Epithelium Epithelial cells are constantly present in urine sediment. At the same time, epithelial cells originating from different parts of the genitourinary system differ in shape and structure (flat, transitional and renal epithelium are distinguished). Cells of squamous epithelium, characteristic

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 chambers of the heart, 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, such as the salivary glands and pancreas, as well as the collecting ducts of the kidney in non-secretory areas. 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. Secretory goblet cells are often scattered among the epithelial cells; 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 included in thyroid gland and gallbladder.

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 this type of epithelium, it appears that the 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 urinary tract, trachea (pseudo-multilayer cylindrical), other respiratory tract (pseudo-multilayer cylindrical ciliated) and is part of the mucous membrane of the olfactory cavities.

II. Stratified 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: demarcation, reduces friction internal organs by secreting 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 layered 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 . As part of this epithelium, there are 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, on the apical surface have ciliated cilia.

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-keratinized epithelium- lines the anterior (oral cavity, pharynx, esophagus) and terminal section (anal rectum) digestive system, cornea. Consists of layers:

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

b) 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. Prechordal plate in the endoderm foregut. Function: mechanical protection.

2. Stratified squamous keratinized 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, ensure regeneration;

The intermediate layer is made up 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.

Integumentary cells - large dome-shaped cells; when the wall of the organ is stretched, the cells are flattened; cells do not divide, gradually exfoliate.

Thus, the structure of the transitional epithelium changes depending on the state of the organ: when the wall is not stretched, the epithelium is thickened due to the “displacement” of some 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.

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 layered 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 . As part of this epithelium, there are 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-keratinized 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 a small amount of 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 keratinized 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.

Read also:

Multirow ciliated epithelium. Structure

Single-layer multirow epithelia

Multi-row (pseudo-stratified) epithelia line the airways - the 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 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.

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 secretion pushes the nucleus into the lower part of the cell 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 in constant motion. 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.

Thus, the inhaled air is cleaned in the airways from harmful particles that can damage the delicate epithelial lining lung alveoli. 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 lying on the basement membrane, and their narrowed apices 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

Epithelium is a separate type of tissue in the human body, which is 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 genitourinary and respiratory system, the mucous membranes of the gastrointestinal tract, form many glands, and so on.

In its turn, epithelial tissues are divided into many types: multilayer, single-layer, 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 parts of the 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 of 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 we examine the movements of the cilia of the ciliated epithelium under an electron microscope, we can see a great resemblance to the movement of the hands of a swimming person. The impact phase is identified, in which the hairs from horizontal position very quickly take a vertical position, and returning to the starting position is the 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 fully justified from a biological point of view, because this secret performs preventive and protective functions for the body. With the normalization and removal of irritating phenomena, the secretion production returns to normal.

External and internal temperature have a greater influence on the work of the cilia of the ciliated epithelium. The oscillation rhythm increases significantly if the outside temperature is high enough. But at a human body temperature above 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 brain stimuli or when they act on 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, prevent hypothermia in winter, monitor the correctness of your breathing.

Integumentary and lining epithelium

The integumentary epithelium is part of the integument of the body in the form of the epidermis and its derivatives (scales, feathers, hair, horns, hooves, etc.), and the lining

In the composition of the mucous and serous membranes, lining the inside of tubular organs and serous cavities. The main function of these epithelia is borderline. Most of them are located on the border between the internal and external environment, which largely determines the nature of their structure and functioning. Comparative histological data indicate the phylogenetic relationship of these epithelia, so they are usually combined into a group of integumentary epithelium.

Single-layer squamous epithelium (Fig. 22-A). It lines the respiratory sections of the lungs, small ducts of the glands, the testicular network, the middle ear cavity, serous membranes. In the latter case, it is known as mesothelium, which indicates its origin from the mesoderm (from both sheets of the splanchnotome). Single-layer squamous epithelium consists of cells whose height is less than their width, the nuclei are flattened. In the place where the nucleus is located, the cell is slightly higher than in other areas. The morpho-physiological polarity in this type of epithelium is less pronounced than in other species, especially in the mesothelium, which, having immersed itself in the internal environment of the body, has lost it. When the layer in the mesothelium is disrupted, giant multinucleated cells are formed. Functions of the mesothelium: delimiting, so

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Single-layer cubic epithelium (Fig. 22-B). Has various origins. Lines the ducts of the glands and tubules of the kidneys. All cells lie on the basement membrane. Their height is approximately equal to their width. The functions of this epithelium are closely related to the functions of the organ in which it is located. This may be delimiting (in the ducts), osmoregulating (in the kidneys and salt glands) and other functions.

Single-layer prismatic (cylindrical) epithelium (Fig. 22-B). It has different origins depending on its location in the body. Lines gastrointestinal tract, gland ducts, renal collecting ducts. All its cells lie on the basement membrane and have morphophysiological polarity. Their height is much greater than their width. In addition to the demarcation function, this epithelium performs specific functions inherent in a particular organ. For example, the prismatic epithelium of the gastric mucosa is glandular - it produces mucus, and is therefore called prismatic mucosal epithelium. The prismatic epithelium of the intestinal mucosa is called bordered, since it bears microvilli at the apical pole - a brush border, due to which parietal digestion and absorption of nutrients occurs.

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Single-layer multirow ciliated epithelium (Fig. 22-D).

It has a complex origin. Lines the airways and some parts of the reproductive system (vas deferens, oviducts). Consists of three types of cells: short ciliated, long intercalary (basal) And

goblet. All cells of the epithelial layer lie on the basement membrane, but the intercalary cells do not reach the upper edge of the layer. These are stem and cambial elements of the epithelium, which differentiate during growth and become ciliated and goblet-shaped. Ciliated cells carry at the apical pole a large number (up to 270) of cilia - organelles of movement. Goblet cells produce mucus (see glandular epithelium). Mucus covers a layer of ciliated epithelium, not only protecting it from external influences, but also facilitating the movement of adhering particles in the airways or reproductive products in the genital tract. Consequently, the ciliated epithelium, in addition to delimiting, also performs transport and protective functions.

Multilayer flat non-keratinizing (slightly keratinizing)

epithelium (Fig. 22-D). Originates from the ectoderm and covers the cornea of ​​the eye, and in some animals, in addition, oral cavity, esophagus, stomach. It has three layers: basal, spinous and flat. The basal layer lies on the basement membrane and is formed by prismatic cells with large oval nuclei, somewhat shifted to the apical pole.

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membrane, differentiate and become part of the spinous layer. The stratum spinosum is formed by several layers of cells of irregular polygonal shape with oval or round nuclei and with small processes in the form of plates and spines that penetrate between the cells, holding them, along with desmosomes, near each other. From the spinous layer, the cells move to the superficial - flat layer 2-3 cells thick. At the same time, they become flat, as if spreading over the underlying cells, with the result that each flat cell occupies an area equal to the apical surface of several basal cells. The nuclei of flat epithelial cells also flatten and become hyperchromic. Connections between cells weaken. Finishing my life cycle, they die and fall off the surface of the epithelium. In farm animals, especially ruminants, the surface cells of this epithelium become keratinized (except for the cornea).

Stratified squamous keratinized (squamous) epithelium

(Fig. 22-E). It originates from the ectoderm and forms the epidermis of the skin, covering the oral cavity and the final portion of the rectum. It has five layers: basal, spinous, granular, shiny and horny. The basal layer, like that of non-keratinizing epithelium, consists of one row of prismatic cells connected by desmosomes both to each other and to the basement membrane. In the cytoplasm of cells there are many free ribosomes, tonophytes are visible

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laments. The stratum spinosum is 4-8 spinous cells thick. In these cells, the number of tonofilaments increases, which are combined into bundles - tonofibrils, visible under a light microscope. The spinous cells still retain the ability to reproduce, which is why sometimes the basal and spinous layers are combined under one name - the germinal layer. Granular layer 2-3 cells thick. The epithelial cells of this layer are flattened in shape with dense nuclei and sharply basophilic grains of keratohyalin, which merge with tonofibrils. The granular layer turns into a shiny layer, consisting of 1-2 rows of dying cells. In this case, the keratohyalin grains merge, the organelles degrade, the nuclei disintegrate, the keratohyalin turns into eleidin, which is oxyphilic and strongly refracts light, which gives the layer its name. The most superficial stratum corneum is formed by many rows (up to 100) of flat dead cells - horny scales, filled with horny substance - keratin. The desmosomes that connect the cells are modified, and neutral fats accumulate between the cells. On skin covered with hair, the stratum corneum is thin - made up of several rows of horny scales.

The function of this epithelium is borderline, protecting deeper tissues from external influences: chemical, thermal, mechanical, pathogenic, etc., which determines the nature of differentiation of epithelial cells. The specialization of the cell is expressed in its keratinization and transformation into a horny scale, which is equal in area to the apical surface of 9-10 basal

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Transitional epithelium(Fig. 22-G). Originates from mesoderm. It lines the renal pelvis, ureters, and bladder - organs that are subject to significant stretching when filled with urine. Consists of three layers: basal, intermediate and integumentary. The cells of the basal layer are small, of different shapes, are cambial, and lie on the basement membrane. Intermediate layer consists of light large cells, the number of rows of which varies greatly depending on the degree of filling of the organ. In an organ free from urine, they have a club-shaped shape and are located one above the other; in a filled organ, they stretch and penetrate into the intercellular spaces. The cells of the covering layer are very large, multinucleate or polyploid, and often secrete mucus, which protects the surface of the epithelial layer from the action of urine.

Epithelium of parenchymal organs

Epithelium, which is part of organs such as the lungs, kidneys, liver, pancreas and salivary glands, testes, ovaries, pituitary gland, thyroid, adrenal glands, thymus, are very diverse and will be considered when studying the corresponding organs. Here we will focus on general principles the structure and functioning of glandular epithelium - a widespread type of epithelial tissue.

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Glandular epithelium. This is a specialized epithelium, the cells of which produce and secrete substances of various natures, called secretions. The glandular epithelium has all the properties of epithelial tissues, despite the fact that it often does not come into contact with the external environment. This is explained by the peculiarities of the work he performs. secretory function. Glandular cells are very diverse in size, shape, and structure, as are the secretions they produce. Nevertheless, many glandular cells are characterized by large size, large nuclear surface, large nucleoli, high content of RNA and protein in the cytoplasm, strong development of structures involved in the process of secretion and the presence at a certain stage of the functional cycle of granules, grains, vacuoles of secretion or its predecessors. The products produced by glandular cells are also very diverse in chemical nature, physical properties, by number and location in the cell.

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Rice. 23. Scheme of types of secretion:

1 - merocrine; 2 - apocrine; 3 - holocrine.

The secretion process occurs in several phases and is called

secretory cycle.

The first phase is the accumulation of initial products by the cell. Through the basal pole, various substances of organic and inorganic nature enter the cell, which are used in the process of secretion synthesis. The second phase is the synthesis of secretion from incoming products in the cytoplasmic reticulum. The synthesis of protein secretions occurs in the granular type, non-protein secretions - in its agranular variety. The third phase is the formation of secretions into granules and their accumulation in the cytoplasm of the cell. Through the cisterns of the cytoplasmic reticulum, the synthesized product arrives at the location of the Golgi apparatus (lamellar complex), where it is condensed and packaged in the form of granules, grains, and vacuoles. After this, the vacuole with a portion of the secretion is detached from the lamellar complex and moves to the apical pole of the cell. The fourth phase - secretion - extrusion proceeds in different ways, and therefore they distinguish between merocrine, apocrine and

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holocrine type of secretion (Fig. 23). At merocrine type the secretion is removed without violating the integrity of the cytolemma. The secretory vacuole approaches the apical pole of the cell, merges with it with its membrane, and a pore is formed through which the contents of the vacuole flow outside the cell. With the apocrine type, partial destruction of the glandular cell occurs. Celebrate macroapocrine secretion when, together with the secretory granule, the apical part of the cell cytoplasm is rejected, and microapocrine secretion when the tips of the microvilli are torn off. At holocrine type secretion, complete destruction of the glandular cell and its transformation into secretion is observed. The fifth phase is the restoration of the original state of the glandular cell.

The phases of the secretory cycle can occur sequentially one after another, or they can occur simultaneously in different parts of the cell. This depends both on the characteristics of the functioning of the cells and on the strength of stimulation of their activity.

Glandular cells are part of some types of integumentary and lining epithelia, and also form specialized organs - glands.

Glands. These are organs whose main function is secretory. Depending on where the secretion is released, exocrine and endocrine glands are distinguished. Exocrine glands have ducts through which the secretion flows either onto the surface of the body or into the cavity of some tube-like

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sti-hormones - are released into the internal environment of the body - into the blood or lymph.

According to the number of cells forming the glands, the latter are unicellular and multicellular. A typical unicellular gland in the body of a vertebrate animal is goblet cell. This type of cell is found in the epithelium of the intestines, airways and genital tracts. They secrete a mucous secretion. The shape of the cage resembles a glass. It has a narrow basal part, in which the nucleus, cisterns of the cytoplasmic reticulum, mitochondria and other organelles are located. The most developed organelle is the Golgi complex, located above the nucleus. It synthesizes and accumulates mucopolysaccharides, which make up the main part of the secretion. Its cisterns gradually transform into secretory vacuoles. As they accumulate, vacuoles occupy the entire middle and apical parts of the cell. The secretory cycle in a goblet cell is completed in 20-30 minutes. The secretion is secreted according to the merocrine type.

Based on their location, endoepithelial and exoepithelial glands are distinguished. Unicellular glands of vertebrates are always endoepithelial- lie in the epithelial layer. Multicellular glands are usually exoepithelial- lie outside the epithelial layer.

Multicellular exocrine glands consist of end sections, formed by glandular cells, and excretory ducts, through which the synthesized secretion is derived. According to the shape of the end sections of the gland there are

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tubular, alveolar (vesicular) and tubular-alveolar (Fig. 24).

If the excretory duct ends in one end section, they speak of a simple unbranched alveolar or tubular gland. If several terminal sections open into the duct, such a gland is called simple branched. When the excretory duct branches, a complex gland is formed. There are complex alveolar, tubular and tubuloalveolar glands. According to the nature of the secretion, the glands are divided into serous - producing protein secretion, mucous and mixed -

protein-mucous.

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Rice. 24. Scheme of the structure of the glands:

I - simple glands; II - simple glands with a branched end section; III - complex glands; a - tubular gland; b - alveolar gland; c - alveolar tubular gland; IV-unicellular gland - goblet cell; 1 - microvilli; 2 - secretion granules; 3- Golgi complex; 4- mitochondria; 5 - core; 6 - endoplasmic reticulum.

Influence of factors. The parenchyma of the glands reacts in the same way to exposure various factors. When exposed to extreme overloads, toxic or infectious lesions, mechanical damage and nerve damage

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