Loose connective. Loose fibrous connective tissue

Loose unformed fibrous connective tissue (LOFCT)

Loose, unformed fibrous connective tissue - “fiber”, surrounds and accompanies 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 membranes of hollow organs.

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

The intercellular substance consists of a ground substance (homogeneous amorphous mass - colloidal 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 great diversity - fibroblastic differentiate cells (stem and semi-stem cells, unspecialized fibroblasts, differentiated fibroblasts, fibrocytes, myofibroblasts, fibroclasts), macrophages, mast cells, plasmacytes, adventitial cells, pericytes, lipocytes, melanocytes, all leukocytes, reticular cell.

Stem and semi-stem cells, unspecialized fibroblasts, differentiated fibroblasts, fibrocytes 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 branched cell with basophilic cytoplasm (due to the large number of free ribosomes), organelles are poorly 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 branched cells with slightly basophilic cytoplasm.

Fibroblastic 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, and therefore is capable of contracting. They take part in wound healing, bringing the edges of the wound closer together during contraction.

The following cells are loose, unformed fibrous connective tissue by quantity - tissue macrophages (synonym: histiocytes), make up 15-20% of cells. Large cells with a polymorphic nucleus are capable of active movement. Of the organelles, lysosomes and mitochondria are well defined. Functions: protective - by phagocytosis and digestion of foreign particles, microorganisms, tissue decay products; participation in cellular cooperation in humoral immunity; production of the antimicrobial protein lysozyme and the antiviral protein interferon, a factor that stimulates granulocyte migration.

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 branched 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: releasing histamine, they participate in the regulation of the permeability of the intercellular substance pvst and the walls of blood vessels, heparin - to regulate blood clotting. In general, mast cells regulate local homeostasis.

Plasmocytes 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 with a sharp apex facing the center, delimited from each other by radial stripes of euchromatin - therefore, the plasmacyte nucleus is torn off from a “wheel with spokes”. Cell diameter is 7-10 microns. Function: they are effector cells of humoral immunity - they produce specific antibodies.

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

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

1. White lipocytes are round cells with a narrow strip of cytoplasm around one large droplet of fat in the center. There are few organelles in the cytoplasm. The small core is located eccentrically. Function: white lipocytes store fat as a reserve (high-calorie energy material and water).

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

Adventitial cells are poorly differentiated cells of loose, unformed fibrous connective tissue, located next to 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 capillaries; participate in the regulation of the lumen of hemocapillaries, thereby regulating the blood supply to surrounding tissues.

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

The intercellular substance of loose, unformed fibrous connective tissue consists of a 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 and fibrocytes.

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

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

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

3) Elastic fibers - thin (d=1-3 microns), less strong (4-6 kg/cm2), but very elastic fibers from the elastin protein (synthesized in fibroblasts). These fibers do not have striations, have a straight course, and often branch. Function: impart elasticity and stretchability.

PBST regenerates well and is involved in restoring the integrity of any damaged organ. In case of significant damage, the organ defect is often filled with a connective tissue scar.

RVST functions:

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

2. The protective function is due to the presence of macrophages, plasma cells and leukocytes in the PBCT. Antigens that break through the I - epithelial barrier of the body, meet with the II barrier - cells of nonspecific (macrophages, neutrophil granulocytes) and immunological defense (lymphocytes, macrophages, eosinophils).

3. Support-mechanical function.

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

Dense fibrous connective tissue (DFCT)

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 located very close to each other (densely) - all these structural features are reflected in a compressed form in the name of this tissue. PVST cells are represented overwhelmingly by fibroblasts and fibrocytes; macrophages, mast cells, plasmacytes, poorly differentiated cells, etc. are found in small numbers (mainly in layers of PVST).

The intercellular substance consists of densely located collagen fibers; there is little ground substance. Based on the location of the fibers, PVST is divided into formed PVST (the fibers are arranged in an orderly manner - parallel to each other) and unformed PVST (the 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 PVST 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 the epithelial tissues, in greater or lesser quantities accompanies blood and lymphatic vessels; is part of the skin and mucous membranes of organs. As layers of membranes containing an abundance of blood 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 having a gelatinous consistency; fibers - collagen and elastic, located relatively loosely and randomly, which is why the tissue is called unformed. Loose fibrous unformed connective tissue, due to the presence of intercellular substance, performs a supporting-trophic function; cells participate in immune reactions and restoration processes in case of tissue damage. The connective tissue differentiates cells of various shapes: adventitial cells, fibroblasts, fibrocytes, histiocytes, mast cells (tissue basophils), plasma cells and fat cells. Adventitial(from lat. adventicus- newcomer, 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, overgrown-

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 motile forms of cells, the peripheral part of the cell contains contractile filaments, cells with big amount contractile filaments - myofibroblasts - promote wound healing. Some fibroblasts are enclosed between densely spaced fibers; such cells are called fibrocytes; they lose the ability to divide, take on an elongated shape and have highly flattened nuclei. Macrophages (histiocytes) cells with the ability of phagocytosis and accumulation of suspended colloidal substances in the cytoplasm participate in general and local protective reactions of the immune system. The nucleus has clearly defined contours. Possessing the ability for directed movement - chemotaxis, macrophages migrate to the site of inflammation, where they become the dominant cells. Macrophages are involved in recognizing, processing and presenting antigen to lymphocytes. During inflammation, cells become irritated, increase in size, exhibit the ability to actively move and turn into structures called polyblasts. Macrophages cleanse the lesion from foreign particles and destroyed cells, but also stimulate the functional activity of fibroblasts. Tissue basophils (mast cells, mast cells) have an irregular oval or round shape, numerous granules (grains) are located in the cytoplasm. The cells contain histamine, which helps dilate blood vessels, and secrete heparin, which prevents blood clotting. Plasmocytes (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 the own layer of the intestinal mucosa, omentum, in the connective tissue between the lobules of the salivary glands, mammary glands, in the lymph nodes, and 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 number of pigment cells - chromatophores, which determine one color or another 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 the blood vessels.

Preparation “Loose fibrous unformed connective tissue of the subcutaneous tissue of the rat”(hematoxylin staining). The preparation is a small area of fixed subcutaneous tissue, stretched in the form of a thin film on a cover glass. At low magnification (x10), the intercellular substance is revealed: a structureless amorphous matrix and two types of fibers - rather wide collagen fibers, ribbon-shaped, and thin thread-like elastic fibers. At high microscope magnification (x40), cells of various shapes differentiate within the connective tissue: adventitial cells - elongated cells with long processes; fibroblasts - have a spindle-shaped 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 participation in the synthesis of high-molecular substances necessary both for the construction of fibers and for the formation of amorphous matter. 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 (mast cells, mast cells) have an irregularly oval or round shape, sometimes with wide short processes; numerous basophilic granules (grains) are located in the cytoplasm. Plasmocytes (plasma cells) can be round or oval shape; the cytoplasm is sharply basophilic, with the exception of only a small rim of cytoplasm near the nucleus - the perinuclear zone; along the periphery of the cytoplasm there are numerous small vacuoles.

Preparation “Adipose tissue of the omentum”. The omentum is a film penetrated by blood vessels. When stained with Sudan III, clusters of yellow, round fat cells are visible. When stained with hematoxylin and eosin, signet ring-shaped fat cells are not stained, the violet nucleus is pushed to the periphery of the cytoplasm (Fig. 31).

In many parts of the animal body, large accumulations of fat cells called adipose tissue form. Due to the peculiarities of natural coloring, specific structure and function, as well as location in mammals, two types of fat cells and, accordingly, two types of adipose tissue are distinguished: white and brown.

White adipose tissue is found in significant quantities in the so-called fat depots: subcutaneous adipose tissue, especially developed in pigs, adipose tissue around the kidneys in the mesentery (perinephric tissue), and 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. During cell development, fatty inclusions

Rice. 31

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

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

The formations in the cytoplasm appear first in the form of small scattered drops, which later merge into one large drop. Total amount of white adipose tissue in animals various types, breeds, sex, age, fatness ranges from 1 to 30% of live weight. Reserve fats are the most high-calorie substances, the oxidation of which releases in the body a large number of energy (1 g fat = 39 kJ). In beef and meat and dairy cattle, groups of fat cells are located in layers of loose fibrous connective tissue skeletal muscles. Meat obtained from such animals has the best taste qualities 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 insulation, protection, and limitation of mobility. Accumulations of fat cells in combination with bundles of collagen fibers in the skin of the soles and paws create good shock-absorbing properties. The role of adipose tissue as a water depot is significant; the formation of water is an important feature of fat metabolism in animals living in arid areas (camels). During fasting, the body primarily uses reserve fats from fat depot cells, in which fatty inclusions decrease and disappear. The adipose tissue of the eye orbit, epicardium, paws is preserved even with severe exhaustion. The color of adipose tissue depends on the species, breed and type of feeding of animals. Most animals, with the exception of pigs and goats, contain pigment in their fat. carotene, imparting yellow adipose tissue. In cattle, the pericardial adipose tissue contains many collagen fibers. Kidney fat called the fatty tissue surrounding the ureters. In the back area, the adipose tissue of pigs contains muscle tissue, and also often hair follicles(stubble) and even hair bags. In the peritoneal area 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. Mesenteric fat often contains blood vessels, for example pigs have more arteries and cattle have more veins. Internal fat is adipose tissue located under the peritoneum and 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 found in significant quantities in rodents and hibernating animals, as well as in newborn animals of other species. The location is predominantly 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 fit very tightly together, resembling in appearance glandular tissue. Numerous nerve fibers intertwined with a dense network approach the cells blood capillaries. Brown adipose tissue cells are characterized by centrally located nuclei and the presence of small fat droplets in the cytoplasm, the fusion of which does not occur into a larger droplet. In the cytoplasm between the fat droplets there are glycogen granules and numerous mitochondria; colored proteins of the electron transport system - cytochromes - give the brown color to this tissue. In the cells of brown adipose tissue, oxidative processes occur intensively, accompanied by the release of a significant amount of energy. However, most of the energy generated is spent not on the synthesis of ATP molecules, but on heat generation. This property of brown tissue lipocytes is important for regulating temperature in newborn animals and warming animals after awakening from hibernation.

Control questions

1. Characterize embryonic connective tissue - mesenchyme.
2. What is the structure of mesenchymal cells?
3. Give structural and functional characteristics of the cells of reticular connective tissue.
4. What structure do reticular fibers have and how can they be identified in histological preparations?
5. Characterize the cells of loose fibrous connective tissue.
6. What is the structure of the intercellular substance?
7. What function does the structureless matrix - the ground substance - perform?
8. What is the structure and function of the fibers of loose fibrous connective tissue?
9. What dye can be used to identify fat inclusions?

In the body, loose fibrous unformed connective tissue is the most common. It is located near epithelial tissues; accompanies blood and lymphatic vessels in greater or lesser quantities; 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 various cells and intercellular substance containing the main (amorphous) substance and a system of collagen and elastic fibers arranged in a disorderly manner, 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 (mast cells); 11 - elastic fibers; 12 - collagen fibers

Prevalence, diversity and large number cellular elements and intercellular substance of loose fibrous unformed connective tissue provide the following functions:

trophic - metabolic processes, regulation of cell nutrition;

protective - participation in immune reactions;

plastic - restoration processes in case of tissue damage;

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

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

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

Adventitial cells (from the Latin adventicus - newcomer, wandering) are the least differentiated, in many ways reminiscent of mesenchyme 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 the Latin fibrin - protein, blastos - sprout) are protein producers and are the 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-shaped shape, a large nucleus that is weakly stained, 1...2 nucleoli are clearly visible. The cytoplasm of the cell periphery is very light, so the contours of the cells are unclear and merge with the main substance. Around the nucleus, on the contrary, the cytoplasm is intensely stained due to the large amount of granular endoplasmic reticulum.

Fibroblasts are motile cells. Microfilaments containing actin are located in their cytoplasm. They contract and movement occurs. The motor activity of fibroblasts increases with the formation of a capsule from 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 with the ability to phagocytose and accumulate suspended colloidal substances in the cytoplasm. Macrophages participate in general and local protective reactions of the immune system (from the 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 and contains clumps of chromatin that are easily stained 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 doctrine of macrophages is I. I. Mechnikov, who united these cells into unified system- macrophage. Later, the pathologist Aschoff proposed calling it the reticuloendothelial system.

Motile, 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 recognition, processing and presentation of antigen to lymphocytes, in intercellular interaction with lymphocytes. Possessing the ability for directed movement - chemotaxis, macrophages migrate to the site of inflammation, where they become the dominant cells in chronic inflammation. At the same time, they not only cleanse the lesion from foreign particles and destroyed cells, but also subsequently stimulate the functional activity of fibroblasts.

During inflammation, macrophages become irritated, increase in size, move and turn into structures called polyblasts.

Electron microscopy reveals long lamellar processes on the surface of macrophages, with the help of which they capture foreign particles during phagocytosis. The processes, like the pseudopodia of an amoeba, surround the foreign particle and merge at the top of the cell. The captured particle ends up 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 filaments - filaments, ensuring 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 captured material.

Macrophages not only participate in phagocytosis, but also present antigen to trigger 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 the immune response.

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

When foreign particles penetrate, many macrophages closely adjoin each other, are connected by processes, and form interdigitations (from the Latin inter - between, digitatio - finger-like formations). This is clearly visible 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, mast cells) are found in all mammals, but the number in animals different types and in connective tissue various organs unequal. In some animals, for example, 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 number of tissue basophils are contained in loose connective tissue near the epidermis, epithelium of the digestive tract, respiratory tract, and uterus. Mast cells are often found in the loose connective tissue between the lobules of the liver, in the kidneys, endocrine organs, mammary gland and other organs.

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

The most characteristic structural feature of tissue basophils is the presence of numerous large (0.3...1 µm) granules, uniformly filling most of the volume of the cytoplasm. The granules are surrounded by a membrane and have unequal electron density.

Located near small blood vessels, tissue basophils are among the first to respond 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, histamine is secreted, which increases capillary permeability, 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 diverse 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, causing the appearance of local and general reactions.

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

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

Cells can be round or oval in shape; on inside lumps of chromatin are located radially in a clearly defined nuclear envelope. Due to the presence of a large amount of RNA, the cytoplasm is strongly basophilic, with the only exception being a small rim of cytoplasm near the nucleus - the perinuclear zone. Along the periphery of the cytoplasm there are numerous small vacuoles.

By origin, plasma cells represent the final stages of the development of B-lymphocytes, which in the areas where they are located are activated, multiply intensively and are converted into plasma cells.

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

Plasmoblast- a large cell with a large nucleus, actively dividing by mitosis. Proplasmocyte much smaller, characterized by pronounced basophilia of the cytoplasm, in which many dilated 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 to synthesize antibodies of a certain type. 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 a carbohydrate component, they are released from the cell. Antibodies are released when cells are destroyed.

In the cytoplasm of plasma cells, acidophilic inclusions are formed in the form of homogeneous structures that are intensely stained with eosin. pink color. In this case, the basophilia of the cytoplasm disappears, the nucleus fragments; gradually rounding out, the acidophilic Roussel body is formed from acidophilic structures, located in the main substance of 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). During embryogenesis, fat cells are formed from mesenchymal cells. The precursors for the formation of new fat cells in the postembryonic period are adventitial cells accompanying blood capillaries.

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

Lobules of various sizes are formed from fat cells. Between the lobules there are layers of loose connective tissue in which small blood vessels and nerve fibers pass. Between the fat cells inside the lobules there 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 signet ring shape, 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 (see color vkp., Fig. III).

In many parts of the animal body, large accumulations of fat cells called adipose tissue form. Due to the peculiarities of natural coloring, structure and function, as well as location, two types of fat cells and, accordingly, two types of adipose tissue are distinguished in mammals: white and brown.

White adipose tissue in the body of animals of different species and breeds is distributed unequally. It is found in significant quantities in the so-called fat depots: subcutaneous fatty 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). In beef and dairy cattle, groups of fat cells are located in layers of loose fibrous unformed connective tissue of skeletal muscles. Meat obtained from such animals has the best taste and is called “marbled”.

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

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

Subcutaneous fatty tissue is of great importance for protecting the body from mechanical damage and protects against heat loss. Fatty tissue along the neurovascular bundles provides relative insulation, protection, and limitation of mobility. Clusters of fat cells combine with bundles of collagen fibers in the skin of the soles and paws to provide shock absorption during movement. Adipose tissue serves as a water depot. The formation of water is an important feature of fat metabolism in animals living in arid areas (camels).

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

The color of adipose tissue depends on the species, 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 pericardial adipose tissue contains many collagen fibers. Kidney fat is the fatty tissue surrounding the ureters.

In the back area, the adipose tissue of pigs contains muscle tissue, as well as often hair follicles (stubble) and hair follicles. 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 fat deterioration. Mesenteric fat often contains blood vessels, for example pigs have more arteries and cattle have more veins.

Viscera is 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 found 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 fit very tightly together, resembling glandular tissue in appearance. Numerous nerve fibers intertwined with a dense network of blood capillaries approach the cells.

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 droplet. In the cytoplasm between the fat droplets there are glycogen granules and numerous mitochondria, colored proteins of the electron transport system -? cytochromes that give the brown color to this tissue.

In the cells of brown adipose tissue, oxidative processes occur intensively with the release of a significant amount of energy. However, most of the energy generated 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 awakening from hibernation.

Pigment cells (pigmentocytes), as a rule, have processes; in the cytoplasm there are a lot of 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 number of pigment cells - chromatophores, which determine one color or another 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 having a gelatinous consistency; collagen and elastic fibers located relatively loosely and randomly.

The main substance contains high molecular weight acidic 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. Near the capillaries and small vessels, in areas containing fatty layers, or in tissue rich in reticular cells, there is little ground substance, but at the boundaries with the epithelium, on the contrary, there is a lot. In these areas, the ground substance, together with the reticular fibers, forms bordering basement membranes, which are often clearly visible.

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

The main substance fills the gaps between cells, fibers, and microvasculature vessels. Structureless ground substance early stages tissue development quantitatively predominates over 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 type of glycosaminoglycans - hyaluronic acid. Unbranched chain 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 look like ribbon-like strands oriented in different directions. The fibers do not branch, they are low-stretch, have high tensile strength (withstand up to 6 kg per 1 mm 2 of cross-section), and are capable of being combined into bundles. When cooked for a long time, collagen fibers form glue (from English, kolla - glue).

The strength of collagen fibers is due to their fine structural organization. Each fiber consists of fibrils with a diameter of up to 100 nm, located parallel to each other and immersed in an interfibrillar substance containing proteins, glycosaminoglycans and proteoglycans. Collagen fibers vary in their degree of maturity. As part of the newly formed inflammatory reaction fibers contain a significant amount of cementing polysaccharide substance, which is capable of reducing silver when sections are treated with silver salts. Therefore, young collagen fibers are often called argyrophilic; in mature fibers the amount of this substance decreases.

During electron microscopy, characteristic transverse striations are observed along the length of the fibril - alternation of dark and light stripes with a certain period of repetition, namely, one dark and one light segment together make up one period with a length of 64...70 nm. This striation is most clearly visible 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 intervals 3...4 nm wide, is revealed.

The fibril consists of thinner protofibrils from the protein tropocollagen. Protofibrils have a length of 280...300 nm and a width of 1.5 nm. The formation of a fibril 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, and narrow secondary dark-colored stripes 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 have the appearance of distinct thin branching homogeneous filaments forming a network. To selectively identify elastic networks, special dyes are used: orcein, resorcinol-fuchsin. Unlike collagen, elastic fibers are not combined into bundles, have low strength, are highly resistant to acids and alkalis, heat, and the hydrolyzing action of enzymes (with the exception of elastase).

By electron microscopy, the structure of the elastic fiber is distinguished by a more transparent amorphous central part, consisting of the elastin protein, and a peripheral part, which contains a large number of electron-dense microfibrils of a glycoprotein nature, shaped like tubes with a diameter of about 10 nm.

The formation of elastic fibers in connective tissue is due to the synthetic and secretory functions of fibroblasts. It is believed that first, a framework of microfibrils is formed in the immediate vicinity of fibroblasts, and then the formation of an amorphous part from the elastin precursor, proelastin, is enhanced. Under the influence of enzymes, proelastin molecules are shortened and converted into small, almost spherical tropoelastin molecules. When elastin is formed, tropoelastin molecules are connected to each other using desmosine and isodesmosine, which are absent in other proteins. In addition, elastin does not contain oxylysine and polar side chains, which makes the elastic fibers highly stable.

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 They live for a short time and are quickly replaced by new ones (this process is called regeneration).
Epithelial tissue is also involved in many other functions: secretion (glands of external and internal secretion), absorption (intestinal epithelium), gas exchange (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 connective tissue elements; such epithelium is called atypical.
Epithelial cells, located in a layer, can lie in many layers (stratified epithelium) or in one layer ( single layer epithelium) . Based on the height of the cells, epithelia are divided into flat, cubic, prismatic, and cylindrical.

Connective tissue.
Consists of cells, intercellular substance and connective tissue fibers. It consists of bones, cartilage, tendons, ligaments, blood, fat, it is present in all organs (loose connective tissue) in the form of the so-called stroma (framework) 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 in the types of connective tissue are determined by the ratios of cellular components and the nature of the intercellular substance.
Dense fibrous connective tissue (muscle tendons, joint ligaments) is dominated by fibrous structures and experiences significant mechanical stress.

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, provide primarily protective and regulatory processes, including through immune mechanisms (macrophages, lymphocytes, tissue basophils, plasma cells).

Material taken from the site www.hystology.ru

In the body, loose connective tissue is the most abundant. This is evidenced by the fact that it accompanies all 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 cavitary organs.

Regardless of the location, 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 local conditions of development and functioning, the quantitative relationship between these three structural elements in different areas is not the same, which determines the organ characteristics of loose connective tissue.

Among the various highly specialized cells in the composition of a given tissue, more sedentary cells (fibroblasts - fibrocytes, lipocytes) are distinguished, the development of which in the process of cellular renewal occurs from precursors located within the loose connective tissue itself. The immediate precursors of other more mobile cells (histiocytic macrophages, tissue basophils, plasma cells) are blood cells, active phase the functioning of which is carried out as part of loose connective tissue. Taken together, all the cells of loose connective tissue represent a single diffusely dispersed apparatus located in an inextricable 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, ensure the main functions of this connective tissue: trophic (metabolic processes and regulation of cell nutrition), protective (participation of cells in immune reactions - phagocytosis, production of immunoglobulins and others substances) and plastic (participation in restoration processes in case of tissue damage).

Cells. Adventitial cells- elongated, stellate-shaped cells with an oval nucleus rich in heterochromatin. The cytoplasm is basophilic and contains a 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, rudiment) - - 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 high-molecular substances necessary both for the construction of fibers and for the formation of the amorphous component of the tissue. 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 the subcutaneous tissue of a rabbit (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 reproduce through 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, spindle-shaped shape with a few short processes. The oval nucleus has a well-defined nucleolus. The cytoplasm in light microscopy of preparations stained with basic dyes is basophilic. Electron microscopy reveals many free polysomes and only short narrow tubules of the granular network in the cytoplasm. Elements of the Golgi complex are located in the perinuclear zone. Mitochondria are few in number 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.

Mature fibroblasts, when viewed from above, are large (diameter up to 50 µm) branched cells, containing light oval nuclei with 1 - 2 large nucleoli and a significant volume of weakly basophilic cytoplasm. The peripheral zone of the cell is stained especially weakly, as a result of which its contours are almost invisible. In cross section, the cell body is flattened, 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 dilated cisterns, to the membranes of which large polysomes are attached. The elements (cisterns, micro- and macrobubbles) of the Golgi complex, distributed throughout the cytoplasm, are also well expressed. Mitochondria of different shapes and sizes are found (Fig. 103).

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

Rice. 103. Electron microgram of a fibroblast section (according to Radostina):

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

α-chains of protein are synthesized in the polysomes of the granular network, and in the cavity of the reticulum components they are linked into the triple helix of the procollagen molecule. The latter are transported by microbubbles into the cisterns of the Golgi complex and then released from the cell as part of secretory granules. On the surface of the fibroblast, the terminal non-spiralized peptide sections are separated from the procollagen molecules, they are converted 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 part of the fibrils as a cementing component.

Fibroblasts have mobility. In the peripheral zone of the cytoplasm there are actin-containing microfilaments, the contraction of which ensures the formation of protrusions and cell movement. The motor activity of fibroblasts increases during 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 connective tissue leads to the fact that some fibroblasts are enclosed between closely spaced fibers. Such cells are called fibrocytes. They lose the ability to divide, take on a highly elongated shape, their cytoplasm volume decreases and their synthetic activity is significantly reduced.

Histiocytes (macrophages) As part of the widespread connective tissue, they are the most numerous group of free, migratory cells belonging to the mononuclear phagocyte system (MPS). In connective tissue layers different organs their number is not the same and, as a rule, increases significantly with inflammation.

Fig. 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 is then 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 Welsh and Storch).

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

Electron microscopy reveals microvilli, pseudopodia, and invaginations on the plasmalemma. The cytoplasm contains a significant amount of lysosomes, phagosomes, granules and lipid inclusions. The granular network is almost undeveloped. Mitochondria and the Golgi complex are more developed in activated macrophages. Using cytochemical methods, various enzymes (acid hydrolases, acid phosphatase isoenzymes, esterases, etc.) are identified in the cytoplasm of histiocytes, with the help of which the absorbed substances are digested.

The concept of the mononuclear phagocyte system (macrophagic 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 fibers.

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

Rice. 106. Types of cells belonging to the mononuclear phagocyte system - 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 location (liver, lungs, abdominal cavity, etc.), macrophages acquire some specific structural features and properties that allow them to be distinguished from each other, but they all share some common structural, ultrastructural and cytochemical features. Due to the presence of contractile microfilaments, which ensure the mobility of the plasmalemma, 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 broken down and processed.

Macrophages are multifunctional cells. The founder of the doctrine of the cytophysiology of cells of the macrophage system is I. I. Mechnikov. To this day, many of the provisions formulated by him about the mechanisms of phagocytosis and the biological significance of this phenomenon are relevant. Macrophagic 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 body.

Macrophages play an important role in the implementation of a protective inflammatory response. Having the ability for directional 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 site of inflammation and become the dominant cells chronic inflammation. At the same time, they not only cleanse the lesion from foreign particles and destroyed cells, but also subsequently stimulate the functional activity of fibroblasts. In the presence of toxic and persistent irritants (some microorganisms, chemicals, poorly soluble materials) in the lesion, a granuloma is formed with the participation of macrophages, in which giant multinucleated cells can be formed 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 performing effector functions.

On the surface of the macrophage plasmalemma there are two types of specific receptors: receptors for the F c part of immunoglobulins and receptors for complement, especially for its component C 3 . Therefore, in the recognition and absorption phase, opsonization of antigens, that is, the preliminary attachment of immunoglobulins or an immunoglobulin complex with complement, is of great importance. Subsequent attachment of such sensitized antigens ( immune complexes) to the corresponding macrophage receptors causes movement of pseudopodia and engulfment of the object of phagocytosis. There are also nonspecific receptors, thanks to which the cell can phagocytose 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, spleen sinuses, and the medulla of lymph nodes. Special types of specialized macrophages are the branching “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 red blood cells are grouped. These macrophages participate in the transfer of accumulated iron to erythroid cells, engulf the nuclei of normocytes and phagocytose damaged and old erythrocytes. Other bone marrow macrophages phagocytose parts of megakaryocytes after separating blood platelets from them. With the help of spleen macrophages, intensive erythrophagocytosis and absorption of aging blood platelets occurs, and macrophages of all lymph-eating organs - phagocytosis of plasma cells and lymphocytes.

Tissue basophils(mast cells, mast cells) are found in most vertebrates and all mammals, but their number in animals of different species and in the connective tissue of different 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 types of cells in the tissue system of the internal environment (for example, guinea pigs have many tissue basophils, but few blood basophils). A significant number of tissue basophils are contained in the subepithelial connective tissue of the skin, digestive tract, respiratory tract, and uterus. They are found in connective tissue layers along small blood vessels in the liver, kidneys, endocrine organs, mammary gland and other organs.

Tissue basophils are often oval or spherical in shape, ranging in size from 10 to 25 microns. The nucleus is centrally located and contains many clumps of condensed chromatin. The most characteristic structural feature of tissue basophils is the presence of numerous large (0.3 - 1 µm) specific granules, uniformly filling most of the cytoplasm and staining metachromatically. Electron microscopy reveals a few mitochondria, polysomes and ribosomes in the cytoplasm. The endoplasmic reticulum and Golgi complex are poorly developed. There are finger-like protrusions on the plasmalemma. Specific granules are surrounded by a membrane and have unequal electron density; some granules contain even more electron-dense grains or platelets.

The characteristic metachromatic coloring 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 diverse pharmacological effect. Cytochemical methods revealed various enzymes in the cytoplasm - acidic and alkaline phosphatase, lipase. Histamine is produced 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 plasmalemma, as well as on blood basophils, there is a significant amount of class E immunoglobulins (IgE). The binding of antigens and the formation of the antigen-antibody complex is accompanied by degranulation and the release of vascular active substances from tissue basophils, causing the appearance of local and general reactions. Histamine increases the permeability of the capillary wall and the underlying substance of 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.

Plasmocytes(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 location with the participation of T-helper cells in macrophages, undergo activation, multiply intensively and turn into mature plasma cells. IN the greatest number Plasmocytes are found in the spleen, lymph nodes, in 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 plasmacyte (Fig. 107).

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

1 - plasma cell precursor (semi-stem cell); 2 - plasmablast; 3 - young plasma cell; 4 - plasma cell with expanded cisterns of the endoplasmic reticulum; 5 - mature plasma cell.

A 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 clearly defined nucleoli are found. Electron microscopy reveals very rare and small cisterns of granular endoplasmic reticulum in the cytoplasm, as well as a large number of free polysomes and ribosomes. A few mitochondria have a light matrix and rare cristae. Among plasmablasts, mitoses are common. The proplasmocyte is characterized by a slightly smaller size, pronounced basophilia of the cytoplasm and an uneven cell surface due to numerous protrusions of the plasmalemma. The cytoplasm contains a large number of dilated cisterns and sacs of granular endoplasmic reticulum. Between the elements of the granular network there are small mitochondria. It is believed that these cells can produce and secrete immunoglobulins. Mature plasma cells are relatively small (8 - 10 µm) oval-shaped cells with pronounced boundaries. In the highly basophilic (pyroninophilic) cytoplasm, a light perinuclear zone is detected. The nucleus is round, eccentrically located and contains large clumps of heterochromatin distributed like the spokes of a wheel. Particularly characteristic in the structure of these cells during electron microscopic examination is the presence in the cytoplasm of numerous long cisterns located close to each other, having a very narrow cavity and close membranes, on outer surface which contain 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 the light chains of immunoglobulins are synthesized

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

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

on polyribosomes of the granular network separately from the 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 to synthesize 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 a carbohydrate component, they are brought to the cell surface and secreted. Antibodies are also released when cells are destroyed.

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

Fat cells(lipocytes) and adipose tissue(textus adiposus). Fat cells are specialized in the synthesis and accumulation of reserve lipids, mainly triglycerides, in the cytoplasm and their utilization in accordance with the energy and other needs of the body. Lipocytes are widespread in loose connective tissue and are often located not singly, but in small groups along small blood vessels. In many parts of the animal body, large accumulations of fat cells called adipose tissue form. During embryogenesis, fat cells arise from mesenchymal cells. The precursors for the formation of new fat cells in the postembryonic period are adventitial cells accompanying blood capillaries.

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

White adipose tissue in the body of animals of different species and breeds is distributed unequally. It is found in significant quantities in fat depots: subcutaneous adipose tissue, especially developed in pigs, adipose tissue around the kidneys, in the mesentery, and in some breeds of sheep at the root of the tail (fat tail). In meat and dairy animals, groups of fat cells are located in the perimysium and endomysium inside the skeletal muscles. 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, when viewed by light microscopy of a histological section stained using fat-soluble substances, has

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

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

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

Lobules of various sizes and shapes are formed from fat cells in adipose tissue. Between the lobules there are layers of loose connective tissue in which small blood vessels and nerve fibers pass. Between the fat cells inside the lobules there 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, and fatness ranges from 1 to 30% of live weight. Reserve fats in adipose tissue are the most high-calorie substances, the oxidation of which releases a large amount of energy in the body (1 g of fat = 39 kJ). Subcutaneous adipose tissue, especially in wild animals, is of great importance for protecting the body from mechanical damage and protects against heat loss. Adipose tissue along the neurovascular bundles, in the capsule and membranes of organs provides their relative insulation, protection and limitation of mobility. Accumulations of fat cells in combination with surrounding bundles of collagen fibers in the skin of the soles and paws create good shock-absorbing properties. The role of adipose tissue as a water depot is significant. The formation of water is an important feature of fat metabolism in animals living in arid areas (camels).

During fasting, the body mobilizes primarily reserve fats from fat depot cells. Fatty inclusions in them decrease and disappear.

The adipose tissue of the eye orbit, epicardium, and paws is preserved even with severe exhaustion.

Brown adipose tissue is present in significant quantities 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, externally resembling glandular tissue. Numerous fibers of the sympathetic nervous system approach the cells; they are intertwined 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, the fusion of which does not occur into a larger droplet. In the spaces between the fat droplets there are numerous mitochondria and a significant amount of glycogen granules. The colored proteins of the electron transport system, cytochromes, contained in mitochondria give the brown color to this tissue.

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

Pigment cells (pigmentocytes), usually of a process form. The cytoplasm contains many dark brown or black grains of pigment 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 color or another 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 makes up a significant part of it. It is represented by collagen and elastic fibers, located relatively loosely and randomly, and the main (amorphous) substance. In the intercellular substance, various 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. The intercellular substance contains sensory 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 elongation, high tensile strength (withstand up to 6 kg per 1 mm 2 cross section), and the ability to unite into bundles. When cooked for a long time, collagen fibers form 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 with a diameter of up to 100 nm, located parallel to each other and immersed in an interfibrillar substance containing glycoproteins, glycosaminoglycans and proteoglycans. Under electron microscope Along the length of the fibril, characteristic transverse banding is observed - alternation of dark and light stripes with a certain period of repetition, namely, one dark segment and one light segment together make up one period with a length of 64 - 70 nm. This banding is most clearly visible 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 intervals 3 - 4 hm wide.

Currently, 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 peculiar monomers (Fig. 110). The formation of a fibril is the result of a characteristic grouping of monomers in the longitudinal and transverse directions. The monomers are arranged in parallel rows and held near each other by covalent cross-links, and in one row there is a gap between the ends of neighboring monomers equal to 0.4 of the length of the period, and in width the monomers of one row are superimposed on the monomers of the neighboring one with a displacement of 1/4 of its length. This alternation of gaps and overlaps creates a banded appearance of fibrils in electron microphotographs. One tropocollagen molecule crosses five light and four dark segments (Fig. 111).

It is also known that the length of the tropocollagen molecule is asymmetrical and where similar amino acid sequences are opposite each other, narrow secondary dark-colored stripes 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 oxylysine and hydroxyproline. Depending on the amino acid composition and the form of association of chains into a triple helix, there are four main types of collagen, which have different localizations in the body. Type I collagen is the most common and is found in

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

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

Rice. 111. Collagen fibril:

A- electron micrograph of a negatively stained collagen fibril (magnitude 180000); B- diagram of the arrangement of tropocollagen molecules, explaining the occurrence of transverse striations (according to Hoxha and Petruski, 1964): 1 - dark segments correspond to the spaces between the ends of the tropocollagen molecules; 2 - light segments correspond to areas of molecular overlap.

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

Collagen fibers vary in their degree of maturity. The composition of newly formed (during an inflammatory reaction) fibers contains a significant amount of interfibrillar cementing nolysaccharide substance, which is capable of reducing 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 µm in loose connective tissue to 15 µm in ligaments). On film preparations of connective tissue stained with hematoxylin and eosin, the fibers appear as weakly defined thin branching homogeneous filaments forming a network. To selectively identify elastic networks, special dyes are used - orcein, resorcinol - fuchsin, etc. Unlike collagen fibers, elastic fibers are not combined into bundles, have low strength, are highly resistant to acids and alkalis, heat and the hydrolyzing action of enzymes (with the exception of elastase).

By electron microscopy, the structure of the elastic fiber reveals a more transparent amorphous central part, consisting of the elastin protein, and a peripheral part, which contains a large number of electron-dense microfibrils of a glycoprotein nature, shaped like tubes 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 connective tissue is due to the synthetic and secretory function of fibroblasts. It is believed that first, a framework of microfibrils is formed in the immediate vicinity of fibroblasts, and then the formation of an amorphous part from the elastin precursor, proelastin, is enhanced. Under the influence of enzymes, proelastin molecules are shortened and converted into small, almost spherical tropoelastin molecules. The latter, during the formation of elastin, are connected to each other using unique substances(desmosine and isodesmosine), absent in other proteins. In addition, elastin does not contain oxylysine and polar side chains, which makes the elastic fibers highly stable.

There are especially many elastic fibers in those connective tissue formations that are characterized by long-term stress and return to its original state after the end of the stretch (occipito-cervical ligament, abdominal flavum 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.

Main substance. All spaces between cells, fibers and microvasculature vessels located in loose connective tissue are filled with structureless ground substance, which in the early stages of tissue development quantitatively predominates over fibers. In different areas of 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. 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 type 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 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 main substance is associated mainly 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 main substance is a factor that affects not only the binding of water and the transport of soluble components contained in the tissue fluid (ions, glucose, amino acids, etc.), but also the migration of cells. Many hormones (corticosteroids, etc.) have a regulatory effect on the state of the main substance, the action of which is directed on the cells, and through them on 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, by synthesizing and secreting hyaluronidase, cause depolymerization of hyaluronic acid of the main substance and in this way accelerate their distribution in the animal’s body.

To stain the main 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).