Epithelial tissues, or Epithelia (from Greek epi - above 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, the mucous membranes of the internal organs and form most of the glands. Distinguish Three types of epithelia:

1) Integumentary epithelia (form various linings),

2) Glandular epithelia (form glands)

3) Sensory epithelia (perform receptor functions and are part of the sense organs).

Functions of epithelium:

1 Demarcation, barrier - The main function of epithelium, all others are its partial manifestations. 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 characteristics of each epithelium. A few exceptions to the general rule are epithelia, which delimit two areas of the internal environment - for example, lining body cavities (mesothelium) or blood vessels (endothelium).

2 Protective - Epithelia provide protection to 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, epithelia can form thick layers, form an outer low-permeable, physically and chemically stable stratum corneum, secrete a protective layer of mucus, produce substances with an antimicrobial effect, etc.).

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

ABOUT Suction- many epithelia actively absorb substances; The most striking examples are the epithelium of the intestine and renal tubules. This function is essentially a special version of the transport function.

© Secretory - Epithelia are the functional leading tissues of most glands.

© excretory - Epithelia are involved in removing from the body (with urine, sweat, bile, etc.) end products of metabolism or (exogenous) compounds introduced into the body (for example, drugs).

ABOUT Sensory (receptive) - Epithelia, 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 Eliteliev include:

J) Arrangement of cells (epithelial cells) in closed layers, Which form Planar linings, Roll up into Tubes Or form Bubbles (follicles); This feature of epithelia is determined by signs (2) and (3);

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

3) The presence of developed intercellular connections, Which determine the 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 sign (4). In epithelial cells there are Apical pole(from the Greek apex - top), free, directed to the external environment, and basal pole, Facing the tissues of the internal environment and associated with Basal membrane. Multilayered epithelia are characterized by Vertical anisomorphy(from the Greek an - negation, iso - identical, 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 connective tissue vessels. Various distances of individual layers of multilayered epithelia from the nutritional source probably enhance (or maintain) their vertical anisomorphy;

8) High regeneration ability- Physiological and reparative - carried out thanks to Cambia(including stem and semi-stem cells) and is due to the borderline position of the epithelium (determining a significant need for active renewal of rapidly deteriorating epithelial cells). Cambial elements in some epithelia are concentrated in certain areas of them (localized cambium), In others, they are evenly distributed among other cells (diffuse cambium).

Details

Epithelial tissues.
Functions: delimiting, barrier, protective, transport, suction, secretory, sensory, excretory.

Morphological characteristics: always borderline position, cell polarity, closeness of cell layers, basement membrane (BM), little intercellular substance, highly pronounced intercellular contacts, rapid renewal and regeneration, no vessels.

Surface epithelia- integumentary (on the surface of the body, mucous membranes of internal organs (stomach, intestines, bladder) and lining (secondary body cavities). 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 germ layer), in pathological conditions - metaplasia, i.e. pass from one type to another (for example, in the respiratory tract, the epithelium in chronic bronchitis changes from single-layer ciliated to multilayer squamous)

1. Surface epithelia.

Structure.

Epithelia are layers of epithelial cells. There is almost no intercellular substance between them; they are interconnected desmosomes(attachment plates contain plakoglobins, desmoplakin, and desmocalmin) in the cleft, SA-binding desmogleins), intermediate(AFs are 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).

Are located on basement membranes 1 micron thick (plates): light 20-40 nm and dark 20-60 nm plates. Light includes an amorphous substance with calcium ions. Dark - an amorphous matrix with proteins (fibrillar structures - collagen type 4), provides mechanical strength. In an amorphous substance - glycoproteins– fibronectin and laminin (induce proliferation and differentiation during regeneration), calcium ions– connection between adhesive molecules of glycoproteins of the basement membrane and hemidesmosomes of epithelioites. Protein glycans and glycosaminoglycans - membrane elasticity and negative charge provide selective permeability and the ability to accumulate toxic substances in pathology.
Epithelial cells are especially tightly connected to the basement membrane in the region of hemidesmosomes. Here, anchor filaments (type 7 collagen) approach the dark plate through the light plate.
Membrane functions: mechanical (attachment), trophic and barrier, morphogenetic (regeneration) and limiting the possibility of invasive epithelial growth, proliferative.

Features of epithelial tissues:
1) does not contain blood vessels (nutrition is diffuse through the membrane from the side of the connecting tissue.
2) has polarity (basal and apical parts have different structures).
3) Capable of regeneration (mitotic division and differentiation of stem cells). Cytokeratins form tonofilaments, exception: endothelium (vimentin)

Classification.

Morphogenetic– the relationship 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, 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 – st. ovarian follicle, ducts of sweat and sebaceous glands.
Transition– lines organs subject to strong stretching – bladder, ureters.

Single layer epithelia. Mononuclear epithelia.

1. Single-layer squamous epithelium:
A) mesothelium– serous membranes (leaves of the pleura, visceral and parietal peritoneum); cells – mesotheliocytes, flat, polygonal in shape and with uneven edges. 1-3 cores. On the free surface there are microvilli. F: secretion and absorption of serous fluid, sliding of internal organs, prevents the formation of adhesions between the organs of the abdominal and thoracic cavities as a result of damage)
B) Endothelium– blood and lymphatic vessels, chambers of the heart. A layer of flat cells - edothelial cells, in 1 layer. Feature: poverty of organelles and the presence of pinocytotic vesicles in the cytoplasm. F – metabolism of substances 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 striations (deep folds of the plasmalemma and mitochondria between them). F reverse suction.

3. Single layer prismatic– middle section of the digestive system: the inner surface of the stomach, small and large intestines, gall bladder, ducts of the liver and pancreas. 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 there is a single-layer prismatic bordered one. Forms the walls of intestinal crypt glands. Borderless crypt epithelial cells – reproduction and differentiation, renewal 5-6 days. Goblet - secretion of mucus (parietal digestion, protection against infections, mechanical and chemical, endocrine (basal-sulfur) - hormones, Paneth cells (apical-granular) - bactericidal substance - lysozyme.

Multinuclear epithelia.

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) – tall, prismatic in shape. 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.

Multilayer epithelia.

1) Stratified squamous non-keratinizing epithelium- cornea of ​​the eye. Oral cavity and esophagus. Basal layer - prismatic epithelial cells at the base. among them are stem cells (mitotic division). Stratum spinosum – cells have an irregular polyangular shape. In these layers, tonofibrils (bundles of tonofilaments made of keratin) are developed, between epithelial cells - 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 of special proteins in the cytoplasm - cytokeratins (acidic and alkaline), fillagrin, keratolin. The main part of the cells are keratinocytes; as they differentiate, they move from the base layers to the outer layers. Melanocytes (pigment), intraepidermal macrophages (Largenhans cells), lymphocytes, Meckel cells.

1. Basal layer – prismatic keratiocytes, synthesize tonofilaments, SKK, in the cytoplasm
2. Layer spinosum - keratinocytes are connected by desmosomes. in the cytoplasm tonofilaments arr. bundles - tonofibrils, keratinosomes - granules containing lipids - appear by exocytosis in the interstitial space-arrangement. cementing keratin substance.
In the basal and spinous layers there are melanocytes, intraepidermal macrophages (Largenhans cells) - together with keratins, proliferative units) Meckel cells.
3. Granular - flattened keratinocytes, in the cytoplasm there are keratinoglian granules (keratin + filaggrin + keratolinin - strengthens the plasmalemma of cells) granules: keratohyalin (profilagrin - form of keratin, keratinosomes - enzymes and lipids (water resistance and barrier)
4. Shiny - in heavily keratinized areas of the epidermis (palms, soles) - flat keratinocytes (no nuclei or organelles). Under the plasmalemma is keratolinin (the granules merge, the inner part of the cells is filled with a light-refracting mass of keratin fibrils, bound by an amorphous matrix containing filaggrin.
5. The stratum corneum - flat polygonal keratonocytes - thick shells covered with seratolinin and keratin fibrills. Filaggrin breaks down into amino acids, which are part of the keratin fibrils. Between the scales there is cement, a product of keratinosomes, rich in lipids, waterproofing. 3-4 weeks – regeneration.

keratinization:
1. Flattening the shape
2. Assembly of CPF by fillagrin into macrofilaments
3. Sample of the horny scale shell
4. Destruction of organelles and nucleus
5. dehydration

3) Transitional epithelium– urinary drainage organs – renal pelvis, ureters, bladder. Cell layers:
1. Basal - small round cambial cells
2. Transitional
3. Superficial - large, 2-3 nuclear, dome-shaped or flattened, depending on the filling of the organ. Plates of the cobblestone plasmalemma, embedding of disc-shaped vesicles.
Regeneration: source - stem cells in the basal layer in multi-row epithelia - basal cells, in single-layer epithelia - the small intestine - crypts, stomach - pits.
The epithelium is well innervated and has receptors.

Peculiarities epithelium: 1) absence of blood vessels (exception: stria vascularis - multilayered epithelium with capillaries); nutrition - diffuse from the lower layers. 2) poor development of the intercellular substance. 3) high ability to regenerate due to cambial cells, which often divide by mitosis. (2 types: physiological - natural renewal of the structure, reparative - the formation of new structures at the site of damage, with the formation of numerous poorly differentiated cells similar to embryonic ones) 4) polarity is expressed in the cells (basal and apical poles, the nucleus is in the basal, and the apical - secretory granules and organelles of special importance - ciliated cilia). 5) located on the basement membrane (it is non-cellular, permeable, has an amorphous substance and fibrils). 6) the presence of intercellular contacts: desmosomes - mechanical contact, connects cells; hemidesmosomes – attaches epithelial cells to the BM; encircling desmosome - tight junction, chemically insulating; nexuses – gap junctions. 7) are always located on the border of 2 environments. They form a layer even in cell culture.

Functions epithelium: 1) Integumentary: delimiting the body from external and internal environments, the connection between them. 2) Barrier (protective). Mechanical protection against damage, chemical influences and microorganisms. 3) Homeostatic, thermoregulation, water-salt metabolism, etc. 4) Absorption: epithelium of the gastrointestinal tract, kidneys 5) Release of metabolic products, such as urea. 6) Gas exchange: lung epithelium, skin. 7) secretory – epithelium of liver cells, secretory glands. 8) transport – movement along the surface of the mucosa.

Basement membrane. In addition to epithelia in muscle and fatty tissues. This is a homogeneous layer (50 - 100 nm.) Underneath it is a layer of reticular fibers. BM is synthesized by epithelial cells and connective tissue cells and contains type 4 collagen. Epithelial cells are connected to the BM by semidesmosomes. Functions of BM: binding and separation of epithelium and connective tissue, providing nutrition to the epithelium, support for cells, and promotes their organization into a layer.

Single layer:

Multi-layer:

By location the epithelium is divided into: integumentary glandular– forms the parenchyma of the glands.

Single layer epithelium. All cells with their basal parts lie on the BM. The apical parts form a free surface.

Single layer flat The epithelium is represented in the body by mesothelium and, according to some data, by endothelium. Mesothelium (serosa) covers the serous membranes (leaves of the pleura, visceral and parietal peritoneum, pericardial sac, etc.). Mesothelial cells - mesotheliocytes are flat, have a polygonal shape and uneven edges. In the part where the nucleus is located in them, the cells are thicker. Some of them contain not one, but two or even three cores. There are microvilli on the free surface of the cell. Serous fluid is released and absorbed through the mesothelium. Thanks to its smooth surface, internal organs can glide easily. 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. The endothelium lines blood and lymphatic vessels, as well as the chambers of the heart. It is a layer of flat cells - endothelial cells, lying in one layer on the basement membrane. Endotheliocytes are distinguished by a relative paucity of organelles and the presence of pinocytotic vesicles in the cytoplasm.

The endothelium, located in the vessels at the border with lymph and blood, participates in the exchange of substances and gases (02, CO2) between them and other tissues. If it is damaged, a change in blood flow in the vessels and the formation of blood clots - thrombi - in their lumen are possible.

Single layer cubic epithelium (epithelium simplex cuboideum) lines part of the renal tubules (proximal and distal). Proximal tubule cells have a brush border and basal striations. The brush border consists of a large number of microvilli . The striation is due to the presence in the basal sections of the cells of deep folds of the plasmalemma and mitochondria located between them. The epithelium of the renal tubules performs the function of reverse absorption (reabsorption) of a number of substances from the primary urine flowing through the tubules into the blood of the intertubular vessels.

Single layer prismatic epithelium. This type of epithelium is characteristic of the middle section 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. Epithelial cells are connected to each other using desmosomes, gap communication junctions, lock-type junctions, and tight junctions (see Chapter IV). Thanks to the latter, the contents of the stomach, intestines and other hollow organs cannot penetrate into the intercellular gaps of the epithelium.

Epithelia develop from all three germ layers, starting from the 3rd-4th week of human embryonic development. Depending on the embryonic source, epithelia of ectodermal, mesodermal and endodermal origin are distinguished. Related types of epithelium, developing from the same germ layer, under pathological conditions can undergo metaplasia, i.e. transition from one type to another, for example, in the respiratory tract, the ectodermal epithelium in chronic bronchitis from a single-layer ciliated one can turn into a multilayer flat one, which is normally characteristic of the oral cavity and is also of ectodermal origin.

Date of publication: 2015-01-24; Read: 3371 | Page copyright infringement

Biological characteristics and commercial significance of ramming the Yeisk estuary

1.2 Morphological characters

Ram Rutilus rutilus heckeli (Nordmann 1840) Maximum body length up to 35 cm, weight up to 1.8 kg, but prevailing from 100 to 400g. The ram has a high, laterally compressed body. Body height is on average 34 - 36% of its length. The dorsal fin has 9-11 rays, the anal fin has 11 rays...

Growing cacti in a school biology classroom

1.3 Distinctive features

Flower buds are formed in the areoles, flowers appear, and in some species leaves appear.

The spines usually develop in the lower part of the areola, with flowers and lateral processes appearing above them. There are central and radial spines...

Genetic and statistical analysis of the combining ability of varieties and forms of spring soft wheat according to the coefficient of economic efficiency of photosynthesis

1.1 Quantitative and qualitative characteristics

There are two main types of variability: quantitative, which can be measured, and qualitative, which is difficult or impossible to measure...

Hypothesis of the emergence of humanity

2.4.

Human community, its distinctive features.

Moral and social prohibitions apply to all members of the community - both weak and strong. They are fundamentally irreducible to the instinct of self-preservation and have the nature of obligations, the violation of which entails punishment...

3. MENDELIAN SIGNS

Patterns of independent monogenic inheritance (laws of G.

Mendel). Types of monogenic inheritance: autosomal recessive and autosomal dominant. Conditions for Mendelianization of characters. Mendelian traits of man

3.2 Mendelian traits of humans

Mendel's laws are valid for monogenic traits, which are also called Mendelian. Most often, their manifestations are of a qualitative alternative nature: brown and blue eye colors, normal blood clotting or hemophilia...

Comprehensive characteristics of the red noctule (Nyctalus noctula) of the fauna of the North Caucasus

3.2 Morphological characters

DIMENSIONS: Weight 1840 g, body length 60 82 mm, tail length 46 54 mm, forearm length 48 58 mm, wingspan 32 40 cm.

DESCRIPTION: Ears are short and wide. The color of the back is fawn, brown-brown, chocolate-brown, reddish-brown, the belly is lighter than the back...

Concepts of modern natural science

1.13 How do you understand the phrase: “Sex-linked traits”? How are these signs stored and transmitted?

Traits inherited with the sex chromosomes X and Y are called sex-linked.

In humans, the Y chromosome contains a number of genes that regulate spermatogenesis, the manifestation of histocompatibility antigens, affecting the size of teeth, etc...

Features of the pest of deciduous trees - lacewing

4.3 Type of larva and its characteristic features

In phytophagous insects, the larva in most cases is the main harmful phase.

Epithelial tissue: structural features, functions and types

Insect larvae are usually classified into two main groups: adult and non-imaginous...

Features of the development of fatigue in children and adolescents and its prevention

2. Signs of fatigue

The following signs indicate the beginning of a student’s fatigue: a decrease in labor productivity (the number of errors and incorrect answers increases...

Concept of human age

Signs of biological age

Not every sign that changes with age can determine a person’s biological age.

In the case of skin aging, gray hair and wrinkles, the functioning of other organs, especially the brain and heart, remains at a high level...

The essence of the difference between living open systems and nonliving ones

2. Properties (signs) of living systems

So, the general properties characteristic of all living things and their differences from similar processes occurring in inanimate nature are: 1) unity of chemical composition, 2) metabolism, 3) self-reproduction (reproduction), 4) heredity...

Factors in the evolution of modern man

2) CHARACTERISTIC SIGNS OF A HUMAN

One of the main problems that immediately confronted scientists was the identification of the line of primates that gave rise to hominids.

Throughout the 19th century. Several hypotheses have been put forward regarding this...

What is immunity and how to increase it?

2.5. Signs of weakened immunity

• Frequent colds (more than 4-6 times a year) Frequent relapses of chronic diseases Herpes, papillomatosis and similar diseases Increased fatigue Allergic diseases 2.6…

Ethnic anthropology: its content and tasks

1.3 Adaptive traits

Since science began to connect the origin of races with the influence of the environment, attempts have been made to prove that each race is best adapted to the conditions in which it was formed...

Classification of epithelial tissues

There are two types of classification of epithelial tissues: morphological and genetic.

Morphological classification of epithelial tissues.

1.Single layer epithelium- All cells of this epithelium lie on the basement membrane.

A) Single row- all cells have the same height, so the nuclei of epithelial cells lie in one row.

— Flat.

The height of epithelial cells is less than their width. (endothelium of blood vessels)

— Cubic.The height and width of the epithelial cells are the same. (covers the distal parts of the nephron tubules)

— Cylindrical(Prismatic). The height of epithelial cells is greater than their width. (Covers the mucous membrane of the stomach, small and large intestines).

b) Multi-row- Cells have different heights, so their nuclei form rows. Moreover, all cells lie on basement membrane.

2.Multilayer epithelium. Cells, having the same size, form a layer. In stratified epithelium, only the bottom layer lies on the basement membrane. All other layers are not in contact with the basement membrane. The name of the stratified epithelium is formed according to the shape of the topmost layer.

A) Multilayered squamous non-keratinizing epithelium.B This epithelium does not undergo the upper layers of keratinization. Covers the cornea of ​​the eye, the mucous membrane of the mouth and esophagus

b) Stratified squamous keratinizing epithelium.B The human body is represented by the epidermis and its derivatives (nails, hair).

V) Multilayer transitional epithelium. Covers mucous membrane of the urinary tract. It has the ability to transform from a two-layer to a pseudo-multilayer.

Genetic classification:

Epidermal type. Formed from ectoderm. Represented by multilayer and multirow epithelium. Performs integumentary and protective functions.

2.Endodermal type. Formed from the endoderm. Represented by single-layer prismatic epithelium. Performs the function of absorption.

3.Coelonephrodermal type. Formed from the mesoderm. Represented by single-layer epithelia. Performs barrier and excretory functions.

4.Ependymoglial type. Formed from the neural tube. Lines the spinal canal and ventricles of the brain.

5.Angiodermal type. from mesenchyme (extraembryonic mesoderm). Represented by vascular endothelium.

Olfactory organ . General morphofunctional characteristics. Cellular composition of the olfactory epithelium. Organ of taste. General morphofunctional characteristics. Taste buds, their cellular composition.

Olfactory organ is a chemoreceptor. It perceives the action of odorant molecules. This is the most ancient type of reception. The olfactory analyzer consists of three parts: the olfactory region of the nasal cavity (peripheral part), the olfactory bulb (intermediate part), and also the olfactory centers in the cerebral cortex.

The source of formation of all parts of the olfactory organ is the neural tube.

The olfactory lining of the peripheral part of the olfactory analyzer is located on the superior and partially middle concha of the nasal cavity.

The general olfactory region has an epithelial-like structure. Olfactory neurosensory cells are spindle-shaped with two processes. Based on their shape, they are divided into rod-shaped and cone-shaped. The total number of olfactory cells in humans reaches 400 million, with a significant predominance of rod-shaped cells.

Organum gustus located in the initial part of the digestive tract and serves to perceive the quality of food.

Taste receptors are small neuroepithelial structures called taste buds (gemmae gustatoriae). They are located in stratified epithelium mushroom-shaped(papillae fungiformes), leaf-shaped(papillae foliatae) and grooved(papillae vallatae) of the papillae of the tongue and in small quantities - in the mucous membrane of the soft palate, epiglottis and posterior wall of the pharynx.

In humans, the number of taste buds reaches 2000 - 3000, of which more than half are located in the grooved papillae.
Each taste bud has the shape of an ellipse and consists of 40 - 60 cells tightly adjacent to each other. among which there are receptor, supporting and basal cells. The apex of the kidney communicates with the oral cavity through an opening - taste pore(porus gustatorius), which leads into a small depression formed by the apical surfaces of taste sensory cells - the taste pit.

TICKET No. 6

1. Structural and functional characteristics of membrane organelles.

Membrane organelles come in two varieties: double-membrane and single-membrane. The double-membrane components are plastids, mitochondria and the cell nucleus.

Single-membrane organelles include the organelles of the vacuolar system - the endoplasmic reticulum, the Golgi complex, lysosomes, vacuoles of plant and fungal cells, pulsating vacuoles, etc.

A common property of membrane organelles is that they are all built from lipoprotein films (biological membranes), which close on themselves so that closed cavities, or compartments, are formed.

The internal contents of these compartments are always different from the hyaloplasm.

General morphofunctional characteristics and classification of cartilaginous tissues. Cellular composition of cartilage tissue. The structure of hyaline, fibrous and elastic cartilage. Perichondrium. Chondrogenesis and age-related changes in cartilage tissue.

Cartilage tissue (textus cartilaginus) forms articular cartilage, intervertebral discs, cartilage of the larynx, trachea, bronchi, and external nose.

Cartilage tissue consists of cartilage cells (chondroblasts and chondrocytes) and dense, elastic intercellular substance.
Cartilage tissue contains about 70-80% water, 10-15% organic substances and 4-7% salts. About 50-70% of the dry matter of cartilage tissue is collagen.

The intercellular substance (matrix), produced by cartilage cells, consists of complex compounds that include proteoglycans, hyaluronic acid, and glycosaminopican molecules.

Cartilage tissue contains two types of cells: chondroblasts (from the Greek chondros - cartilage) and chondrocytes.

Chondroblasts are young round or ovoid cells capable of mitotic division.

Chondrocytes are mature large cells of cartilage tissue.

Welcome

They are round, oval or polygonal, with processes and developed organelles.

The structural and functional unit of cartilage is chondron, formed by a cell or an isogenic group of cells, a pericellular matrix and a lacuna capsule.

In accordance with the structural features of cartilage tissue, three types of cartilage are distinguished: hyaline, fibrous and elastic cartilage.

Hyaline cartilage (from the Greek hyalos - glass) has a bluish color. Its main substance contains thin collagen fibers. Articular, costal cartilages and most of the cartilages of the larynx are built from hyaline cartilage.

Fibrous cartilage, the main substance of which contains a large number of thick collagen fibers, has increased strength.

The cells located between the collagen fibers have an elongated shape, they have a long rod-shaped nucleus and a narrow rim of basophilic cytoplasm. Fibrous rings of intervertebral discs, intra-articular discs and menisci are built from fibrous cartilage. This cartilage covers the articular surfaces of the temporomandibular and sternoclavicular joints.

Elastic cartilage is elastic and flexible.

The matrix of elastic cartilage, along with collagen, contains a large number of complexly intertwined elastic fibers. The epiglottis, wedge-shaped and corniculate cartilages of the larynx, the vocal process of the arytenoid cartilages, the cartilage of the auricle, and the cartilaginous part of the auditory tube are built from elastic cartilage.

Perichondrium (perichondrium) - a dense vascularized connective tissue membrane covering the cartilage of growing bones, costal hyaline cartilage, laryngeal cartilages, etc.

Articular cartilage lacks perichondrium. The perichondrium serves for the growth and repair of cartilage tissue. It consists of two layers - outer (fibrous) and inner (chondrogenic, cambial). The fibrous layer contains fibroblasts that produce collagen fibers and passes into the surrounding connective tissue without sharp boundaries.

The chondrogenic layer contains immature chondrogenic cells and chondroblasts. During the process of ossification, the perichondrium is transformed into periosteum.

Chondrogenesis is the process of formation of cartilage tissue.

Related information:

Search on the site:

Epithelial cells are epithelial cells. Peculiarities epithelium: 1) absence of blood vessels (exception: stria vascularis - multilayered epithelium with capillaries); nutrition - diffuse from the lower layers. 2) poor development of the intercellular substance. 3) high ability to regenerate due to cambial cells, which often divide by mitosis.

(2 types: physiological - natural renewal of the structure, reparative - the formation of new structures at the site of damage, with the formation of numerous poorly differentiated cells similar to embryonic ones) 4) polarity is expressed in the cells (basal and apical poles, the nucleus is in the basal, and the apical - secretory granules and organelles of special importance - ciliated cilia).

5) located on the basement membrane (it is non-cellular, permeable, has an amorphous substance and fibrils). 6) the presence of intercellular contacts: desmosomes - mechanical contact, connects cells; hemidesmosomes – attaches epithelial cells to the BM; encircling desmosome - tight junction, chemically insulating; nexuses – gap junctions. 7) are always located on the border of 2 environments.

They form a layer even in cell culture.

Functions epithelium: 1) Integumentary: delimiting the body from external and internal environments, the connection between them. 2) Barrier (protective). Mechanical protection against damage, chemical influences and microorganisms. 3) Homeostatic, thermoregulation, water-salt metabolism, etc.

4) Absorption: epithelium of the gastrointestinal tract, kidneys 5) Release of metabolic products, such as urea. 6) Gas exchange: lung epithelium, skin. 7) secretory – epithelium of liver cells, secretory glands. 8) transport – movement along the surface of the mucosa.

Basement membrane. In addition to epithelia in muscle and fatty tissues.

This is a homogeneous layer (50 - 100 nm.) Underneath it is a layer of reticular fibers. BM is synthesized by epithelial cells and connective tissue cells and contains type 4 collagen. Epithelial cells are connected to the BM by semidesmosomes. Functions of BM: binding and separation of epithelium and connective tissue, providing nutrition to the epithelium, support for cells, and promotes their organization into a layer.

Classification. Morphofunctional:

Single layer: Single-row (flat, cubic, cylindrical), multi-row.

Multi-layer: Non-keratinizing (flat, transitional), Keratinizing

By location the epithelium is divided into: integumentary– covers or lines organs (digestive tube, respiratory tract) and glandular– forms the parenchyma of the glands.

Single layer epithelium. All cells with their basal parts lie on the BM.

The apical parts form a free surface.

Single layer flat The epithelium is represented in the body by mesothelium and, according to some data, by endothelium.

Mesothelium (serosa) covers the serous membranes (leaves of the pleura, visceral and parietal peritoneum, pericardial sac, etc.). Mesothelial cells - mesotheliocytes are flat, have a polygonal shape and uneven edges.

In the part where the nucleus is located in them, the cells are thicker. Some of them contain not one, but two or even three cores. There are microvilli on the free surface of the cell. Serous fluid is released and absorbed through the mesothelium.

Thanks to its smooth surface, internal organs can glide easily. 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. The endothelium lines blood and lymphatic vessels, as well as the chambers of the heart. It is a layer of flat cells - endothelial cells, lying in one layer on the basement membrane. Endotheliocytes are distinguished by a relative paucity of organelles and the presence of pinocytotic vesicles in the cytoplasm.

The endothelium, located in the vessels at the border with lymph and blood, participates in the exchange of substances and gases (02, CO2) between them and other tissues.

If it is damaged, a change in blood flow in the vessels and the formation of blood clots - thrombi - in their lumen are possible.

Single layer cubic epithelium (epithelium simplex cuboideum) lines part of the renal tubules (proximal and distal).

Proximal tubule cells have a brush border and basal striations. The brush border consists of a large number of microvilli . The striation is due to the presence in the basal sections of the cells of deep folds of the plasmalemma and mitochondria located between them.

Welcome

The epithelium of the renal tubules performs the function of reverse absorption (reabsorption) of a number of substances from the primary urine flowing through the tubules into the blood of the intertubular vessels.

Single layer prismatic epithelium. This type of epithelium is characteristic of the middle section 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. Epithelial cells are connected to each other using desmosomes, gap communication junctions, lock-type junctions, and tight junctions (see.

Chapter IV). Thanks to the latter, the contents of the stomach, intestines and other hollow organs cannot penetrate into the intercellular gaps of the epithelium.

Sources of development of epithelial tissues. Epithelia develop from all three germ layers, starting from the 3rd-4th week of human embryonic development. Depending on the embryonic source, epithelia of ectodermal, mesodermal and endodermal origin are distinguished.

Related types of epithelium, developing from the same germ layer, under pathological conditions can undergo metaplasia, i.e. transition from one type to another, for example, in the respiratory tract, the ectodermal epithelium in chronic bronchitis from a single-layer ciliated one can turn into a multilayer flat one, which is normally characteristic of the oral cavity and is also of ectodermal origin.

Date of publication: 2015-01-24; Read: 3372 | Page copyright infringement

studopedia.org - Studopedia.Org - 2014-2018 (0.001 s)…

Epithelial tissue

Histology(histos - fabric, logos - teaching) - teaching on textiles. Textile is a historically established system of histological elements (cells and intercellular substance), united on the basis of the similarity of morphological characteristics, functions performed and sources of development. The process of tissue formation is called histogenesis.

Fabrics have many characteristics by which they can be distinguished from one another.

These may be features of structure, function, origin, nature of renewal, differentiation. There are various classifications of tissues, but the most common is the classification based on morphofunctional characteristics that provide the most general and significant characteristics of tissues.

In accordance with this, four types of tissues are distinguished: integumentary (epithelial), internal environment (support-trophic), muscle and nervous.

Epithelia- a group of tissues widely distributed in the body. They have different origins (their ectoderm, mesoderm and endoderm develop) and perform various functions (protective, trophic, secretory, excretory, etc.).

Epithelia are one of the most ancient types of tissue in origin. Their primary function is borderline—separating the organism from its environment.

Epithelia share common morphofunctional characteristics:

1. All types of epithelial tissues consist only of cells - epithelial cells. Between the cells there are thin intermembrane gaps in which there is no intercellular substance. They contain a supra-membrane complex - the glycocalyx; substances entering and secreted by the cells arrive here.

The cells of all epithelia are located tightly to each other, forming layers. Only in the form of layers can epithelium function.

Cells connect to each other in various ways (desmosomes, gap junctions, or tight junctions).

3. Epithelia are located on a basement membrane that separates them from the underlying connective tissue. The basement membrane is 100 nm-1 µm thick and consists of proteins and carbohydrates. Blood vessels do not penetrate the epithelium, so their nutrition occurs diffusely through the basement membrane.

4. Epithelial cells have morphofunctional polarity.

They distinguish two poles: basal and apical. The nucleus of epithelial cells is shifted to the basal pole, and almost all of the cytoplasm is located at the apical pole. Cilia and microvilli may be located here.

Epithelia have a well-expressed ability to regenerate; they contain stem, cambial and differentiated cells.

Depending on the function performed, the epithelium is divided into integumentary, absorptive, excretory, secretory and others. Morphological classification divides epithelia depending on the shape of epithelial cells and the number of their layers in the layer. There are single-layer and multilayer epithelia.

The structure and distribution of single-layer epithelia in the body

Single-layer epithelia form a layer one cell thick.

If all the cells in the epithelial layer are the same height, they speak of single-layer single-row epithelium. Depending on the height of the epithelial cells, single-row epithelium is flat, cubic and cylindrical (prismatic). If the cells in a layer of single-layer epithelium are of different heights, then they speak of multirow epithelium.

Without exception, all epithelial cells of any single-layer epithelium are located on the basement membrane.

Single-layer squamous epithelium. Lines the respiratory sections of the lungs (alveoli), small gland ducts, testicular network, middle ear cavity, serous membranes (mesothelium).

Originates from mesoderm. Single-layer squamous epithelium consists of one row of cells, the height of which is less than their width, the nuclei are flattened. The mesothelium covering the serous membranes is capable of producing serous fluid and takes part in the transport of substances.

Single-layer cubic epithelium. Lines the ducts of the glands and tubules of the kidneys. All cells lie on the basement membrane. Their height is approximately equal to their width, the nuclei are round, located in the center of the cells. Has various origins.

Single-layer cylindrical (prismatic) epithelium. Lines the gastrointestinal tract, gland ducts, and collecting ducts of the kidneys.

All its cells lie on the basement membrane and have morphological polarity. Their height is much greater than their width. The cylindrical epithelium in the intestine has microvilli (brush border) at the apical pole, which increase the area of ​​parietal digestion and absorption of nutrients. Has various origins.

Single-layer multirow ciliated (ciliated) epithelium. Lines the airways and some parts of the reproductive system (vas deferens and oviducts).

Consists of three types of cells: short intercalary, long ciliated and goblet. All cells are located in one layer on the basement membrane, but the intercalary cells do not reach the upper edge of the layer. These cells differentiate during growth and become ciliated or goblet-shaped. Ciliated cells bear a large number of cilia at the apical pole. Goblet cells produce mucus.

Structure and distribution of multilayered epithelia in the body

Multilayer epithelia are formed by several layers of cells lying on top of each other, so that only the deepest, basal layer of epithelial cells comes into contact with the basement membrane.

In it, as a rule. stem and cambial cells lie. During the process of differentiation, cells move outward. Depending on the shape of the cells of the surface layer, stratified squamous keratinizing, stratified squamous non-keratinizing and transitional epithelia are distinguished.

Stratified squamous keratinizing epithelium. Originates from the ectoderm.

Forms the surface layer of the skin - the epidermis, the final part of the rectum. It has five layers: basal, spinous, granular, shiny and horny. Basal layer consists of a single row of tall cylindrical cells, tightly connected to the basement membrane and capable of reproduction.

Layer spinosum has a thickness of 4-8 rows of spinous cells. The spinous cells retain a relative ability to reproduce. Basal and spinous cells together form germinal zone. Granular layer 2-3 cells thick. Epithelial cells are flattened in shape with dense nuclei and grains of keratohyalin, stained basophilically (dark blue).

Shiny layer consists of 2-3 rows of dying cells. Keratohyalin grains merge with each other, the nuclei disintegrate, keratohyalin turns into eleidin, which is colored oxyphilic (pink) and strongly refracts light. Most superficial layer horny.

It is formed by many rows (up to 100) of flat dead cells, which are horny scales filled with the horny substance keratin. The skin with hair has a thin layer of horny scales. The stratified squamous keratinizing epithelium performs a border function and protects deep-lying tissues from external influences.

Multilayered squamous non-keratinizing (weakly keratinizing) epithelium. It comes from the ectoderm and covers the cornea of ​​the eye, the oral cavity, the esophagus and part of the stomach of some animals.

It has three layers: basal, spinous and flat. Basal layer lies on the basement membrane, formed by prismatic cells with large oval nuclei, somewhat shifted to the apical pole. The cells of the basal layer divide and move upward. They lose contact with the basement membrane, differentiate and become part of the spinous layer. Layer spinosum formed by several layers of cells of irregular polygonal shape with oval or round nuclei.

The cells have small processes in the form of plates and spines that penetrate between the cells and hold them close to each other.

2 Classification, structure and functional significance of single-layer epithelium

Cells move from the stratum spinosum to the superficial layer - flat layer, 2-3 cells thick. The shape of cells and their nuclei is flattened. The connections between cells weaken, the cells die and slough off from the surface of the epithelium. In ruminants, the surface cells of this epithelium in the oral cavity, esophagus and proventriculus become keratinized.

Transitional epithelium. Originates from mesoderm. It lines the renal pelvis, ureters and bladder - organs that are subject to significant stretching when filled with urine.

Consists of three layers: basal, intermediate and integumentary. Cells basal layer small, of different shapes, are cambial, lie on the basement membrane. Intermediate layer consists of light large cells, the number of rows of which varies greatly depending on the degree of filling of the organ.

Cells cover layer very large, multinucleate or polyploid, often secrete mucus, which protects the surface of the epithelial layer from the action of urine.

Glandular epithelium

Glandular epithelium is a widespread type of epithelial tissue, the cells of which produce and secrete substances of various natures called secrets.

Glandular cells are very diverse in size, shape, and structure, as are the secretions they produce. The process of secretion formation occurs in several stages and is called secretory cycle.

First phase- accumulation of initial products by the cell.

Through the basal pole, various substances of organic and inorganic nature enter the cell, which are used in the process of secretion synthesis.

Second phase- synthesis of secretion from incoming products in the cytoplasmic reticulum. The synthesis of protein secretions occurs in the granular endoplasmic reticulum, and non-protein secretions in the agranular reticulum. Third phase- formation of secretions into granules and their accumulation in the cytoplasm of the cell. Through the cisterns of the cytoplasmic reticulum, the synthesized product enters the Golgi apparatus, where it is condensed and packaged in the form of granules, grains and vacuoles.

After this, the vacuole with a portion of the secretion is detached from the Golgi apparatus and moves to the apical pole of the cell. Fourth phase- secretion removal (extrusion).

Depending on the nature of secretion, three types of secretion are distinguished.

1. Merocrine type. The secretion is removed without violating the integrity of the cytolemma. The secretory vacuole approaches the apical pole of the cell, merges with it with its membrane, and a pore is formed through which the contents of the vacuole flow outside the cell.

Apocrine type. Partial destruction of the glandular cell occurs. Distinguish macroapocrine secretion, when the apical part of the cell cytoplasm is rejected along with the secretory granule, and microapocrine secretion when the tips of the microvilli are torn off.

Holocrine type. There is complete destruction of the glandular cell and its transformation into a secretion.

Fifth phase- restoration of the original state of the glandular cell, observed with the apocrine type of secretion.

Organs are formed from the glandular epithelium, the main function of which is to produce secretions.

These organs are called glands. They are of external secretion, or exocrine, and internal secretion, or endocrine. Exocrine glands have excretory ducts that open on the surface of the body or into the cavity of a tubular organ (for example, sweat, lacrimal or salivary glands).

Endocrine glands do not have excretory ducts; their secretions are called hormones. Hormones enter directly into the blood. Endocrine glands are the thyroid gland, adrenal glands, etc.

Depending on the structure of the gland, there are unicellular (goblet cells) and multicellular.

Multicellular glands have two components: the terminal section, where the secretion is produced, and the excretory duct, through which the secretion is removed from the gland. Depending on the structure of the end section, the glands are distinguished as alveolar, tubular and alveolar-tubular.

Excretory ducts can be simple or complex. Depending on the chemical composition of the secreted secretion, glands are distinguished into serous, mucous and serous-mucous.

Based on their location in the body, glands are classified into wall glands (liver, pancreas) and wall glands (gastric, uterine, etc.).

Epithelial tissue

Epithelial tissue (epithelium) covers the surface of the body, lines the walls of hollow internal organs, forming the mucous membrane, glandular (working) tissue of the glands of external and internal secretion. The epithelium is a layer of cells lying on the basement membrane; there is almost no intercellular substance. The epithelium does not contain blood vessels. Epithelial cells are nourished diffusely through the basement membrane.

Epithelial cells are tightly connected to each other and form a mechanical barrier that prevents the penetration of microorganisms and foreign substances into the body. Epithelial tissue cells live for a short time and are quickly replaced by new ones (this process is called regeneration).

Epithelial tissue is also involved in many other functions: secretion (exocrine and endocrine glands), absorption (intestinal epithelium), gas exchange (lung epithelium).

The main feature of the epithelium is that it consists of a continuous layer of tightly adjacent 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 accumulations of cells - glands: liver, pancreas, thyroid, salivary glands, etc. In the first case, it lies on the basement membrane, which separates the epithelium from the underlying connective tissue . However, there are exceptions: epithelial cells in the lymphatic tissue alternate with elements of connective tissue, such epithelium is called atypical.

The main function of the epithelium is to protect the relevant organs from mechanical damage and infection. In those places where body tissue is subjected to constant stress and friction and “wears out,” epithelial cells multiply at high speed. Often, in areas of high stress, the epithelium becomes denser or keratinized.

The epithelial cells are held together by a cementitious substance containing hyaluronic acid. Since there are no blood vessels approaching the epithelium, the supply of oxygen and nutrients occurs by diffusion through the lymphatic system. Nerve endings can penetrate the epithelium.

Signs of epithelial tissue

Ш Cells are arranged in layers

Ш There is a basement membrane

Ш Cells are closely connected to each other

Ш Cells have polarity (apical and basal parts)

Ш Absence of blood vessels

Ш Lack of intercellular substance

Ш High regeneration ability

Morphological classification

Epithelial cells located in a layer can lie in many layers ( stratified epithelium) or in one layer ( single layer epithelium). Cells are classified according to their height epithelium: flat, cubic, prismatic, cylindrical.

Single layer epithelium

Single layer cuboidal epithelium formed by cubic-shaped cells, is a derivative of three germ layers (outer, middle and inner), located in the tubules of the kidneys, excretory ducts of the glands, and bronchi of the lungs. Single-layer cubic epithelium performs absorptive, secretory (in the tubules of the kidneys) and delimiting (in the ducts of the glands and bronchi) functions.

Rice.

Single layer squamous epithelium - mesothelium, of mesodermal origin, lines the surfaces of the pericardial sac, pleura, peritoneum, omentum, performing delimiting and secretory functions. The smooth surface of the mesathelium promotes the sliding of the heart, lungs, and intestines in their cavities. Through the mesothelium, the exchange of substances occurs between the fluid that fills the secondary cavities of the body and the blood vessels embedded in the layer of loose connective tissue.

Rice.

Single-layer columnar (or prismatic) epithelium ectodermal origin, lining the inner surface of the gastrointestinal tract, gall bladder, excretory ducts of the liver and pancreas. The epithelium is formed by prismatic cells. In the intestines and gall bladder, this epithelium is called bordered, as it forms numerous outgrowths of the cytoplasm - microvilli, which increase the surface of the cells and promote absorption. The cylindrical epithelium of mesodermal origin, lining the inner surface of the fallopian tube and uterus, has microvilli and ciliated cilia, the vibrations of which contribute to the advancement of the egg.

Rice.

Single layer multirow ciliated epithelium -cells of this epithelium of various shapes and heights have ciliated cilia, the vibrations of which help remove foreign particles deposited on the mucous membrane. This epithelium lines the airways and is of ectodermal origin. The functions of single-layer multirow ciliated epithelium are protective and delimiting.

Rice.

Stratified epithelium

The epithelium, based on the nature of its structure, is divided into integumentary and glandular.

Integumentary (surface) epithelia- These are border tissues located on the surface of the body, the mucous membranes of internal organs and secondary body cavities. They separate the body and its organs from their environment and participate in the metabolism between them, performing the functions of absorbing substances and excreting metabolic products. For example, through the intestinal epithelium, the products of food digestion are absorbed into the blood and lymph, and through the renal epithelium, a number of nitrogen metabolism products, which are waste products, are released. In addition to these functions, the integumentary epithelium performs an important protective function, protecting the underlying tissues of the body from various external influences - chemical, mechanical, infectious and others. For example, the skin epithelium is a powerful barrier to microorganisms and many poisons. Finally, the epithelium covering the internal organs creates the conditions for their mobility, for example, for the movement of the heart during its contraction, the movement of the lungs during inhalation and exhalation.

Glandular epithelium- a type of epithelial tissue, which consists of epithelial glandular cells, which in the process of evolution acquired the leading property of producing and secreting secretions. Such cells are called secretory (glandular) - glandulocytes. They have exactly the same general characteristics as the integumentary epithelium. Located in the glands of the skin, intestines, salivary glands, endocrine glands, etc. Among the epithelial cells are secretory cells, of which there are 2 types.

Ш exocrine - release their secretion into the external environment or the lumen of the organ.

Ш endocrine - release their secretion directly into the bloodstream.

epithelial tissue cell function

Multilayer epithelium is divided into three types: non-keratinizing, keratinizing and transitional. Stratified non-keratinizing epithelium consists of three layers of cells: basal, styloid and squamous.

Transition the epithelium lines organs that are subject to strong stretching - the bladder, ureters, etc. When the volume of the organ changes, the thickness and structure of the epithelium also changes.

The presence of a large number of layers allows it to perform a protective function. Multilayer non-keratinizing the epithelium lines the cornea, oral cavity and esophagus, and is a derivative of the outer germ layer (ectoderm).

Multilayered squamous keratinizing epithelium - epidermis, it lines the skin. In thick skin (palm surfaces), which is constantly under stress, the epidermis contains 5 layers:

III basal layer - contains stem cells, differentiated cylindrical and pigment cells (pigmentocytes).

The stratum spinosum consists of polygonal cells containing tonofibrils.

III granular layer - the cells acquire a rhomboid shape, the tonofibrils disintegrate and inside these cells the protein keratohyalin is formed in the form of grains, this is where the process of keratinization begins.

The stratum lucidum is a narrow layer, in which the cells become flat, they gradually lose their intracellular structure, and keratohyalin turns into eleidin.

The third stratum corneum contains horny scales that have completely lost their cell structure and contain the protein keratin. With mechanical stress and deterioration of blood supply, the process of keratinization intensifies.

In thin skin that does not experience stress, there is no granular and shiny layer. The main function of the stratified keratinizing epithelium is protective.

Even in a school anatomy course, children are taught a simple biological pattern in the structure of living multicellular creatures: the basis of everything is the cell. A group of them gives rise to tissues, which, in turn, form organs. The latter are combined into systems that carry out life activities, metabolic processes, and so on.

Therefore, what tissues are, their structure and functions, is studied from the middle stage of the school curriculum. Let's consider what types of tissues are found in the human body, what the epithelial variety of these structures is and what its significance is.

Animal tissues: classification

Tissues, their structure and functions, features of development and functioning are of great importance in the life of all living beings that are capable of their formation. They perform a protective function, secretory, organ-forming, nutritional, thermal insulation and many others.

In total, 4 types of tissues can be distinguished, characteristic of the structure of the human body and highly organized animals.

1. Various types of epithelial tissue or integumentary tissue (skin).
2. Connective tissue, represented by several main types: bone, blood, adipose and others.
3. Nervous, formed by peculiar branched cells.
4. Muscle tissue that, together with the skeleton, forms the musculoskeletal system of the entire body.

Each of the listed tissues has its own location, method of formation and performs certain functions.

General characteristics of epithelial tissue

If we characterize the types of epithelial tissues in general, then we should highlight several main features that they all possess, each to a greater or lesser extent. For example:

• the absence of substance located between the cells, which makes the structures tightly adjacent to each other;
• a unique method of nutrition, which does not consist in the absorption of oxygen from but in diffusion through the basement membrane from the connective tissue;
• unique ability to restore, that is, regenerate the structure;
• the cells of this tissue are called epithelial cells;
• each epithelial cell has polar ends, so the entire tissue ultimately has polarity;
• under any type of epithelium there is a basement membrane, which is important;
• This tissue is localized in the body in layers or strands in certain places.

Thus, it turns out that the varieties of epithelial tissue are united by common patterns in location and structural organization.

Types of epithelial tissue

There are three main ones.

1. The superficial epithelium of its structure is especially dense, because it primarily performs a protective function. Forms a barrier between the outside world and the inside of the body (skin, outer coverings of organs). In turn, this type includes several more components, which we will consider further.
2. Glandular epithelial tissues. Glands whose ducts open outward are exogenous. These include lacrimal, sweat, milky, and sebaceous genitals.
3. Secretory varieties of epithelial tissue. Some scientists believe that some of it eventually turns into epithelial cells and forms this type of structure. The main function of such an epithelium is to perceive irritations, both mechanical and chemical, transmitting a signal about this to the appropriate authorities of the body.

These are the main types of epithelial tissue that are distinguished as part of the human body. Now let's look at the detailed classification of each of them.

Classification of epithelial tissues

It is quite capacious and complex, since the structure of each epithelium is multifaceted, and the functions performed are very different and specific. In general, all existing types of epithelium can be combined into the following system. The entire integumentary epithelium is divided in this way.

1. Single layer. The cells are arranged in one layer and are in direct contact with the basement membrane and are in contact with it. His hierarchy is like this.

A) Single-row, divided into:

• cylindrical;
• flat;
• cubic.

Each of these types can be bordered or borderless.

B) Multi-row, including:

• prismatic ciliated (ciliated);
• prismatic unciliated.

2. Multilayer. The cells are arranged in several rows, so contact with the basement membrane occurs only at the deepest layer.

A) Transitional.

B) Keratinizing flat.

B) Non-keratinizing, divided into:

• cubic;
• cylindrical;
• flat.

The glandular epithelium also has its own classification. It is divided into:

• unicellular;
• multicellular epithelium.

In this case, the glands themselves can be endocrine, releasing secretions into the blood, and exocrine, having ducts into the epithelium in question.

Sensory tissue is not divided into structural units. It consists of nerve cells transformed into epithelial cells that form it.

Single layer squamous epithelium

It got its name from the structure of its cells. Its epithelial cells are thin and flattened structures that are tightly connected to each other. The main task of such an epithelium is to ensure good permeability for molecules. Therefore, the main localization locations are:

• alveoli of the lungs;
• walls of blood vessels and capillaries;
• lines the cavities of the inner side of the peritoneum;
• covers the serous membranes;
• forms some renal ducts and renal corpuscles.

The epithelial cells themselves are of mesothelial or endothelial origin and are characterized by the presence of a large oval nucleus in the center of the cell.

Cuboidal epithelium

Such types of epithelial tissue as single-layer and multilayer cubic epithelium have a somewhat special cell structure in shape. That's why they got their name. They are slightly irregularly shaped cubes.

Single-layer cubic is localized in the kidney tubules and performs the functions of a permeable membrane there. The nuclei in such cells are round and displaced towards the cell wall.

The stratified cuboidal epithelium is arranged as a series of deep layers in contact with the basement membrane. All other external structures cover it on top in the form of flat scales of epithelial cells. This type of tissue forms many organs:

• cornea of ​​the eye;
• esophagus;
• oral cavity and others.

Prismatic epithelium single layer

This is one of the types of tissues also called epithelial. The structural features and functions are explained by the shape of the cells: cylindrical, elongated. Main locations:

• intestines;
• small and rectal intestine;
• stomach;
• some kidney tubules.

The main function is to increase the suction surface of the working body. In addition, specialized ducts that secrete mucus open here.

Types of epithelial tissues: single-layer multirow

This is a type of integumentary epithelium. Its main task is to provide the outer covering of the respiratory tract, which is lined with it. All cells are in close contact with the basement membrane; their nuclei are round and located at unequal levels.

This epithelium is called ciliated because the edges of the epithelial cells are framed by cilia. In total, 4 types of cells included in this structure can be distinguished:

• basal;
• ciliated;
• long insert;
• goblet mucus-forming.

In addition, single-layer multirow epithelium is found in the genital ducts and the corresponding system (in the oviducts, testes, and so on).

Stratified transitional epithelium

The most important distinguishing feature of any multilayer epithelium is that its cells can be stem cells, that is, those that are capable of differentiation into any other types of tissue.

Specifically, transitional epithelial cells are part of the bladder and the corresponding ducts. They are divided into three large groups, united by a common ability - to form tissues with high extensibility.

1. Basal cells are small cells with round nuclei.
2. Intermediate.
3. Superficial - very large cells, most often in the shape of a dome.

There is no contact with the membrane in these tissues, so nutrition is diffuse from the loose connective tissue located underneath. Another name for this type of epithelium is urothelium.

Stratified non-keratinizing epithelium

This type includes the epithelial tissues of the body that line the inner surface of the cornea of ​​the eye, the structures of the oral cavity and the esophagus. All epithelial cells can be divided into three types:

• basal;
• spiny;
• flat cells.

In organs they form cords of a flat structure. They are called non-keratinizing for their ability to desquamate over time, that is, to be removed from the surface of the organ, being replaced by younger analogues.

Stratified keratinizing epithelium

Its definition may sound like this: it is an epithelium, the upper layers of which are capable of redifferentiation and the formation of hard scales - corneas. Among all the integumentary epithelium, this is the only one that is characterized by such a feature. Everyone can see it with the naked eye, because the main organ of this layer is the skin. The composition includes epithelial cells of different structures, which can be combined into several main layers:

• basal;
• spiny;
• grainy;
• brilliant;
• horny.

The latter is the densest and thickest, represented by horny scales. It is their desquamation that we observe when the skin of the hands begins to peel off under the influence of unfavorable environmental conditions or old age. The main protein molecules of this tissue are keratin and filaggrin.

Glandular epithelium

In addition to the integumentary epithelium, the glandular epithelium is also of great importance. It is another form that epithelial tissue has. The tissues under consideration and their classification are very important for a correct understanding of their location and functions in the body.

Thus, the glandular epithelium is very different from the integumentary epithelium and all its varieties. Its cells are called glandulocytes, they are an integral part of various glands. In total, two main types can be distinguished:

• exogenous glands;
• endogenous.

Those that release their secretions directly into the glandular epithelium, rather than into the blood, belong to the second group. These include: salivary, milk, sebaceous, sweat, lacrimal, genital.

There are also several options for secretion, that is, the removal of substances to the outside.

1. Eccrine - cells secrete compounds, but do not lose their structural integrity.
2. Apocrine - after the secretion is removed, they are partially destroyed.
3. Holocrine - cells are completely destroyed after performing functions.

The work of the glands is very important and significant. For example, their function is protective, secretory, signaling, and so on.

Basal membrane: functions

All types of epithelial tissues are in close contact with at least one of their layers with a structure such as the basement membrane. Its structure consists of two stripes - a light one, consisting of calcium ions, and a dark one, including various fibrillar compounds.

It is formed from the joint production of connective tissue and epithelium. The functions of the basement membrane are as follows:

• mechanical (hold epithelial cells together, maintaining the integrity of the structure);
• barrier - for substances;
• trophic - providing nutrition;
• morphogenetic - ensuring high regeneration ability.

Thus, the joint interaction of epithelial tissue and the basement membrane leads to the harmonious and orderly functioning of the body and the integrity of its structures.

In general, not only epithelial tissue is very important. Tissues and their classification are covered at all levels of education related to medicine and anatomy, which proves the importance of these topics.