in the glands of the skin, intestines, salivary glands, endocrine glands, etc. Among the epithelial cells are secretory cells, there are 2 types of them.
Ш exocrine - secrete their secret into the external environment or the lumen of the organ.
SH endocrine - secrete their secret directly into the bloodstream.
epithelial tissue cell function
Stratified epithelium is divided into three types: non-keratinized, keratinized and transitional. Stratified non-keratinized epithelium consists of three layers of cells: basal, styloid and flat.
Transition epithelium lines organs subject to strong stretching - bladder, ureters, etc. When the volume of the organ changes, the thickness and structure of the epithelium also changes.
Availability a large number layers allows you to perform a protective function. multilayer non-keratinizing the epithelium lines the cornea, oral cavity and esophagus, is a derivative of the outer germ layer (ectoderm).
Stratified squamous keratinized epithelium - the epidermis, it lines skin. In thick skin palmar surfaces), which is constantly under load, the epidermis contains 5 layers:
III basal layer - contains stem cells, differentiated cylindrical and pigment cells (pigmentocytes).
Spiny layer - cells of a polygonal shape, they contain tonofibrils.
III granular layer - the cells acquire a rhomboid shape, tonofibrils disintegrate and keratohyalin protein is formed inside these cells in the form of grains, this begins the process of keratinization.
The shiny layer is a narrow layer, in which the cells become flat, they gradually lose their intracellular structure, and keratohyalin turns into eleidin.
Ш stratum corneum - contains horny scales, which have completely lost the structure of cells, contain the protein keratin. With mechanical stress and with a deterioration in blood supply, the process of keratinization intensifies.
In thin skin, which is not stressed, there is no granular and shiny layers. The main function of the stratified keratinizing epithelium is protective.
Types of epithelium
- Single layered squamous epithelium(endothelium and mesothelium). The endothelium lines the inside of the blood vessels lymphatic vessels, cavity of the heart. Endothelial cells are flat, poor in organelles and form an endothelial layer. The exchange function is well developed. They create conditions for blood flow. When the epithelium is broken, blood clots form. The endothelium develops from the mesenchyme. The second variety - mesothelium - develops from the mesoderm. Lines everything serous membranes. Consists of flat polygonal-shaped cells interconnected by jagged edges. Cells have one, rarely two flattened nuclei. The apical surface has short microvilli. They have absorptive, excretory and delimiting functions. The mesothelium provides free sliding of the internal organs relative to each other. The mesothelium secretes a mucous secretion onto its surface. The mesothelium prevents the formation of connective tissue adhesions. They regenerate quite well by mitosis.
- Single layered cuboidal epithelium develops from endoderm and mesoderm. On the apical surface there are microvilli that increase the working surface, and in the basal part of the cytolemma forms deep folds, between which mitochondria are located in the cytoplasm, so the basal part of the cells looks striated. Lines the small excretory ducts of the pancreas bile ducts and renal tubules.
- Single layered columnar epithelium found in the organs of the middle part of the digestive canal, digestive glands, kidneys, gonads and genital tract. In this case, the structure and function are determined by its localization. It develops from the endoderm and mesoderm. The gastric mucosa is lined by a single layer of glandular epithelium. It produces and secretes a mucous secretion that spreads over the surface of the epithelium and protects the mucous membrane from damage. The cytolemma of the basal part also has small folds. The epithelium has a high regeneration.
- The renal tubules and intestinal mucosa are lined with border epithelium. In the intestinal epithelium, border cells, enterocytes, predominate. At their top are numerous microvilli. In this zone, parietal digestion and intensive absorption of food products occur. Mucous goblet cells produce mucus on the surface of the epithelium, and small endocrine cells are located between the cells. They secrete hormones that provide local regulation.
- Single layered stratified ciliated epithelium. It lines the airways and is of ectodermal origin. In it, cells of different heights, and nuclei are located at different levels. Cells are arranged in layers. Loose connective tissue with blood vessels lies under the basement membrane, and highly differentiated ciliated cells predominate in the epithelial layer. They have a narrow base and a wide top. At the top are shimmering cilia. They are completely immersed in slime. Between the ciliated cells are goblet cells - these are unicellular mucous glands. They produce a mucous secret on the surface of the epithelium.
There are endocrine cells. Between them are short and long intercalary cells, these are stem cells, poorly differentiated, due to them, cell proliferation occurs. Ciliated cilia make oscillatory movements and move the mucous membrane along the airways to the external environment.
- Stratified squamous nonkeratinized epithelium. It develops from the ectoderm, lines the cornea, the anterior alimentary canal and the anal alimentary canal, the vagina. Cells are arranged in several layers. On the basement membrane lies a layer of basal or cylindrical cells. Some of them are stem cells. They proliferate, separate from the basement membrane, turn into polygonal cells with outgrowths, spikes, and the totality of these cells forms a layer of spiny cells, located in several floors. They gradually flatten and form a surface layer of flat ones, which are rejected from the surface into the external environment.
- Stratified squamous keratinized epithelium- epidermis, it lines the skin. In thick skin (palmar surfaces), which is constantly under stress, the epidermis contains 5 layers:
- 1 - basal layer - contains stem cells, differentiated cylindrical and pigment cells (pigmentocytes).
- 2 - prickly layer - cells of a polygonal shape, they contain tonofibrils.
- 3 - granular layer - cells acquire a diamond shape, tonofibrils disintegrate and keratohyalin protein is formed inside these cells in the form of grains, this begins the process of keratinization.
- 4 - shiny layer - a narrow layer, in which the cells become flat, they gradually lose their intracellular structure, and keratohyalin turns into eleidin.
- 5 - the stratum corneum - contains horny scales, which have completely lost the structure of the cells, contain the protein keratin. With mechanical stress and with a deterioration in blood supply, the process of keratinization intensifies.
In thin skin, which is not stressed, there is no granular and shiny layer.
- Stratified cuboidal and columnar epithelium are extremely rare - in the area of the conjunctiva of the eye and the area of \u200b\u200bthe junction of the rectum between single-layer and stratified epithelium.
- transitional epithelium(uroepithelium) lines urinary tract and allantois. Contains a basal layer of cells, part of the cells gradually separates from the basal membrane and forms an intermediate layer of pear-shaped cells. On the surface there is a layer of integumentary cells - large cells, sometimes two-row, covered with mucus. The thickness of this epithelium varies depending on the degree of stretching of the wall of the urinary organs. The epithelium is able to secrete a secret that protects its cells from the effects of urine.
- glandular epithelium- a kind of epithelial tissue, which consists of epithelial glandular cells, which in the process of evolution have acquired the leading property to produce and secrete secrets. Such cells are called secretory (glandular) - glandulocytes. They have exactly the same general characteristics as the integumentary epithelium. Among the epithelial cells are secretory cells, there are 2 types of them.
- exocrine - secrete their secret into the external environment or the lumen of an organ.
- endocrine - secrete their secret directly into the bloodstream.
Located in the glands of the skin, intestines, salivary glands, endocrine glands, etc.
Characteristics
Key Features epithelial tissues - rapid regeneration and the absence of blood vessels.
Classification.
There are several classifications of epithelium, which are based on various features: origin, structure, functions. Of these, the most widely used morphological classification, which takes into account mainly the ratio of cells to the basement membrane and their shape.
Single layer epithelium can be single-row and multi-row. In a single-row epithelium, all cells have the same shape- flat, cubic or prismatic, their cores lie on the same level, that is, in one row. Such an epithelium is also called isomorphic.
Stratified epithelium it is 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 stratified squamous keratinizing. In the absence of keratinization, the epithelium is called stratified squamous non-keratinized.
transitional epithelium lines organs subject to strong stretching - the bladder, ureters, etc. When the volume of the organ changes, the thickness and structure of the epithelium also changes.
As well as morphological classification, used ontophylogenetic classification, created by the Russian histologist N. G. Khlopin. It is based on the features of the development of epithelium from tissue rudiments.
epidermal type The epithelium is formed from the ectoderm, has a multi-layer or multi-row structure, and is adapted to perform primarily a protective function.
Enterodermal type The epithelium develops from the endoderm, is single-layer prismatic in structure, carries out the processes of absorption of substances, and performs a glandular function.
Whole nephrodermal type the epithelium develops from the mesoderm, the structure is single-layer, flat, cubic or prismatic; performs a barrier or excretory function.
Ependymoglial type It is represented by a special epithelium lining, for example, the cavities of the brain. The source of its formation is the neural tube.
see also
See what "Epithelial tissue" is in other dictionaries:
epithelial tissue- Rice. 1. Single layer epithelium. Rice. 1. Single-layer epithelium: A - prismatic border; B - multi-row prismatic flicker; B - cubic; G - flat; 1 - prismatic cells; 2 - connective tissue; … Veterinary encyclopedic Dictionary
- (epithelium), a layer of closely spaced cells covering the surface of the body and lining all its cavities. Most of the glands (glandular epithelium) also consist of the epithelium. The squamous epithelium consists of flattened cells that have the shape of ... ... Biological encyclopedic dictionary
epithelial tissue- dermis membrane. hypodermis. endoderm. epithelium. endothelium. mesothelium. ependyma. sarcolemma. epicardium pericardium. endocardium. sclera. hymen. pleura...
This term has other meanings, see Fabric (meanings). Tissue is a system of cells and intercellular substance, united by a common origin, structure and functions. The structure of the tissues of living organisms is studied by science ... ... Wikipedia
animal tissue- tissues: connective. epithelial. muscular. nervous. body. flesh. meat muscle tissue (pulled out a piece of meat). pulp. histogenesis. blastema. mesoglea. slime. slimy. transudate. transudation. exudate. exudation. tissue fluid... Ideographic Dictionary of the Russian Language
The historically established community of cells and intercellular substance, united by the unity of origin, structure and function. There are four types of tissues in the human body: epithelial, connective, muscle and nervous. Each fabric... medical terms- Brown adipose tissue ... Wikipedia
Characteristic morphological features of epithelial tissues
Epithelial tissues are a set of differons of polarly differentiated cells that are tightly adjacent to each other, located in the form of a layer on the basement membrane; they lack blood vessels and very little or no intercellular substance.
Functions. Epithelium covers the surface of the body, secondary cavities of the body, internal and outer surface hollow internal organs, form the secretory sections and excretory ducts of the exocrine glands. Their main functions are: delimiting, protective, suction, secretory, excretory.
Histogenesis. Epithelial tissues develop from all three germ layers. Epithelia of ectodermal origin are predominantly multilayered, while those developing from the endoderm are always single-layered. From the mesoderm, both single-layer and stratified epithelium develop.
Classification of epithelial tissues
1. Morphofunctional classification takes into account the structural features and functions performed by one or another type of epithelium.
According to the structure of the epithelium are divided into single-layer and multilayer. Main principle this classification is the ratio of cells to the basement membrane (Table 1). The functional specificity of single-layer epithelium is usually determined by the presence of specialized organelles. So, for example, in the stomach, the epithelium is single-layer, prismatic, single-row glandular. The first three definitions characterize the structural features, and the last one indicates that the epithelial cells of the stomach perform a secretory function. In the intestine, the epithelium is single-layered, prismatic, single-row bordered. The presence of a brush border in epitheliocytes suggests a suction function. In the airways, in particular in the trachea, the epithelium is single-layer, prismatic, multi-row ciliated (or ciliated). It is known that cilia in this case play a protective function. Stratified epithelium perform protective and glandular functions.
Table 1. Comparative characteristics single-layer and multilayer epithelium.
|
SINGLE-LAYER EPITHELIUM |
MULTILAYER EPITHELIUM |
|
All epithelial cells are in contact with the basement membrane: |
Not all epithelial cells are in contact with the basement membrane: |
|
1) single layer flat; 2) single-layer cubic (low prismatic); 3) single-layer prismatic (cylindrical, columnar) It happens: |
1) multilayer flat non-keratinizing contains three layers of different cells: basal, intermediate (spiky) and superficial; 5 layers: basal, spiny, granular, shiny and horny; the basal and spinous layers make up germ layer epithelium, since the cells of these layers are capable of dividing. |
Ontophylogenetic classification (according to N. G. Khlopin). This classification takes into account from which embryonic primordium this or that epithelium developed. According to this classification, epidermal (skin), enterodermal (intestinal), colognephrodermal, ependymoglial and angiodermal types of epithelium are distinguished.
For example, epithelium skin type covers the skin, lines the oral cavity, esophagus, glandless chambers of the multichamber stomach, vagina, urethra, border department of the anal canal; epithelium of the intestinal type lines the single-chamber stomach, abomasum, intestines; the epithelium of the whole nephrodermal type lines the body cavities (mesothelium of the serous membranes), forms the tubules of the kidneys; ependymoglial type of epithelium lines the ventricles of the brain and the central canal spinal cord; angiodermal epithelium lines the cavities of the heart and blood vessels.
For single-layer and multilayer epithelium, the presence of special organelles is characteristic - desmosomes, semi-desmosomes, tonofilaments and tonofibrils. In addition, single-layer epithelium can have cilia and microvilli on the free surface of cells (see the Cytology section).
All types of epithelium are located on the basement membrane (Fig. 7). The basement membrane consists of fibrillar structures and an amorphous matrix containing complex proteins - glycoproteins, proteoglycans and polysaccharides (glycosaminoglycans).
Rice. 7. Scheme of the structure of the basement membrane (according to Yu. K. Kotovsky).
BM, basement membrane; WITH - Light plate; T - dark plate. 1 - cytoplasm of epitheliocytes; 2 - core; 3 - hemidesmosomes; 4 - keratin tonofilaments; 5 - anchor filaments; 6 - plasmolemma of epitheliocytes; 7 - anchoring filaments; 8 - loose connective tissue; nine - Hemocapillary.
The basement membrane regulates the permeability of substances (barrier and trophic function), prevents the invasion of the epithelium into the connective tissue. The glycoproteins contained in it (fibronectin and laminin) promote the adhesion of epithelial cells to the membrane and induce their proliferation and differentiation in the process of regeneration.
By location and function of the epithelium divided into: superficial (cover the organs from the outside and from the inside) and glandular (form the secretory sections and excretory ducts of the exocrine glands).
Surface epithelium are border tissues that separate the body from external environment and participate in the exchange of substances and energy between the body and external environment. They are located on the surface of the body (integumentary), mucous membranes of internal organs (stomach, intestines, lungs, heart, etc.) and secondary cavities (lining).
glandular epithelium have a pronounced secretory activity. Glandular cells - glandulocytes are characterized by a polar arrangement of organelles general meaning, well-developed EPS and the Golgi complex, the presence of secretory granules in the cytoplasm.
The process of functional activity of a glandular cell associated with the formation, accumulation and secretion of a secret outside of it, as well as the restoration of the cell after secretion is called secretory cycle.
In the process of the secretory cycle, the initial products (water, various inorganic substances and low molecular weight organic compounds: amino acids, monosaccharides, fatty acids, etc.) enter the glandulocytes from the blood, from which the secret is synthesized with the participation of organelles of general importance and accumulates in the cells, and then by exocytosis is released into the external ( exocrine glands ) or internal ( Endocrine glands ) environment.
The secretion (extrusion) is carried out by diffusion or in the form of granules, but can also be done by converting the entire cell into a common secretory mass.
Regulation of the secretory cycle is carried out with the participation of humoral and nervous mechanisms.
Epithelial regeneration
Different types of epithelium are characterized by high regenerative activity. It is carried out at the expense of cambial elements, which divide by mitosis, constantly replenishing the loss of wearing out cells. Glandular cells that secrete according to the merocrine and apocrine type, in addition, are able to maintain their vital activity not only through reproduction, but also through intracellular regeneration. In the holocrine glands, constantly dying glandulocytes are replaced during the secretory cycle by dividing stem cells located on the basement membrane (cellular regeneration).
1. Epithelial tissue is a layer of cells.
2. There is no intercellular substance.
3. Cells lie on the basement membrane.
4. There are no blood vessels (exception: vascular strip of the inner ear).
5. Nutrition of the epithelial tissue is carried out diffusely through the basement membrane from the underlying loose fibrous connective tissue containing a large number of blood vessels.
6. Cells have polarity.
a) the apical surface of epitheliocytes is characterized by the presence of a brush border (intestinal epithelium) and cilia (ciliated epithelium of the trachea).
7. for the basal surface - the presence of a basal labyrinth (the epithelium of the proximal and distal tubules of the kidney).
c) for lateral surfaces - the presence of intercellular contacts.
8. Have a high ability to regenerate.
9. Epithelial cells are able to develop from all 3 germ layers: ectoderm, mesoderm, endoderm.
10. By function, two subgroups are distinguished:
1) coverslips e(have a boundary position between the internal environment of the body and its environment).
2) glandular (line the terminal secretory sections of the exocrine glands
B. Morphofunctional classification of epithelium.
B. Histogenetic classification of epithelia (according to Prof. N.G. Khlopin, 1946)
The classification of epithelia is based on determination (determining the path of development on a genetic basis) and the development of the epithelium from certain embryonic rudiments and germ layers. That. allocate:
1. skin type epithelium - ectodermal;
2. epithelium of the intestinal type - endodermal;
3. whole nephrodermal epithelium - mesodermal;
4. epithelium of the neuroglial type - develops from the neural tube;
5. angiodermal type epithelium - develops from the mesenchyme.
Each type of epithelial tissue includes several varieties of epithelium, which are characterized by specific and morphological features, such as: single-layer, multi-layer, multi-row.
The cell shape can be: flat, cubic and prismatic.
1. Epithelium of the epidermal type develop from the skin ectoderm and prechordal plate.
From the skin ectoderm develop:
Stratified squamous keratinized epithelium - epidermis
Stratified squamous nonkeratinized epithelium of the cornea and organs oral cavity
Stratified transitional epithelium of the urinary tract.
From the prechordal plate develop:
Stratified squamous nonkeratinized epithelium of the pharynx and esophagus
Single layered ciliated epithelium respiratory tract
Single layer alveolar epithelium of the lung
The epithelium of the thyroid parathyroid gland
Epithelium thymus(thymus) and anterior pituitary.
2. Enterodermal type epithelium develop from intestinal endoderm:
Single-layered highly prismatic epithelium of the gastrointestinal tract
Epithelium of the liver of the gallbladder and pancreas.
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Epithelia cover the surface of the body, serous cavities of the body, the inner and outer surfaces of many internal organs, form the secretory sections and excretory ducts of the exocrine glands. The epithelium is a layer of cells, under which there is a basement membrane.
epithelium subdivided into coverslips, which line the body and all the cavities present in the body, and glandular that produce and secrete the secret.
Functions:
delimiting / barrier / (contact with the external environment);
protective (the internal environment of the body from the damaging effects of mechanical, physical, chemical factors environment; production of mucus with antimicrobial activity);
metabolism between the organism and the environment;
secretory;
excretory;
development of germ cells, etc.;
receptor / sensory /.
Development: from all 3 germ layers:
Skin ectoderm;
Intestinal endoderm: - prechordal plate;
Mesoderm: - neural plate.
General signs of the structure of the epithelium:
Cells lie close to each other, forming a continuous layer.
Heteropolarity - apical (apex) and basal parts of cells differ in structure and function; and in stratified epithelium- difference in the structure and function of the layers.
It consists only of cells, the intercellular substance is practically absent (desmosomes).
The epithelium is always located on the basement membrane (carbohydrate-protein-lipid complex with the thinnest fibrils) and is separated from the underlying loose connective tissue.
The epithelium is involved in secretion.
Characterized by increased regenerative capacity, due to borderline.
does not have its own blood vessels, it feeds diffusely through the basement membrane, due to the vessels of the underlying loose connect. fabrics.
Well innervated (many nerve endings).
Classification of epithelial tissue Morphofunctional classification (A. A. Zavarzina):
Structure diagram various kinds epithelium:
(1 - epithelium, 2 - basement membrane; 3 - underlying connective tissue)
A - single-layer single-row cylindrical,
B - single-layer single-row cubic,
B - single-layer single-row flat;
G - single-layer multi-row;
D - multilayer flat non-keratinizing,
E - multilayer flat keratinizing;
F 1 - transitional with a stretched wall of the organ,
F 2 - transitional when sleeping.
I. Single layer epithelium.
(all epithelial cells are in contact with the basement membrane)
1. Single-layered epithelium (isomorphic)(All nuclei of epitheliocytes are located at the same level, because the epithelium consists of the same cells. Regeneration of a single-layer single-row epithelium occurs due to stem (cambial) cells, evenly scattered among other differentiated cells).
a) single layer flat(consists of one layer of sharply flattened cells of a polygonal shape (polygonal); the base (width) of the cells is greater than the height (thickness); there are few organelles in the cells, mitochondria, single microvilli are found, pinocytic vesicles are visible in the cytoplasm.
Mesothelium covers the serous membranes (pleura, visceral and parietal peritoneum, pericardial sac, etc.). Cells- mesotheliocytes flat, have polygonal shape and jagged edges. On the free surface of the cell there are microvilli (stomata). Occurs through the mesothelium secretion and absorption of serous fluid. Thanks to its smooth surface, sliding of the internal organs is easily carried out. 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.
Endothelium lines the 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 distinguished by the relative poverty of organelles and the presence of pinocytic vesicles in the cytoplasm. Endothelium participates in the metabolism and gases(O 2, CO 2) between vessels and other tissues. If it is damaged, it is possible to change the blood flow in the vessels and the formation of blood clots in their lumen - blood clots.
b) single-layer cubic(on a section of cells, the diameter (width) is equal to the height. It occurs in the excretory ducts of the exocrine glands, in the convoluted (proximal and distal) renal tubules.) The epithelium of the renal tubules performs the function reverse suction (reabsorption) a number of substances from the primary urine flowing through the tubules into the blood of the intertubular vessels.
c) single-layer cylindrical (prismatic)(on the slice, the width of the cells is less than the height). Lines the inner surface of the stomach, small and large intestines, gallbladder, a number of ducts of the liver and pancreas. Ep. cells are closely interconnected, the contents of the cavity of the stomach, intestines and other hollow organs cannot penetrate into the intercellular gaps.
single-layer prismatic glandular, present in the stomach, in the canal cervix, specialized in the continuous production of mucus;
single-layered prismatic limbic, lining the intestine, on the apical surface of the cells there are a large number of microvilli; suction specialized.
single-layer prismatic ciliated (ciliated), lines the fallopian tubes; epitheliocytes have cilia on the apical surface.
2. Single-layer multi-row ciliated epithelium (pseudostratified or anizimorphic)
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 tall, prismatic. 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 intercalated cages(poorly differentiated and among them stem cells; provide regeneration);
- endocrine cells whose hormones are locally regulated muscle tissue airways.
On the bottom row:
- Basal cells low, lie on the basement membrane in the depth of the epithelial layer. They belong to cambial cells.
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