Epithelial tissues, or epithelium (erithelia), cover the surface of the body, mucous and serous membranes of internal organs (stomach, intestines, bladder, etc.), and also form most of the glands. In this regard, there are integumentary and glandular epithelium.
Integumentary epithelium is the border tissue. It separates the body (internal environment) from the external environment, but at the same time participates in the metabolism of the body with the environment, performing the functions of absorption of substances (absorption) and excretion of metabolic products (excretion). For example, through the intestinal epithelium, the products of food digestion are absorbed into the blood and lymph, which serve as a source of energy and building material for the body, and through the renal epithelium, a number of products of nitrogen metabolism, which are toxins for the body, are excreted. In addition to these functions, the integumentary epithelium performs an important protective function, protecting the underlying tissues of the body from various external influences - chemical, mechanical, infectious, etc. For example, the skin epithelium is a powerful barrier to microorganisms and many poisons. Finally, the epithelium covering the internal organs located in the body cavities creates conditions for their mobility, for example, for heart contraction, lung excursion, etc.
glandular epithelium performs a secretory function, that is, it forms and secretes specific products - secrets that are used in the processes occurring in the body. For example, pancreatic secretion is involved in the digestion of proteins, fats, and carbohydrates in the small intestine.
SOURCES OF DEVELOPMENT OF EPITHELIAL TISSUES
Epithelia develop from all three germ layers starting from the 3-4th week of human embryonic development. Depending on the embryonic source, epithelia of ectodermal, mesodermal and endodermal origin are distinguished.
Structure. Epithelia are involved in the construction of many organs, and therefore they show a wide variety of morphophysiological properties. Some of them are common, allowing to distinguish epithelium from other tissues of the body.
Epithelia are layers of cells - epitheliocytes (Fig. 39), which have a different shape and structure in different types of epithelium. There is no intercellular substance between the cells that make up the epithelial layer and the cells are closely connected with each other through various contacts - desmosomes, tight contacts, etc. The epithelium is located on the basement membranes (lamellae). Basement membranes are about 1 µm thick and consist of an amorphous substance and fibrillar structures. The basement membrane contains carbohydrate-protein-lipid complexes, on which its selective permeability to substances depends. Epithelial cells can be connected to the basement membrane by hemi-desmosomes, similar in structure to the halves of desmosomes.
The epithelium does not contain blood vessels. Nutrition of epitheliocytes is diffusely carried out through the basement membrane from the side of the underlying connective tissue, with which the epithelium is in close interaction. Epithelia have polarity, i.e., the basal and apical sections of the entire epithelial layer and its constituent cells have a different structure. Epithelium has a high ability to regenerate. The restoration of the epithelium occurs due to mitotic division and differentiation of stem cells.
CLASSIFICATION
There are several classifications of epithelium, which are based on various features: origin, structure, function. Of these, the most widespread is the morphological classification, which takes into account the ratio of cells to the basement membrane and their shape on the free, apical (from Latin arex - top) part of the epithelial layer (Scheme 2).
In morphological classification reflects the structure of the epithelium, depending on their function.
According to this classification, first of all, single-layer and multilayer epithelium are distinguished. In the first, all epithelial cells are connected to the basement membrane, in the second, only one lower layer of cells is directly connected to the basement membrane, while the remaining layers are deprived of such a connection and are connected to each other. In accordance with the shape of the cells that make up the epithelium, they are divided into flat, cubic and prismatic (cylindrical). At the same time, in stratified epithelium, only the shape of the outer layers of cells is taken into account. For example, the corneal epithelium is stratified squamous, although its lower layers consist of prismatic and winged cells.
Single layer epithelium can be single-row and multi-row. In a single-row epithelium, all cells have the same shape - flat, cubic or prismatic, and, therefore, their nuclei lie on the same level, that is, in one row. Such an epithelium is also called isomorphic (from the Greek isos - equal). A single-layer epithelium, which has cells of various shapes and heights, the nuclei of which lie at different levels, that is, in several rows, is called multi-row, or pseudo-stratified.
Stratified epithelium it can be keratinized, non-keratinized and transitional. The epithelium, in which keratinization processes occur, associated with the transformation of the cells of the upper layers into horny scales, is called stratified squamous keratinizing. In the absence of keratinization, the epithelium is stratified squamous non-keratinizing.
transitional epithelium lines organs subject to strong stretching - the bladder, ureters, etc. When the volume of the organ changes, the thickness and structure of the epithelium also change.
Along with the morphological classification, ontophylogenetic classification, created by the Soviet histologist N. G. Khlopin. It is based on the features of the development of epithelium from tissue rudiments. It includes epidermal (skin), enterodermal (intestinal), colognephrodermal, ependymoglial and angiodermal types of epithelium.
epidermal type The epithelium is formed from the ectoderm, has a multi-layer or multi-row structure, is adapted to perform primarily a protective function (for example, keratinized stratified squamous epithelium of the skin).
Enterodermal type The epithelium develops from the endoderm, is single-layer prismatic in structure, carries out the processes of absorption of substances (for example, the single-layered epithelium of the small intestine), performs a glandular function.
Whole nephrodermal type The epithelium is of mesodermal origin, in structure it is single-layer, flat, cubic or prismatic, performs mainly a barrier or excretory function (for example, the squamous epithelium of the serous membranes - mesothelium, cubic and prismatic epithelium in the urinary tubules of the kidneys).
Ependymoglial type It is represented by a special epithelium lining, for example, the cavities of the brain. The source of its formation is the neural tube.
to the angiodermal type refers to the endothelial lining of blood vessels, which is of mesenchymal origin. Structurally, the endothelium is a single-layered squamous epithelium.
STRUCTURE OF DIFFERENT TYPES OF COVERING EPITHELIUM
Single layered squamous epithelium (epithelium simplex squamosum).
This type of epithelium is represented in the body by endothelium and mesothelium.
Endothelium (entothelium) lines the blood and lymphatic vessels, as well as the chambers of the heart. It is a layer of flat cells - endotheliocytes, lying in one layer on the basement membrane. Endotheliocytes are distinguished by the relative poverty of organelles and the presence of pinocytic vesicles in the cytoplasm.
The endothelium is involved in the exchange of substances and gases (O2, CO2) between the blood and other tissues of the body. If it is damaged, it is possible to change the blood flow in the vessels and the formation of blood clots in their lumen - blood clots.
Mesothelium (mesothelium) covers the serous membranes (pleura, visceral and parietal peritoneum, pericardial sac, etc.). Mesothelial cells - mesotheliocytes are flat, have a polygonal shape and uneven edges (Fig. 40, A). At the site of the nuclei, the cells are somewhat thickened. Some of them contain not one, but two or even three nuclei. There are single microvilli on the free surface of the cell. Through the mesothelium, serous fluid is secreted and absorbed. Thanks to its smooth surface, sliding of the internal organs is easily carried out. The mesothelium prevents the formation of connective tissue adhesions between the organs of the abdominal and thoracic cavities, the development of which is possible if its integrity is violated.
Single layer cuboidal epithelium (epithelium simplex cubuideum). It lines part of the renal tubules (proximal and distal). The cells of the proximal tubules have a brush border and basal striation. The striation is due to the concentration of mitochondria in the basal sections of the cells and the presence of deep folds of the plasmalemma here. The epithelium of the renal tubules performs the function of reabsorption (reabsorption) of a number of substances from the primary urine into the blood.
Single layer prismatic epithelium (epithelium simplex columnare). This type of epithelium is characteristic of the middle part of the digestive system. It lines the inner surface of the stomach, small and large intestines, gallbladder, a number of ducts of the liver and pancreas.
In the stomach, in a single layer of prismatic epithelium, all cells are glandular, producing mucus, which protects the stomach wall from the rough influence of food lumps and the digestive action of gastric juice. In addition, water and some salts are absorbed into the blood through the epithelium of the stomach.
In the small intestine, a single-layer prismatic (“border”) epithelium actively performs the function of absorption. The epithelium is formed by prismatic epithelial cells, among which goblet cells are located (Fig. 40, B). Epitheliocytes have a well-defined striated (brush) suction border, consisting of many microvilli. They are involved in the enzymatic breakdown of food (parietal digestion) and the absorption of the formed products into the blood and lymph. Goblet cells secrete mucus. Covering the epithelium, mucus protects it and underlying tissues from mechanical and chemical influences.
Along with the border and goblet cells, there are basal-granular endocrine cells of several types (EC, D, S, J, etc.) and apical-granular glandular cells. The hormones of endocrine cells secreted into the blood take part in the regulation of the function of the organs of the digestive apparatus.
Multi-row (pseudostratified) epithelium (epithelium pseudostratificatum). It lines the airways - the nasal cavity, trachea, bronchi, and a number of other organs. In the airways, the multilayered epithelium is ciliated, or ciliated. It distinguishes 4 types of cells: ciliated (ciliated) cells, short and long intercalated cells, mucous (goblet) cells (Fig. 41; see Fig. 42, B), as well as basal-granular (endocrine) cells. Intercalary cells are probably stem cells capable of dividing and turning into ciliated and mucous cells.
Intercalated cells are attached to the basement membrane with a wide proximal part. In ciliated cells, this part is narrow, and their wide distal part faces the lumen of the organ. Due to this, three rows of nuclei can be distinguished in the epithelium: the lower and middle rows are the nuclei of intercalary cells, the upper row is the nuclei of ciliated cells. The tops of the intercalated cells do not reach the surface of the epithelium; therefore, it is formed only by the distal parts of the ciliated cells, covered with numerous cilia. Mucous cells have a goblet or ovoid shape and secrete mucins on the surface of the formation.
Dust particles that have entered the respiratory tract with air settle on the mucous surface of the epithelium and, by the movement of its ciliated cilia, are gradually pushed into the nasal cavity and further into the external environment. In addition to ciliated, intercalary and mucous epitheliocytes, several types of endocrine, basal-granular cells (EC-, P-, D-cells) were found in the epithelium of the airways. These cells secrete biologically active substances into the blood vessels - hormones, with the help of which local regulation of the respiratory system is carried out.
Stratified squamous non-keratinized epithelium (epithelium stratificatum squamosum noncornificatum). Covers the outside of the cornea of the eye, lines the mouth and esophagus. Three layers are distinguished in it: basal, spiny (intermediate) and flat (superficial) (Fig. 42, A).
Basal layer consists of epithelial cells of a prismatic shape, located on the basement membrane. Among them are stem cells capable of mitotic division. Due to the newly formed cells entering into differentiation, there is a change in the epitheliocytes of the overlying layers of the epithelium.
Spiny layer consists of cells of irregular polygonal shape. In the basal and spinous layers, tonofibrils (tonofilament bundles) are well developed in epitheliocytes, and desmosomes and other types of contacts are between epithelial cells. The upper layers of the epithelium are formed by squamous cells. Finishing their life cycle, they die and fall off the surface of the epithelium.
Stratified squamous keratinized epithelium (epithelium stratificatum squamosum cornificatum). It covers the surface of the skin, forming its epidermis, in which the process of transformation (transformation) of epithelial cells into horny scales - keratinization takes place. At the same time, specific proteins (keratins) are synthesized in the cells and more and more accumulate, and the cells themselves gradually move from the lower layer to the overlying layers of the epithelium. In the epidermis of the skin of the fingers, palms and soles, 5 main layers are distinguished: basal, spiny, granular, shiny and horny (Fig. 42, B). The skin of the rest of the body has an epidermis in which there is no shiny layer.
Basal layer consists of cylindrical epithelial cells. In their cytoplasm, specific proteins are synthesized that form tonofilaments. Here are the stem cells. Stem cells divide, after which some of the newly formed cells differentiate and move to the overlying layers. Therefore, the basal layer is called germinal, or germinal (stratum germinativum).
Spiny layer It is formed by polygonal-shaped cells, which are firmly interconnected by numerous desmosomes. In place of desmosomes on the surface of the cells there are tiny outgrowths - "spikes" directed towards each other. They are clearly visible with the expansion of intercellular spaces or with wrinkling of cells. In the cytoplasm of spiny cells, tonofilaments form bundles - tonofibrils.
In addition to epitheliocytes, in the basal and spiny layers there are pigment cells, which are process-shaped in shape - melanocytes, containing granules of black pigment - melanin, as well as epidermal macrophages - dendrocytes and lymphocytes, which form a local immune surveillance system in the epidermis.
Granular layer consists of flattened cells, the cytoplasm of which contains tonofibrils and grains of keratohyalin. Keratogialin is a fibrillar protein that can later turn into eleidin in the cells of the overlying layers, and then into keratin - a horny substance.
glitter layer made up of squamous cells. Their cytoplasm contains the highly refractive light eleidin, which is a complex of keratohyalin with tonofibrils.
stratum corneum very powerful in the skin of the fingers, palms, soles and relatively thin in the rest of the skin. As the cells move from the luminous layer to the stratum corneum, nuclei and organelles gradually disappear with the participation of lysosomes, and the complex of keratohyalin with tonofibrils turns into keratin fibrils and the cells become horny scales resembling flat polyhedrons in shape. They are filled with keratin (horny substance), consisting of densely packed keratin fibrils, and air bubbles. The outermost horny scales, under the influence of lysosome enzymes, lose contact with each other and constantly fall off the surface of the epithelium. They are replaced by new ones due to the reproduction, differentiation and movement of cells from the underlying layers. The stratum corneum of the epithelium is characterized by significant elasticity and poor thermal conductivity, which is important for protecting the skin from mechanical influences and for the processes of thermoregulation of the body.
Transitional epithelium (epithelium transitionale). This type of epithelium is typical for urinary organs - the pelvis of the kidneys, ureters, bladder, the walls of which are subject to significant stretching when filled with urine. It distinguishes several layers of cells - basal, intermediate, superficial (Fig. 43, A, B).
Basal layer formed by small rounded (dark) cells. The intermediate layer contains cells of various polygonal shapes. The superficial layer consists of very large, often two- and three-nuclear cells, which have a domed or flattened shape, depending on the state of the organ wall. When the wall is stretched due to the filling of the organ with urine, the epithelium becomes thinner and its surface cells flatten. During the contraction of the wall of the organ, the thickness of the epithelial layer increases sharply. At the same time, some cells in the intermediate layer are “squeezed out” upwards and take on a pear-shaped shape, while the superficial cells located above them are domed. Tight junctions were found between the surface cells, which are important for preventing the penetration of fluid through the wall of an organ (for example, the bladder).
Regeneration. The integumentary epithelium, occupying a borderline position, is constantly under the influence of the external environment, therefore epithelial cells wear out and die relatively quickly.
The source of their recovery are epithelial stem cells. They retain the ability to divide throughout the life of the organism. Reproducing, part of the newly formed cells enters into differentiation and turns into epithelial cells, similar to the lost ones. Stem cells in stratified epithelium are located in the basal (rudimentary) layer, in stratified epithelia they include intercalary (short) cells, in single-layer epithelium they are located in certain areas, for example, in the small intestine in the epithelium of the crypts, in the stomach in the epithelium of the necks of their own glands and etc. The high capacity of the epithelium for physiological regeneration serves as the basis for its rapid restoration under pathological conditions (reparative regeneration).
Vascularization. The integumentary epithelium does not have blood vessels, with the exception of the vascular strip (stria vascularis) of the inner ear. Nutrition for the epithelium comes from vessels located in the underlying connective tissue.
innervation. The epithelium is well innervated. It has numerous sensitive nerve endings - receptors.
Age changes. With age, a weakening of the renewal processes is observed in the integumentary epithelium.
STRUCTURE OF THE GRANULAR EPITHELIUM
The glandular epithelium (epithelium glandulare) consists of glandular, or secretory, cells - glandulocytes. They carry out the synthesis, as well as the release of specific products - secrets on the surface of the skin, mucous membranes and in the cavity of a number of internal organs [external (exocrine) secretion] or into the blood and lymph [internal (endocrine) secretion].
Through secretion, many important functions are performed in the body: the formation of milk, saliva, gastric and intestinal juice, bile, endocrine (humoral) regulation, etc.
Most glandular cells with external secretion (exocrine) are distinguished by the presence of secretory inclusions in the cytoplasm, a developed endoplasmic reticulum, and the polar arrangement of organelles and secretory granules.
Secretion (from Latin secretio - separation) is a complex process that includes 4 phases:
- uptake of raw products by glandulocytes,
- synthesis and accumulation of secret in them,
- secretion from glandulocytes - extrusion
- and restoration of their structure.
These phases can occur in glandulocytes cyclically, that is, one after the other, in the form of a so-called secretory cycle. In other cases, they occur simultaneously, which is characteristic of diffuse or spontaneous secretion.
First phase of secretion consists in the fact that various inorganic compounds, water and low molecular weight organic substances enter the glandular cells from the blood and lymph into the glandular cells from the basal surface: amino acids, monosaccharides, fatty acids, etc. Sometimes larger molecules of organic substances penetrate into the cell through pinocytosis, for example proteins.
In the second phase secrets are synthesized from these products in the endoplasmic reticulum, moreover, protein ones with the participation of the granular endoplasmic reticulum, and non-protein ones with the participation of the agranular endoplasmic reticulum. The synthesized secret moves through the endoplasmic reticulum to the zone of the Golgi complex, where it gradually accumulates, undergoes chemical restructuring and takes the form of granules.
In the third phase the resulting secretory granules are released from the cell. Secretion is secreted differently, and therefore there are three types of secretion:
- merocrine (eccrine)
- apocrine
- holocrine (Fig. 44, A, B, C).
With the merocrine type of secretion, glandular cells completely retain their structure (for example, cells of the salivary glands).
With the apocrine type of secretion, partial destruction of glandular cells (for example, cells of the mammary glands) occurs, i.e., together with secretory products, either the apical part of the cytoplasm of glandular cells (macroapocrine secretion) or the tops of microvilli (microapocrine secretion) are separated.
The holocrine type of secretion is accompanied by the accumulation of fat in the cytoplasm and the complete destruction of glandular cells (for example, cells of the sebaceous glands of the skin).
Fourth phase of secretion is to restore the original state of glandular cells. Most often, however, the repair of cells occurs as they are destroyed.
Glandulocytes lie on the basement membrane. Their form is very diverse and varies depending on the phase of secretion. The nuclei are usually large, with a rugged surface, which gives them an irregular shape. In the cytoplasm of glandulocytes, which produce protein secrets (for example, digestive enzymes), the granular endoplasmic reticulum is well developed.
In cells synthesizing non-protein secrets (lipids, steroids), an agranular cytoplasmic reticulum is expressed. The Golgi complex is extensive. Its shape and location in the cell change depending on the phase of the secretory process. Mitochondria are usually numerous. They accumulate in places of greatest cell activity, i.e., where a secret is formed. In the cytoplasm of cells, secretory granules are usually present, the size and structure of which depend on the chemical composition of the secret. Their number fluctuates in connection with the phases of the secretory process.
In the cytoplasm of some glandulocytes (for example, those involved in the formation of hydrochloric acid in the stomach), intracellular secretory tubules are found - deep protrusions of the cytolemma, the walls of which are covered with microvilli.
The cytolemma has a different structure on the lateral, basal, and apical surfaces of cells. On the lateral surfaces, it forms desmosomes and tight closing contacts (terminal bridges). The latter surround the apical (apical) parts of the cells, thus separating the intercellular gaps from the lumen of the gland. On the basal surfaces of cells, the cytolemma forms a small number of narrow folds penetrating into the cytoplasm. Such folds are especially well developed in the cells of the glands that secrete a secret rich in salts, for example, in the ductal cells of the salivary glands. The apical surface of the cells is covered with microvilli.
In glandular cells, polar differentiation is clearly visible. It is due to the direction of secretory processes, for example, with external secretion from the basal to the apical part of the cells.
GLANDS
Glands (glandulae) perform a secretory function in the body. Most of them are derivatives of the glandular epithelium. The secrets produced in the glands are important for the processes of digestion, growth, development, interaction with the external environment, etc. Many glands are independent, anatomically designed organs (for example, the pancreas, large salivary glands, thyroid gland). Other glands are only part of the organs (for example, the glands of the stomach).
The glands are divided into two groups:
- endocrine glands or endocrine glands
- glands of external secretion, or exocrine (Fig. 45, A, B, C).
Endocrine glands produce highly active substances - hormones that enter directly into the blood. That is why these glands are composed only of glandular cells and do not have excretory ducts. These include the pituitary gland, epiphysis, thyroid and parathyroid glands, adrenal glands, pancreatic islets, etc. All of them are part of the endocrine system of the body, which, together with the nervous system, performs a regulatory function.
exocrine glands produce secrets that are released into the external environment, i.e., on the surface of the skin or in the cavities of organs lined with epithelium. In this regard, they consist of two parts:
- secretory, or end, divisions (pirtiones terminalae)
- excretory ducts.
The terminal sections are formed by glandulocytes lying on the basement membrane. The excretory ducts are lined with various types of epithelium, depending on the origin of the glands. In glands derived from enterodermal epithelium (for example, in the pancreas), they are lined with single-layered cuboidal or prismatic epithelium, and in glands that develop from ectodermal epithelium (for example, in the sebaceous glands of the skin), they are lined with stratified non-keratinizing epithelium. Exocrine glands are extremely diverse, differing from each other in structure, type of secretion, i.e., the method of secretion and its composition.
These features are the basis for the classification of glands. By structure, exocrine glands are divided into the following types (Scheme 3).
simple glands have a non-branching excretory duct, complex glands - branching (see Fig. 45, B). It opens in unbranched glands one at a time, and in branched glands several terminal sections, the shape of which can be in the form of a tube or sac (alveolus) or an intermediate type between them.
In some glands, derivatives of the ectodermal (stratified) epithelium, for example, in salivary glands, in addition to secretory cells, there are epithelial cells that have the ability to contract - myoepithelial cells. These cells, having a process shape, cover the terminal sections. Their cytoplasm contains microfilaments containing contractile proteins. Myoepithelial cells, when contracted, compress the terminal sections and, therefore, facilitate the secretion of secretions from them.
The chemical composition of the secret may be different, in connection with this, the exocrine glands are divided into
- protein (serous)
- mucous
- protein-mucous (see Fig. 42, E)
- sebaceous.
In mixed glands, two types of secretory cells can be present - protein and mucous. They form either individually terminal sections (purely proteinaceous and purely mucous), or together mixed terminal sections (proteinaceous-mucous). Most often, the composition of the secretory product includes protein and mucous components with only one of them predominating.
Regeneration. In the glands, in connection with their secretory activity, processes of physiological regeneration are constantly taking place.
In the merocrine and apocrine glands, which contain long-lived cells, the restoration of the initial state of glandulocytes after secretion from them occurs by intracellular regeneration, and sometimes by reproduction.
In the holocrine glands, restoration is carried out due to the reproduction of special, stem cells. The newly formed cells from them then, by differentiation, turn into glandular cells (cellular regeneration).
Vascularization. The glands are abundantly supplied with blood vessels. Among them there are arteriolo-venular anastomoses and veins equipped with sphincters (closing veins). Closing the anastomoses and sphincters of the closing veins leads to an increase in pressure in the capillaries and ensures the release of substances used by glandulocytes to form a secret.
innervation. Carried out by the sympathetic and parasympathetic nervous system. Nerve fibers follow in the connective tissue along the course of the blood vessels and excretory ducts of the glands, forming nerve endings on the cells of the terminal sections and excretory ducts, as well as in the walls of the vessels.
In addition to the nervous system, the secretion of the exocrine glands is regulated by humoral factors, i.e., the hormones of the endocrine glands.
Age changes. In old age, changes in the glands can manifest themselves in a decrease in the secretory activity of glandular cells and a change in the composition of secretions produced, as well as in a weakening of regeneration processes and in the growth of connective tissue (glandular stroma).
Epithelial tissue covers the entire outer surface of the human body, lines all body cavities. Lines the mucous membrane of hollow organs, serous membranes, is part of the glands of the body. Therefore, they distinguish integumentary and glandular epithelium.
Epithelial tissue is located on the border of the external and internal environment of the body. And participates in the metabolism between the body and the external environment. Performs protective role (skin epithelium). Performs functions suction(intestinal epithelium) allocation(renal tubular epithelium) gas exchange(epithelium of the alveoli of the lungs). This fabric has a high regeneration. glandular epithelium, which forms gland, able to allocate secrets. This ability to produce and release substances necessary for life is called secretion. This epithelium is called secretory.
Distinctive features of epithelial tissue:
-Epithelial tissue is located on the border of the external and internal environment of the body.
- It consists of epithelial cells, these cells form solid layers.
- In these layers there are no blood vessels.
-Nutrition this tissue occurs through diffusion through the basement membrane, which separates the epithelial tissue from the underlying loose connective tissue and serves as a support for the epithelium.
IN integumentary epithelium secrete single layer epithelium and stratified.
IN single layer epithelium all cells are located on the basement membrane.
IN multilayer epithelium only the lower layer of cells lies on the basement membrane. The upper layers lose their connection with it and form several layers.
single layer epithelium happens single and multi-row.
epithelial cells - epitheliocytes. In epithelial cells secrete two parts. 1. Basal part - directed towards the underlying tissue. 2. Apical part - facing the free surface. In the basal part lies the nucleus.
The apical part contains organelles, inclusions, microvilli, and cilia. According to the shape of the cells, the epithelium is flat, cubic, cylindrical (prismatic).
Rice. No. 1. Types of epithelium.
Single layered squamous epithelium– mesothelium - covers the serous membranes - pleura, epicardium, peritoneum.
Single layered squamous epithelium – endothelium - lines mucous membrane circulatory and lymphatic vessels.
Single layer cubic epithelium covers renal tubules, excretory ducts of glands And small bronchi.
Single layer prismatic epithelium lines mucous membrane of the stomach.
Single layer prismatic bordered epithelium lines intestinal mucosa.
Single layer multi-row prismatic ciliated epithelium covers fallopian tubes and respiratory tract.
Stratified squamous epithelium on the basis of keratinization of the upper layers of cells are divided into keratinized and non-keratinized.
Stratified squamous keratinized epithelium – epidermis. It covers the surface of the skin. The epidermis consists of many tens of layers of cells. Cells on the surface of the skin die, turning into horny scales. They destroy the nucleus and cytoplasm and accumulate keratin.
Stratified squamous nonkeratinized epithelium lines the cornea of the eye, oral cavity, esophagus.
There is a transitional form of stratified epithelium - transition. It covers the urinary tract renal pelvis, bladder, i.e. organs that can change their volume.
glandular epithelium makes up the bulk of the body's glands. Glands in the body perform a secretory function. The secret he secretes is necessary for the processes taking place in the body. Some glands are independent organs, such as the pancreas, large salivary glands. Other glands are part of organs, such as glands in the intestinal wall, stomach. Most glands are derivatives of the epithelium.
Distinguish glands external secretion - exocrine. They have excretory ducts and secrete their secret into the body cavity or onto the surface of the body. These are the mammary glands, sweat, salivary.
There is endocrine glands - endocrine. They do not have excretory ducts and secrete their secret into the internal environment of the body - blood or lymph. Their secret is hormones.
There are glands of mixed secretion. They have endocrine and exocrine parts, such as the pancreas.
Fig No. 2. Types of glands.
exocrine glands are very diverse. Allocate unicellular and multicellular glands.
Unicellular glands- goblet cells, located in the intestinal epithelium, they produce mucus in the respiratory tract.
In multicellular glands, there are secretory and excretory duct. The secretory section is made up of cells - glandulocytes, who produce the secret. Depending on whether the excretory duct branches or not, they allocate simple and complex glands.
According to the shape of the secretory department, they are distinguished tubular, alveolar and alveolar-tubular glands.
Depending on how the secret is formed and in what way it is released from the cells, there are merocrine, apocrine and holocrine glands.
Merocrine glands are the most common. They secrete their secret into the duct without destroying the cytoplasm of the secretory cells.
In apocrine glands, there is a partial destruction of the cytoplasm of secretory cells. The apical part of the cell is destroyed and is part of the secret. Then the destroyed cell is restored. These glands include the mammary and sweat glands.
In holocrine gland secretion is accompanied by cell death. These destroyed cells are the secret of the gland. These glands include the sebaceous glands.
By the nature of the secret distinguish between mucous, protein and mixed (protein-mucous) glands.
fabrics is a system of cells and intercellular substance having the same structure, origin and functions.
intercellular substance is a product of cell activity. It provides communication between cells and creates a favorable environment for them. It may be liquid e.g. blood plasma; amorphous- cartilage; structured- muscle fibers; solid- bone tissue (in the form of salt).
Tissue cells have a different shape that determines their function. Fabrics are divided into four types:
- epithelial- border tissues: skin, mucosa;
- connective- the internal environment of our body;
- muscle;
- nervous tissue.
Epithelial (borderline) tissues- line the surface of the body, the 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 the blood vessels through the basement membrane.
Features: there are many cells, there is little intercellular substance and it is represented by a basement membrane.
Epithelial tissues perform the following functions:
- protective;
- excretory;
- suction.
Classification of epithelia. According to the number of layers, single-layer and multi-layer are distinguished. The shape is distinguished: flat, cubic, cylindrical.
If all epithelial cells reach the basement membrane, this single layer epithelium, and if only cells of one row are connected to the basement membrane, while others are free, this is multilayer. The single layer epithelium can be single row And multi-row, which depends on the location of the nuclei. Sometimes mononuclear or multinuclear epithelium has ciliated cilia facing the external environment.
Scheme of the structure of various types of epithelium(according to Kotovsky). A - single-layer cylindrical epithelium; B - single-layer cubic epithelium; B - single-layer squamous epithelium; G - multi-row epithelium; D - stratified squamous non-keratinized epithelium; E - stratified squamous keratinized epithelium; G - transitional epithelium with a stretched wall of the organ; F 1 - with a collapsed wall of the organ
Single layered squamous epithelium- lines the surface of the serous membranes: pleura, lungs, peritoneum, pericardium of the heart.
Single layered cuboidal epithelium- forms the walls of the tubules of the kidneys and the excretory ducts of the glands.
Single layered columnar epithelium- forms the gastric mucosa.
Border epithelium- a single-layer cylindrical epithelium, on the outer surface of the cells of which there is a border formed by microvilli that ensure the absorption of nutrients - lines the mucous membrane of the small intestine.
Ciliated epithelium(ciliated epithelium) - pseudo-stratified epithelium, consisting of cylindrical cells, the inner edge of which, that is, facing the cavity or channel, is equipped with constantly oscillating hair-like formations (cilia) - cilia ensure the movement of the egg in the tubes; removes microbes and dust in the respiratory tract.
Stratified epithelium located on the border of the organism and the external environment. If keratinization processes take place in the epithelium, i.e., the upper layers of cells turn into horny scales, then such a multilayer epithelium is called keratinizing (skin surface). Stratified epithelium lines the mucous membrane of the mouth, food cavity, horny eye.
transitional epithelium lines the walls of the bladder, renal pelvis, ureter. When filling these organs, the transitional epithelium is stretched, and cells can move from one row to another.
glandular epithelium- forms glands and performs a secretory function (releasing substances - secrets that are either excreted into the external environment or enter the blood and lymph (hormones)). The ability of cells to produce and secrete substances necessary for the vital activity of the body is called secretion. In this regard, such an epithelium is also called the secretory epithelium.
Details
epithelial tissues.
Functions: delimiting, barrier, protective, transport, suction, secretory, sensory, excretory.
Morphological features: always borderline position, polarity of cells, closeness of cell layers, basement membrane (BM), little intercellular substance, pronounced intercellular contacts, rapid renewal and regeneration, no blood vessels.
Surface epithelium- integumentary (on the surface of the body, mucous membranes of internal organs (stomach, intestines, bladder) and lining (secondary cavities of the body). They perform the function of absorption and excretion of metabolic products.
glandular epithelium- secretory function, excretory function (hormones, etc.)
Sources of development of epithelial tissues:
They develop from three germ layers at 3-4 weeks of embryonic development.
Related types of epithelium (from 1 germinal layer), in pathological conditions - metaplasia, i.e. pass from one type to another (for example, in the respiratory tract, the epithelium in chronic bronchitis passes from a single-layer ciliated to a multi-layered squamous)
1. Surface epithelium.
Structure.
Epithelium - layers of epithelial cells. There is almost no intercellular substance between them, they are interconnected desmosomes(attachment plates contain placoglobins, desmoplakin, and desmocalmin) in the gap CA-binding desmogleins), intermediate(AF is attached to e-cadherin through actin and vinculin, the connection of the cytoskeleton with the μl substance), slotted(tubular connexons) and tight contacts(occludin, SA, mg).
located on basement membranes 1 µm thick (plates): light 20-40nm and dark 20-60nm plates. Light includes an amorphous substance with calcium ions. Dark - an amorphous matrix with proteins (fibrillar structures - type 4 collagen), provides mechanical strength. In an amorphous substance glycoproteins– fibronectin and laminin (induce proliferation and differentiation during regeneration), calcium ions– connection between adhesive molecules of basement membrane glycoproteins and epithelial hemidesmosomes. Protein glycans and glycosaminoglycans - membrane elasticity and negative charge provide selective permeability, the ability to accumulate toxic substances in pathology.
The epithelial cells are especially strongly associated with the basement membrane in the region of the hemidesmosomes. Here anchor filaments (collagen type 7) approach the dark plate through the light one.
Membrane functions: mechanical (attachment), trophic and barrier, morphogenetic (regeneration) and limiting the possibility of invasive growth of the epithelium, proliferative.
Features of epithelial tissues:
1) does not contain blood vessels (nutrition is diffuse through the membrane from the side of the connective tissue.
2) has polarity (the basal and apical parts have a different structure).
3) Capable of regeneration (mitotic division and differentiation of stem cells). Cytokeratins form tonofilaments, except for the endothelium (vimentin)
Classification.
Morphogenetic- the ratio of cells to the basement membrane and their shape.
Single layer epithelium All cells are connected to the basement membrane. A) single-row (isomorphic) - all cells have the same shape (flat, cubic or prismatic, the nuclei lie on the same level). B) multi-row (anisomorphic)
multilayer- flat keratinizing and many others. Pl. non-keratinizing. Prismatic - mammary gland, pharynx, larynx. Cubic - art. ovarian follicle, ducts of sweat and sebaceous glands.
Transition- lines organs subject to strong stretching - the bladder, ureters.
Single layer epithelium. mononuclear epithelium.
1. Single layer squamous epithelium:
A) mesothelium- serous membranes (pleura, visceral and parietal peritoneum) cells - mesotheliocytes, flat, polygonal shape and with uneven edges. 1-3 cores. On the free surface - microvilli. F: secretion and absorption of serous fluid, sliding of internal organs, prevents the formation of adhesions between the organs of the abdominal and chest cavities as a result of damage)
B) Endothelium- blood and lymphatic vessels, chambers of the heart. A layer of flat cells - endotheliocytes, in 1 layer. Feature: the poverty of organelles and the presence of pinocytic vesicles in the cytoplasm. F - metabolism and gases. Blood clots.
2. Single layer cubic- lines part of the renal tubules (proximal and distal). The cells have a brush border (microvilli) and basal striation (deep folds of the plasmalemma and mitochondria between them). F reverse suction.
3. Single layer prismatic- the middle part of the digestive system: the inner surface of the stomach, small and large intestine, gallbladder, ducts of the liver and pancreas. They are connected by desmosomes and gap junctions. (in the stomach - glandular cells, produce mucus. Due to the gastric dimples - renewal of the epithelium).
In the small intestine - a single-layer prismatic limbic. Forms walls of intestinal glands-crypts. Bandless epithelial cells of crypts - reproduction and differentiation, renewal 5-6 days. Goblet - secretion of mucus (parietal digestion, protection against infections, mechanical and chemical, endocrine (basal-sulphurous) - hormones, Paneth cells (apical-granular) - bactericidal substance - lysozyme.
multinucleated epithelium.
They line the airways (nasal cavity, trachea, bronchi). Ciliated.
1. Basal cells are low. On BM. deep in the epithelial layer. cambial. Divide and differentiate into ciliated and goblet - regeneration.
2. Ciliated (ciliated) - high, prismatic. The apical surface is covered with cilia. Purify the air.
3. Goblet cells - mucus (mucins)
4. Endocrine cells - regulation of muscle tissue.
In the top row - ciliated. Lower - basal, middle - intercalary, goblet and endocrine.
Stratified epithelium.
1) Stratified squamous non-keratinized epithelium- the cornea of the eye. Oral cavity and esophagus. Basal layer - prismatic epithelial cells on the base.m. among them are stem cells (mitotic division). Spiny layer - irregularly polygonal cells. In these layers, tonofibrils (bundles of keratin tonofilaments) are developed, between epitheliocytes - desmosomes, etc. The upper layers are flat cells.
2) Keratinizing- covers the surface of the skin. arr. its epidermis (keratinization, keratinization) with differentiation of keratinoids into horny scales. In connection with the synthesis and accumulation in the cytoplasm of special proteins - cytokeratins (acidic and alkaline), filaggrin, keratolin. The main part of the cells - keratinocytes, as they differentiate, move from the bases of the sl to the overlying layers. Melanocytes (pigmented), intraepidermal macrophages (Largenhans cells), lymphocytes, Meckel cells.
1. Basal layer - prismatic keratiocytes, synthesize tonofilaments, HSCs in the cytoplasm
2. Spiny layer - keratinocytes are connected by desmosomes. in the cytoplasm, tonofilaments arr. bundles - tonofibrils, keratinosomes appear - granules containing lipids - by exocytosis in the intercl space - arr. cementing keratin in-va.
In the basal and spiny layers, melanocytes, intraepidermal macrophages (Largenhans cells - together with keratins arr proliferative units) Meckel cells.
3. Granular - flattened keratinocytes, in the cytoplasm keratinoglian granules (keratin + filaggrin + keratolinin - strengthens the plasma membrane of cells) granules: keratohyalin (prophyllagrin - keratin arr, keratinosomes - enzymes and lipids (water impermeability and barrier)
4. Shiny - in heavily keratinized areas of the epidermis (palms, soles) - flat keratinocytes (no nuclei and organelles). Under the plasmolemma - keratolinin (the granules merge, the inner part of the cells is filled with a light-refracting mass of keratin fibrils, glued with an amorphous matrix containing filaggrin.
5. The stratum corneum - flat polygonal keratocytes - thick shells arr serotolinin and keratin fibrils. Filaggrin breaks down into amino acids, which are part of the keratin fibrils. Between the scales - cement in-in, a product of keratins, rich in lipids, waterproofing. 3-4 weeks - regeneration.
Cornification:
1. Flattening the shape
2. Assembly of CPF by phyllagrin into macrofilaments
3. Arr of the shell of the horny scale
4. Destruction of organelles and nucleus
5. dehydration
3) Transitional epithelium- urinary organs - renal pelvis, ureters, bladder. Cell layers:
1. Basal - small rounded cambial cells
2. Transitional
3. Superficial - large, 2-3 nuclear, dome-shaped or flattened, depending on the filling of the organ. Plates of the plasmolemma "cobblestone", incorporation of disc-shaped vesicles.
Regeneration: source - stem cells in the basal layer in multi-row epithelium - basal cells, in single-layer - small intestine - crypts, stomach - pits.
The epithelium is well innervated and has receptors.
Epithelial tissues are divided into superficial, including integumentary and lining, and glandular epithelium. integumentary is the epidermis of the skin lining- this is the epithelium that covers the cavities of various organs (stomach, bladder, etc.), glandular - is part of the glands.
Surface epithelium is located on the border between the internal and external environment and performs the following functions: protective, barrier, receptor and metabolic, since nutrients are absorbed into the body through the epithelium (intestinal) and metabolic products are excreted from the body through the epithelium (renal).
glandular epithelium is part of the glands that produce secrets and hormones necessary for the body, i.e., performs a secretory function.
The surface epithelium differs from other tissues in six main ways:
1) is located in layers;
2) lies on the basement membrane, consisting of an amorphous substance, including proteins, lipids and carbohydrates, fibronectins, laminins, as well as thin fibrils containing type IV collagen; the basement membrane consists of light and dark layers and performs the following functions: barrier, trophic, exchange, anti-invasive, morphogenetic; attaches to itself a layer of epithelium; connective tissue is always located under the basement membrane;
3) there is no intercellular substance in it, therefore, epithelial cells are tightly adjacent to each other and are connected using intercellular contacts:
a) dense (zonula accludens),
b) serrated or finger-shaped (junctio intercellularis denticulatae),
c) desmosomes (desmosoma), etc.;
4) the absence of blood vessels, since the nutrition of the epithelium is carried out from the side of the connective tissue through the basement membrane;
5) epithelial cells have polar differentiation, i.e., each cell has a basal end facing the basement membrane and an apical end facing the opposite direction, which is explained by the borderline position of the tissue; in the cytolemma of the basal part of the cell, sometimes there is a basal striation, on the lateral surface - intercellular contacts, on the apical surface - microvilli, in some cases forming a suction border;
6) integumentary epithelial tissue has a high ability to regenerate.
Classification of epithelial surface tissues. Epithelial surface tissues are classified according to 2 criteria:
1) depending on the structure of the epithelial tissue and the relationship to the basement membrane;
2) depending on the origin (phylogenetic classification according to N. G. Khlopin).
Morphological classification. The surface epithelium is divided into single-layer and multilayer.
Single layer epithelium in turn, they are divided into single-row and multi-row, or pseudo-multilayer. Single row epithelium divided into flat, cubic and prismatic, or columnar. Stratified epithelium always prismatic.
Stratified epithelium subdivided into multi-layer flat keratinizing, multi-layer flat non-keratinizing, multi-layer cubic (multi-layer prismatic always non-keratinizing) and, finally, transitional. The name flat, cubic or prismatic depends on the shape of the cells of the surface layer. If the surface layer of cells has a flattened shape, then the epithelium is called flat, and all the underlying layers can have a different shape: cubic, prismatic, irregular, etc. A single-layer epithelium differs from a multilayer one in that all its cells are located on the basement membrane, while while in the stratified epithelium, only one basal layer of cells is associated with the basement membrane, and the remaining layers are located one on top of the other.
Phylogenetic classification according to N. G. Khlopin. According to this classification, 5 types of epithelial tissues are distinguished:
1) epidermal epithelium - develops from the ectoderm (for example, skin epithelium);
2) enterodermal epithelium - develops from the endoderm and lines the middle section of the gastrointestinal tract (stomach, small and large intestines);
3) whole nephrodermal epithelium - develops from the mesoderm and lines the pleura, peritoneum, pericardium, renal tubules;
4) ependymoglial epithelium - develops from the neural tube, lines the ventricles of the brain and the central canal of the spinal cord;
5) angiodermal epithelium - develops from the mesenchyme, lines the chambers of the heart, blood and lymphatic vessels.
Single layered squamous epithelium(epithelium squamosum simplex) is divided into endothelium (endothelium) and mesothelium (mesothelium).
Endothelium develops from the mesenchyme, lines the chambers of the heart, blood and lymphatic vessels. Endothelial cells - endotheliocytes have an irregular flattened shape, the edges of the cells are indented, contain one or more flattened nuclei, the cytoplasm is poor in organelles of general importance, contains many pinocytic vesicles. On the luminal surface of endotheliocytes there are short microvilli. What's happened luminal surface? This is the surface facing the lumen of an organ, in this case a blood vessel or a chamber of the heart.
Endothelial function- exchange of substances between blood and surrounding tissue. When the endothelium is damaged, blood clots form in the vessels, blocking their lumen.
Mesothelium(mesothelium) develops from the leaves of the splanchnotome, lines the peritoneum, pleura, pericardium. Mesotheliocyte cells have a flattened irregular shape, the edges of the cells are indented; cells contain one, sometimes several flattened nuclei, the cytoplasm is poor in organelles of general importance, it contains pinocytic vesicles, indicating the function of metabolism; on the luminal surface there are microvilli that increase the surface of the cells. The function of the mesothelium is to provide a smooth surface to the serous membranes. This facilitates the sliding of organs in the abdominal, chest and other cavities; through the mesothelium, there is an exchange of substances between the serous cavities and the underlying connective tissue of their walls. The mesothelium secretes the fluid contained in these cavities. If the mesothelium is damaged, adhesions can form between the serous membranes, hindering the movement of organs.
Single layered cuboidal epithelium(epithelium cuboideum simplex) is found in the renal tubules, excretory ducts of the liver. The shape of the cells is cubic, the nuclei are round, organelles of general importance are developed: mitochondria, EPS, lysosomes. On the apical surface there are numerous microvilli forming a striated border (limbus striatus) rich in alkaline phosphatase (AP). On the basal surface there is a basal striation (stria basalis), which is a fold of the cytolemma, between which mitochondria are located. The presence of a striated border on the surface of epitheliocytes indicates the absorption function of these cells, the presence of basal striation indicates reabsorption (reabsorption) of water. The source of development of the renal epithelium is the mesoderm, or rather, the nephrogenic tissue.
columnar epithelium(epithelium columnare) is located in the small and large intestines and stomach. Columnar (prismatic) epithelium of the stomach lines the mucous membrane of this organ, develops from the intestinal endoderm. The cells of the epithelium of the gastric mucosa have a prismatic shape, an oval nucleus; in their light cytoplasm, a smooth ER, the Golgi complex, and mitochondria are well developed; in the apical part, there are secretory granules containing a mucous secretion. Thus, the surface epithelium of the gastric mucosa is glandular. Therefore, its functions:
1) secretory, i.e., the production of a mucous secret that envelops the gastric mucosa;
2) protective - the mucus secreted by the glandular epithelium protects the mucous membrane from chemical and physical influences;
3) suction - water, glucose, alcohol are absorbed through the integumentary (aka glandular) epithelium of the stomach.
Columnar (border) epithelium of the small and large intestines(epithelium columnare cum limbus striatus) lines the mucous membrane of the small and large intestines, develops from the intestinal endoderm; characterized by the fact that it has a prismatic shape. The cells of this epithelium are connected to each other using tight contacts, or end plates, i.e., intercellular gaps are closed with contacts. The cells have well developed organelles of general importance, as well as tonofilaments that form the cortical layer. In the region of the lateral surfaces of these cells, closer to their base, there are desmosomes, finger-like or serrated contacts. On the apical surface of columnar epithelioditis there are microvilli (up to 1 µm high and up to 0.1 µm in diameter), the distance between which is 0.01 µm or less. These microvilli form a suction, or striated, border (limbus striatus). Functions of the border epithelium: 1) parietal digestion; 2) absorption of cleavage products. Thus, a sign confirming the absorption function of this epithelium is: 1) the presence of an absorption border and 2) single layer.
The composition of the epithelium of the small and large intestines includes not only columnar epithelial cells. Between these epithelial cells there are also goblet epitheliocytes (epitheliocytus caliciformis), which perform the function of secreting a mucous secretion; endocrine cells (endocrinocyti) that produce hormones; poorly differentiated cells (stem), devoid of a border, which perform a regenerative function and due to which the intestinal epithelium is updated within 6 days; in the epithelium of the gastrointestinal tract, cambial (stem) cells are located compactly; finally, there are cells with acidophilic granularity.
Pseudo-stratified (multi-row) epithelium(epithelium pseudostratificatum) is single-layer, since all its cells lie on the basement membrane. Why then is this epithelium called multi-row? Because its cells have different shapes and sizes, and, consequently, their nuclei are located at different levels and form rows. The nuclei of the smallest cells (basal, or short intercalary) are located closer to the basement membrane, the nuclei of medium-sized cells (long intercalations) are localized higher, the nuclei of the tallest cells (ciliated) are the most distant from the basement membrane. The multilayered epithelium is located in the trachea and bronchi, the nasal cavity (develops from the prechordal plate), in the male vas deferens (develops from the mesoderm).
In the multi-row epithelium, 4 types of cells are distinguished:
1) ciliated epitheliocytes (epitheliocytus ciliatus);
2) small and large intercalated cells (epitheliocytus intercalatus parvus et epitheliocytus intercalatus magnus);
3) goblet cells (exocrinocytus caliciformis);
4) endocrine cells (endocrinocytus).
ciliated epitheliocytes- These are the highest cells of the pseudostratified epithelium of the mucous membrane of the respiratory tract. The nuclei of these cells are oval in shape and, as already mentioned, are the most distant from the basement membrane. In their cytoplasm there are organelles of general importance. The basal narrow end of these cells is connected with the basal membrane; at the wide apical end there are cilia (cilii) 5–10 µm long. At the base of each cilium there is an axial thread (filamenta axialis), which consists of 9 pairs of peripheral and 1 pair of central microtubules. The axial thread connects to the basal body (modified centriole). Cilia, carrying out oscillatory movements directed against the inhaled air, remove dust particles that have settled on the surface of the mucous membranes of the trachea and bronchi.
Ciliated epitheliocytes are also part of the epithelium of the mucous membrane of the fallopian tubes and uterus, although this epithelium does not belong to the multilayer.
Small intercalated cells respiratory tract - the smallest, have a triangular shape, with a wide basal end lie on the basement membrane. The function of these cells- regenerative; they are cambial or stem cells. In the trachea, bronchi, nasal cavity and epidermis of the skin, cambial cells are located diffusely.
Large intercalated cells higher than small intercalary ones, but their apical part does not reach the surface of the epithelium.
goblet cells(exocrinocytus caliciformis) are glandular cells (unicellular glands). Until such time as these cells have time to accumulate a secret, they have a prismatic shape. In their cytoplasm there is a flattened nucleus, a smooth ER, the Glgi complex and mitochondria are well developed. Granules of mucous secretion accumulate in their apical part. As these granules accumulate, the apical part of the cell expands and the cell takes on the shape of a goblet, which is why it is called goblet. The function of goblet cells is the secretion of mucous secretion, which, enveloping the mucous membrane of the trachea and bronchi, protects it from chemical and physical influences.
endocrinocytes in the composition of the multi-row epithelium of the respiratory tract, otherwise called basal-granular or chromaffin cells, perform a hormonal function, i.e. they secrete the hormones norepinephrine and serotonin, which regulate the contractility of the smooth muscles of the bronchi and trachea.
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