Loose connective. Loose fibrous connective tissue

Loose irregular fibrous connective tissue (RVCT)

Loose unformed fibrous connective tissue - "fiber", surrounds and accompanies the blood and lymphatic vessels, is located under the basement membrane of any epithelium, forms layers and partitions inside all parenchymal organs, forms layers in the composition of the shells of hollow organs.

Loose unformed fibrous connective tissue consists of cells and intercellular substance, and the ratio of these two components is approximately the same.

The intercellular substance consists of the main substance (homogeneous amorphous mass - colloid system- gel) and fibers (collagen, elastic, reticular) located randomly and at a considerable distance from each other, i.e. loose, which is reflected in the name of the fabric.

The cells of this tissue are characterized by a wide variety - cells of fibroblastic differon (stem and semi-stem cells, unspecialized fibroblast, differentiated fibroblast, fibrocyte, myofibroblast, fibroclast), macrophage, mast cell, plasmocyte, adventitial cell, pericyte, lipocyte, melanocyte, all leukocytes, reticular cell.

Stem and semi-stem cells, unspecialized fibroblast, differentiated fibroblast, fibrocyte - these are the same cells at different "ages".

Stem and semi-stem cells are small reserve cells that rarely divide.

A poorly specialized fibroblast is a small, weakly outgrowth cell with a basophilic cytoplasm (due to the large number of free ribosomes), organelles are weakly expressed; actively divides by mitosis, does not take a significant part in the synthesis of intercellular substance; as a result of further differentiation, it turns into differentiated fibroblasts.

Differentiated fibroblasts are the most functionally active cells this series: synthesize fiber proteins (elastin, collagen) and organic components of the main substance (glycosaminoglycans, proteoglycans).

Fibrocyte is a mature and aging cell of this series; spindle-shaped, weakly protruding cells with weakly basophilic cytoplasm.

Fibroblast cells are the most numerous (up to 75% of all tissue cells) and produce most of the intercellular substance. The antagonist is a fibroclast - a cell with a high content of lysosomes with a set of hydrolytic enzymes, which ensures the destruction of the intercellular substance.

Myofibroblast is a cell containing contractile actomyosin proteins in the cytoplasm, therefore, they are able to contract. They take part in the healing of wounds, bringing together the edges of the wound during contraction.

The following cells of loose, unformed fibrous connective tissue by number - tissue macrophages (synonym: histiocytes), make up 15-20% of cells. Large cells with a polymorphic nucleus, able to actively move. Of the organelles, lysosomes and mitochondria are well expressed. Functions: protective - by phagocytosis and digestion of foreign particles, microorganisms, tissue decay products; participation in cellular cooperation in humoral immunity; the production of the antimicrobial protein lysozyme and the antiviral protein interferon, a factor stimulating the migration of granulocytes.

Mast cell (synonyms: tissue basophil, mast cell, mast cell) - makes up 10% of all cells of loose, unformed fibrous connective tissue. Usually located around blood vessels. A round-oval, sometimes process-like cell with a diameter of up to 20 microns; there are a lot of basophilic granules in the cytoplasm. The granules contain heparin and histamine. Functions: by releasing histamine, they are involved in the regulation of the permeability of the intercellular substance RST and the walls of blood vessels, heparin - to regulate blood clotting. In general, mast cells regulate local homeostasis.

Plasma cells - are formed from B-lymphocytes. In morphology, they are similar to lymphocytes, although they have their own characteristics. The core is round; heterochromatin is located in the form of pyramids facing the center with a sharp top, delimited from each other by radial stripes of euchromatin - therefore, the nucleus of the plasma cell is torn off with a "wheel with spokes". The cell diameter is 7-10 microns. Function: they are effector cells of humoral immunity - they produce specific antibodies.

Leukocytes are always present in loose, irregular fibrous connective tissue.

Lipocytes (synonyms: adipocyte, fat cell). There are white and brown fat cells:

1. White lipocytes - rounded cells with a narrow strip of cytoplasm around one large drop of fat in the center. There are few organelles in the cytoplasm. A small nucleus is located eccentrically. Function: white lipocytes accumulate fat in reserve (high-calorie energy material and water).

2. Brown lipocytes - rounded cells with a central location of the nucleus. Fat inclusions in the cytoplasm are detected in the form of numerous small droplets. The cytoplasm contains many mitochondria high activity iron-containing (brown) oxidative enzyme cytochrome oxidase. Function: brown lipocytes do not accumulate fat, but, on the contrary, “burn” it in mitochondria, and the heat released in this case is used to warm the blood in the capillaries, i.e. participation in thermoregulation.

Adventitial cells - poorly differentiated cells of loose, unformed fibrous connective tissue, located next to the blood vessels. They are reserve cells and can differentiate into other cells, in particular fibroblasts.

Pericytes - located in the thickness of the basement membrane of the capillaries; participate in the regulation of the lumen of hemocapillaries, thereby regulating the blood supply to surrounding tissues.

Melanocytes - process cells with inclusions of melanin pigment in the cytoplasm. Origin: from cells migrated from the neural crest. Function: UV protection.

The intercellular substance of loose, unformed fibrous connective tissue consists of the ground substance and fibers.

1. The main substance is a homogeneous, amorphous, gel-like, structureless mass of polysaccharide macromolecules associated with tissue fluid. The organic part of the main substance is synthesized in fibroblasts, fibrocytes.

2. Fibers - the second component of the intercellular substance. There are collagen, elastic and reticular fibers.

1) Collagen fibers underneath light microscope- thicker (diameter from 3 to 130 microns), having a tortuous (wavy) course. They consist of collagen protein synthesized in fibroblasts, fibrocytes. Under a polarizing microscope, collagen fibers have longitudinal and transverse striations. Collagen fibers do not stretch and are very tear-resistant (6 kg/mm2). Function - provide mechanical strength to loose, unformed fibrous connective tissue.

2) Reticular fibers - are considered a type of (immature) collagen fibers, i.e. similar in chemical composition and ultrastructure, but unlike collagen fibers, they have a smaller diameter and strongly branching form a looped network (hence the name: "reticular" - translated as mesh or looped). The constituent components are synthesized in fibroblasts, fibrocytes. In loose, unformed fibrous connective tissue, they are found in small numbers around blood vessels.

3) Elastic fibers - thin (d = 1-3 microns), less durable (4-6 kg / cm2), but very elastic fibers from elastin protein (synthesized in fibroblasts). These fibers do not have striation, have a straight course, and often branch out. Function: give elasticity, the ability to stretch.

RVST regenerates well and is involved in restoring the integrity of any damaged organ. With significant damage, the organ defect is often replenished with a connective tissue scar.

RVST functions:

1. Trophic function: located around the vessels, RVST regulates the metabolism between the blood and tissues of the organ.

2. The protective function is due to the presence of macrophages, plasmocytes and leukocytes in RVST. Antigens that have broken through the I - epithelial barrier of the body, meet with the II barrier - cells of nonspecific (macrophages, neutrophilic granulocytes) and immunological protection (lymphocytes, macrophages, eosinophils).

3. Support-mechanical function.

4. Plastic function - participates in the regeneration of organs after damage.

Dense fibrous connective tissue (PVCT)

A common feature for PVST is the predominance of the intercellular substance over the cellular component, and in the intercellular substance, the fibers predominate over the main amorphous substance and are very close (dense) to each other - all these structural features are reflected in the name of this tissue in a compressed form. PVCT cells are overwhelmingly represented by fibroblasts and fibrocytes; macrophages, mast cells, plasmocytes, poorly differentiated cells, etc. are found in a small amount (mainly in layers of PVCT).

The intercellular substance consists of densely arranged collagen fibers, the main substance is small. According to the location of the fibers, PVST is divided into formed PVST (fibers are arranged in an orderly manner - parallel to each other) and unformed PVST (fibers are arranged randomly). Formed PVST includes tendons, ligaments, aponeuroses, fascia, and unformed PVST includes the reticular layer of the dermis, capsules of parenchymal organs. In PVST between collagen fibers there are layers of RVST with blood vessels and nerve fibers.

PVST regenerates well due to mitosis of poorly specialized fibroblasts and their production of intercellular substance (collagen fibers) after differentiation into mature fibroblasts. The function of PVST is to provide mechanical strength.

Loose fibrous unformed connective tissue is the most common, located next to epithelial tissues, accompanies blood and lymphatic vessels in more or less quantity; is part of the skin and mucous membranes of organs. As layers of membranes containing an abundance of vessels, loose fibrous tissue is found in all tissues and organs (Fig. 30).

The intercellular substance is represented by two components: the main (amorphous) substance - a structureless matrix with a gelatinous consistency; fibers - collagen and elastic, located relatively loose and randomly, therefore the tissue is called unformed. Loose fibrous unformed connective tissue, due to the presence of intercellular substance, performs a support-trophic function, cells participate in immune reactions and recovery processes in tissue damage. As part of the connective tissue, cells of various shapes are differentiated: adventitial, fibroblasts, fibrocytes, histiocytes, mast cells (tissue basophils), plasma cells and fat cells. adventitial(from lat. adventicus- alien, wandering) cells are the least differentiated, located along outer surface capillaries, being cambial, actively divide by mitosis and differentiate into fibroblasts, myofibroblasts and lipocytes. fibroblasts(from lat. fibrin- protein; blastos- sprout, overgrowth -

Rice. thirty

• 7 - macrophage; 2 - amorphous intercellular substance; 3 - plasma cell;
• 4 - fat cell; 5 - endothelium; 6 - adventitial cell; 7 - pericyte;
• 8 - endothelial cell; 9 - fibroblast; 10 - elastic fiber; 11 - mast cell; 12 - collagen fiber current) - protein producers, are permanent and most numerous cells. In mobile cell forms, the peripheral part of the cell contains contractile filaments, cells with big amount contractile filaments - myofibroblasts - promote wound healing. Part of the fibroblasts is enclosed between densely spaced fibers, such cells are called fibrocytes, they lose the ability to divide, take an elongated shape and have strongly flattened nuclei. Macrophages (histiocytes) cells that have the ability to phagocytosis and accumulation of suspended colloidal substances in the cytoplasm are involved in general and local protective reactions of the immune system. The nucleus has well-defined contours. Possessing the ability to directed movement - chemotaxis, macrophages migrate to the focus of inflammation, where they become dominant cells. Macrophages are involved in the recognition, processing and presentation of antigen to lymphocytes. During inflammation, cells become irritated, increase in size, become mobile, and transform into structures called polyblasts. Macrophages cleanse the focus of foreign particles and destroyed cells, but also stimulate the functional activity of fibroblasts. Tissue basophils (labrocytes, mast cells) have an irregularly oval or rounded shape, numerous granules (grains) are located in the cytoplasm. The cells contain histamine, which dilates blood vessels, and secrete heparin, which prevents blood from clotting. Plasma cells (plasma cells) synthesize and secrete the bulk of immunoglobulins - antibodies (proteins formed in response to the action of an antigen). These cells are found in their own layer of the intestinal mucosa, the omentum, in the connective tissue between the lobules of the salivary, mammary glands, in the lymph nodes, and in the bone marrow. pigment cells have processes, in the cytoplasm there are many dark brown or black grains of pigment from the melanin group. The connective tissue of the skin of lower vertebrates - reptiles, amphibians, fish - contains a significant amount of pigment cells - chromatophores, which determine one or another color of the outer cover and perform a protective function. Pigment cells in mammals are concentrated mainly in the sclera, choroid and iris, ciliary body. Fat cells (lipocytes) are formed from adventitial cells of loose connective tissue, which are usually located in groups along blood vessels.

The drug "Loose fibrous unformed connective tissue of the subcutaneous tissue of the rat"(stained with hematoxylin). The drug is a small area of ​​fixed subcutaneous tissue, stretched in the form of a thin film on a coverslip. At a low magnification (x10), the intercellular substance is revealed: a structureless amorphous matrix and two types of fibers - rather wide collagen fibers having a ribbon-like shape, and thin filamentous elastic fibers. With a high magnification of the microscope (x40), cells of various shapes differentiate in the connective tissue: adventitial cells - elongated cells with long processes; fibroblasts - have a spindle shape, since the central part is significantly thickened. The nucleus is large, weakly stained, one or two nucleoli are clearly visible. Ectoplasm is very light, endoplasm, on the contrary, is intensely stained due to the presence of a large amount of granular endoplasmic reticulum, which is due to the participation in the synthesis of high-molecular substances necessary both for building fibers and for the formation of an amorphous substance. Macrophages in the cytoplasm contain many vacuoles, which indicates active participation in metabolism, the contours of the cytoplasm are clear, the processes are in the form of pseudopodia, so the cell is similar to an amoeba. Tissue basophils (labrocytes, mast cells) have an irregularly oval or round shape, sometimes with wide short processes; numerous basophilic granules (grains) are located in the cytoplasm. Plasma cells (plasma cells) may be round or oval shape; the cytoplasm is sharply basophilic, with the exception of only a small rim of the cytoplasm near the nucleus - the perinuclear zone, along the periphery of the cytoplasm there are numerous small vacuoles.

The preparation "Adipose tissue of the omentum". The omentum is a film penetrated by blood vessels. When stained with Sudan III, accumulations of yellow rounded fat cells are visible. When stained with hematoxylin and eosin, the cricoid fat cells are not stained, the violet core is pushed to the periphery of the cytoplasm (Fig. 31).

In many parts of the animal body, significant accumulations of fat cells are formed, called adipose tissue. In connection with the peculiarities of the natural coloration, the specifics of the structure and function, as well as the location in mammals, there are two types of fat cells and, accordingly, two types of adipose tissue: white and brown.

White adipose tissue a significant amount is contained in the so-called fat depots: subcutaneous adipose tissue, especially developed in pigs, adipose tissue around the kidneys in the mesentery (perinephric tissue), in some breeds of sheep at the root of the tail (fat tail). The structural unit of white adipose tissue is spherical fat cells, up to 120 microns in diameter. With the development of cells, fatty

Rice. 31

A- total preparation of the omentum (Sudan III and hematoxylin); b- preparation of subcutaneous adipose tissue (hematoxylin and eosin): 7 - lipocyte; 2 - blood vessel;

3 - a piece of adipose tissue; 4 - fibers and cells of loose connective tissue

The values ​​in the cytoplasm appear first in the form of small scattered drops, later merging into one large drop. The total amount of white adipose tissue in the body of animals various kinds, breeds, sex, age, fatness ranges from 1 to 30% of live weight. Spare fats are the most high-calorie substances, during the oxidation of which the body releases a large number of energy (1 g of fat = 39 kJ). In cattle of meat and meat and dairy breeds, groups of fat cells are located in layers of loose fibrous connective tissue. skeletal muscle. The meat obtained from such animals has the best palatability and is called "marble". Subcutaneous adipose tissue has great importance to protect the body from mechanical damage from heat loss. Adipose tissue along the neurovascular bundles provides relative isolation, protection and limitation of mobility. Accumulations of fat cells combined with bundles of collagen fibers in the skin of the soles and paws create good cushioning properties. The role of adipose tissue as a depot of water is significant; the formation of water is an important feature of the metabolism of fats in animals living in arid regions (camels). During starvation, the body primarily uses spare fats from fat depot cells, in which fatty inclusions decrease and disappear. Adipose tissue of the eye orbit, epicardium, paws is preserved even with severe exhaustion. The color of adipose tissue depends on the type, breed and type of feeding of animals. Most animals, with the exception of pigs and goats, contain a pigment in their fat. carotene, imparting yellow adipose tissue. In cattle, the adipose tissue of the pericardium contains many collagen fibers. kidney fat called the fatty tissue surrounding the ureters. In the back area, adipose tissue of pigs contains muscle tissue, as well as often hair follicles(stubble) and even hair bags. In the peritoneal region there is an accumulation of adipose tissue, the so-called mesenteric or mesenteric fat, which contains a large number of lymph nodes that accelerate oxidative processes and spoilage of fat. Blood vessels are often found in mesenteric fat, for example pigs have more arteries and cattle have more veins. Internal fat is a fatty tissue located under the peritoneum, contains a large number of fibers located in oblique and perpendicular directions. Sometimes pigment grains are found in the adipose tissue of pigs, in such cases brown or black spots are detected.

brown adipose tissue it is present in significant quantities in rodents and hibernating animals, as well as in newborn animals of other species. Location mainly under the skin between the shoulder blades, in the cervical region, mediastinum and along the aorta. Brown adipose tissue consists of relatively small cells that are very tightly adjacent to each other, resembling in appearance glandular tissue. Numerous nerve fibers are approaching the cells, braided with a dense network. blood capillaries. Brown adipose tissue cells are characterized by centrally located nuclei and the presence of small fat droplets in the cytoplasm, which do not merge into a larger drop. In the cytoplasm, between the fat drops, there are glycogen granules and numerous mitochondria, stained proteins of the transport electron system - cytochromes give the brown color to this tissue. In the cells of brown adipose tissue, oxidative processes are intense, accompanied by the release of a significant amount of energy. However, most of the generated energy is spent not on the synthesis of ATP molecules, but on heat generation. This property of brown tissue lipocytes is important for temperature regulation in newborn animals and for warming animals after waking up from hibernation.

Control questions

• 1. Describe the embryonic connective tissue - mesenchyme.
• 2. What is the structure of mesenchymal cells?
• 3. Give a structural and functional characteristic of the cells of the reticular connective tissue.
• 4. What is the structure of reticular fibers and how can they be detected on histological preparations?
• 5. Describe the cells of loose fibrous connective tissue.
• 6. What is the structure of the intercellular substance?
• 7. What is the function of the structureless matrix - the main substance?
• 8. What is the structure and function of loose fibrous connective tissue fibers?
• 9. What dye can be used to detect fat inclusions?

In the body, loose fibrous unformed connective tissue is the most common. It is located near epithelial tissues; in greater or lesser quantities accompanies the blood, lymphatic vessels; is part of the skin and mucous membranes; in the form of layers with vessels, it is found in all tissues and organs.

Loose fibrous unformed connective tissue (Fig. 31) consists of a variety of cells and intercellular substance containing the main (amorphous) substance and a system of collagen and elastic fibers arranged randomly, therefore the tissue is unformed (see color incl., Fig. II) .

Rice. 31.

I- macrophage (histiocyte); 2 - amorphous intercellular substance; 3 - plasmaitis; 4 - fat cells; 5 - blood cells in a blood vessel; 6 - smooth muscle cell 7 - adventitial cell; 8 - endothelial cell; 9 - fibroblast; 10 - mast cells (labrocytes); 11 - elastic fibers; 12 - collagen fibers

The prevalence, diversity and abundance cellular elements and intercellular substance of loose fibrous irregular connective tissue provide the following functions:

trophic - metabolic processes, regulation of cell nutrition;

protective - participation in immune reactions;

plastic - recovery processes in tissue damage;

supporting - the formation of the stroma of organs, the binding of tissues of organs to each other.

Cells of loose fibrous unformed connective tissue together represent a single diffusely dispersed apparatus, which is inextricably linked with blood cells and the lymphoid system of the body.

Loose fibrous unformed connective tissue contains a variety of highly specialized cells: adventitial, fibroblasts, macrophages, mast, plasma, fat, pigment.

Adventitial cells (from lat. adventicus - alien, wandering) are the least differentiated, in many ways resemble mesenchymal cells, have an elongated stellate shape, often with long processes. These cells are located along the outer surface of the capillaries. Since adventitial cells are cambial, they actively divide by mitosis and differentiate into fibroblasts, myofibroblasts, and lipocytes.

Fibroblasts (from lat. fibrin - protein, blastos - sprout) - protein producers, are permanent and most numerous cells. During embryonic development, fibroblasts are formed directly from mesenchymal cells, in the postembryonic period. Fibroblasts are formed from adventitial cells during regeneration.

Fibroblasts have a spindle shape, a large nucleus, which is weakly stained, 1–2 nucleoli are clearly visible. The cytoplasm of the periphery of the cell is very light, so the contours of the cells are indistinct and merge with the ground substance. Around the nucleus, the cytoplasm, on the contrary, is stained intensely, due to the large amount of granular endoplasmic reticulum.

Fibroblasts are mobile cells. Their cytoplasm contains microfilaments containing actin. They contract and move. The motor activity of fibroblasts is enhanced by the formation of a capsule from the connective tissue during wounds.

In adult animals, fibroblasts have a small amount of cytoplasm; such highly differentiated cells are called fibrocytes.

Macrophages (histiocytes) are cells that have the ability to phagocytosis and the accumulation of suspended colloidal substances in the cytoplasm. Macrophages are involved in general and local protective reactions of immunity (from Latin immunitas - liberation from something).

Under culture conditions, macrophages are firmly attached to the glass surface and acquire a flattened shape.

The nucleus of macrophages has clearly defined contours, contains clumps of chromatin, which stains well with basic dyes. The cytoplasm contains many vacuoles, which indicates an active participation in metabolism. The contours of the cytoplasm are clear, the processes are in the form of pseudopodia, so the cell looks like an amoeba.

The founder of the theory of macrophages is I. I. Mechnikov, who combined these cells into single system- macrophage. The pathologist Aschoff later proposed calling it the reticuloendothelial system.

Mobile, actively phagocytic free macrophages are formed from various sources: adventitial cells, monocytes, lymphocytes, and hematopoietic stem cells. Circulating blood monocytes represent a mobile population of relatively immature macrophages on their way from the bone marrow to organs and tissues.

According to the classification of the World Health Organization (1972), macrophages are united in the System of mononuclear phagocytes - SMF.

Macrophages are involved in many immune reactions: in the recognition, processing and presentation of antigen to lymphocytes, in intercellular interaction with lymphocytes. Possessing the ability to directed movement - chemotaxis, macrophages migrate to the focus of inflammation, where they become dominant cells in chronic inflammation. At the same time, they not only cleanse the focus of foreign particles and destroyed cells, but also stimulate the subsequent functional activity of fibroblasts.

In inflammation, macrophages enter a state of irritation, increase in size, move around and turn into structures called polyblasts.

With electron microscopy, long lamellar processes are visible on the surface of macrophages, with the help of which they capture foreign particles during phagocytosis. The processes, like amoeba pseudopodia, surround the foreign particle and merge at the top of the cell. The captured particle is inside the cytoplasm, surrounded by lysosomes and gradually digested.

Depending on the location (liver, lungs, abdomen etc.) macrophages acquire some specific features structures and properties. However, all macrophages share some common ultrastructural and cytochemical features. Due to the presence of contractile threads - filaments providing the mobility of the plasmalemma, the cells of this system are capable of forming various devices that facilitate the capture of particles. One of the main ultrastructural features of macrophages is the presence of numerous lysosomes in the cytoplasm, which break down and process the captured material.

Macrophages are involved not only in phagocytosis, but also present an antigen to launch a chain of immune reactions leading to the formation of immunity. The main functions by which macrophages participate in immune responses can be divided into four types: chemotaxis; phagocytosis; secretion of biologically active compounds; processing of the antigen (processing) and presentation of the antigen to immunocompetent cells that form an immune response.

In the presence of toxic and persistent irritants (some microorganisms, chemicals, poorly soluble substances) in the focus, a granuloma is formed with the participation of macrophages, in which giant multinucleated cells can form by cell fusion.

When foreign particles penetrate, many macrophages tightly adjoin each other, connect with processes, form interdigitations (from Latin inter - between, digitatio - finger-shaped formations). This is clearly seen in tissue culture: the formation of giant multinucleated cells is preceded by the formation of interdigitations. Sometimes a giant multinucleated cell is formed by repeated division of the nucleus of one macrophage by amitosis.

Mast cells (tissue basophils, labrocytes) are found in all mammals, but the number in animals different types and in connective tissue various bodies unequal. In some animals, for example, in guinea pigs, there are many tissue basophils, but few blood basophils: an inversely proportional relationship between these cells indicates a similar biological significance.

A significant amount of tissue basophils is found in loose connective tissue near the epidermis, the epithelium of the digestive tract, respiratory tract, and uterus. Often mast cells are found in the loose connective tissue between the lobules of the liver, in the kidneys, endocrine organs, mammary gland and other organs.

In shape, tissue basophils are often oval or spherical, ranging in size from 10 to 25 microns. The nucleus is located centrally and always contains many lumps of condensed chromatin. Electron microscopic studies in the cytoplasm reveal mitochondria, ribosomes; the endoplasmic reticulum and the Golgi complex are poorly developed.

The most characteristic structural feature of tissue basophils is the presence of numerous large (0.3 ... 1 μm) granules that evenly fill most of the cytoplasm volume. The granules are surrounded by a membrane and have different electron densities.

Located near small blood vessels, tissue basophils are among the first to react to the penetration of antigens. The characteristic metachromatic staining of tissue basophil granules is due to the presence of heparin and histamine. Degranulation of tissue basophils caused by various factors, leads to the release of heparin - a substance that prevents blood clotting. On the contrary, without destroying the integrity of the granules, the secretion of histamine occurs, which increases the permeability of capillaries, stimulates the migration of eosinophils, and the activation of macrophages.

In addition, the granules of tissue basophils contain the most important biological amines - serotonin, dopamine, which have a variety of pharmachologic effect. Tissue basophils are involved in the development of allergic and anaphylactic reactions.

On cytoplasmic membrane tissue basophils, as well as blood basophils, contain a significant amount of class E immunoglobulins (IgE). The binding of antigens and the formation of an antigen-antibody complex is accompanied by degranulation and the release of vascular-active substances from tissue basophils, which cause the appearance of local and general reactions.

Plasma cells (plasmocytes) synthesize and secrete the bulk of immunoglobulins - antibodies - proteins that are formed in response to the introduction of an antigen.

Plasma cells are usually found in their own layer of the intestinal mucosa, omentum, in the connective tissue between the lobules of the salivary, mammary glands, in the lymph nodes, and bone marrow.

Cells may be round or oval; on inside of a clearly defined nuclear envelope, clumps of chromatin are arranged radially. The cytoplasm, due to the presence of a large amount of RNA, is sharply basophilic, with the exception of only a small rim of the cytoplasm near the nucleus - the perinuclear zone. There are numerous small vacuoles along the periphery of the cytoplasm.

By origin, plasma cells are the final stages of development of B-lymphocytes, which are activated in the areas of their location, intensively multiply and transform into plasma cells.

The formation of a plasma cell from an activated B-lymphocyte with the participation of T-helpers and macrophages goes through the following stages: B-lymphocyte -» plasmablast -> proplasmocyte -> plasma cell. The transformation of these cell forms occurs within 24 hours.

plasmablast- a large cell with a large nucleus, actively dividing by mitosis. Proplasmocyte much less, it is characterized by a pronounced basophilia of the cytoplasm, in which many expanded cisterns of the granular endoplasmic reticulum appear.

The plasma cell (mature plasma cell) contains a small, eccentrically located nucleus in which clumps of chromatin are distributed like the spokes of a wheel. The protein-synthesizing mechanism is programmed for the synthesis of antibodies of a certain variety. Each plasma cell of a certain clone is capable of synthesizing several thousand immunoglobulin molecules in 1 hour.

At the final stage of development, plasma cells contain a powerful protein-synthesizing apparatus, with the help of which they synthesize immunoglobulins - antibodies. The synthesized molecules enter the lumen of the cisterns, then into the Golgi complex, from there, after the addition of the carbohydrate component, they are released from the cell. Antibodies are released when the cell is destroyed.

In the cytoplasm of plasma cells, acidophilic inclusions are formed in the form of homogeneous structures that are intensely stained with eosin in pink color. In this case, the basophilia of the cytoplasm disappears, the nucleus is fragmented; gradually rounding, the acidophilic body of Roussel is formed from the acidophilic structures, located in the main substance of the loose fibrous unformed connective tissue. Roussel's body consists of globulins and a complex of globulins with carbohydrates.

Fat cells (lipocytes) are located mainly near blood vessels, and can also form deposits of adipose tissue (textus adiposus). In embryogenesis, fat cells are formed from mesenchymal cells. Precursors for the formation of new fat cells in the postembryonic period are adventitial cells that accompany the blood capillaries.

Fat cells synthesize and accumulate storage lipids in the cytoplasm, mainly triglycerides.

Slices of various sizes are formed from fat cells. Between the lobules are layers of loose connective tissue, in which small blood vessels and nerve fibers pass. Between the fat cells inside the lobules are individual connective tissue cells (fibrocytes, tissue basophils), a network of thin argyrophilic fibers and blood capillaries.

Fatty substances are detected using special dyes (Sudan III, Sudan IV, osmium tetroxide). Lipocytes have a cricoid shape, most of the cell volume is occupied by one large drop of fat, the oval nucleus and cytoplasm are located on the periphery of the cell (see tsv.vkp., Fig. III).

In many parts of the animal body, significant accumulations of fat cells are formed, called adipose tissue. In connection with the peculiarities of the natural coloration, structure and function, as well as the location, two types of fat cells are distinguished in mammals and, accordingly, two types of adipose tissue: white and brown.

White adipose tissue in the body of animals of different species and breeds is distributed unevenly. It is contained in a significant amount in the so-called fat depots: subcutaneous adipose tissue, especially developed in pigs, adipose tissue around the kidneys in the mesentery (perirenal fiber), in some breeds of sheep at the root of the tail (fat tail). In cattle of meat and meat and dairy breeds, groups of fat cells are located in layers of loose fibrous unformed connective tissue of skeletal muscles. The meat obtained from such animals has the best taste and is called "marble".

The structural unit of white adipose tissue is spherical fat cells up to 120 microns in diameter. With the development of cells, fatty inclusions in the cytoplasm first appear in the form of small scattered drops, later merging into one large drop.

The total amount of white adipose tissue in the body of animals of various species, breeds, sex, age, fatness ranges from 1 to 30% of live body weight. Spare fats are the most high-calorie substances; when they are oxidized in the body, a large amount of energy is released (1 g of fat = 39 kJ).

Subcutaneous adipose tissue is of great importance for protecting the body from mechanical damage, protects against heat loss. Adipose tissue along the neurovascular bundles provides relative isolation, protection, and limitation of mobility. Accumulations of fat cells combined with bundles of collagen fibers in the skin of the soles and paws create cushioning when moving. Adipose tissue serves as a water depot. The formation of water is an important feature of the metabolism of fats in animals living in arid regions (camels).

During starvation, the body primarily uses spare fats from fat depot cells, in which fatty inclusions decrease and disappear. Adipose tissue of the eye orbit, epicardium, paws is preserved even with severe exhaustion.

The color of adipose tissue depends on the type, breed and type of feeding of animals. In most animals, with the exception of pigs and goats, the fat contains the pigment carotene, which gives the yellow color to adipose tissue. In cattle, the adipose tissue of the pericardium contains many collagen fibers. Renal fat is the fatty tissue that surrounds the ureters.

In the back area, adipose tissue of pigs contains muscle tissue, as well as often hair follicles (bristle) and hair bags. In the area of ​​the peritoneum there is an accumulation of adipose tissue - the so-called mesenteric, or mesenteric, fat, which contains a very large number of lymph nodes that accelerate oxidative processes and spoilage of fat. Blood vessels are often found in mesenteric fat, for example pigs have more arteries and cattle have more veins.

Internal fat is a fatty tissue located under the peritoneum. It contains a large number of fibers located in oblique and perpendicular directions. Sometimes pigment grains are found in the adipose tissue of pigs, in such cases brown or black spots are detected.

brown adipose tissue it is present in significant quantities in rodents and hibernating animals, as well as in newborn animals of other species. This tissue is located mainly under the skin between the shoulder blades, in the cervical region, in the mediastinum and along the aorta. Brown adipose tissue consists of relatively small cells that are very tightly adjacent to each other, resembling glandular tissue in appearance. Numerous nerve fibers approach the cells, braided with a dense network of blood capillaries.

Brown adipose tissue cells are characterized by centrally located nuclei and the presence of small fat droplets in the cytoplasm that do not merge into a large drop. In the cytoplasm between the fat drops are glycogen granules and numerous mitochondria, stained proteins of the transport electron system -? cytochromes that give brown color to this tissue.

In the cells of brown adipose tissue, oxidative processes intensively occur with the release of a significant amount of energy. However, most of the generated energy is spent not on the synthesis of ATP molecules, but on heat generation. This property of brown tissue lipocytes is important for temperature regulation in newborn animals and for warming animals after waking up from hibernation.

Pigment cells (pigmentocytes), as a rule, have processes, in the cytoplasm there are a lot of dark brown or black pigment grains from the melanin group. The connective tissue of the skin of lower vertebrates: reptiles, amphibians, fish contains a significant amount of pigment cells - chromatophores, which determine one or another color of the outer cover and perform a protective function. In mammals, pigment cells are concentrated mainly in the tissues of the eyeball - the sclera, choroid and iris, as well as in the ciliary body.

It is represented by two components: the main (amorphous) substance - a structureless matrix with a gelatinous consistency; collagen and elastic fibers, located relatively loose and randomly.

The composition of the main substance includes high-molecular acid mucopolysaccharides: hyaluronic acid, chondroitinsulfuric acid, heparin. These chemical components are released from both cells and blood plasma. The amount of these substances in different parts of the connective tissue is not the same. around capillaries and small vessels, in areas containing fatty layers, or in tissue rich in reticular cells, the main substance is small, and on the borders with the epithelium, on the contrary, there is a lot. In these areas, the ground substance, together with the reticular fibers, forms the boundary basement membranes, which are often clearly visible.

The state of the basic substance can change, depending on this, the type of basement membrane also changes. If the main substance is liquid, then the boundary layer has a fibrous structure; if dense, then the contours of the fibers do not protrude and the membrane looks homogeneous.

The main substance fills the gaps between cells, fibers, vessels of the microvasculature. Structureless ground substance on early stages tissue development quantitatively prevails over the fibers.

The main substance is a gel-like mass, capable of changing its consistency over a wide range, which significantly affects its functional properties. In terms of chemical composition, it is a very labile complex consisting of glycosaminoglycans, proteoglycans, glycoproteins, water, and inorganic salts. The most important chemical high-polymer substance in this complex is a non-sulfated variety of glycosaminoglycans - hyaluronic acid. Unbranched chains of molecules hyaluronic acid, form numerous bends and form a kind of molecular network, in the cells and channels of which tissue fluid is located and circulates. Due to the presence of such molecular spaces in the main substance, there are conditions for the movement of various substances from the blood capillaries and products of cellular metabolism in the opposite direction - to the blood and lymphatic capillaries for subsequent excretion from the body.

Collagen fibers have the form of ribbon-like strands oriented in different directions. The fibers do not branch, they are of low stretch, have high tensile strength (withstand up to 6 kg per 1 mm 2 of cross section), and are able to combine into bundles. With prolonged cooking, collagen fibers form glue (from English, kolla - glue).

The strength of collagen fibers is due to the fine structural organization. Each fiber consists of fibrils up to 100 nm in diameter, arranged parallel to each other and immersed in an interfibrillar substance containing proteins, glycosaminoglycans and proteoglycans. Collagen fibers are not the same in terms of their maturity. As part of the newly formed inflammatory response fibers there is a significant amount of a cementing polysaccharide substance that is able to restore silver when treated with silver salts. Therefore, young collagen fibers are often called argyrophilic, in mature fibers the amount of this substance decreases.

Electron microscopy along the length of the fibril shows a characteristic transverse striation - the alternation of dark and light bands with a certain repetition period, namely, one dark and one light segment together make up one period 64 ... 70 nm long. This striation is most clearly seen on negatively stained preparations of collagen fibrils. On positively stained preparations of collagen fibrils, in addition to the main dark-light periodicity, a complex pattern of thinner electron-dense stripes separated by narrow gaps 3–4 nm wide is revealed.

The fibril consists of thinner tropocollagen protein protofibrils. Protofibrils are 280...300 nm long and 1.5 nm wide. Fibril formation is the result of a characteristic grouping of monomers in the longitudinal and transverse directions.

The tropocollagen molecule has an asymmetric structure, where similar amino acid sequences are opposite each other, narrow secondary dark-colored bands appear. Each tropocollagen molecule is a helix of three polypeptide chains held together by hydrogen bonds. The unique structure of tropocollagen is due to high content glycine, oxylysine and hydroxyproline.

Elastic fibers have different thicknesses (from 0.2 microns in loose connective tissue to 15 microns in ligaments). On film preparations of connective tissue stained with hematoxylin and eosin, the fibers look like pronounced thin branching homogeneous threads that form a network. For the selective detection of elastic networks, special dyes are used: orcein, resorcinol-fuchsin. Unlike collagen fibers, elastic fibers do not combine into bundles, have low strength, high resistance to acids and alkalis, heat, and the hydrolyzing action of enzymes (with the exception of elastase).

Electron microscopy in the structure of the elastic fiber distinguishes between a more transparent amorphous central part, consisting of elastin protein, and a peripheral part, which contains a large number of electron-dense microfibrils of a glycoprotein nature, having the shape of tubules with a diameter of about 10 nm.

The formation of elastic fibers in the connective tissue is due to the synthetic and secretory functions of fibroblasts. It is believed that at first, in the immediate vicinity of fibroblasts, a framework of microfibrils is formed, and then the formation of an amorphous part from the precursor of elastin, proelastin, is enhanced. Under the influence of enzymes, proelastin molecules shorten and turn into small, almost spherical tropoelastin molecules. During the formation of elastin, tropoelastin molecules are interconnected with the help of desmosine and isodesmosine, which are absent in other proteins. In addition, elastin does not contain oxylysin and polar side chains, which leads to high stability of elastic fibers.

Epithelial (integumentary) tissue, or epithelium, is a boundary layer of cells that lines the integument of the body, the mucous membranes of all internal organs and cavities, and also forms the basis of many glands. The epithelium separates the organism (internal environment) from the external environment, but at the same time serves as an intermediary in the interaction of the organism with the environment. Epithelial cells are tightly connected to each other and form a mechanical barrier that prevents the penetration of microorganisms and foreign substances into the body. Cells epithelial tissue live for a short time and are quickly replaced by new ones (this process is called regeneration).
Epithelial tissue is also involved in many other functions: secretion (external and internal secretion), absorption (intestinal epithelium), gas exchange (lung epithelium).
The main feature of the epithelium is that it consists of a continuous layer of densely packed cells. The epithelium can be in the form of a layer of cells lining all surfaces of the body, and in the form of large clusters of cells - glands: liver, pancreas, thyroid, salivary glands, etc. In the first case, it lies on the basement membrane, which separates the epithelium from the underlying connective tissue . However, there are exceptions: epithelial cells in the lymphatic tissue alternate with elements of connective tissue, such an epithelium is called atypical.
epithelial cells, located in a layer, can lie in many layers (stratified epithelium) or in one layer ( single layer epithelium) . According to the height of the cells, the epithelium is divided into flat, cubic, prismatic, cylindrical.

Connective tissue.
Consists of cells, intercellular substance and connective tissue fibers. It consists of bones, cartilage, tendons, ligaments, blood, fat, it is in all organs (loose connective tissue) in the form of the so-called stroma (skeleton) of organs.
In contrast to epithelial tissue, in all types of connective tissue (except adipose tissue), the intercellular substance predominates over the cells in volume, i.e., the intercellular substance is very well expressed. The chemical composition and physical properties of the intercellular substance are very diverse in different types of connective tissue. For example, blood - the cells in it “float” and move freely, since the intercellular substance is well developed.
In general, connective tissue makes up what is called the internal environment of the body. It is very diverse and is represented by various types - from dense and loose forms to blood and lymph, the cells of which are in the liquid. The fundamental differences between the types of connective tissue are determined by the ratio of cellular components and the nature of the intercellular substance.
In dense fibrous connective tissue (tendons of muscles, ligaments of joints), fibrous structures predominate, it experiences significant mechanical loads.

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

The material is taken from the site www.hystology.ru

In the body, loose connective tissue is the most common. This is evidenced by the fact that it accompanies all the blood and lymphatic vessels in greater or lesser quantities, forms numerous layers inside the organs, and is part of the skin and mucous membranes of the internal cavity organs.

Regardless of localization, loose connective tissue consists of a variety of cells and intercellular substance containing the main (amorphous) substance and a system of collagen and elastic fibers. In accordance with the local conditions of development and functioning, the quantitative ratio between these three structural elements in different areas is not the same, which determines the organ features of loose connective tissue.

Among the various highly specialized cells in the composition of this tissue, more sedentary cells (fibroblasts - fibrocytes, lipocytes) are distinguished, the development of which in the process of cell renewal occurs from precursors located within the most loose connective tissue. The immediate precursors of other more mobile cells (histiocytes - macrophages, tissue basophils, plasma cells) are blood cells, active phase functioning of which is carried out as part of loose connective tissue. Together, all the cells of the loose connective tissue represent a single diffusely dispersed apparatus, located in an inseparable functional connection with cells vascular blood and lymphoid system of the body.

The ubiquity of loose connective tissue, the diversity and large number of cellular elements capable of reproduction and migration provide the main functions of this connective tissue: trophic (metabolic processes and regulation of cell nutrition), protective (cell participation in immune reactions - phagocytosis, production of immunoglobulins and others). substances) and plastic (participation in recovery processes in tissue damage).

Cells. adventitial cells- elongated stellate cells with an oval nucleus rich in heterochromatin. The cytoplasm is basophilic and contains few organelles. They are located along the outer surface of the capillary wall and are relatively poorly differentiated cellular elements capable of mitotic division and transformation into fibroblasts, myofibroblasts and lipocytes (Fig. 102).

fibroblasts(fibra - fiber, blastos - sprout, germ) - - permanent and most numerous cells of all types of connective tissue. These are the main cells that are directly involved in the formation of intercellular structures. They synthesize and secrete macromolecular substances necessary both for the construction of fibers and for the formation of an amorphous tissue component. During embryonic development, fibroblasts arise directly from mesenchymal cells. In the postembryonic period and during regeneration, the main precursors of fibroblasts are adventitial

Rice. 102. Loose connective tissue of rabbit subcutaneous tissue (according to Yasvoin):

1 - capillary endothelium; 2 - adventitial cambial cell; 3 - fibroblasts; 4 - histiocyte; 5 - fat cell.

cells. In addition, young forms of these cells retain the ability to multiply by mitotic division.

According to the degree of maturity and, consequently, according to the structural characteristics and functional activity, three types of fibroblasts are distinguished. Poorly differentiated fibroblasts have an elongated, fusiform shape with a few short processes. The oval nucleus has a well-defined nucleolus. Cytoplasm under light microscopy of preparations stained with basic dyes, basophilic. Electron microscopy in the cytoplasm reveals many free polysomes and only short narrow tubules of the granular network. Elements of the Golgi complex are located in the perinuclear zone. Mitochondria are few and have a dense matrix. It is believed that such immature cells have a low level of synthesis of specific proteins. Their function is reduced to the synthesis and secretion of glycosaminoglycans.

When viewed from above, mature fibroblasts are large (diameter up to 50 microns) process cells, contain light oval nuclei with 1–2 large nucleoli and a significant amount of weakly basophilic cytoplasm. The peripheral zone of the cell stains especially weakly, as a result of which its contours are almost invisible. In cross section, a flattened cell body, spindle-shaped, since its central part, containing the nucleus, is significantly thickened. Electron microscopically, the cytoplasm of a mature fibroblast is characterized by a developed granular endoplasmic reticulum, consisting of elongated and expanded cisterns, to the membranes of which large polysomes are attached. The elements (cistern, micro- and macrobubbles) of the Golgi complex are also well expressed, distributed throughout the cytoplasm. Mitochondria of various shapes and sizes are found (Fig. 103).

Functionally, mature fibroblasts are cells with complex synthetic and secretory activity. They simultaneously synthesize and excrete several types of specific proteins (procollagen, proelastin, enzymatic proteins) and various glycosaminoglycans. The ability to synthesize protein of collagen fibers is most clearly expressed. On

Rice. 103. Electronic microgram of a fibroblast site (according to Radostina):

1 - core; 2 - granular endoplasmic reticulum; 3 - mitochondria.

α-chains of the protein are synthesized in the polysomes of the granular network, and in the cavity of the reticulum components they are bound into a triple helix of the procollagen molecule. The latter, with the help of microbubbles, are transferred to the tanks of the Golgi complex and then, as part of secretory granules, are released from the cell. On the surface of the fibroblast, the terminal non-spiralized peptide sections are separated from the procollagen molecules, they turn into tropocollagen molecules, which, polymerizing, form collagen microfibrils and fibrils (Fig. 104). Glycosaminoglycans are formed in the Golgi complex. Accumulating between cells, they create conditions for the concentration and polymerization of tropocollagen molecules, and are also included in fibrils as a cementing component.

Fibroblasts are mobile. Actin-containing microfilaments are located in the peripheral zone of the cytoplasm, with the reduction of which the formation of protrusions and cell movement are ensured. The motor activity of fibroblasts is enhanced in the regenerative phase of the inflammatory reaction during the formation of a connective tissue capsule.

Fibroblasts with a large number of contractile filaments appear in the granulation tissue - myofibroblasts, which contribute to wound closure.

Fiber formation in the connective tissue leads to the fact that part of the fibroblasts is enclosed between closely spaced fibers. Such cells are called fibrocytes. They lose the ability to divide, take a strongly elongated shape, their cytoplasmic volume decreases and synthetic activity is significantly reduced.

Histiocytes (macrophages) in the composition of the widespread connective tissue, they are the most numerous group of free, capable of migrating cells belonging to the system of mononuclear phagocytes (MPS). in connective tissue layers various organs their number is not the same and, as a rule, increases significantly with inflammation.

Pic. 104. Scheme of collagen fibril formation:

A - amino acids (proline, lysine, etc.) absorbed by the fibroblast are included in the protein synthesized on the ribosomes of the endoplasmic reticulum. The protein enters the Golgi complex, and then is excreted from the cell in the form of tropocollagen molecules, from which collagen fibrils are formed outside the cell; 1 - fibroblast; 2 3 - Golgi complex; 4 - mitochondria; 5 - tropocollagen molecules; 6 - collagen fibril (according to Welsch and Storch).

With light microscopy of stained film preparations, histiocytes have a variety of shapes and sizes (10–50 μm), are located singly or in groups. In comparison with fibroblasts, they are distinguished by more defined, but uneven boundaries and intensely stained cytoplasm, in which there are vacuoles and inclusions. The nucleus is small, oval, slightly concave, contains many clumps of heterochromatin, and therefore it is darker (Fig. 105).

Microvilli, pseudopodia, intussusceptions are noted on the plasmalemma by electron microscopic examination. The cytoplasm contains a significant amount of lysosomes, phagosomes, granules and lipid inclusions. The granular network is almost not developed. Mitochondria and the Golgi complex are more developed in activated macrophages. Cytochemical methods in the cytoplasm of histiocytes reveal a variety of enzymes (acid hydrolases, isoenzymes of acid phosphatase, esterases, etc.), with the help of which digestion of absorbed substances occurs.

The concept of the system of mononuclear phagocytes (macrophage system). This system includes

Rice. 105. Loose connective tissue in a film: preparation:

1 - fibroblasts; 2 - histiocytes; 3 - tissue basophil; 4 - collagen fibers; 5 - elastic fibres.

cells located in many tissues and organs with intensive endocytosis (phagocytosis and pinocytosis) of macromolecular substances of exogenous and endogenous nature, particles, microorganisms, viruses, cells, cellular decay products, etc. All macrophages, regardless of localization, originate from the hematopoietic stem cell red bone marrow, and their immediate precursors are monocytes peripheral blood. Monocytes that have left the vessel and entered the appropriate microenvironment adapt to the new environment and turn into organ- and tissue-specific macrophages (Fig. 106).

Rice. 106. Varieties of cells belonging to the system of mononuclear phagocytes - SMF (according to Van Furth, 1980).

Thus, circulating blood monocytes represent a mobile population of relatively immature cells of future mature macrophages on their way from the bone marrow to organs and tissues. Under culture conditions, macrophages are able to firmly attach to the glass surface and acquire a flattened shape.

Depending on the localization (liver, lungs, abdominal cavity, etc.), macrophages acquire some specific structural features and properties that make it possible to distinguish them from each other, but they all share some common structural, ultrastructural, and cytochemical features. Due to the presence of contractile microfilaments that ensure the mobility of the plasmolemma, the cells of this system are capable of forming various devices (villi, pseudopodia, protrusions) that facilitate the capture of particles. One of the main ultrastructural features of macrophages is the presence of numerous lysosomes and phagosomes in their cytoplasm. With the participation of lysosomal enzymes (phosphatase, esterase, etc.), the phagocytosed material is split and processed.

Macrophages are multifunctional cells. The founder of the theory of cytophysiology of cells of the macrophage system is II Mechnikov. Until now, many of the provisions formulated by him on the mechanisms of phagocytosis and the biological significance of this phenomenon are relevant. The macrophage system, due to the ability of its cells to absorb and digest various products exo- and endogenous origin represents one of the most important protective systems involved in maintaining stability internal environment organism.

Macrophages play an important role in the implementation of a protective inflammatory response. Possessing the ability to directed movement, determined by chemotactic factors (substances secreted by bacteria and viruses, antigen-antibody immune complexes, tissue decay products, lymphocyte mediators, etc.), macrophages migrate to the focus of inflammation and become dominant cells. chronic inflammation. At the same time, they not only cleanse the focus of foreign particles and destroyed cells, but also subsequently stimulate the functional activity of fibroblasts. If there are toxic and persistent irritants in the focus (some microorganisms, chemicals, poorly soluble materials), a granuloma is formed with the participation of macrophages, in which giant multinucleated cells can form by cell fusion.

Macrophages are essential in many immunological reactions: in antigen recognition, its processing and presentation to lymphocytes, in intercellular interaction with T- and B-lymphocytes, and in the performance of effector functions.

There are two types of specific receptors on the surface of the macrophage plasmolemma: receptors for the F c part of immunoglobulins and receptors for complement, especially for its C 3 component. Therefore, in the phase of recognition and absorption, opsonization of antigens is of great importance, that is, the preliminary attachment of immunoglobulins or an immunoglobulin-complement complex to them. Subsequent attachment of such sensitized antigens ( immune complexes) to the corresponding macrophage receptors causes the movement of pseudopodia and the absorption of the object of phagocytosis. There are also nonspecific receptors, thanks to which the cell can phagocytize denatured proteins or indifferent particles (polystyrene, dust, etc.). With the help of pinocytosis, macrophages are able to recognize and absorb soluble antigens (globular proteins, etc.).

Most of the absorbed antigenic substances in many phagocytes are completely destroyed. This function of eliminating excess antigens that have penetrated into the internal environment of the body is characteristic of macrophages of the liver, sinuses of the spleen, and the medulla of the lymph nodes. Special varieties of specialized macrophages are the process "dendritic" cells of the B-zones and the "interdigitating" cells of the T-zones of the lymph nodes and spleen. On the surface of their numerous processes, the original or partially processed immunogenic antigens are concentrated and stored. In these zones, macrophages enter into cooperative interaction with B- and T-lymphocytes for the development of both humoral and cellular immunity.

Cells of the mononuclear phagocyte system are active participants in myeloid and lymphoid hematopoiesis. Macrophages in the red bone marrow are a kind of centers around which the precursors of developing erythrocytes are grouped. These macrophages are involved in the transfer of accumulated iron to the cells of the erythroid series, absorb the nuclei of normocytes and phagocytize damaged and old erythrocytes. Other macrophages in the bone marrow phagocytize portions of megakaryocytes after platelet separation from them. With the help of macrophages of the spleen, intensive erythrophagocytosis and absorption of aging platelets occur, and macrophages of all lymphoid organs - phagocytosis of plasmocytes and lymphocytes.

Tissue basophils(labrocytes, mast cells) are found in most vertebrates and in all mammals, however, their number in animals of different species and in the connective tissue of various organs is not the same. In some animals, an inversely proportional relationship is noted between the number of tissue basophils and blood basophils, which indicates a similar biological significance of these cell types in the system of tissues of the internal environment (for example, guinea pigs have many tissue basophils, but few blood basophils). A significant amount of tissue basophils is found in the subepithelial connective tissue of the skin, digestive tract, respiratory tract, and uterus. They are found in the connective tissue layers along the small blood vessels in the liver, kidneys, endocrine organs, mammary gland and other organs.

In shape, tissue basophils are often oval or spherical, ranging in size from 10 to 25 microns. The nucleus is located centrally, it has many lumps of condensed chromatin. The most characteristic structural feature of tissue basophils is the presence of numerous large (0.3–1 µm) specific granules that evenly fill most of the cytoplasm and stain metachromatically. Electron-microscopically, a few mitochondria, polysomes and ribosomes are found in the cytoplasm. The endoplasmic reticulum and the Golgi complex are poorly developed. There are finger-like protrusions on the plasmolemma. Specific granules are surrounded by a membrane and have unequal electron density; some granules contain even more electron-dense grains or plates.

The characteristic metachromatic staining of the granules is due to the presence of sulfated glycosaminoglycan - heparin. In addition, the granules of tissue basophils contain the most important biological amines - histamine, serotonin, dopamine, which have a variety of pharmacological effects. Cytochemical methods in the cytoplasm revealed various enzymes - acidic and alkaline phosphatase, lipase. Histamine is formed from the amino acid histidine by histidine decarboxylase, which is a marker enzyme for mast cells.

Located near small blood vessels, tissue basophils are one of the first cells to respond to the penetration of antigens from the blood. On their plasmolemma, as well as in blood basophils, there is a significant amount of class E immunoglobulins (IgE). The binding of antigens and the formation of an antigen-antibody complex is accompanied by degranulation and the release of vascular active substances from tissue basophils, which cause the appearance of local and general reactions. Histamine increases the permeability of the capillary wall and the main substance of the connective tissue, stimulates the migration of eosinophils, activates macrophages, etc. Heparin prevents blood clotting. The participation of tissue basophils in the development of allergic and anaphylactic reactions has been established.

Degranulation of tissue basophils can be caused by various physical factors- trauma, sudden temperature effects, etc.

Plasma cells(plasma cells) functionally - effector cells immunological reactions humoral type, that is, reactions accompanied by an increase in circulating antibodies in the blood, with the help of which the antigens that caused their formation are neutralized. These are highly specialized cells of the body that synthesize and secrete the bulk of various antibodies (immunoglobulins).

By origin, plasma cells represent the final stages of development of antigen-stimulated B-lymphocytes. which, at their locations with the participation of T-helper cells in macrophages, are activated, multiply intensively and turn into mature plasma cells. IN most plasma cells are found in the spleen, lymph nodes, as part of the connective tissue of the mucous membranes of the digestive canal and respiratory tract, in the interstitial connective tissue of various glands of the body.

The development of plasma cells from stimulated B-lymphocytes occurs through the stages of plasmablast (immunoblast), proplasmocyte and plasma cell (Fig. 107).

Rice. 107. Scheme of development of plasmocytes (according to Weiss):

1 - precursor of the plasma cell (half-stem cell); 2 - plasmablast; 3 - young plasmacyte; 4 - plasmocyte with expanded cisterns of the endoplasmic reticulum; 5 - Mature plasmacyte.

Plasmablast is a large cell (up to 30 microns in diameter) with a light centrally located nucleus. In the latter, small granules of chromatin located along the periphery and 1–2 pronounced nucleoli are found. Electron microscopically in the cytoplasm reveal very rare and small tanks of the granular endoplasmic reticulum, as well as a large number of free polysomes and ribosomes. A few mitochondria have a light matrix and rare cristae. Mitoses are common among plasmablasts. The proplasmocyte is characterized by a somewhat smaller size, a pronounced basophilia of the cytoplasm, and an uneven cell surface due to numerous protrusions of the plasmolemma. The cytoplasm contains a large number of dilated cisterns and sacs of the granular endoplasmic reticulum. Between the elements of the granular network are small mitochondria. It is believed that these cells can produce and secrete immunoglobulins. Mature plasmocytes are relatively small (8 - 10 microns) oval-shaped cells with pronounced boundaries. In the strongly basophilic (pyroninophilic) cytoplasm, a light perinuclear zone is found. The nucleus is rounded, located eccentrically and contains large clumps of heterochromatin distributed in the form of wheel spokes. Especially characteristic in the structure of these cells during electron microscopic examination is the presence in the cytoplasm of numerous, close to each other, long cisterns with a very narrow cavity and contiguous membranes, on outer surface containing numerous polysomes. In the perinuclear zone with a lighter cytoplasm, these cisterns are absent; centrioles and a well-developed Golgi complex are located in it (Fig. 108).

Thus, in the final stage of development, plasma cells contain a powerful protein-synthesizing apparatus, with the help of which the synthesis of immunoglobulin molecules (antibodies) is carried out. It has been established that immunoglobulin light chains are synthesized

Rice. 108. Scheme of the ultramicroscopic structure of a plasma cell (according to Bessie):

1 - granular endoplasmic reticulum; 2 - chromatin; 3 - nucleolus; 4 - nuclear membrane; 5 - the time of the nuclear membrane; 6 - free ribosomes; 7 - Golgi complex; 8 - centrioles; 9 - secretory vesicles.

on polyribosomes of the granular network separate from heavy chains. The latter are separated from polyribosomes after the formation of their complex with light chains. Since the entire protein-synthesizing mechanism is programmed for the synthesis of antibodies of only one type, each plasma cell of a certain clone is capable of synthesizing several thousand immunoglobulin molecules in one hour. The synthesized molecules enter the lumen of the cisterns, and then into the Golgi complex, from where, after the addition of the carbohydrate component, they are brought to the cell surface and released. The release of antibodies also occurs when the cell is destroyed.

The transformation of a B-lymphocyte into a plasma cell lasts about a day; the duration of the active antibody-producing activity of mature plasma cells is several days. Mature plasma cells are not capable of dividing, they age, die, and are engulfed by macrophages.

fat cells(lipocytes) and adipose tissue(textus adiposus). Fat cells are specialized in the synthesis and accumulation of storage lipids in the cytoplasm, mainly triglycerides, and their utilization in accordance with the energy and other needs of the body. Lipocytes are widely distributed in loose connective tissue and are more often located not singly, but in small groups along the course of small blood vessels. In many parts of the animal body, significant accumulations of fat cells are formed, called adipose tissue. In embryogenesis, fat cells arise from mesenchymal cells. Precursors for the formation of new fat cells in the postembryonic period are adventitial cells that accompany the blood capillaries.

In connection with the peculiarities of the natural coloration of cells, the specifics of their structure and function, as well as the location, two types of fat cells are distinguished in mammals and, accordingly, two types of adipose tissue: white and brown.

White adipose tissue in the body of animals of different species and breeds is distributed unevenly. It is found in a significant amount in fat depots: subcutaneous adipose tissue, especially developed in pigs, adipose tissue around the kidneys, in the mesentery, in some breeds of sheep at the root of the tail (fat tail). In animals of meat and meat and dairy breeds, groups of fat cells are located in the perimysium and endomysium inside the skeletal muscles. The meat obtained from such animals has the best qualities ("marbled" meat).

The structural unit of white adipose tissue is spherical large (up to 120 microns in diameter) mature fat cells with a characteristic microscopic structure(Fig. 109). Most of the cell volume is occupied by one large drop of fat. The oval nucleus and cytoplasm are located at the periphery of the cell. Such a cell, under light microscopy of a histological section stained with fat-dissolving substances, has

Rice. 109. Scheme of the structure of cells of white adipose tissue:

1 - the nucleus of the fat cell; 2 - the cavity left after the dissolution of a drop of fat; 3 - connective tissue.

ring-shaped. As a result of the dissolution of fat, a light vacuole remains in the place of the fat drop in the cell. Electron microscopy in the perinuclear zone reveals mainly elongated mitochondria, other organelles are poorly expressed. With the development of cells, fatty inclusions in the cytoplasm first appear in the form of small scattered drops, later merging into one large drop. Fatty substances in cells can be detected using special dyes (Sudan III, Sudan IV, osmium tetroxide).

Slices of various sizes and shapes are formed from fat cells in adipose tissue. Between the lobules are layers of loose connective tissue, in which small blood vessels and nerve fibers pass. Between the fat cells inside the lobules are individual connective tissue cells (fibrocytes, tissue basophils), a network of thin argyrophilic fibers and blood capillaries.

The total amount of white adipose tissue in the body of animals of various species, breeds, sex, age, fatness ranges from 1 to 30% of live weight. Spare fats in adipose tissue are the most high-calorie substances, during the oxidation of which a large amount of energy is released in the body (1 g of fat \u003d 39 kJ). Subcutaneous adipose tissue, especially in wild animals, is of great importance for protecting the body from mechanical damage, protects against heat loss. Adipose tissue along the neurovascular bundles, in the capsule and membranes of the organs provides their relative isolation, protection and limitation of mobility. Accumulations of fat cells in combination with bundles of collagen fibers surrounding them in the skin of the soles and paws create good cushioning properties. The role of adipose tissue as a depot of water is significant. The formation of water is an important feature of the metabolism of fats in animals living in arid regions (camels).

During starvation, the body primarily mobilizes spare fats from fat depot cells. They reduce and disappear fatty inclusions.

Adipose tissue of the eye orbit, epicardium, paws is preserved even with severe exhaustion.

The color of adipose tissue depends on the type, breed and type of feeding of animals. In most animals, with the exception of pigs and goats, the fat contains the pigment carotene, which gives the yellow color to adipose tissue.

Brown adipose tissue is found in significant amounts in rodents and hibernating animals, as well as in newborn animals of other species. It is located mainly under the skin between the shoulder blades, in the cervical region, in the mediastinum and along the aorta.

It consists of relatively small cells, very tightly adjacent to each other, resembling outwardly glandular tissue. Numerous fibers of the sympathetic nervous system approach the cells, they are braided with a dense network of blood capillaries. Brown adipose tissue cells, in comparison with white adipose tissue cells, are characterized by a centrally located nucleus and the presence of small fat droplets in the cytoplasm, which do not merge into a larger droplet. Numerous mitochondria and a significant amount of glycogen granules are located between the fat droplets. The colored proteins of the electron transport system, cytochromes, contained in the mitochondria, give the brown color to this tissue.

In the cells of brown adipose tissue, oxidative processes are intense, accompanied by the release of a significant amount of energy. However, most of the generated energy is spent not on the synthesis of ATP molecules, but on heat generation. This property of brown tissue lipocytes is important for temperature regulation in newborn animals and for warming animals after waking up from hibernation.

Pigment cells (pigmentocytes), as a rule, process form. The cytoplasm contains many dark brown or black pigment grains from the melanin group. A significant number of pigment cells - chromatophores in the connective tissue of the skin of lower vertebrates - reptiles, amphibians, fish, in which they determine one or another color of the outer cover and perform a protective function. In mammals, pigment cells are concentrated mainly in the connective tissue of the wall of the eyeball - the sclera, choroid and iris, as well as in the ciliary body.

intercellular substance loose connective tissue is a significant part of it. It is represented by collagen and elastic fibers, located relatively loose and randomly, and the main (amorphous) substance. In the intercellular substance, a variety of enzymatic metabolic processes are carried out, the movement of various substances and cellular elements, self-assembly and rearrangement of fibers in accordance with the direction of action mechanical factors. Sensory cells are located in the intercellular substance nerve endings, continuously sending to the central nervous system signals about his condition.

Collagen fibers- the main fibers that provide the mechanical strength of the fabric. In loose connective tissue, they look like ribbon-like strands oriented in different directions. The fibers do not branch, they are characterized by low extensibility, high tensile strength (withstand up to 6 kg per 1 mm 2 of cross section), the ability to combine into bundles. When cooked for a long time, collagen fibers form a glue (colla), hence the name of the fibers.

The strength of collagen fibers is due to their finer structural organization. Each fiber consists of fibrils up to 100 nm in diameter, arranged parallel to each other and immersed in an interfibrillar substance containing glycoproteins, glycosaminoglycans and proteoglycans. Under electron microscope a characteristic transverse banding is observed along the length of the fibril - alternation of dark and light bands with a certain repetition period, namely, a dark olive and one light segment together make up one period 64 - 70 nm long. This banding is most clearly seen on negatively stained preparations of collagen fibrils. Electron microscopy of positively stained fibrils, in addition to the main dark-light periodicity, reveals a complex pattern of thinner electron-dense stripes separated by narrow gaps 3–4 hm wide.

At present, the characteristic pattern of the structure of a collagen fibril is explained by the specificity of its macromolecular organization. The fibril consists of thinner microfibrils formed by tropocollagen protein molecules. The latter have a length of 280 - 300 nm and a width of 1.5 nm and are a kind of monomers (Fig. 110). Fibril formation is the result of a characteristic grouping of monomers in the longitudinal and transverse directions. The monomers are stacked in parallel rows and are held near each other by covalent cross-links, and in one row between the ends of neighboring monomers there is a gap equal to 0.4 of the period length, and in width the monomers of one row are superimposed on the monomers of the neighboring one with an offset of 1/4 of its length. This alternation of gaps and overlaps creates a banded appearance of fibrils on electron micrographs. One tropocollagen molecule crosses five light and four dark segments (Fig. 111).

It is also known that the length of the tropocollagen molecule is asymmetric, and where similar amino acid sequences are opposite each other, narrow secondary dark-colored bands appear. Each tropocollagen molecule is a helix of three polypeptide chains held together by hydrogen bonds. The unique structure of tropocollagen is due to its particularly high content of glycine (up to 30%), as well as oxylysin and hydroxyproline. Depending on the amino acid composition and the form of chains combining into a triple helix, there are four main types of collagen that have different localization in the body. Type I collagen is the most abundant and is found in

Rice. 110. Scheme of the structure of collagen fibers:

A - spiral structure collagen macromolecules (according to Rich); small light circles- glycine; large light circles- proline; hatched circles- hydroxyproline; B - diagram of the structure of collagen fibers; 1 - bundle of fibrils; 2 - fibril; 3 - protofibril; 4 is a collagen molecule.

Rice. 111. Collagen fibril:

A- electron micrograph of a negatively stained collagen fibril (magnitude 180,000); B- layout of tropocollagen molecules, explaining the occurrence of transverse striation (according to Hodja and Petrusky, 1964): 1 - dark segments correspond to the gaps between the ends of tropocollagen molecules; 2 - light segments correspond to molecular overlap zones.

connective tissue of the skin, tendons and bones. Type 11 collagen is found predominantly in hyaline and fibrous cartilage. Collagen predominates in the skin of embryos, the wall of blood vessels, and ligaments III type, and in the basal membranes - type IV collagen, the polypeptide chains of which contain a particularly large amount of oxylysin.

Collagen fibers are not the same in terms of their maturity. The composition of newly formed (with an inflammatory reaction) fibers contains a significant amount of interfibrillar cementing nolisaccharide substance, which is able to restore silver when sections are treated with silver salts. Therefore, young collagen fibers are often called argyrophilic. In mature collagen fibers, the amount of this substance decreases, and they lose argyrophilia.

elasticfibers have different thicknesses (from 0.2 microns in loose connective tissue to 15 microns in ligaments). On hematoxylin and eosin-stained film preparations of connective tissue, the fibers represent weakly expressed thin branching homogeneous threads that form a network. For the selective detection of elastic networks, special dyes are used - orcein, resorcinol - fuchsin, etc. Unlike collagen fibers, elastic fibers do not combine into bundles, they have low strength, high resistance to acids and alkalis, heat and to the hydrolyzing action of enzymes (with the exception of elastase).

Electron microscopy in the structure of the elastic fiber distinguishes between a more transparent amorphous central part, consisting of elastin protein, and a peripheral part, which contains a large number of electron-dense microfibrils of a glycoprotein nature, having the shape of tubules with a diameter of about 10 nm. The latter, together with the interfibrillar polysaccharide component, form a sheath around the homogeneous part.

The formation of elastic fibers in the connective tissue is due to the synthetic and secretory function of fibroblasts. It is believed that at first, in the immediate vicinity of fibroblasts, a framework of microfibrils is formed, and then the formation of an amorphous part from the precursor of elastin, proelastin, is enhanced. Under the influence of enzymes, proelastin molecules shorten and turn into small, almost spherical tropoelastin molecules. The latter, during the formation of elastin, are interconnected with the help of unique substances(desmosine and isodesmosine), which are absent in other proteins. In addition, elastin does not contain oxylysin and polar side chains, which leads to high stability of elastic fibers.

There are especially many elastic fibers in those connective tissue formations that are characterized by continuous stress and return at the end of the stretch to its original state (occipito-cervical ligament, abdominal yellow fascia). The high elasticity of these fibers, combined with the relative inextensibility of collagen fibers, creates a flexible and durable system in the connective tissue of the skin and in the walls of blood vessels.

Base substance. All gaps between cells, fibers and vessels of the microvasculature located in the loose connective tissue are filled with a structureless basic substance, which quantitatively prevails over the fibers in the early stages of tissue development. In different parts of the developed connective tissue, the amount of the main substance is not the same, its significant content is in the subepithelial zones of the connective tissue.

The main substance is a gel-like mass, capable of changing its consistency over a wide range, which significantly affects its functional properties. By chemical composition, it is a very labile complex consisting of glycosaminoglycans, proteoglycans, glycoproteins, water and inorganic salts. The most important chemical high-polymer substance in this complex is a non-sulfated variety of glycosaminoglycans - hyaluronic acid. Unbranched long chains hyaluronic acid molecules form numerous bends and form a kind of molecular network, in the cells and channels of which tissue fluid is located and circulates. Due to the presence of such molecular spaces in the main substance, there are conditions for the movement of various substances from the blood capillaries to the cells of the connective and other tissues and products of cellular metabolism in the opposite direction - to the blood and lymphatic capillaries for their subsequent release from the body.

The formation of the basic substance is mainly associated with two sources: the synthesis and release of substances from cells (mainly from fibroblasts) and their entry from the blood. Substances entering the intercellular spaces undergo polymerization. The polymerized or depolymerized state of the basic substance is a factor affecting not only the binding of water and the transport of soluble components (ions, glucose, amino acids, etc.) contained in the tissue fluid, but also cell migration. Many hormones (corticosteroids, etc.) have a regulatory effect on the state of the basic substance, the action of which is directed to the cells, and through them to the components of the intercellular substance. Under the influence of biogenic amines and the enzyme hyaluronidase, the permeability of the main substance increases. Some microorganisms, synthesizing and releasing hyaluronidase, cause depolymerization of hyaluronic acid of the main substance and in this way accelerate their distribution in the animal body.

For staining the basic substance (hyaluronic acid), basic dyes are used that have a particularly high affinity for acidic (anionic) sites - for example, alcian blue or cationic metachromatic dyes (toluidine blue).