Single-layer multirow ciliated epithelium (pseudostratified or anisimorphic)

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

This epithelium consists of 5 types of cells:

In the top row:

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

In 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 intercalary cells (poorly differentiated and among them stem cells; provide regeneration);
• - Endocrine cells, the hormones of which carry out local regulation muscle tissue airways.

In the bottom row:

Basal cells are low, lying on the basement membrane deep in the epithelial layer. They belong to cambial cells.

Multilayer epithelium.

1. Multilayer flat non-keratinizing lining the anterior ( oral cavity, pharynx, esophagus) and final section (anal rectum) digestive system, cornea. Function: mechanical protection. Source of development: ectoderm. The prechordal plate is part of the foregut endoderm.

Consists of 3 layers:

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

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

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

Multilayered squamous epithelia have nuclear polymorphism:

• -nuclei of the basal layer are elongated, located perpendicular to the basement membrane,
• -the nuclei of the intermediate (spinous) layer are round,
• -the nuclei of the superficial (granular) layer are elongated and located parallel to the basement membrane.
• 2. Stratified squamous keratinization is the epithelium of the skin. Develops from the ectoderm, performs a protective function - protection from mechanical damage, radiation, bacterial and chemical exposure, distinguishes the body from environment.
• Ш In thick skin (palm surfaces), which is constantly under stress, the epidermis contains 5 layers:
  • 1. basal layer - consists of prismatic (cylindrical) keratinocytes, in the cytoplasm of which keratin protein is synthesized, forming tonofilaments. Keratinocyte differon stem cells are also located here. Therefore, the basal layer is called germinal, or rudimentary.
  • 2. stratum spinosum - formed by polygonal-shaped keratinocytes, which are firmly connected to each other by numerous desmosomes. In place of desmosomes on the surface of cells there are tiny projections - “spines” directed towards each other. 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. In addition to keratinocytes, in the basal and spinous layers there are process-shaped melanocytes with granules of black pigment - melanin, intraepidermal macrophages (Langerhans cells) and Merkel cells, which have small granules and are in contact with afferent nerve fibers.
  • 3. granular layer - the cells acquire a diamond-shaped shape, the tonofibrils disintegrate and inside these cells the protein keratohyalin is formed in the form of grains, this is where the process of keratinization begins.
  • 4. stratum lucidum - a narrow layer, in which the cells become flat, they gradually lose their intracellular structure (not nuclei), and keratohyalin turns into eleidin.
  • 5. stratum corneum - contains horny scales that have completely lost their cell structure, are filled with air bubbles, and contain the protein keratin. With mechanical stress and deterioration of blood supply, the process of keratinization intensifies.
• Ш In thin skin that does not experience stress, there is no granular and shiny layer.

The basal and spinous layers constitute the germinal layer of the epithelium, since the cells of these layers are capable of division.

4. Transitional (urothelium)

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

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

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

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

• - when the wall is not stretched, the epithelium is thickened due to the “displacement” of some cells from the basal layer into the intermediate layer;
• - when the wall is stretched, the thickness of the epithelium decreases due to flattening cover cells and the transition of some cells from the intermediate layer to the basal layer.

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

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

Glandular epithelium

The glandular epithelium is specialized for the production of secretions.

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

The glandular epithelium forms glands:

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

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

Principles of classification of exocrine glands:

I. According to the structure of the excretory ducts:

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

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

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

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

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

IV. By type of secretion:

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

V. By localization:

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

VI. By the nature of the secret:

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

Secretion phases:

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

Glandular epithelial cells are characterized by the presence of organelles: EPS of granular or agranular type (depending on the nature of the secretion), lamellar complex, mitochondria.

Epithelial tissue, or epithelium, covers the outside of the body, lining the body cavities and internal organs, and also forms most of the glands.

Varieties of epithelium have significant variations in structure, which depends on the origin (epithelial tissue develops from all three germ layers) of the epithelium and its functions.

However, all species have common features that characterize epithelial tissue:

1. The epithelium is a layer of cells, due to which it can protect the underlying tissues from external influences and carry out exchanges between external and internal environment; Violation of the integrity of the formation leads to a weakening of its protective properties, leading to the possibility of infection.
2. It is located on the connective tissue (basal membrane), from which nutrients are supplied to it.
3. Epithelial cells have polarity, i.e. parts of the cell (basal) lying closer to the basement membrane have one structure, and the opposite part of the cell (apical) has another; Each part houses different components of the cell.
4. Has a high ability to regenerate (recovery). Epithelial tissue does not contain intercellular substance or contains very little of it.

Epithelial tissue formation

Epithelial tissue is made up of epithelial cells that are tightly connected to each other and form a continuous layer.

Epithelial cells are always located on the basement membrane. It delimits them from the loose connective tissue that lies below, performing a barrier function, and prevents the germination of the epithelium.

The basement membrane plays important role in the trophism of epithelial tissue. Since the epithelium is vascularless, it receives nutrition through the basement membrane from the connective tissue vessels.

Classification by origin

Depending on their origin, epithelium is divided into six types, each of which occupies a specific place in the body.

1. Cutaneous - develops from the ectoderm, localized in the oral cavity, esophagus, cornea, and so on.
2. Intestinal - develops from the endoderm, lines the stomach, small and large intestine
3. Coelomic - develops from the ventral mesoderm, forms serous membranes.
4. Ependymoglial - develops from the neural tube, lining the cavities of the brain.
5. Angiodermal - develops from mesenchyme (also called endothelium), lines blood and lymphatic vessels.
6. Renal - develops from the intermediate mesoderm, found in the renal tubules.

Features of the structure of epithelial tissue

According to the shape and function of the cells, the epithelium is divided into flat, cubic, cylindrical (prismatic), ciliated (ciliated), as well as single-layer, consisting of one layer of cells, and multilayer, consisting of several layers.

Table of functions and properties of epithelial tissue
Epithelium type	Subtype	Location	Functions
Single layer single row epithelium	Flat	Blood vessels	Secretion of biologically active substances, pinocytosis
	Cubic	Bronchioles	Secretory, transport
	Cylindrical	Gastrointestinal tract	Protective, adsorption of substances
Single layer multi-row	Columnar	Vas deferens, duct of epididymis	Protective
	Pseudo multilayer ciliated	Respiratory tract	Secretory, transport
Multilayer	Transitional	Ureter, bladder	Protective
	Flat non-keratinizing	Oral cavity, esophagus	Protective
	Flat keratinizing	Skin	Protective
	Cylindrical	Conjunctiva	Secretory
	Cubic	Sweat glands	Protective

Single layer

Single layer flat the epithelium is formed by a thin layer of cells with uneven edges, the surface of which is covered with microvilli. There are mononuclear cells, as well as with two or three nuclei.

Single layer cubic consists of cells with the same height and width, characteristic of the excretory duct of the glands. Single-layer columnar epithelium is divided into three types:

1. Bordered - found in the intestines, gall bladder, has adsorbing abilities.
2. Ciliated - characteristic of the oviduct, in the cells of which at the apical pole there are movable cilia (promote the movement of the egg).
3. Glandular - localized in the stomach, produces mucous secretion.

Single layer multi-row The epithelium lines the airways and contains three types of cells: ciliated, intercalated, goblet and endocrine. Together they ensure normal operation respiratory system, protect against the entry of foreign particles (for example, the movement of cilia and mucous secretions help remove dust from the respiratory tract). Endocrine cells produce hormones for local regulation.

Multilayer

Multilayer flat non-keratinizing the epithelium is located in the cornea, anal rectum, etc. There are three layers:

• The basal layer is formed by cylinder-shaped cells, they divide mitotically, some of the cells belong to the stem;
• spinous layer - cells have processes that penetrate between the apical ends of the cells of the basal layer;
• layer of flat cells - located on the outside, constantly dying and peeling off.

Stratified epithelium

Multilayer flat keratinizing epithelium covers the surface of the skin. There are five different layers:

1. Basal - formed by poorly differentiated stem cells, together with pigment cells - melanocytes.
2. The spinous layer together with the basal layer form the growth zone of the epidermis.
3. The granular layer is built of flat cells, in the cytoplasm of which the keratoglian protein is located.
4. The shiny layer got its name because characteristic appearance by microscopic examination histological preparations. It is a uniform shiny stripe, which stands out due to the presence of elaidin in flat cells.
5. The stratum corneum consists of horny scales filled with keratin. The scales that are closer to the surface are susceptible to the action of lysosomal enzymes and lose contact with the underlying cells, so they are constantly exfoliated.

Transitional epithelium located in the kidney tissue, urinary canal, and bladder. Has three layers:

• Basal - consists of cells with intense coloring;
• intermediate - with cells of various shapes;
• integumentary - has large cells with two or three nuclei.

It is common for transitional epithelium to change shape depending on the state of the organ wall; they can flatten or acquire a pear-shaped shape.

Special types of epithelium

Acetowhite - This is an abnormal epithelium that becomes intensely white when exposed to acetic acid. Its appearance during colposcopic examination allows us to identify pathological process in the early stages.

Buccal - collected from the inner surface of the cheek, it is used for genetic testing and establishing family relationships.

Functions of epithelial tissue

Located on the surface of the body and organs, the epithelium is a border tissue. This position determines its protective function: protecting the underlying tissues from harmful mechanical, chemical and other influences. In addition, through the epithelium occur metabolic processes- absorption or excretion of various substances.

The epithelium that is part of the glands has the ability to form special substances - secretions, and also secrete them into the blood and lymph or into the ducts of the glands. This epithelium is called secretory or glandular.

Differences between loose fibrous connective tissue and epithelial tissue

Epithelial and connective tissue perform various functions: protective and secretory in the epithelium, supporting and transport in the connective tissue.

The cells of epithelial tissue are tightly connected to each other, there is practically no intercellular fluid. Connective tissue contains a large amount of intercellular substance; the cells are not tightly connected to each other.

The cells are thin, flattened, contain little cytoplasm, the disc-shaped nucleus is located in the center (Fig. 8.13). The edges of the cells are uneven, so that the surface as a whole resembles a mosaic. Between neighboring cells there are often protoplasmic connections, thanks to which these cells are tightly connected to each other. Flat epithelium is found in Bowman's capsules of the kidneys, in the lining of the alveoli of the lungs and in the walls of capillaries, where, due to its thinness, it allows the diffusion of various substances. It also forms the smooth lining of hollow structures such as blood vessels and heart chambers, where it reduces friction of flowing fluids.

Cuboidal epithelium

It is the least specialized of all epithelia; as its name indicates, its cells are cubic in shape and contain a centrally located spherical nucleus (Fig. 8.14). If you look at these cells from above, you can see that they have a pentagonal or hexagonal outline. Cuboidal epithelium lines the ducts of many glands, for example salivary glands and pancreas, as well as the collecting ducts of the kidney in areas that are not secretory. Cuboidal epithelium is also found in many glands (salivary, mucous, sweat, thyroid), where it performs secretory functions.

Columnar epithelium

These are tall and rather narrow cells; due to this shape, there is more cytoplasm per unit area of ​​the epithelium (Fig. 8.15). Each cell has a nucleus located at its base. Among epithelial cells secretory goblet cells are often scattered; According to its functions, the epithelium can be secretory and (or) absorptive. Often on the free surface of each cell there is a well-defined brush border formed microvilli, which increase the absorptive and secreting surfaces of the cell. Columnar epithelium lines the stomach; mucus secreted by goblet cells protects the gastric mucosa from the effects of its acidic contents and from digestion by enzymes. It also lines the intestines, where again mucus protects it from self-digestion and at the same time creates a lubricant that facilitates the passage of food. IN small intestine digested food is absorbed through the epithelium into the bloodstream. Columnar epithelium lines and protects many renal tubules; it is also part of the thyroid gland and gall bladder.

Ciliated epithelium

The cells of this tissue are usually cylindrical in shape, but bear numerous cilia on their free surfaces (Fig. 8.16). They are always associated with goblet cells that secrete mucus, which is propelled by the beating of cilia. Ciliated epithelium lines the oviducts, ventricles of the brain, the spinal canal and the respiratory tract, where it facilitates the movement of various materials.

Pseudostratified (multi-row) epithelium

When examining histological sections of epithelium of this type, it seems that cell nuclei lie at several different levels because not all cells reach the free surface (Fig. 8.17). However, this epithelium consists of only a single layer of cells, each of which is attached to a basement membrane. Pseudostratified epithelium lines the urinary tract, trachea (pseudostratified cylindrical), other respiratory tracts (pseudostratified cylindrical ciliated) and is part of the mucous membrane of the olfactory cavities.

Each type of fabric has many characteristic features. They lie in the features of the structure, the set of functions performed, the origin, and the nature of the update mechanism. These tissues can be characterized by several criteria, but the most common is morphofunctional affiliation. This classification of tissues makes it possible to most fully and significantly characterize each type. Depending on the morphofunctional characteristics, the following are distinguished (integumentary), supporting-trophic muscular and nervous.

Features general morphofunctional characteristics

Epithelia include a group of tissues widely distributed in the body. They can differ in origin, that is, develop from ectoderm, mesoderm or endoderm, and also perform different functions.

List of general morphofunctional features characteristic of all epithelial tissues:

1. Consist of cells called epithelial cells. Between them there are thin intermembrane gaps, in which there is no supramembrane complex (glycocalyx). It is through it that substances enter the cells and through it they are removed from the cells.

2. The cells of epithelial tissues are located very densely, which causes the formation of layers. It is their presence that allows the fabric to perform its functions. The methods of connecting cells to each other can be different: using desmosomes, gap junctions or tight junctions.

3. Connective and epithelial tissues, which are located one below the other, are separated by a basement membrane consisting of proteins and carbohydrates. Its thickness is 100 nm - 1 micron. There are no epithelia inside blood vessels, and therefore, their nutrition is carried out diffusely, using the basement membrane.

4. Epithelial cells are characterized by morphofunctional polarity. They have a basal and apical pole. The nucleus of epithelial cells is located closer to the basal one, and almost all the cytoplasm is located at the apical one. There may be clusters of cilia and microvilli.

5. Epithelial tissue are distinguished by a well-expressed ability to regenerate. They are characterized by the presence of stem, cambial and differentiated cells.

Different approaches to classification

From an evolutionary point of view, epithelial cells formed earlier than cells of other tissues. Their primary function was to separate the body from external environment. On modern stage During evolution, epithelial tissues perform several functions in the body. According to this characteristic, the following types of tissue are distinguished: integumentary, absorptive, excretory, secretory and others. Classification of epithelial tissues according to morphological characteristics takes into account the shape of epithelial cells and the number of their layers in the layer. Thus, single-layer and multilayer epithelial tissues are distinguished.

Characteristics of single-layer single-row epithelia

The structural features of epithelial tissue, which is usually called single-layer, are that the layer consists of a single layer of cells. When all cells of the layer are characterized by the same height, then we are talking about single-layer single-row epithelium. The height of epithelial cells determines the subsequent classification, according to which they speak of the presence of flat, cubic and cylindrical (prismatic) single-layer single-row epithelium in the body.

Single-layer squamous epithelium is localized in the respiratory sections of the lungs (alveoli), small gland ducts, testes, middle ear cavity, serous membranes (mesothelium). Formed from mesoderm.

The localization sites of single-layer cuboidal epithelium are the ducts of the glands and the tubules of the kidneys. The height and width of the cells are approximately the same, the nuclei are round and located in the center of the cells. The origin may vary.

This type of single-layer, single-row epithelial tissue, such as cylindrical (prismatic) epithelium, is located in the gastrointestinal tract, glandular ducts, and collecting ducts of the kidneys. The height of the cells significantly exceeds the width. Has different origins.

Characteristics of single-layer multirow ciliated epithelium

If single-layer epithelial tissue forms a layer of cells of varying heights, then we are talking about multirow ciliated epithelium. This tissue lines the surfaces of the airways and some parts of the reproductive system (vas deferens and oviducts). The structural features of epithelial tissue of this type are that its cells are of three types: short intercalary, long ciliated and goblet. All of them are located in one layer, but the intercalary cells do not reach top edge layer. As they grow, they differentiate and become ciliated or goblet-shaped. A feature of ciliated cells is the presence of a large number of cilia at the apical pole, which are capable of producing mucus.

Classification and structure of multilayer epithelia

Epithelial cells can form several layers. They are located on top of each other, therefore, direct contact with the basement membrane is only in the deepest, basal layer of epithelial cells. It contains stem and cambial cells. When they differentiate, they move outward. The criterion for further classification is the shape of the cells. Thus, stratified squamous keratinizing, stratified squamous non-keratinizing and transitional epithelia are distinguished.

Characteristics of stratified squamous keratinizing epithelium

Formed from ectoderm. This tissue consists of the epidermis, which is the surface layer of the skin, and the final portion of the rectum. The structural features of epithelial tissue of this type are the presence of five layers of cells: basal, spinous, granular, shiny and horny.

The basal layer is a single row of tall cylindrical cells. They are tightly bound to the basement membrane and have the ability to reproduce. The thickness of the stratum spinosum ranges from 4 to 8 rows of spinous cells. The granular layer contains 2-3 rows of cells. Epithelial cells have a flattened shape, the nuclei are dense. The shiny layer is 2-3 rows of dying cells. The stratum corneum, closest to the surface, consists of a large number of rows (up to 100) of flat-shaped dead cells. These are horny scales containing the horny substance keratin.

The function of this tissue is to protect deep-lying tissues from external damage.

Features of the structure of multilayered squamous non-keratinizing epithelium

Formed from ectoderm. Locations include the cornea of ​​the eye, the oral cavity, the esophagus and part of the stomach of some animal species. It has three layers: basal, spinous and flat. The basal layer is in contact with the basement membrane and consists of prismatic cells with large oval nuclei, somewhat shifted to the apical pole. The cells of this layer, dividing, begin to move upward. Thus, they cease to be in contact with the basement membrane and pass into the spinous layer. These are several layers of cells with an irregular polygonal shape and an oval nucleus. The spinous layer passes into the superficial - flat layer, the thickness of which is 2-3 cells.

Transitional epithelium

The classification of epithelial tissues provides for the presence of the so-called transitional epithelium, formed from the mesoderm. Localization sites are the ureters and bladder. The three layers of cells (basal, intermediate and integumentary) differ greatly in structure. The basal layer is characterized by the presence of small cambial cells of various shapes lying on the basement membrane. In the intermediate layer, the cells are light and large, and the number of rows may vary. This directly depends on how full the organ is. In the covering layer, the cells are even larger, they are characterized by multinucleation, or polyploidy, and are capable of secreting mucus, which protects the surface of the layer from harmful contact with urine.

Glandular epithelium

Characteristics of epithelial tissues were incomplete without a description of the structure and functions of the so-called glandular epithelium. This type of tissue is widespread in the body; its cells are capable of producing and secreting special substances - secretions. The size, shape, and structure of glandular cells are very diverse, as is the composition and specialization of the secretions.

The process during which secretions are formed is quite complex, occurs in several stages and is called the secretory cycle.

The structural features of epithelial tissue consisting of are determined primarily by its purpose. From this type of tissue, organs are formed, the main function of which will be the production of secretions. These organs are usually called glands.

Single-layer multirow ciliated epithelium.

II. Multilayer epithelium.

1. Multilayer flat non-keratinizing

2. Multilayer flat keratinizing

3. Transitional

In a single-layer ep. all cells, without exception, are directly connected (in contact) with the basement membrane. In single-layer single-row epithelium, all cells are in contact with the basement membrane; have the same height, so the cores are located at the same level.

Single layer squamous epithelium- 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 and single microvilli are found, and pinocytotic vesicles are visible in the cytoplasm. Single-layer squamous epithelium lines the serous integument (peritoneum, pleura, pericardial sac). Regarding the endothelium (the cells lining the blood and lymph vessels, the cavities of the heart), there is no consensus among histologists: some classify the endothelium as a single-layer squamous epithelium, while others classify it as a connective tissue with special properties. Sources of development: endothelium develops from mesenchyme; single-layer squamous epithelium of the serous integument - from splanchnotomes (ventral part of the mesoderm). Functions: delimiting, reduces friction of internal organs by releasing serous fluid.

Single layer cuboidal epithelium- when cut, the diameter (width) of the cells is equal to the height. It is found in the excretory ducts of the exocrine glands and in the convoluted renal tubules.

Single-layer prismatic (cylindrical) epithelium - on a section, the width of the cells is less than the height. Depending on the characteristics of the structure and function, they are distinguished:

- single-layer prismatic glandular, found in the stomach, in the cervical canal, specialized for the continuous production of mucus;

Single-layer prismatic bordered, lining the intestine, on the apical surface of the cells there is a large number of microvilli; specialized for suction.

- single-layer prismatic ciliated, lining the fallopian tubes; epithelial cells have cilia on the apical surface.

Regeneration of single-layer single-row epithelium occurs due to stem (cambial) cells evenly scattered among other differentiated cells.

Single-layer multirow ciliated epithelium- 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 . Within this epithelium there are different types of cells:

- short and long intercalary cells (poorly differentiated and among them stem cells; provide regeneration);

- goblet cells - have the shape of a glass, do not perceive dyes well (white in the preparation), produce mucus;

- ciliated cells with ciliated cilia on the apical surface.

Function: purification and humidification of passing air.

Stratified epithelium- consists of several layers of cells, with only the lowest row of cells in contact with the basement membrane.

1. Stratified squamous non-keratinizing epithelium- lines the anterior (oral cavity, pharynx, esophagus) and final section (anal rectum) of the digestive system, the cornea. Consists of layers:

a) basal layer - cylindrical epithelial cells with weakly basophilic cytoplasm, often with a mitotic figure; in small quantities stem cells for regeneration;

b) stratum spinosum - consists of a significant number of layers of spinose-shaped cells, the cells are actively dividing.

c) integumentary cells - flat, aging cells, do not divide, and gradually peel off from the surface. Source of development: ectoderm. The prechordal plate is part of the foregut endoderm. Function: mechanical protection.

2. Stratified squamous keratinizing epithelium- This is the epithelium of the skin. It develops from the ectoderm, performs a protective function - protection from mechanical damage, radiation, bacterial and chemical exposure, demarcates the body from the environment. Consists of layers:

a) basal layer- in many ways similar to a similar layer of stratified non-keratinizing epithelium; additionally: contains up to 10% melanocytes - process cells with inclusions of melanin in the cytoplasm - provide protection from UV rays; there is a small number of Merkel cells (part of the mechanoreceptors); dendritic cells with a protective function by phagocytosis; epithelial cells contain tonofibrils (special purpose organelle - provide strength).

b) layer spinosum- from epithelial cells with spine-like projections; there are dendrocytes and blood lymphocytes; epithelial cells are still dividing.

c) granular layer- from several rows of elongated flattened oval cells with basophilic granules of keratohyalin (the precursor of the horny substance - keratin) in the cytoplasm; cells don't divide.

d) shiny layer- cells are completely filled with elaidin (formed from keratin and decay products of tonofibrils), which reflects and strongly refracts light; Under a microscope, the boundaries of cells and nuclei are not visible.

e) layer of horny scales- consists of horny plates of keratin containing bubbles with fat and air, keratosomes (corresponding to lysosomes). The scales peel off from the surface.

3. Transitional epithelium- lines hollow organs, the wall of which is capable of strong stretching (pelvis, ureters, bladder). Layers:

- basal layer (from small dark low-prismatic or cubic cells - poorly differentiated and stem cells, provide regeneration;

- intermediate layer - made of large pear-shaped cells, with a narrow basal part, in contact with the basement membrane (the wall is not stretched, so the epithelium is thickened); when the wall of the organ is stretched, the pyriform cells decrease in height and are located among the basal cells.

— cover cells - large dome-shaped cells; when the organ wall is stretched, the cells flatten; the cells do not divide and gradually exfoliate.

Thus, the structure of the transitional epithelium changes depending on the state of the organ: when the wall is not stretched, the epithelium is thickened due to the “displacement” of some cells from the basal layer into the intermediate layer; when the wall is stretched, the thickness of the epithelium decreases due to the flattening of the integumentary cells and the transition of some cells from the intermediate layer to the basal layer. Sources of development: ep. pelvis and ureter - from the mesonephric duct (derivative of segmental legs), ep. bladder - from the endoderm of the allantois and the endoderm of the cloaca . The function is protective.

GLANDROUS EPITHELIA

Ferrous ep. (PVC) is specialized for the production of secretions. PVCs form glands:

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

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

Principles of classification of exocrine glands:

I. According to the structure of the excretory ducts:

1. Simple- the excretory duct does not branch.

2. Complex- the excretory duct branches.

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

1. Alveolar- secretory department in the form of an alveoli, vesicle.

2. Tubular- secret tube-shaped section.

3. Alveolar-tubular(mixed form).

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

1. Unbranched- one secretor opens into one excretory duct -

department

2. Branched- several secretions open into one excretory duct

tor departments.

IV. By type of secretion:

1. Merocrine- during secretion, the integrity of the cells is not violated. Characteristics

terno for most glands.

2. Apocrine(apex - apex, crinio - secretion) - during secretion, the top of the cells is partially destroyed (torn off) (example: mammary glands).

3. Holocrines- during secretion, the cell is completely destroyed. Ex: sebaceous glands of the skin.

V. By localization:

1. Endoepithelial- a single-celled gland in the thickness of the integumentary epithelium. Ex: goblet cells in the intestinal epithelium and air duct. ways.

2. Exoepithelial glands- the secretory department lies outside the epithelium, in the underlying tissues.

VI. By the nature of the secret:

Protein, mucous, mucous-protein, sweat, sebaceous, milk, etc.

Secretion phases:

1. Entry into the glandular cells of the starting materials for the synthesis of secretions (amino acids, lipids, minerals, etc.).

2. Synthesis (in EPS) and accumulation (in PC) of secretion in glandular cells.

3. Isolation of the secret.

Glandular epithelial cells are characterized by the presence of organelles: EPS of granular or agranular type (depending on the nature of the secretion), lamellar complex, mitochondria.

Regeneration of glandular epithelium- in most glands, regeneration of the glandular epithelium occurs through the division of poorly differentiated (cambial) cells. Some glands (salivary glands, pancreas) do not have stem and poorly differentiated cells and intracellular regeneration occurs in them - i.e. renewal of worn-out organelles inside the cells, in the absence of the ability to divide cells.

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Multirow ciliated epithelium. Structure

Single-layer multirow epithelia

Multirow (pseudostratified) epithelia line the airways - nasal cavity, trachea, bronchi, and a number of other organs. In the airways, the multirow epithelium is ciliated and contains cells that differ in shape and function. Basal cells are low, lying on the basement membrane deep in the epithelial layer. They belong to the cambial cells, which divide and differentiate into ciliated and goblet cells, thus participating in the regeneration of the epithelium. Ciliated (or ciliated) cells are tall and prismatic in shape. Their apical surface is covered with cilia. In the airways, with the help of flexion movements (the so-called “flickering”), they clear the inhaled air of dust particles, pushing them towards the nasopharynx. Goblet cells secrete mucus onto the surface of the epithelium. All these and other types of cells have different shapes and size, therefore 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.

Rice. Multirow ciliated epithelium of the dog's trachea (magnification: approx. 10, immersion):

1 - ciliated cell, 2 - cilia, 3 - basal granules forming a solid line, 4 - secretion in the goblet cell, 5 - nucleus of the goblet cell, 6 - intercalary cell, 7 - basal cell

At first glance, multilayer epithelium gives the impression of being multilayered because the brightly colored cell nuclei are arranged in several rows. In fact, it is a single-layer epithelium, because all cells are attached to the basement membrane with their lower ends. The arrangement of the nuclei in several rows is due to the fact that the cells that make up the epithelial layer have different sizes and shapes.

The free surface of the multirow epithelium, bordering the lumen of the trachea, is lined with closely adjacent prismatic ciliated cells. Wide above, they narrow strongly downward and are attached to the basement membrane with a thin stalk.
The free surface of the ciliated cells is covered with a thin, dense cuticle, forming a double-contour border. Thin short protoplasmic projections pass through the pores of the cuticle - cilia, which form a continuous layer on the surface of the epithelial lining of the trachea.

Cilia extend from basal granules lying in the protoplasm of cells directly under the cuticle. On the preparation at high magnification, individual grains are not visible and appear as a solid black line. Individual grains can only be distinguished under an immersion lens.

Between the ciliated cells lie individual goblet-shaped mucous unicellular glands.

Widened at the top, they also taper strongly at the bottom. The upper expanded flask-shaped part of these cells is usually filled with a fine-meshed mucous secretion, which flows onto the surface of the ciliated epithelium. The secret pushes the core into bottom part cells and compresses it, as a result of which the nuclei often have a crescent shape. Mucous cells lack cilia.

In the submucosa of the trachea there are mixed (protein-mucosal) glands, which also secrete secretions through the ducts onto the free surface of the trachea. Due to this, the surface of the cilia is always covered with a layer of viscous liquid, to which dust particles, microbes, etc., present in the inhaled air, stick. The cilia of the trachea are located in constant movement. They shoot outward, as a result of which the layer of liquid always moves towards the nasal cavity and is removed from the body. The cavity of not only the trachea, but also other airways is lined with the same ciliary cover.

In this way, the inhaled air is cleaned in the airways from harmful particles that can damage the delicate epithelial lining of the alveoli of the lung. Air humidification also occurs here.

In addition to tall ciliated and mucous cells, the upper ends of which reach the free surface of the epithelium, there are intermediate, or intercalary, cells that lie deep in the epithelium and do not reach its free surface.

In the tracheal epithelium, two types of intercalary cells are distinguished. Some of them, the taller ones, have a spindle-shaped shape, their lower thin ends are attached to the basement membrane, the nucleus is located in the expanded middle part, and the upper thin ends are wedged between the ciliated cells, but never reach the lumen of the trachea.

Other, much lower intercalary cells are conical in shape, their wide bases lie on the basement membrane, and the narrowed apices are located between other cells. In accordance with the different heights of the intercalary cells, their spherical nuclei lie at different levels in the lower part of the epithelial layer.

Thus, in the multirow epithelium of the trachea, the lower rows of nuclei belong to various intercalary cells, and the upper row belongs to prismatic ciliated cells. The nuclei of mucous cells have an irregular shape, are brighter in color and are located in the layer without any particular order. 

Human ciliated epithelium

called epithelium separate species tissues in the human body, which are the cellular layers that line the surfaces of internal organs, cavities and surfaces of the body. Epithelial tissues participate in the life of almost all systems and organs; the epithelium covers the organs of the genitourinary and respiratory systems, the mucous membranes of the gastrointestinal tract, forms many glands, and so on.

In turn, epithelial tissues are divided into many types: multilayered, single-layered, transitional, one of which includes ciliated epithelium.

What is ciliated epithelium

Ciliated epithelium can be single-layered or multilayered, but have one unifying feature, which determined the name of this type of tissue: the presence of mobile cilia or hairs. This type of tissue lines many organs, e.g. respiratory tract, some departments genitourinary system, parts of the central nervous system etc.

The flickering and movement of cilia and hairs is not random; such actions are strictly coordinated, both in an individual cell and in the entire tissue layer covering a certain area of ​​the human body. This movement is explained on the basis scientific research, carried out using microscopic electron examination. This is attributed to the processes of ATP (adenosine triphosphate) breakdown, but at what exact moment and at what stage this coordinated movement occurs, scientists have not yet determined.

Key Features

The cells that make up the ciliated epithelium look like cylinders covered with hairs. Such cells are always in close interaction with other goblet-shaped cells, which secrete a special mucous fraction. Thanks to the movement of the cilia of the ciliated epithelium, this mucus can move or flow. As a specific example of such interaction and movement, one can cite the processes of a person swallowing solid food: mucus moved directly into the throat by the cilia of the ciliated epithelium helps the further passage of solid substances through the digestive tract. In addition, the same mucus and the action of the cilia of the ciliated epithelium help create obstacles for harmful bacteria, dust particles and dirt on the way to the lungs and other respiratory organs.

The main factors influencing the activity of the ciliated epithelium

If considered under electron microscope movements of the cilia of the ciliated epithelium, you can notice a great resemblance to the movement of the hands of a swimming person. A shock phase is distinguished, in which the hairs very quickly move from a horizontal position to vertical position, and return to the starting position – reverse phase.

Ciliated epithelium

Moreover, the first phase proceeds 3 times faster than the second.

The work of the ciliated epithelium is very clearly visible in the respiratory organs, in which the cilia are surrounded by bronchial secretion, which in turn consists of two layers - the upper (dense) and the lower (liquid).

The cilia of the ciliated epithelium work well in the lower part. The upper part is more viscous and is intended to prevent and retain foreign particles. In the presence of irritating factors The production of bronchial secretions increases significantly. Such factors include microbes, smoke phenomena, and dust. Such processes are completely justified from a biological point of view, because this secretion performs preventive and protective functions for the body. With the normalization and removal of irritating phenomena, secretion production returns to normal.

The work of the cilia of the ciliated epithelium is more influenced by external and internal temperature. The rhythm of oscillations increases significantly if the external temperature is high enough. But at a temperature human body over 40 degrees (namely, this temperature can be observed in the presence of colds and inflammatory processes in the body) hair vibrations slow down greatly. The same phenomenon is observed with a strong decrease in body temperature.

An interesting fact is that the cilia and hairs of the ciliated epithelium act independently, regardless of external influences. For example, their activity and movements are absolutely independent of stimulation of the brain or when affecting some parts of the spinal cord.

In addition, a number of clinical and scientific studies have confirmed that it is the reliability of the ciliated epithelium that affects the body’s ability to resist various infectious diseases. Secretion production can be regulated sufficiently in simple ways: drink plenty of fluids in hot weather, avoid hypothermia in winter, make sure your breathing is correct.