Tissue is a collection of cells and intercellular substance. It has common structural features and performs the same functions. There are four types of tissues in the body: epithelial, nervous, muscular and connective.

The structure of the epithelial and animals is primarily due to its localization. Epithelial tissue is the boundary layer of cells lining the integument of the body, mucous membranes internal organs and cavities. Also, many glands in the body are formed precisely by the epithelium.

general characteristics

Structure epithelial tissue has a number of features inherent only to the epithelium. main feature lies in the fact that the tissue itself has the form of a continuous layer of cells that fit tightly to each other.

The epithelium, lining all surfaces in the body, looks like a layer, while in the liver, pancreas, thyroid, salivary and other glands, it is an accumulation of cells. In the first case, it is located on top of the basement membrane separating the epithelium from connective tissue... But there are exceptions when the structure of epithelial and connective tissue is considered in the context of their interaction. In particular, in the lymphatic system, there is an alternation of epithelial and connective tissue cells. This type of epithelium is called atypical.

High regenerative capacity is another feature of the epithelium.

The cells of this tissue are polar, which is due to the difference in the basal and apical parts of the cell center.

The structure of epithelial tissue is largely due to its borderline position, which, in turn, makes the epithelium an important link in metabolic processes. This tissue is involved in the absorption of nutrients from the intestines into the blood and lymph, in the excretion of urine through the epithelium of the kidneys, etc. Also, one should not forget about the protective function, which consists in protecting tissues from damaging influences.

The structure of the substance that forms the basement membrane shows that it contains a large amount of mucopolysaccharides, and also has a network of thin fibrils.

How is epithelial tissue formed?

The structural features of the epithelial tissue of animals and humans are largely dictated by the fact that its development is carried out from all three. This feature is inherent only in this type of tissue. Ectoderm gives rise to the epithelium of the skin, oral cavity, a significant part of the esophagus, the cornea of ​​the eye; endoderm - epithelium gastrointestinal tract; and the mesoderm is the epithelium of the urogenital organs and serous membranes.

In embryonic development, it begins to form at the most early stages... Since the placenta contains a sufficient amount of epithelial tissue, it is a participant in the metabolism between the mother and the fetus.

Maintaining the integrity of epithelial cells

The interaction of neighboring cells in the formation is possible due to the presence of desmosomes. These are special multiple structures of submicroscopic size, which consist of two halves. Each of them, thickening in certain places, occupies the adjacent surfaces of neighboring cells. In the slit-like space between the halves of the desmosome there is a substance of carbohydrate origin.

In cases where the intercellular spaces are wide, desmosomes are located at the ends of cytoplasmic bulges directed towards each other on the contacting cells. If you examine a couple of these bulges under a microscope, you can find that they look like an intercellular bridge.

V small intestine the integrity of the layer is maintained due to the fusion of the cell walls of neighboring cells at the points of contact. Such places are often referred to as end plates.

There are other cases where there are no special structures to ensure integrity. Then the contact of neighboring cells is carried out due to the contact of flat or winding surfaces of the cells. The edges of the cells can overlap each other in tiles.

Epithelial tissue cell structure

The peculiarities of epithelial tissue cells include the presence of a plasma membrane on their surface.

In cells participating in the release of metabolic products, folding is observed in the plasma membrane of the basal part of the cell body.

Epithelial cells - this is how the cells that form epithelial tissues are called in science. Structural features, functions of epithelial cells are closely related. So, according to their shape, they are divided into flat, cubic and columnar. The core is dominated by euchromatin, due to which it has a light color. The nucleus is large enough, its shape coincides with the shape of the cell.

The pronounced polarity determines the location of the nucleus in the basal part, above it are the mitochondria, the Golgi complex and the centrioles. In cells that perform a secretory function, the endoplasmic reticulum and the Golgi complex are especially well developed. The epithelium, experiencing a great mechanical stress, in its cells has a system of special threads - tonofibrils, which create a kind of barrier designed to protect cells from deformation.

Microvilli

Some cells, or rather their cytoplasm, on the surface can form tiny, outwardly directed outgrowths - microvilli. Their largest accumulations are found on the apical surface of the epithelium in small intestine and the main sections of the convoluted tubules of the kidneys. Due to the parallel arrangement of microvilli in the cuticles of the intestinal epithelium and the brush border of the kidneys, stripes are formed that can be seen under an optical microscope. In addition, the microvilli in these areas contain a number of enzymes.

Classification

The structural features of epithelial tissues of different localization make it possible to classify them according to several criteria.

Depending on the shape of the cells, the epithelium can be cylindrical, cubic and flat, and depending on the location of the cells, it can be single-layered or multi-layered.

Also, glandular epithelium is secreted, which performs a secretory function in the body.

Unilamellar epithelium

The name of the monolayer epithelium speaks for itself: in it, all cells are located on the basement membrane in one layer. If, in this case, the shape of all cells is the same (that is, they are isomorphic), and are at the same level, then they speak of a single-row epithelium. And if in a single-layer epithelium there is an alternation of cells of different shapes, their nuclei are located at different levels, then this is a multi-row or anisomorphic epithelium.

Stratified epithelium

In stratified epithelium, only the lower layer is in contact with the basement membrane, while the other layers are above it. The cells of different layers differ in shape. The structure of this type of epithelial tissue makes it possible to distinguish several types of multilayer epithelium, depending on the shape and condition, multilayer flat, multilayer keratinizing (there are keratinized scales on the surface), multilayer non-keratinizing.

There is also the so-called transitional epithelium lining the organs of the excretory system. Depending on whether or is stretched, the fabric acquires different kind... So, when the bladder is stretched, the epithelium is in a thinned state and forms two layers of cells - basal and integumentary. And when bladder is in a compressed (reduced) form, the epithelial tissue thickens sharply, the cells of the basal layer become polymorphic and their nuclei are at different levels. The integumentary cells become pear-shaped and layered on top of each other.

Histogenetic classification of epithelia

The structure of the epithelial tissue of animals and humans is often the subject of scientific and medical research. In these cases, the histogenetic classification developed by Academician N.G. Khlopin is used more often than others. According to her, there are five types of epithelium. The criterion is from which primordia the tissue developed during embryogenesis.

1. Epidermal type, the origin of which was given by the ectoderm and the prechordal plate.

2. Enterodermal type, the development of which originated from the intestinal endoderm.

3. Coelonephrodermal type, which developed from the coelomic lining and nephrotome.

4. Angiodermal type, the development of which began from the area of ​​the mesenchyme that forms the vascular endothelium, which is called angioblast.

5. Ependymoglial type, which originated from the neural tube.

Features of the structure of epithelial tissues that form the glands

The glandular epithelium performs a secretory function. This type of tissue is a collection of glandular (secretory) cells called granulocytes. Their function is to carry out synthesis, as well as the release of specific substances - secrets.

It is thanks to secretion that the body is able to perform many important functions. The glands secrete secretions on the surface of the skin and mucous membranes, inside the cavities of a number of internal organs, as well as into the blood and lymph. In the first case, we are talking about exocrine, and in the second - about endocrine secretion.

Exocrine secretion allows the production of milk (in female body), gastric and intestinal juices, saliva, bile, sweat and sebum. The secrets of the endocrine glands are hormones that perform humoral regulation in organism.

The structure of this type of epithelial tissue may be different due to the fact that granulocytes can receive different shape... It depends on the phase of secretion.

Both types of glands (endocrine and exocrine) can be composed of a single cell (unicellular) or multiple cells (multicellular).

Tissue - location in the body, types, functions, structure

Tissues are a system of cells and intercellular substance that have the same structure, origin and function.

The intercellular substance is a waste product of cells. It provides communication between cells and forms a favorable environment for them. It can be liquid, such as blood plasma; amorphous - cartilage; structured - muscle fibers; hard - bone tissue (in the form of salt).

Tissue cells have different shape which defines their function. There are four types of fabrics:

• epithelial - borderline tissues: skin, mucous membranes;
• connective - the internal environment of our body;
• muscle;
• nervous tissue.

Epithelial tissue

Epithelial (borderline) tissues - line the surface of the body, mucous membranes of all internal organs and cavities of the body, serous membranes, and also form the glands of external and internal secretion. The epithelium lining the mucous membrane is located on the basement membrane, and the inner surface is directly facing the external environment. Its nutrition is accomplished by the diffusion of substances and oxygen from blood vessels through the basement membrane.

Features: there are many cells, there is little intercellular substance and it is represented by the basement membrane.

Epithelial tissues perform the following functions:

• protective;
• excretory;
• suction.

Classification of the epithelium. According to the number of layers, a distinction is made between single-layer and multi-layer. They are distinguished by shape: flat, cubic, cylindrical.

If all epithelial cells reach the basement membrane, it is a single-layer epithelium, and if only cells of one row are connected to the basement membrane, and the others are free, it is multilayer. Monolayer epithelium can be single-row and multi-row, depending on the level of the nuclei. Sometimes the mononuclear or multinucleated epithelium has ciliated cilia facing the external environment.

Stratus epithelium Epithelial (integumentary) tissue, or epithelium, is the boundary layer of cells that lines the integument of the body, the mucous membranes of all internal organs and cavities, and also forms the basis of many glands.

Glandular epithelium The epithelium separates the organism (internal environment) from the external environment, but at the same time serves as an intermediary in the interaction of the organism with the environment. Epithelial cells are tightly connected to each other and form a mechanical barrier that prevents the penetration of microorganisms and foreign substances into the body. Cells of epithelial tissue live for a short time and are quickly replaced by new ones (this process is called regeneration).

Epithelial tissue is also involved in many other functions: secretion (glands of external and internal secretion), absorption (intestinal epithelium), gas exchange (epithelium of the lungs).

The main feature of the Epithelium is that it consists of a continuous layer of tightly attached cells. The epithelium can be in the form of a layer of cells lining all surfaces of the body, and in the form of large clusters of cells - glands: liver, pancreas, thyroid, salivary glands, etc. In the first case, it lies on the basement membrane, which separates the epithelium from the underlying connective tissue ... However, there are exceptions: epithelial cells in lymphatic tissue alternate with elements of connective tissue, such an epithelium is called atypical.

Epithelial cells located in a layer can lie in many layers (stratified epithelium) or in one layer (unilamellar epithelium). According to the height of the cells, epitheliums are distinguished: flat, cubic, prismatic, cylindrical.

Monolayer squamous epithelium - lines the surface of the serous membranes: pleura, lungs, peritoneum, pericardium of the heart.

Monolayer cubic epithelium - forms the walls of the kidney tubules and excretory ducts of the glands.

Monolayer columnar epithelium - forms the gastric mucosa.

The limb epithelium is a single-layer columnar epithelium, on the outer surface of the cells of which there is a border formed by microvilli that ensure the absorption of nutrients - it lines the mucous membrane of the small intestine.

Ciliated epithelium (ciliated epithelium) is a pseudo-stratified epithelium, consisting of cylindrical cells, the inner edge of which, that is, facing a cavity or canal, is equipped with constantly vibrating hair-like formations (cilia) - the cilia ensure the movement of the egg in the tubes; in the respiratory tract removes germs and dust.

The stratified epithelium is located at the border of the body and the external environment. If keratinization processes occur in the epithelium, that is, the upper layers of cells turn into horny scales, then such a stratified epithelium is called keratinizing (skin surface). The stratified epithelium lines the mucous membrane of the mouth, alimentary cavity, and the cornea of ​​the eye.

The transitional epithelium lines the walls of the bladder, renal pelvis, and ureter. When these organs are filled, the transitional epithelium is stretched, and the cells can move from one row to another.

Glandular epithelium - forms glands and performs a secretory function (secretes substances - secrets that are either excreted into the external environment, or enter the blood and lymph (hormones)). The ability of cells to produce and excrete substances necessary for the life of the body is called secretion. In this regard, this epithelium is also called secretory epithelium.

Connective tissue

Connective tissue Consists of cells, intercellular substance and connective tissue fibers. It consists of bones, cartilage, tendons, ligaments, blood, fat, it is in all organs (loose connective tissue) in the form of the so-called stroma (frame) of organs.

In contrast to epithelial tissue, in all types of connective tissue (except for adipose tissue), the intercellular substance predominates over the cells in volume, that is, the intercellular substance is very well expressed. Chemical composition and physical properties intercellular substance is very diverse in different types connective tissue. For example, blood - cells in it "float" and move freely, since the intercellular substance is well developed.

In general, connective tissue makes up what is called the internal environment of the body. It is very diverse and is represented by various types - from dense and loose forms to blood and lymph, the cells of which are in the liquid. Fundamental differences in the types of connective tissue are determined by the ratio of cellular components and the nature of the intercellular substance.

In dense fibrous connective tissue (muscle tendons, ligaments of joints), fibrous structures predominate, it experiences significant mechanical stress.

Loose fibrous connective tissue is extremely common in the body. On the contrary, it is very rich in cellular forms of various types. Some of them are involved in the formation of tissue fibers (fibroblasts), others, which is especially important, provide primarily protective and regulatory processes, including through immune mechanisms (macrophages, lymphocytes, tissue basophils, plasma cells).

Bone

Bone tissue The bone tissue that forms the bones of the skeleton is highly durable. It maintains the shape of the body (constitution) and protects the organs located in the cranium, chest and pelvic cavities, and participates in mineral metabolism. The tissue consists of cells (osteocytes) and intercellular substance, which contains nutrient channels with blood vessels. The intercellular substance contains up to 70% of mineral salts (calcium, phosphorus and magnesium).

In its development, bone tissue passes through the fibrous and lamellar stages. In different parts of the bone, it is organized in the form of a compact or cancellous bone substance.

Cartilage tissue

Cartilage tissue consists of cells (chondrocytes) and extracellular substance (cartilage matrix), characterized by increased elasticity. It performs a supporting function, as it forms the bulk of the cartilage.

There are three types of cartilaginous tissue: hyaline, which is part of the cartilage of the trachea, bronchi, ends of the ribs, articular surfaces of bones; elastic, forming the auricle and epiglottis; fibrous, located in the intervertebral discs and joints of the pubic bones.

Adipose tissue

Adipose tissue is like loose connective tissue. The cells are large, filled with fat. Adipose tissue performs nutritional, shape-forming and thermoregulatory functions. Adipose tissue is classified into two types: white and brown. In humans, white adipose tissue predominates, part of it surrounds organs, maintaining their position in the human body and other functions. The amount of brown adipose tissue in humans is small (it is present mainly in a newborn baby). The main function of brown adipose tissue is heat production. Brown adipose tissue maintains the body temperature of animals during hibernation and the temperature of newborn babies.

Muscle

Muscle cells are called muscle fibers because they are constantly stretched in one direction.

The classification of muscle tissue is carried out on the basis of the structure of the tissue (histologically): by the presence or absence of transverse striation, and based on the mechanism of contraction - voluntary (as in skeletal muscle) or involuntary (smooth or cardiac muscle).

Muscle tissue has excitability and the ability to actively contract under the influence nervous system and some substances. Microscopic differences make it possible to distinguish two types of this tissue - smooth (non-striated) and striated (striated).

Smooth muscle tissue has a cellular structure. It forms the muscular membranes of the walls of internal organs (intestines, uterus, bladder, etc.), blood and lymph vessels; its reduction occurs involuntarily.

Striated muscle tissue consists of muscle fibers, each of which is represented by many thousands of cells that have fused, in addition to their nuclei, into one structure. It forms skeletal muscle. We can shorten them at will.

A type of striated muscle tissue is the heart muscle, which has unique abilities. During life (about 70 years), the heart muscle contracts more than 2.5 million times. No other fabric has this potential for durability. The cardiac muscle tissue has a transverse striation. However, unlike skeletal muscle, there are special areas here where muscle fibers close. Due to this structure, the contraction of one fiber is quickly transmitted to neighboring ones. This ensures the simultaneous contraction of large areas of the heart muscle.

Also, the structural features of muscle tissue are that its cells contain bundles of myofibrils formed by two proteins - actin and myosin.

Nerve tissue

Nervous tissue consists of two types of cells: nerve cells (neurons) and glial cells. Glial cells adhere closely to the neuron, performing supporting, nutritional, secretory and protective functions.

Neuron is the basic structural and functional unit of nervous tissue. Its main feature is the ability to generate nerve impulses and transmit excitation to other neurons or muscle and glandular cells of working organs. Neurons can be made up of a body and processes. Nerve cells are designed to conduct nerve impulses... Having received information on one part of the surface, the neuron very quickly transmits it to another part of its surface. Since the processes of the neuron are very long, information is transmitted over long distances. Most neurons have two types of processes: short, thick, branching near the body - dendrites and long (up to 1.5 m), thin and branching only at the very end - axons. Axons form nerve fibers.

A nerve impulse is an electrical wave traveling at high speed along a nerve fiber.

Depending on the functions performed and the structural features, all nerve cells are divided into three types: sensitive, motor (executive) and intercalary. Motor fibers, which are part of the nerves, transmit signals to muscles and glands, sensory fibers transmit information about the state of organs to the central nervous system.

Now we can combine all the information received into a table.

Types of fabrics (table)

Epithelial tissue or Epithelium (from the Greek epi - over and thele - nipple, thin skin) - Border tissues, Which are located on the border with the external environment, cover the surface of the body, line its cavities, mucous membranes of internal organs and form most of the glands. Distinguish Three types of epithelium:

1) Integumentary epithelium (form a variety of pavements),

2) Glandular epithelium (form glands)

3) Sensory epithelium (perform receptor functions, are part of the sense organs).

Functions of the epithelium:

1 Dividing, barrier - The main function of the epithelium, all the rest are its particular manifestations. The epithelia form barriers between the internal environment of the body and the external environment; the properties of these barriers (mechanical strength, thickness, permeability, etc.) are determined by the specific structural and functional features of each epithelium. Few exceptions from general rule serve as epithelium, delimiting two areas of the internal environment - for example, lining body cavities (mesothelium) or vessels (endothelium).

2 Protective - The epithelia provide protection of the internal environment of the body from the damaging effects of mechanical, physical (temperature, radiation), chemical and microbial factors. The protective function can be expressed in different ways (for example, the epithelium can form thick layers, form the outer low-permeable, physically and chemically resistant stratum corneum, secrete a protective layer of mucus, produce substances with antimicrobial action, etc.).

3 Transport - May manifest as substance transfer Through Layers of epithelial cells (for example, from the blood through the endothelium of small vessels into surrounding tissues) or On their surface(for example, transport of mucus by the ciliated epithelium of the respiratory tract or ovopitis by the ciliated epithelium of the fallopian tube). Substances can be transported across the epithelial layer by mechanisms of diffusion, transport mediated by protein carriers, and vesiculosis; and other transport.

O Suction- many epithelia actively absorb substances; the most striking examples are the epithelium of the intestine and renal tubules. This function is essentially a private variant of the transport function.

© Secretory - The epithelia are the functionally leading tissues of most of the glands.

© Excretory - The epithelium is involved in the removal from the body (with urine, sweat, bile, etc.) of the final metabolic products or (exogenous) compounds introduced into the body (for example, drugs).

O Sensory (receptor) - The epithelium, being on the border of the internal environment of the body and the external environment, perceive signals (mechanical, chemical) emanating from the latter.

General morphological features Eliteleev include:

J) The arrangement of cells (epithelial cells) in closed layers, Which form Plane pavements, Collapsed into Tubules Or shape Vesicles (follicles); This feature of the epithelium is due to signs (2) and (3);

2) The minimum amount of intercellular substance, Narrow intercellular spaces;

3) The presence of developed intercellular connections, Which cause a strong connection of epithelial cells with each other in a single layer;

4) Border position (usually between the tissues of the internal environment and the external environment);

5) Cell polarity- As a consequence of the feature (4). In epitheliocytes, there are Apical pole(from the Greek apex - top), free, directed to the external environment, and Basal pole, Appears to the tissues of the internal environment and associated with Basal membrane... Stratified epithelium is characterized by Vertical anisomorphy(from the Greek. an - negation, iso - the same, morphe - form) - unequal morphological properties of cells of different layers of the epithelial layer;

6) Location on the basement membrane - a special structural formation (see structure below), which is located between the epithelium and the underlying loose fibrous connective tissue;

7) Absence Vessels; The epithelium is nourished by Diffusion of substances through the basement membrane from the vessels of the connective tissue. The different removal of individual layers of stratified epithelium from the power source probably enhances (or maintains) their vertical anisomorphism;

8) High regeneration capacity- Physiological and reparative - carried out thanks to Cambia(including stem and semi-stem cells) and is due to the border position of the epithelium (determining a significant need for active renewal of rapidly wearing epithelial cells). Cambial elements in some epithelium are concentrated in their specific areas (localized cambium), In others, they are evenly distributed among the rest of the cells. (diffuse cambium).

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

Varieties of the epithelium have significant structural variations, depending 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 exchange between the external and internal environment; violation of the integrity of the formation leads to a weakening of its protective properties, to the possibility of infection penetration.
2. It is located on the connective tissue (basement membrane), from which nutrients are supplied to it.
3. Epithelial cells are polarized, 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 contains different components of the cell.
4. Possesses a high ability to regenerate (recover). Epithelial tissue does not contain intercellular substance or contains very little of it.

Epithelial tissue formation

Epithelial tissue is built of epithelial cells, which are tightly connected to each other and form a continuous layer.

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

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

Classification by origin

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

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

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 duct-excretory glands. The single-layer columnar epithelium is divided into three types:

1. Bordered - found in the intestines, gallbladder, has adsorbing properties.
2. Ciliated - is characteristic of the oviducts, in the cells of which there are mobile cilia at the apical pole (they facilitate the movement of the egg).
3. Glandular - localized in the stomach, produces a mucous secret.

Single layer multi-row the epithelium lines the airways and contains three types of cells: ciliated, intercalated, goblet, and endocrine. Together they ensure the normal functioning of the respiratory system, protect against the ingress of foreign particles (for example, the movement of cilia and mucous secretions help to 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 cells in the form of a cylinder, they divide by the mitotic pathway, 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;
• a layer of flat cells - they are outside, constantly die off and peel off.

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

1. Basal - formed by poorly differentiated stem cells, together with pigment - melanocytes.
2. The spinous layer together with the basal layer form the growth zone of the epidermis.
3. The granular layer is built from flat cells, in the cytoplasm of which the keratoglian protein is located.
4. The shiny layer got its name from its characteristic appearance during microscopic examination of histological preparations. It is a homogeneous shiny strip, 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 their connection with the underlying cells, therefore they constantly peel off.

Transitional epithelium is located in the renal tissue, urinary tract, bladder. Has three layers:

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

It is common for the 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

Aceto-white - it is an abnormal epithelium that becomes intensely white when exposed to acetic acid. Its appearance during colposcopic examination makes it possible to identify the pathological process in the early stages.

Buccal - collected from the inner surface of the cheek, is used for genetic examination and the establishment of family ties.

Functions of epithelial tissue

Located on the surface of the body and organs, the epithelium is a border tissue. This situation determines its protective function: protection of 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, which is part of the glands, has the ability to form special substances - secrets, and also to release 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

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

The cells of the epithelial tissue are tightly interconnected, there is practically no intercellular fluid. There is a large amount of intercellular substance in the connective tissue, the cells are not tightly connected to each other.

The cell is part of the tissue that makes up the human and animal organisms.

Textile - it is a system of cells and extracellular structures, united by the unity of origin, structure and functions.

As a result of the interaction of the organism with the external environment, which has developed in the course of evolution, four types of tissues with certain functional characteristics have appeared: epithelial, connective, muscular and nervous.

Each organ is made up of various tissues that are closely related to each other. For example, the stomach, intestines, and other organs are composed of epithelial, connective, smooth muscle and nervous tissues.

The connective tissue of many organs forms the stroma, and the epithelial tissue forms the parenchyma. Function digestive system cannot be performed completely if its muscular activity is impaired.

Thus, the various tissues that make up a particular organ provide the main function of this organ.

EPITELIAL TISSUE

Epithelial tissue (epithelium)covers all outer surface human and animal bodies, lining the mucous membranes of hollow internal organs (stomach, intestines, urinary tract, pleura, pericardium, peritoneum) and is part of the endocrine glands. Allocate integumentary (superficial) and secretory (glandular) epithelium. Epithelial tissue is involved in the exchange of substances between the body and the external environment, performs a protective function (skin epithelium), functions of secretion, absorption (intestinal epithelium), excretion (renal epithelium), gas exchange (lung epithelium), has a great regenerative capacity.

Depending on the number of cell layers and the shape of individual cells, the epithelium is distinguished multilayer - keratinizing and non-keratinizing, transition and single-layer - simple columnar, simple cubic (flat), simple squamous (mesothelium) (Fig. 3).

V squamous epithelium the cells are thin, compacted, contain little cytoplasm, the discoid nucleus is located in the center, its edge is uneven. The squamous epithelium lines the alveoli of the lungs, the walls of the capillaries, blood vessels, and heart cavities, where, due to its thinness, it diffuses various substances and reduces the friction of flowing fluids.

Cubic epithelium lines the ducts of many glands, and also forms kidney tubules, performs a secretory function.

Cylindrical epithelium consists of tall and narrow cells. It lines the stomach, intestines, gall bladder, renal tubules, and is also part of the thyroid gland.

Rice. 3. Different kinds epithelium:

A - single layer flat; B - single-layer cubic; V - cylindrical; G — single-layer ciliated; D — gratifying; E - multilayer keratinizing

Cells ciliated epithelium usually have the shape of a cylinder, with many cilia on the free surfaces; lining the oviducts, ventricles of the brain, spinal canal and respiratory tract, where it provides the transport of various substances.

Multi-row epithelium lines the urinary tract, trachea, respiratory tract and is part of the mucous membrane of the olfactory cavities.

Stratified epithelium consists of several layers of cells. It lines the outer surface of the skin, the lining of the esophagus, the inner surface of the cheeks, and the vagina.

Transitional epithelium is located in those organs that are subjected to strong stretching (bladder, ureter, renal pelvis). The thickness of the transitional epithelium prevents urine from entering the surrounding tissue.

Glandular epithelium makes up the bulk of those glands in which epithelial cells are involved in the formation and secretion of substances necessary for the body.

There are two types of secretory cells - exocrine and endocrine. Exocrine cells secrete a secret on the free surface of the epithelium and through the ducts into the cavity (stomach, intestines, respiratory tract, etc.). Endocrine called glands, the secret (hormone) of which is secreted directly into the blood or lymph (pituitary gland, thyroid, thymus, adrenal glands).

In structure, exocrine glands can be tubular, alveolar, tubular-alveolar.