Which fabric contains elastic fibers? Connective tissue

Connective tissue is also called internal tissue. It is part of every organ and forms layers between the organs, as if connecting them. Connective tissue covers blood vessels and nerves, participates in the formation of the human skeleton and the skeleton of its individual organs, and in the formation of blood and lymph.

Connective tissue performs the following functions: trophic, protective, supporting (mechanical) and plastic.

Trophic, or nutritious, function is that blood, which belongs to connective tissue, carries nutrients throughout the body. In addition, by dressing the vessels, the connective tissue along with them penetrates into all tissues and organs.

Protective function connective tissue is associated not only with its mechanical properties (bones - dense formations - protect organs), but also with the fact that its cells have the ability to phagocytosis: they absorb and digest harmful substances. Connective tissue is also involved in the formation of protective bodies that create immunity (immunity to diseases).

Support functionConnective tissue is determined mainly by the intercellular substance.

Plastic function connective tissue is expressed in its high ability to regenerate and adapt to environmental conditions. This tissue is formed from the middle germ layer of the mesoderm, from the so-called germinal connective tissue (mesenchyme).

Connective tissue consists of cells and intercellular substance, in which the ground substance and fibers are secreted. Unlike other types of tissue, intercellular substance predominates in it, while there are few cells. In different types of connective tissue, the quantitative ratio of intercellular substance and cells is different.

The ground substance of connective tissue contains many fibers. Some of them, located in the form of thick straight or somewhat convoluted ribbons, do not branch, consist of a special adhesive substance and are called collagen or adhesive fibers. They are poorly stretchable and very durable. Another type of fiber is Elastic. They are thinner and branching. These fibers are less strong than collagen, but have greater elasticity and elasticity (like rubber, they can stretch and then return to their original shape).

The main cells of the tissue are fibroblasts, fibrocytes, macrophages, mast cells and plasma cells. It may contain fat cells, pigment cells and even white blood cells.

Fibroblasts- the main type of connective tissue cells. They have an irregular or spindle-shaped (elongated) shape. Their core is quite large and oval in shape. Fibroblasts participate in the formation of intercellular substance and fibers, in wound healing, and the development of scar tissue. Fibroblasts that have completed their life cycle are called fibrocytes.

Macrophagescan be of various shapes: round, elongated, irregular. Their shell is folded, with a large number of microvilli, with the help of which they capture foreign substances. These cells usually have one nucleus, small in size, oval or bean-shaped. Macrophages are the main defenders of the human body. They destroy microbes and neutralize toxic (poisonous) substances.

Mast cellsThey have an irregular shape, short wide processes, and a small core. There are many grains in the cytoplasm. Mast cells have a well-developed ability for amoeboid movements. They participate in the formation of intercellular substance and regulation of its composition, produce substances that prevent blood clotting and the deposition of salts in the walls of blood vessels.

Plasma cells oval or round in shape participate in the formation of protective bodies, especially react when a foreign protein is introduced into the body.

Fat cellscontain fat in the cytoplasm, pushing the nucleus to the periphery. Their number in loose connective tissue is variable. With increased nutrition, the number of fat cells increases sharply.

Pigment cells - these are the same fibroblasts or fibrocytes, in the cytoplasm of which there is a lot of coloring matter - pigment.

According to the functions performed, which are determined to a large extent by the physicochemical characteristics of the intercellular substance (it can be liquid, dense and very hard), connective tissue is divided into protective-trophic and supporting. Protective-trophic connective tissue includes: blood, lymph, reticular, or reticular, tissue, loose fibrous tissue and endothelium. Supporting connective tissue includes: dense fibrous tissue, cartilage and bone tissue. As the intercellular substance becomes denser, the trophic function of the tissue decreases and the supporting function increases.

Blood- This is a type of connective tissue with a liquid intercellular substance and specific cells. The intercellular substance of blood is its liquid part - plasma, which contains the formed elements (cells) of blood. By volume, plasma makes up 55-60%, and formed elements 40-45% of all blood. In the adult body there are 4.5-5 liters of blood.

Plasma. Blood plasma consists of inorganic and organic substances. It contains about 91% inorganic substances (90% is water and 1% mineral substances), and about 9% organic substances. The main part of organic matter is proteins - 7%. There are 3 types of them - fibrinogen, albumin and globulins. Fibrinogen takes part in blood clotting, albumins transport poorly water-soluble substances (including drugs), and globulins ensure the formation of protective bodies. The amount of globulins increases sharply during infectious diseases. Blood plasma devoid of fibrinogen is called blood serum. It is used for therapeutic or prophylactic purposes to create immunity (passive immunization), and therapeutic serums are prepared. Blood plasma also contains organic substances of a non-protein nature (urea, fat, amino acids, etc.), although in very small quantities.

Formed elements of blood . There are three types of them: red blood cells - erythrocytes, white blood cells - leukocytes and platelets - platelets.

Rice. 6. Human blood smear: 1 - red blood cells; 2, 3, 4, 8 - granular forms of leukocytes; 5, 6, 7 - lymphocytes; 9 - blood plate

Red blood cells(erythros - red, cytos - cell) are specific highly differentiated cells that, during development, have lost their nucleus, mitochondria, reticular apparatus and cell center (Fig. 6). In frogs, fish, and birds, red blood cells contain nuclei (Fig. 7). In the cytoplasm of red blood cells there is a complex protein - hemoglobin, with the help of which gas exchange in the body is carried out: oxygen is transferred from the lungs to the tissues, and carbon dioxide is transferred from the tissues to the lungs. The membrane of red blood cells is very thin, and gases are exchanged through it. The red blood cell has the shape of a biconcave disk, which increases its surface, facilitating better contact of hemoglobin with the transported gases. The absence of a nucleus in the cell also appears to allow for greater oxygen uptake.

Rice. 7. Blood smear of a frog: 1 - red blood cells: a - nucleus, b - cytoplasm; 2 - leukocytes; 3 - platelet

The size of red blood cells is small, only 7-8 microns, so they pass quite easily through the thinnest blood vessels - capillaries. 1 mm 3 of blood contains 4.5-5.0 million, and in total there are 25-28 trillion red blood cells. If it were possible to place them side by side, it would create a chain that would be enough to encircle the globe 3 times along the equator. The total surface of red blood cells circulating in the blood is more than 1/4 hectare. In men, the number of red blood cells is slightly higher than in women; in children - more than in adults; Residents of high mountain areas, where there is less oxygen in the air, have more than residents of the plains. Even with a short-term (1-2 months) stay in mountainous areas, the number of red blood cells increases, which is important for conducting sports training there. With increased muscle activity, they also become larger due to the increased demand for oxygen. Red blood cells do not have the ability to move independently; they move through the blood vessels with the blood flow. However, they are very elastic; when they move in the capillaries, you can clearly see how they lengthen, flatten, changing their shape. The lifespan of red blood cells is 80-120 days. Red blood cells break down in the spleen and are formed in the red bone marrow. According to available data, 1/100 of the red blood cells are destroyed every day, i.e., in a little more than 3 months, all red blood cells are renewed.

Leukocytes- these are cells with a nucleus. They are larger than red blood cells (up to 10 microns), capable of independent amoeboid movement, and can exit the capillaries into the underlying tissue.

Depending on the nature of the cytoplasm, the presence of inclusions in it in the form of grains of protein, pigment, and also depending on the shape of the nucleus, leukocytes are divided into granular and non-granular. The former have granularity in the cytoplasm and a segmented nucleus, divided into separate parts. Depending on the type of granularity and its relationship to dyes, neutrophils, basophils and eosinophils are distinguished, which are found in certain quantitative ratios in the blood. The change in this ratio in various diseases determines not only their nature, but also their outcome.

Non-granular forms of leukocytes do not contain inclusions in the cytoplasm; their nucleus is not divided into parts, has a round shape and is most often located in the center of the cell. Non-granular leukocytes include lymphocytes and monocytes.

1 mm 3 of blood contains 6 - 8 thousand leukocytes. Their number may increase after eating, during infectious diseases, and especially after intense muscle activity. The lifespan of leukocytes varies: from several days to 2 - 3 months. When an infection enters the body, they die in significant numbers in the fight against it. Granular forms of leukocytes are produced in the red bone marrow, and lymphocytes are produced in the spleen and lymph nodes.

The main function of leukocytes is protective. They guard the health of the body, helping it fight various diseases. They perform a protective function by participating in phagocytosis and in the formation of protective bodies. In addition, leukocytes produce enzymes that regulate blood clotting and vascular permeability. Finally, individual forms of lymphocytes can form cells of various types of connective tissue (fibroblasts, macrophages, smooth muscle cells), which is important in recovery processes.

Platelets, or blood platelets, are round or oval-shaped bodies measuring only 1 - 2 microns in size. They do not contain a kernel. There are 200 - 300 thousand of them in 1 mm 3 of blood. The lifespan of platelets is 5 - 8 days. Blood platelets take part in blood clotting.

Lymph, like blood, consists of a liquid part - lymphoplasm - and formed elements. Unlike blood plasma, it contains less protein, but more metabolic products. Of the formed elements, lymphocytes predominate in it, erythrocytes are absent.

Reticular tissue consists of irregularly shaped cells. In contact with each other, they form a kind of network. In the loops of this network there is an intercellular substance containing a large number of reticulin fibers entwining the surface of the cells. Hematopoietic organs (bone marrow, spleen, lymph nodes) are built from reticular tissue.

Loose fibrous connective tissue - this is the tissue in which all the structural elements of connective tissue are most clearly expressed: intercellular substance, fibers and cells (Fig. 8). It covers blood vessels and nerves, forms subcutaneous tissue, and participates in the structure of almost all organs.

Rice. 8. Loose connective tissue: 1 - mast cells; 2 - fibroblasts and macrophages; 3 - collagen fibers (a - fibrils); 4 - elastic fibers

Endothelial tissue (endothelium) is related to connective tissue only in origin, while in structure it resembles epithelial tissue. Its cells are flat and located on the basement membrane. There is little intercellular substance in this tissue. Endothelium lines the inner surface of blood vessels, giving it a smooth, shiny appearance; Metabolism occurs through the endothelial cells of the capillaries; They also perform a protective function.

Dense fibrous connective tissue has a characteristic feature - it is dominated by collagen fibers, which are collected in bundles oriented depending on the direction of traction forces. There are few cells here (mainly fibroblasts), and they are located between the fiber bundles. Ligaments, tendons, fascia, intermuscular septa, periosteum, perichondrium, etc. are built from this tissue (Fig. 9).

Rice. 9. Dense fibrous connective tissue (tendons in longitudinal section): 1 - first order bundles (collagen fibers); 2 - fibrocytes; 3 - beams of the second order; 4 - connective tissue (a - adipose tissue, b - artery); 5 - vein

In tendons and ligaments, bundles of collagen fibers are located in parallel, in fascia, aponeuroses, intermuscular septa - in layers above each other (the thicker the fascia, the more layers), and the direction of the fibers in different layers is different: in some - at a right angle, in others - under sharp, which gives these formations special strength. If the dense fibrous connective tissue is dominated by elastic fibers, it is called elastic connective tissue. The presence of elastic fibers helps an organ or part of the body return to its original position after changing shape.

Cartilage tissue(cartilage) in its physicochemical properties and functional features differs sharply from other types of connective tissue. Its intercellular substance is quite dense, and therefore it mainly performs supporting and protective (mechanical) functions. There are three types of cartilage: hyaline, or vitreous, collagen-fibrous and elastic. Cartilage tissue does not have blood vessels. Metabolism (nutrition and removal of waste products) is carried out through the vessels of the connective tissue membrane covering the outside of the cartilage (perichondrium). Nutrients from the vessels of the perichondrium penetrate into the intercellular substance of the cartilage. The cartilage that covers the articular surfaces of bones receives nutrients from the synovial fluid that fills the joint cavity or from nearby bone vessels. The growth of cartilage occurs due to the perichondrium.

Hyaline cartilagehas the greatest distribution in the human body. Its intercellular substance is translucent, bluish-white. Cartilage cells are located in special cavities surrounded by a capsule, which is denser than the intercellular substance. Hyaline cartilage forms the anterior ends of the ribs, the cartilage of the trachea, bronchi, most of the cartilage of the larynx and covers the articular surfaces of bones. In the embryonic period, a significant part of the skeleton consists of hyaline cartilage. In old age, lime may be deposited in hyaline cartilage (Fig. 10).

Rice. 10. Hyaline (vitreous) cartilage: 1 - perichondrium; 2 - cartilage (a - young cartilage cells, b - intercellular substance, c - cartilage cells, d - cartilage capsule, e - separate groups of cells)

Collagen fibrocartilage less elastic, but more durable. Its intercellular substance contains a large number of bundles of collagen fibers located more or less parallel. The cells are located between the fiber bundles. The intervertebral discs, the cartilage connecting the pubic bones, are built from this cartilage (Fig. 11).

Rice. 11. Collagen-fibrous cartilage: 1 - cartilage cells; 2 - collagen fibers

Elastic cartilage less durable, but very elastic, calcification never occurs in it. In the intercellular substance of cartilage there are many elastic fibers that intertwine with each other, forming a dense network. Its cells resemble the shape of a candle flame and are located 2-3 in capsules between the fibers. Elastic cartilage is located where great resistance to acting forces is not required. The auricle, epiglottis, wall of the external auditory canal and auditory tube are built from it (Fig. 12).

Rice. 12. Elastic cartilage of the auricle: 1 - perichondrium; 2 - cartilage (a - main substance, b - elastic fibers, c - cartilage cell, d - cartilage capsule, e - separate group of cells)

Boneis the densest of all types of connective tissue. Its intercellular substance consists of fibers, which are often connected into bundles, and the ground substance, in which there is a large percentage of inorganic compounds, mainly calcium salts, so the supporting function of the bone is most pronounced. However, despite its density, bone tissue is a living system; it undergoes changes throughout a person’s life, accompanied by the renewal of its constituent elements, which ensures its adaptability to environmental conditions (Fig. 13).

Rice. 13. Bone (transverse cut of tubular bone): A - compact substance, B - spongy substance; 1 - periosteum; 2 - external common system of bone plates; 3 - osteon (a - Haversian canal); 4 - insertion system of plates; 5 - internal common plate system

Restructuring of bone tissue depends on age, nutrition, function of the internal secretion organs and other factors. The most pronounced changes in bone tissue occur during muscle activity: not only the internal structure of bone tissue changes, but also the shape of the organs - the bones that it forms.

There are three types of cellular elements in bone tissue: osteocytes, osteoblasts and osteoclasts.

Osteocyte(oss - bone, cytos - cell) - the main cell of bone tissue - has an irregular shape, a large number of long processes with which it contacts neighboring cells. These bone cells lie in special cavities.

Osteoblasts- creators, creators of bone tissue. They are located where the process of bone formation occurs. Their shape can be cubic, pyramidal or angular. As bone tissue forms, osteoblasts transform into osteocytes.

Osteoclasts- multinucleate cells. They are larger than osteocytes and osteoblasts. Each osteoclast can have up to 50 nuclei. A small depression is formed at the point of contact of the osteoclast with the bone substance. Osteoclasts lie in such depressions, coves. These cells destroy bone tissue, in its place a new one is formed. Both processes continuously occur in bone tissue - both the process of destruction and the process of creation, ensuring the reconstruction of the bone.

There are two types of bone tissue: coarse-fiber and fine-fiber, or lamellar.

Rough fibrous bone tissue It is found to a greater extent in the fetus; in adults it is found only in the places where muscle tendons attach to the bones, in the sutures between the bones of the skull. In the intercellular substance of coarse-fibrous bone tissue, the bundles of fibers are thick, located parallel, at an angle, or in the form of a network. Osteocytes have a flattened shape.

Fine fiber , or lamellar, bone the most highly differentiated. Its structural and functional unit is the bone plate. In the intercellular substance of the plate, the fibers are thin and oriented in certain directions parallel to each other. Osteocytes lie between the laminae or within the laminae. The plates are arranged so that the fibers in two adjacent plates run almost at right angles, which ensures special strength and elasticity of bone tissue. Almost all the bones of the adult human skeleton are built from fine-fiber bone tissue.

The concept of connective tissues combines tissues that are not identical in morphology and functions, but have some common properties and develop from a single source - mesenchyme.

Structural and functional features connective tissues

internal location in the body;
predominance of intercellular substance over cells;
variety of cell forms;
the common source of origin is mesenchyme.

Functions of connective tissues

trophic (metabolic);
supporting;
protective (mechanical, nonspecific and specific immunological);
reparative (plastic).

Classification of connective tissues

blood and lymph;
the connective tissues themselves are fibrous: loose and dense (formed and unformed); special: reticular, fatty, mucous, pigmented;
skeletal tissues - cartilaginous: hyaline, elastic, fibrous-fibrous; bone: lamellar, reticulo-fibrous.

Characteristics of loose fibrous connective tissue

It consists of cells and intercellular substance, which in turn consists of fibers (collagen, elastic, reticular) and amorphous substance. Morphological features that distinguish loose fibrous connective tissue from other types of connective tissue:

variety of cell forms (9 cell types);
the predominance of amorphous substance over fibers in the intercellular substance.

Functions of loose fibrous connective tissue:

trophic;
supporting forms the stroma of parenchymal organs;
protective - nonspecific and specific (participation in immune reactions) protection;
depot of water, lipids, vitamins, hormones;
reparative (plastic).

Structural and functional characteristics of cell types

Fibroblasts

The predominant population of cells is loose fibrous connective tissue. They are heterogeneous in degree of maturity and functional specificity and therefore are divided into the following subpopulations:

poorly differentiated cells;
differentiated or mature cells, or fibroblasts themselves;
old fibroblasts (definitive) fibrocytes, as well as specialized forms of fibroblasts;
myofibroblasts;
fibroclasts.

Macrophages

- cells that perform a protective function, primarily through phagocytosis of large particles, which is where their name comes from.

Protective function of macrophages manifests itself in different forms:

nonspecific protection - protection through phagocytosis of exogenous and endogenous particles and their intracellular digestion;
release of lysosomal enzymes and other substances into the extracellular environment: pyrogen, interferon, hydrogen peroxide, singlet oxygen and others;
specific or immunological defense - participation in a variety of immune reactions.

Tissue basophils

(mast cells, mast cells) are true cells of loose fibrous connective tissue. The function of these cells is to regulate local tissue homeostasis, that is, to maintain the structural, biochemical and functional constancy of the microenvironment. This is achieved through the synthesis by tissue basophils and the subsequent release into the intercellular environment of glycosaminoglycans (heparin and chondroitinsulfuric acids), histamine, serotonin and other biologically active substances, which affect both the cells and intercellular connective tissue, and especially the microvasculature, increasing permeability hemocapillaries and, thereby increasing the hydration of the intercellular substance. In addition, mast cell products influence immune processes, as well as inflammation and allergy processes. The sources of mast cell formation have not yet been established.

Mast cells take part in immune reactions. When certain antigenic substances enter the body, plasma cells synthesize immunoglobulins class E, which are then adsorbed on the cytolemma of mast cells. When these same antigens enter the body again, antigen-antibody immune complexes are formed on the surface of mast cells, which cause a sharp degranulation of tissue basophils, and the above-mentioned biologically active substances released in large quantities cause the rapid development of allergic and anaphylactic reactions.

Plasma cells

(plasmocytes) are cells of the immune system - effector cells of humoral immunity.

Fat cells

(adipocytes) are found in loose connective tissue in different quantities, in different parts of the body and in different organs.

Functions of fat cells:

energy resource depot;
water depot;
depot of fat-soluble vitamins.

The source of the formation of fat cells are adventitial cells, which under certain conditions accumulate lipids and turn into adipocytes.

Pigment cells

- (pigmentocytes, melanocytes) are process-shaped cells containing pigment inclusions - melanin - in the cytoplasm. Pigment cells are not true connective tissue cells, since, firstly, they are localized not only in connective tissue, but also in epithelial tissue, and secondly, they are not formed from mesenchymal cells, but from neural crest neuroblasts. Synthesizing and accumulating pigment in the cytoplasm melanin(with the participation of specific hormones), pigmentocytes perform a protective function: protecting the body from excess ultraviolet radiation.

Adventitial cells

localized in the adventitia of blood vessels. They have an elongated and flattened shape. The cytoplasm is weakly basophilic and contains a small number of organelles.

Perezits

The cells are flattened in shape, localized in the wall of the capillaries, in the splitting of the basement membrane. They promote the movement of blood in the capillaries, taking them over.

Leukocytes- lymphocytes and neutrophils. Normally, loose fibrous connective tissue necessarily contains blood cells in varying quantities - lymphocytes and neutrophils. In inflammatory conditions, their number increases sharply (lymphocytic or neutrophil infiltration). These cells perform a protective function.
Intercellular substance of connective tissue

It consists of two structural components:

basic or amorphous substance;
fibers

Basic or amorphous substance consists of proteins and carbohydrates.

Fibrous component intercellular substance is represented by collagen, elastic and reticular fibers. In different organs the ratio of these fibers is not the same. Collagen fibers predominate in loose connective fibrous tissue.

Collagen(glue-giving) fibers are white and vary in thickness (from 1-3 to 10 or more microns). They have high strength and low extensibility, do not branch, swell when placed in water, and when placed in acids and alkalis they increase in volume and shorten by 30%.

Elastic fibers characterized by high elasticity, that is, the ability to stretch and contract, but low strength, resistant to acids and alkalis, and do not swell when immersed in water.

Reticular fibers in their chemical composition they are close to collagen, since they consist of collagen protein (type 3) and a carbohydrate component.

Dense fibrous connective tissue differs from loose one in the predominance of the fibrous component in the intercellular substance over the amorphous one.

Tendon consists mainly of dense, formed connective tissue, but also contains loose fibrous connective tissue that forms layers.

Connective tissues with special properties

These include reticular, adipose, mucous and pigment tissue.

Reticular tissue

consists of reticular cells and reticular fibers. This tissue forms the stroma of all hematopoietic organs (with the exception of the thymus) and, in addition to the supporting function, performs other functions: it provides trophism for hematopoietic cells, influences the direction of their differentiation in the process of hematopoiesis and immunogenesis, carries out phagocytosis of antigenic substances and the presentation of antigenic determinants to immunocompetent cells.

Adipose tissue

consists of accumulations of fat cells and is divided into two types: white and brown adipose tissue. White adipose tissue widespread in various parts of the body and in internal organs, unequally expressed in different subjects and throughout ontogenesis. It consists of a cluster of typical adipocyte fat cells. Groups of fat cells form lobules of adipose tissue, between which there are thin layers of connective tissue containing blood vessels and nerves. Metabolic processes actively occur in fat cells.

Functions of white adipose tissue

energy depot (macroergs);
water depot;
depot of fat-soluble vitamins;
thermal protection;
mechanical protection of certain organs (eyeball and others).

Brown adipose tissue occurs only in newborns.

Mucous connective tissue

Pigment connective tissue

Connective tissue composition

Connective tissue forms the basis of the body, providing its strength. It not only forms organs, but also participates in all metabolic processes. It consists of cells, fibers and the main substance connecting them.

The main substance ensures the process of connecting cells and fibers. The main substance contains glycosaminoglycans - substances formed by polysaccharides and protein. The characteristics of the main substance in each organ depend on the ratio of various glycosaminoglycans, and this, in turn, determines its functions and structure. An important property of glycosaminoglycans is the ability to complicate or simplify their structure under the influence of various enzymes. For example, this property causes an increase in the permeability of blood vessels (their walls are lined with connective tissue) in the area of any inflammation; when this process is completed, the permeability of the vascular walls again becomes normal. The division of glycosaminoglycans into simpler compounds occurs when infections enter the body, intoxication (poisoning), hypoxia (lack of oxygen) and during the production of antibodies. Connective tissue includes two types of fibers: collagen and elastic. They are made up of proteins rich in certain amino acids, many of which are not found in other proteins.

Main functions of connective tissue

General signs of diseases

It should be noted that connective tissue diseases most often affect not only the musculoskeletal system, but also all other organs in which it is present. For example, this group includes such serious illnesses as rheumatism, as well as lupus erythematosus and scleroderma, which are characterized by severe damage to the skin and internal organs. In this case, a pathology called “systemic connective tissue disease” is diagnosed. There are a number of signs that are common to almost all connective tissue diseases.

In addition to the general symptoms listed, each connective tissue disease, of course, has special symptoms unique to it.

Connective tissue is found everywhere in the body. This fabric has the most varieties. This includes fat and bones with cartilage and tendons. Blood is also the connective tissue of our body. The main feature of any connective tissue is the presence of intercellular substance produced by the cells themselves. This substance consists of 2 components: amorphous and fibrous.

Concerning amorphous component, then it is represented by glycosaminoglycans (represent polysaccharides) and proteoglycans (consist of glycosaminoglycans with the addition of 5-10% protein). The consistency of the tissue depends on the amount of the amorphous component. For example, it is almost absent in blood plasma, because blood is liquid. In the composition of cartilage tissue, the amorphous component is present in large quantities, which provides it with the necessary properties.

Fibrous component The intercellular substance is represented by 2 types of fibers: collagen and elastic. Collagen fibers consist of collagen protein, have a diameter of 10 microns, long and crimped. Gives fabric strength. Collagen fibers tend to swell. Elastic fibers consist of the protein elastin, are less convoluted and have a diameter of 1 micron. The main function of elastic fibers is to impart elasticity (can be extended 2-3 times) to the fabric and return it to its original position after stretching. Reticular fibers are immature collagen fibers. Because they can be colored with silver salts, they are also called argyrophilic.

Localization and functions of connective tissue

According to its location in the body, connective tissue often occupies an intermediate position between other tissues, connecting different types of tissues into a single whole. For example, a layer of connective tissue called the dermis nourishes the superficial layer of skin through the basement membrane. Based on the above, we list the main functions of connective tissue in the body:

mechanical, supporting and shaping functions. This tissue makes up the body's support system: bones, cartilage, fascia, tendons, ligaments. It is part of the capsule and stroma of most organs, connects various types of tissues with each other;
protective and immune functions. Fascia protects muscle tissue, and skeletal bones protect many vital organs, including the heart and brain, from damage. Many subtypes of connective tissue are capable of phagocytosis and the production of immune bodies;
trophic function and storage function. By playing the role of an intermediary between various tissues, connective tissue can provide nutrition to them. The example with the dermis and epidermis was discussed above. As for the storage function, a good example is adipose tissue, which is the main depot of fat in the body;
exchange function. Connective tissue contributes to metabolism and maintaining a constant internal environment of the body;
plastic function. Connective tissue is involved in compensatory and adaptive reactions and tissue regeneration when damaged. Compensatory-adaptive reactions are the processes by which the body maintains a constant internal environment when the external environment surrounding the body changes or in the presence of an internal pathological process in the body itself.

Classification of connective tissue

We will adhere to the following classification. Connective tissue is divided into connective tissue itself and skeletal tissue. Skeletal is represented by bone and cartilage tissue. The connective tissue itself is divided into fibrous and tissues with special properties. Now let's look at these fabrics in more detail.

Fibrous connective tissue

There are loose, dense shaped and dense unshaped fibrous tissue.

present in the walls of all blood and lymphatic vessels, forms the stroma of many internal organs. The amorphous component of the intercellular substance (colloid) of loose tissue is capable of retaining fluid, thereby forming edema. The number of collagen and elastic fibers in loose connective tissue is very small, and those that exist are directed in different directions. Let's look at the types of cells typical for this subtype of tissue and their functions:

fibroblasts- the most numerous group of cells, the main function of which is the synthesis of all components of the intercellular substance. Under the influence of complex chemical processes, the proteins collagen and elastin are formed in them - the main material for the construction of the corresponding fibers. The second name is “weaver cells”. Mature fibroblasts that have completed their development cycle are called fibrocytes;
macrophages (histiocytes)– cells capable of phagocytosis, i.e. to the capture and digestion of foreign particles, bacteria, extracellular structures. They secrete lysozyme (against bacteria), pyrogens (increase in body temperature), interferon (against viruses) into the extracellular substance;
tissue basophils (mast cells - mast cells)- cells whose task is the secretion of histamine and heparin. Heparin prevents blood clotting, and histamine is released during inflammation. In particular, histamine contributes to the manifestation of allergic reactions;
poorly differentiated cells- a kind of “bench”. Can transform into other types of cells if necessary. These include lymphocytes, pericytes (C. Rouge cells);
plasmocytes (plasma cells) are responsible for humoral (non-cellular) immunity. Gamma globulins are synthesized when an antigen is detected in the body.

Both subtypes of dense connective tissue have a large number of closely spaced fibers. There are few cellular elements and amorphous components in them. Dense, unshaped fibrous fabric forms the connective tissue base of the skin (mesh layer). Its collagen and elastic fibers are intertwined, but go in different directions. Dense decorated fiber fabric has fibers strictly ordered in direction depending on the characteristics of the organ. This subtype of tissue forms muscle tendons, ligaments, membranes, and fascia.

Connective tissue with special properties

These tissues are a collection of homogeneous cells that perform a specific function. Let's consider 4 subtypes of these fabrics:

adipose tissue– represented by lipocyte cells and is a fat depot. It is divided into white and brown. Brown adipose tissue is characteristic only of newborns. Adipose tissue is localized in the subcutaneous fat layer, near the kidneys, in the mesentery, and in the omentum. Layers of loose connective tissue divide the fatty tissue into lobules. Fat is involved in thermoregulation processes and is a reserve of bound water;

reticular tissue consists of cells connected to each other by long reticular processes (the so-called reticular network). The intercellular substance contains many reticular fibers, which in terms of extensibility occupy an intermediate position between elastic and collagen. It forms the basis of the bone marrow, lymph nodes, and is part of the spleen, kidneys, and intestinal mucosa. The main function of reticular tissue is the formation of new blood cells;

mucous or gelatinous connective tissue occurs only at the embryonic stage in the umbilical cord. The jelly-like structure helps protect the umbilical vessels from compression and mechanical injury. This fabric is also called Wharton's jelly;
pigment connective tissue with consists of melanocyte cells containing the pigment melanin. Accumulations of this tissue are found in the scrotum area, around the nipples, anal ring, iris, and also in birthmarks.

Cartilaginous connective tissue

Cartilage tissue is a type of skeletal tissue and has its own morphological characteristics. The amorphous substance here is very dense due to the concentration of the above-mentioned glycominoglycans and proteoglycans. On top of the cartilage, the entire surface is covered with a layer called perichondrium, due to which the growth of cartilage occurs. Amorphous and fibrous components are synthesized in young cells - chondroblasts located in the inner layer of the perichondrium. The cartilage itself does not have blood vessels; its nutrition comes from the capillaries of the perichondrium. With age, chondroblasts become covered with a special capsule and become part of the cartilage. Now they have become chondrocytes. The intercellular substance of cartilage tissue is so dense that when chondrocytes divide, the daughter cells cannot move away from the mother. Therefore, chondrocytes are located in groups in a small cavity. There are three types of cartilage:

elastic cartilage forms the auricles, part of the auditory tube and external auditory canal, epiglottis, cartilages of the larynx, i.e. anatomical formations where the cartilaginous base is subject to bending. The intercellular substance is rich in elastic fibers, however, collagen fibers are also present. Elastic cartilage has a yellowish color, is less transparent than hyaline cartilage and, unlike it, almost never calcifies in old age;

fibrocartilage forms intervertebral discs, is part of intra-articular discs and menisci, as well as the temporomandibular and sternoclavicular joints. The intercellular substance is rich in collagen fibers. In older people it becomes calcified.

Bone tissue and its types

The main cells of any bone are osteocytes located in the calcified intercellular substance, which practically does not contain an amorphous component. Between the osteocytes there are osein (collagen) fibers and inorganic salts. This tissue forms our skeleton and at the same time is a depot of minerals, such as calcium and phosphorus. There are 3 types of bone tissue cells:

osteoblasts – young cells synthesizing intercellular substance. They are located in the vascular-rich surface layer of bone - the periosteum. During development, osteoblasts transform into osteocytes;
osteocytes represent the main substance of bone;
osteoclasts – destroyer cells. Bone substance is constantly renewed, so aging bone is destroyed by osteoclasts, and the vacant space is taken by young osteocytes. Osteoclasts also play an important role in the formation of bones in the embryonic period, destroying cartilage which is replaced by bone tissue.

There are several types of bone tissue. Rough fibrous bone textile It is distinguished by a random and multidirectional arrangement of ossein fibers. Occurs in embryos and young organisms. In adults, it can only be found in the sutures of the skull and places where the tendons are attached to the bones. In other parts of the body, as the organism develops, coarse fibrous tissue is replaced by lamellar tissue.

Lamellar bone tissue It is a set of bone plates, inside and between which there are parallel bundles of ossein fibers. This fabric comes in 2 types:

Connective tissues belong to the tissues of the internal environment and are classified into connective tissue itself and skeletal tissue (cartilage and bone). The connective tissue itself is divided into 1) fibrous, including loose and dense, which is divided into formed and unformed 2) tissues with special properties (fatty, mucous, reticular and pigmented).

The composition of loose and dense connective tissue includes cells and intercellular substance. Loose connective tissue has many cells and the main intercellular substance, while dense connective tissue has few cells and the main intercellular substance and many fibers. Depending on the ratio of cells and intercellular substance, these tissues perform different functions. In particular, loose connective tissue performs a trophic function to a greater extent and a supporting-mechanical function to a lesser extent; dense connective tissue performs a supporting-mechanical function to a greater extent.

GENERAL FUNCTIONS OF CONNECTIVE TISSUE:

trophic;
mechanical protection function (skull bones)
musculoskeletal (bone, cartilage tissue, tendons, aponeuroses)
shape-forming function (the sclera of the eye gives the eye a certain shape)
protective function (phagocytosis and immunological defense);
plastic function (ability to adapt to new environmental conditions, participation in wound healing);
participation in maintaining homeostasis of the body.

LOOSEN CONNECTIVE TISSUE (textus connectivus collagenosus laxus) includes cells and intercellular substance, which consists of the main intercellular substance and fibers: collagen, elastic and reticular. Loose connective tissue is located under the basement membranes of the epithelium, accompanies blood and lymphatic vessels, and forms the stroma of organs.

CELLS:

q fibroblasts,

q macrophages,

q plasma cells,

q tissue basophils (mast cells, mast cells),

q adipocytes (fat cells)

q pigment cells (pigmentocytes, melanocytes),

q adventitial cells,

q reticular cells

q blood leukocytes.

Thus, connective tissue includes several cell differons.

FIBROBLAST DIFFERON: stem cell, semi-stem cell, precursor cell, poorly differentiated fibroblasts, differentiated fibroblasts and fibrocytes. Myofibroblasts and fibroclasts can develop from poorly differentiated fibroblasts. Fibroblasts develop in embryogenesis from mesenchymal cells, and in the postnatal period - from stem and adventitial cells.

POORLY DIFFERENTIATED FIBROBLASTS have an elongated shape, about 25 microns in length, contain few processes, the cytoplasm is stained basophilically, since it contains a lot of RNA and ribosomes. The nucleus is oval, contains clumps of chromatin and a nucleolus. FUNCTION is the ability to undergo mitotic division and further differentiation, as a result of which they turn into differentiated fibroblasts. Among fibroblasts there are long-lived and short-lived.

DIFFERENTIATED FIBROBLASTS(fibroblastocytus) have an elongated, flattened shape, about 50 µm in length, contain many processes, weakly basophilic cytoplasm, well-developed granular ER, and have lysosomes. Collagenase was found in the cytoplasm. The nucleus is oval, weakly basophilic, contains loose chromatin and nucleoli. Along the periphery of the cytoplasm there are thin filaments, thanks to which fibroblasts are able to move in the intercellular substance.

FUNCTIONS OF FIBROBLASTS. The main function is secretory. 1) secrete molecules of collagen, elastin and reticulin, from which collagen, elastic and reticulin fibers are polymerized, respectively; secretion of proteins is carried out by the entire surface of the plasmalemma, which is involved in the assembly of collagen fibers; 2) secrete glycosaminoglycans, which are part of the main intercellular substance (keratin sulfates, heparin sulfates, chondriatine sulfates, dermatan sulfates and hyaluronic acid); 3) secrete fibronectin (adhesive substance); 4) proteins connected to glycosaminoglycans (proteoglycans). In addition, fibroblasts perform a weakly expressed phagocytic function. Thus, differentiated fibroblasts are the cells that actually form connective tissue. Where there are no fibroblasts there cannot be connective tissue.

Fibroblasts function actively in the presence of vitamin C, Fe, Cu and Cr compounds in the body. With hypovitaminosis, the function of fibroblasts weakens, i.e. renewal of connective tissue fibers stops, glycosaminoglycans, which are part of the main intercellular substance, are not produced, this leads to weakening and destruction of the body’s ligamentous apparatus, for example, dental ligaments. At the same time, teeth are destroyed and fall out. As a result of the cessation of hyaluronic acid production, the permeability of the capillary walls and surrounding connective tissue increases, which leads to pinpoint hemorrhages. This disease is called scurvy.

FIBROCYTES are formed as a result of further differentiation of differentiated fibroblasts. They contain nuclei with rough clumps of chromatin; they lack nucleoli. Fibrocytes are reduced in size, there are few poorly developed organelles in the cytoplasm, and functional activity is reduced.

MYOFIBROBLASTS develop from poorly differentiated fibroblasts. Myofilaments are well developed in their cytoplasm, so they are able to perform a contractile function. Myofibroblasts are present in the wall of the uterus during pregnancy. Due to myofibroblasts, a significant increase in the mass of smooth muscle tissue of the uterine wall occurs during pregnancy.

FIBROCLASTS also develop from poorly differentiated fibroblasts. In these cells, lysosomes are well developed, containing proteolytic enzymes that take part in the lysis of intercellular substance and cellular elements. Fibroclasts take part in the resorption of muscle tissue of the uterine wall after childbirth. Fibroclasts are found in healing wounds, where they take part in cleansing wounds from necrotic tissue structures.

MACROPHAGES(macrophagocytus) develop from HSCs, monocytes, they are found everywhere in the connective tissue, especially in places where the circulatory and lymphatic network of vessels is richly developed. The shape of macrophages can be oval, rounded, elongated, size - up to 20-25 microns in diameter. There are pseudopodia on the surface of macrophages. The surface of macrophages is sharply outlined; on their cytolemma there are receptors for antigens, immunoglobulins, lymphocytes and other structures.

CORE macrophages have an oval, round or elongated shape and contain rough clumps of chromatin. There are multinucleated macrophages (giant cells of foreign bodies, osteoclasts). The CYTOPLASM of macrophages is weakly basophilic, contains many lysosomes, phagosomes, and vacuoles. Organelles of general importance are moderately developed.

FUNCTIONS OF MACROPHAGES numerous. The main function is phagocytic. With the help of pseudopodia, macrophages capture antigens, bacteria, foreign proteins, toxins and other substances and, with the help of lysosome enzymes, digest them, carrying out intracellular digestion. In addition, macrophages perform a secretory function. They secrete lysozyme, which destroys the bacterial membrane, pyrogen, which increases body temperature, interferon, which inhibits the development of viruses, secrete interleukin 1, under the influence of which DNA synthesis increases in B and T lymphocytes, a factor that stimulates the formation of antibodies in B lymphocytes, a factor that stimulating the differentiation of T- and B-lymphocytes, a factor that stimulates the chemotaxis of T-lymphocytes and the activity of T-helper cells, a cytotoxic factor that destroys malignant tumor cells. Macrophages take part in immune reactions. They represent lymphocyte antigens.

In total, macrophages are capable of direct phagocytosis, antibody-mediated phagocytosis, secretion of biologically active substances, and presentation of antigens to lymphocytes.

MACROPHAGIC SYSTEM includes all cells of the body that have three main characteristics: 1) perform a phagocytic function, 2) on the surface of their cytolemma there are receptors for antigens, lymphocytes, immunoglobulins, etc., 3) they all develop from monocytes. An example of such macrophages are:

q 1) macrophages (histiocytes) of loose connective tissue; 2) Kupffer cells of the liver; 3) pulmonary macrophages; 4) giant cells of foreign bodies; 5) osteoclasts of bone tissue; 6) retroperitoneal macrophages; 7) glial macrophages of nervous tissue.

The founder of the theory about the macrophage system in the body is I.I. Mechnikov. He first understood the role of the macrophage system in protecting the body from bacteria, viruses and other harmful factors.

TISSUE BASOPHILES (mast cells, mast cells)

probably develop from blood stem cells, but this has not been established for sure. The shape of mast cells is oval, round, elongated, etc. The NUCLEI are compact and contain coarse clumps of chromatin. CYTOPLASM is weakly basophilic, containing basophilic granules with a diameter of up to 1.2 microns. The granules contain: 1) crystalloid, lamellar, mesh and mixed structures; 2) histamine; 3) heparin; 4) serotonin, 5) chondriatic sulfuric acids; 6) hyaluronic acid. The cytoplasm contains enzymes:

1) lipase; 2) acid phosphatase; 3) alkaline phosphatase; 4) adenosine triphosphatase (ATPase); 5) cytochrome oxidase and 6) histidine decarboxylase, which is a marker enzyme for mast cells. FUNCTIONS

tissue basophils are that, by releasing heparin, they reduce the permeability of the capillary wall and inflammation processes, by releasing histamine they increase the permeability of the capillary wall and the main intercellular substance of the connective tissue, i.e. regulate local homeostasis, enhance inflammatory processes and cause allergic reactions. The interaction of mast cells with an allergen leads to their degranulation, because on their plasmalemma there are receptors for type E immunoglobulins. Labrocytes play a leading role in the development of allergic reactions.

PLASMO CYTES develop during the differentiation of B-lymphocytes, have a round or oval shape, diameter - 8-9 microns, the cytoplasm is stained basophilic. However, there is an area near the nucleus that is not stained and is called the “perinuclear courtyard”, in which the Golgi complex and the cell center are located. The nucleus is round or oval, the perinuclear court is shifted to the periphery, and contains rough clumps of chromatin arranged in the form of spokes in a wheel. The cytoplasm has a well-developed granular EPS and many ribosomes. The remaining organelles are moderately developed. The FUNCTION of plasma cells is to produce immunoglobulins, or antibodies.

ADIPOCYTES(fat cells) are located in loose connective tissue in the form of individual cells or groups. Single adipocytes have a round shape; the entire cell is occupied by a drop of neutral fat, consisting of glycerol and fatty acids. In addition, there are cholesterol, phospholipids, and free fatty acids. The cytoplasm of the cell, together with the flattened nucleus, is pushed toward the cytolemma. The cytoplasm contains small mitochondria, pinocytosis vesicles and the enzyme glycerol kinase.

FUNCTIONAL VALUE adipocytes is that they are sources of energy and water. Adipocytes most often develop from poorly differentiated adventitial cells, in the cytoplasm of which lipid droplets begin to accumulate. Absorbed from the intestine into the lymphatic capillaries, lipid droplets called chylomicrons are transported to the sites where adipocytes and adventitial cells are located. Under the influence of lipoprotein lipases secreted by capillary endothelial cells, chylomicrons are broken down into glycerol and fatty acids, which enter either the adventitia or the fat cell. Inside the cell, glycerol and fatty acids are combined into neutral fat by the action of glycerol kinase.

If the body needs energy, adrenaline is released from the adrenal medulla, which is captured by the adipocyte receptor. Adrenaline stimulates adenylate cyclase, under the influence of which a signaling molecule is synthesized, i.e. cyclic adenosine monophosphate (cAMP). cAMP stimulates adipocyte lipase, under the influence of which neutral fat is broken down into glycerol and fatty acids, which are released by the adipocyte into the lumen of the capillary, where they combine with protein and are transported in the form of lipoprotein to those places where energy is needed.

Insulin stimulates the deposition of lipids in adipocytes and prevents their release from these cells. Therefore, if there is not enough insulin in the body (diabetes), then adipocytes lose lipids, and patients lose weight.

PIGMENT CELLS(melanocytes) are found in connective tissue, although they are not connective tissue cells themselves; they develop from the neural crest. Melanocytes have a process form, light cytoplasm, poor in organelles, containing granules of the melanin pigment.

ADVENTIAL CELLS located along blood vessels, have a spindle shape, weakly basophilic cytoplasm containing ribosomes and RNA.

FUNCTIONAL VALUE The difference lies in the fact that they are poorly differentiated cells capable of mitotic division and differentiation into fibroblasts, myofibroblasts, and adipocytes in the process of accumulating lipid droplets in them.

There is a lot of connective tissue LEUKOCYTES, which circulate in the blood for several hours, then migrate to the connective tissue, where they perform their functions.

PERICYTES are part of the capillary wall and have a process shape. The processes of pericytes contain contractile filaments, the contraction of which narrows the lumen of the capillary.

INTERCELLULAR SUBSTANCE of loose connective tissue includes collagen, elastic and reticular fibers, as well as ground (amorphous) substance.

COLLAGEN FIBERS

(fibra collagenica) consist of collagen protein, have a thickness of 1-10 microns, an indefinite length, and a tortuous course. Collagen proteins have 14 varieties (types).

q Type 1 COLLAGEN is found in bone tissue fibers and the reticular layer of the dermis.

q COLLAGEN II type is found in hyaline and fibrous cartilage and in the vitreous body of the eye.

q Type III COLLAGEN is part of reticular fibers.

q Type IV COLLAGEN is present in the fibers of the basement membranes and lens capsule.

q Type V COLLAGEN is located around those cells that produce it (smooth myocytes, endothelial cells), forming a pericellular or pericellular skeleton.

Other types of collagen have been little studied.

FORMATION OF COLLAGEN FIBERS carried out in the process of four levels of organization. Level I is called molecular, or intracellular; II - supramolecular, or extracellular; III - fibrillar and IV - fiber.

v I LEVEL OF ORGANIZATION is characterized by the fact that collagen molecules (tropocollagen) with a length of 280 nm and a diameter of 1.4 nm are synthesized on the granular EPS of fibroblasts. Molecules consist of 3 chains of amino acids, alternating in a certain order. These molecules are released from fibroblasts by the entire surface of their cytolemma.

v II LEVEL of organization, characterized by the fact that collagen molecules (tropocollagen) are connected at their ends, resulting in the formation of protofibrils. 5-6 protofibrils are connected by their lateral surfaces and fibrils with a diameter of about 10 nm are formed.

v LEVEL III (fibrillar) is characterized by the fact that the formed fibrils are connected by their lateral surfaces, resulting in the formation of microfibrils with a diameter of 50-100 nm. These fibrils exhibit light and dark stripes (cross-striations) approximately 64 nm wide.

v IV LEVEL of organization (fibrous) is that microfibrils are connected by their lateral surfaces, resulting in the formation of collagen fibers with a diameter of 1-10 microns.

FUNCTIONAL VALUE collagen fibers is that they impart mechanical strength to connective tissue. For example, a mass of 70 kg can be suspended on a collagen thread with a diameter of 1 mm. Collagen fibers swell in solutions of acids and alkalis. They anastomose with each other.

ELASTIC FIBERS

thinner ones, have a straight course, connecting with each other, form a wide-loop network, and consist of the protein elastin. The formation of elastic fibers undergoes 4 levels of organization: 1) molecular, or intracellular; 2) supramolecular or extracellular; 3) fibrillar; 4) fiber.

v LEVEL 1 is characterized by the formation of balls or globules with a diameter of about 2.8 nm on the granular EPS of fibroblasts, which are released from the cell.

v LEVEL II (supramolecular) is characterized by the connection of globules into chains (protofibrils) with a diameter of about 3.5 nm.

v III LEVEL (fibrillar) as a result of which proteoglycans are layered on protofibrils in the form of a shell and fibrils with a diameter of 10 nm are formed.

v LEVEL IV (fibrous) as a result of which the fibrils, joining, form a bundle, or tube. These tubes are called oxytalan fibers. Then an amorphous substance is introduced into the lumen of these tubes. When the amount of amorphous substance in the forming fibers increases to 50% in relation to fibrils, these fibers will turn into elaunin fibers, when the amount of amorphous substance reaches 90% - these fibers are mature, elastic fibers. Oxytalan and elaunin are immature elastic fibers.

FUNCTIONAL VALUE elastic fibers is that they give elasticity to connective tissue. Elastic fibers have less tensile strength than collagen fibers, but are more stretchable.

RETICULAR FIBERS consist of type III collagen protein. These proteins are also produced by fibroblasts. The formation of reticulin fibers also undergoes 4 levels of organization in the same way as collagen fibers. The fibrils of reticular fibers have striations in the form of light and dark stripes 64-67 nm wide (as in collagen fibers). Reticular fibers are less strong but more extensible than collagen fibers, but they are stronger and less extensible than elastic fibers. Reticulin fibers intertwine to form a network.

BASIC (AMORPHOUS) INTERCELLULAR SUBSTANCE

(sustantia fundamentalis) has a semi-liquid consistency. It is formed partly due to blood plasma, from which water, mineral salts, albumins, globulins and other substances come; partly due to the functional activity of fibroblasts and tissue basophils. In particular, fibroblasts secrete sulfated (chondriotin sulfates, keratin sulfates, heparin sulfates, dermatan sulfates) and non-sulfated (hyaluronic acid) glycosaminoglycans into the intercellular substance; glycoproteins (proteins connected to short saccharide chains). The consistency and permeability of the main intercellular substance mainly depends on the amount of hyaluronic acid. The most liquid basic intercellular substance is located near the blood and lymphatic vessels. At the border with epithelial tissue, the main intercellular substance is denser and is found in greater quantities.

FUNCTIONAL VALUE The main intercellular substance is that through it the exchange of substances occurs between the bloodstream of the capillaries and parenchyma cells. In the main intercellular substance, polymerization of collagen, elastic and reticulin fibers occurs. The main substance ensures the vital activity of connective tissue cells.

The intensity of metabolism depends on the permeability of the main intercellular substance. Permeability depends on the amount of free water, hyaluronic acid, hyaluronidase activity, glycosaminoglycan and histamine concentrations. The more glycosaminoglycans (hyaluronic acid), the less permeability. Hyaluronidase destroys hyaluronic acid and thereby increases permeability. Histamine also increases the permeability of the main intercellular substance. Basophilic granulocytes and mast cells take part in the regulation of the permeability of the main substance of connective tissue, releasing either heparin or histamine, as well as eosinophilic granulocytes, which destroy histamine using the enzyme histaminase.

Hyaluronidase is found in bacteria and viruses. Thanks to hyaluronidase, these microorganisms increase the permeability of basement membranes, the main intercellular substance and the capillary wall and penetrate into the internal environment of the body, causing various diseases.

DENSE CONNECTIVE TISSUE characterized by the smallest number of cellular elements and the main intercellular substance; fibers, mainly collagen, predominate in it.

Dense connective tissue is divided into unformed and formed. An example of unformed connective tissue is the reticular layer of the dermis.

DENSE CONNECTIVE TISSUE is represented by tendons, ligaments, muscle aponeuroses, joint capsules, membranes of some organs, tunica albuginea of the eye, male and female gonads, dura mater, periosteum and perichondrium.

TENDON (tendo) consists of parallel fibers, forming bundles of the 1st, 2nd and 3rd orders. First-order bundles are separated from each other by tendon cells, or fibrocytes; several first-order bundles are folded into second-order bundles, which are separated from each other by a layer of loose connective tissue called endotendium; several bundles of the second order are folded into bundles of the third order. The tendon itself can be a bundle of the third order. III-order bundles are surrounded by a layer of loose connective tissue called peritendium.

In the layers of loose connective tissue of endotenonium and peritenonium, blood and lymphatic vessels and nerve fibers pass, ending in neurotendon spindles, i.e. sensitive nerve endings of tendons.

FUNCTIONAL VALUE tendons is that with their help the muscles are attached to the bone skeleton.

CONNECTIVE TISSUE PLATES (fascia, aponeuroses, tendon centers, etc.) are characterized by a parallel layer-by-layer arrangement of collagen fibers. The collagen fibers of one layer of the plate are located at an angle relative to the fibers of the other layer. Fibers from one layer can move into the adjacent layer. Therefore, layers of aponeuroses, fascia, etc. quite difficult to separate. Thus, connective tissue plates differ from tendons in that collagen fibers are located in them not in bundles, but in layers. Fibrocytes and fibroblasts are located between the layers of collagen fibers.

Ligaments (ligamentum) are similar in structure to tendons, but differ from tendons in a less strict arrangement of fibers. Among the ligaments, the nuchal ligament (ligamentum nuche) stands out, which differs in that instead of collagen fibers it contains elastic fibers.

In capsules, tunica albuginea, periosteum, perichondrium, dura mater, unlike fascia and aponeuroses, there is no strict arrangement of collagen fibers.

DENSE UNFORMED CONNECTIVE TISSUE, located in the reticular layer of the skin, is distinguished by an irregular (multidirectional) arrangement of collagen and elastic fibers, and develops from the dermatome of mesodermal somites. FUNCTIONAL VALUE This fabric is to provide mechanical strength to the skin.

FABRICS WITH SPECIAL PROPERTIES include fatty, reticular, mucous and pigment. A feature of these tissues is the predominance of one type of cell. For example, adipocytes predominate in adipose tissue, melanocytes predominate in pigment tissue, etc.

RETICULAR TISSUE (textus reticularis) is the stroma of the hematopoietic organs with the exception of the thymus, in which the stroma is epithelial tissue. Reticular tissue consists of reticular cells and reticulin fibers closely associated with these cells and the main intercellular substance. RETICULAR CELLS are divided into 3 types: 1) fibroblast-like cells, which perform the same function as fibroblasts of loose connective tissue, i.e. produce type III collagen, which makes up reticulin fibers, and secrete the main intercellular substance; 2) macrophage reticulocytes, which perform a phagocytic function, and 3) poorly differentiated cells, which during the process of differentiation turn into fibroblast-like reticulocytes.

Reticulin fibers are woven into the processes of fibroblast-like reticulocytes and together with them form a network (reticulum), in the loops of which hematopoietic cells are located. Reticular fibers are stained with silver and are therefore called argentophilic. Precollagen (immature collagen) fibers are also stained with silver and are also called argentophilic, but they have nothing to do with reticulin fibers.

ADIPOSE TISSUE is divided into white and brown adipose tissue. WHITE ADIPOSE TISSUE is located in the subcutaneous fatty tissue. It is especially abundant in the skin of the abdomen, thighs, buttocks, in the lesser and greater omentum, retroperitoneally (retroperitoneal). It consists of adipocyte fat cells, the cytoplasm of which is filled with a drop of neutral fat. Adipocytes in adipose tissue form lobules surrounded by layers of loose connective tissue, in which blood and lymphatic capillaries and nerve fibers pass.

During prolonged fasting, lipids are released from adipocytes, which acquire a star-shaped shape, and the person loses weight. When nutrition is restored, inclusions of glycogen first appear in adipocytes, then drops of lipids, which combine into one large drop, pushing the nucleus and cytoplasm to the periphery of the cell.

However, lipids from adipocytes do not quickly disappear during fasting in all parts of the body. For example, the adipose tissue of the subcutaneous fatty tissue of the palmar surface of the hands, the soles of the feet, and the orbits of the eyes is preserved after prolonged fasting, because this tissue performs a support-mechanical (shock-absorbing) function.

Brown adipose tissue in the body of newborns is located in the subcutaneous fat in the neck, shoulder blades, along the spinal column and behind the sternum. Adipocytes of this tissue are characterized by the fact that they have a polygonal shape, relatively small sizes, their round nuclei are located in the center, and lipid droplets are diffusely scattered in the cytoplasm. The cytoplasm contains many mitochondria, which contain iron-containing brown pigments called cytochromes.

FUNCTIONAL VALUE brown adipose tissue is that it has a high oxidative capacity, and a lot of thermal energy is released, which warms the body of an infant.

When adrenaline and norepinephrine act on adipocytes of adipose tissue, lipids are broken down. When the body is starved, brown adipose tissue changes less significantly than white adipose tissue. Numerous capillaries run between the adipocytes of brown adipose tissue.

MUCOUS CONNECTIVE TISSUE is located in the umbilical cord of the fetus. It consists of mukocytes (fibroblast-like cells), relatively few collagen fibers, and a lot of basic intercellular substance containing a large amount of hyaluronic acid. Mucocyte function: produce a lot of hyaluronic acid and few collagen molecules. Due to the rich content of hyaluronic acid, mucous tissue (textus mucosus) has high elasticity.

FUNCTIONAL VALUE mucous tissue is that, due to its elasticity, the blood vessels of the umbilical cord are not compressed when it is compressed or bent.

PIGMENT TISSUE is poorly represented among representatives of the white race. It is found in the iris, around the nipples, the anus and in the scrotum. The main cells of this tissue are pigment cells that develop from the neural crest.