Fibrous tissue structure and functions. Structure and functions of connective tissue, main cell 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:

1. trophic;
2. mechanical protection function (skull bones)
3. musculoskeletal (bone, cartilage tissue, tendons, aponeuroses)
4. shape-forming function (the sclera of the eye gives the eye a certain shape)
5. protective function (phagocytosis and immunological defense);
6. plastic function (ability to adapt to new environmental conditions, participation in wound healing);
7. 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 digest them with the help of lysosome enzymes, 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 stimulating 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 was the first to understand 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% relative 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.

Distinctive characteristic of dense fibrous connective tissue:

· very high content of fibers that form thick bundles that occupy the bulk of the fabric volume;

· small amount of basic substance;

· predominance of fibrocytes.

· the main property is high mechanical strength.

Unformed dense connective tissue– this type of tissue is characterized by a disordered arrangement of collagen bundles forming a three-dimensional network. The spaces between the fiber bundles contain the main amorphous substance, which unites the tissue into a single skeleton, cells - fibrocytes (mainly) and fibroblasts, blood vessels, and nerve elements. Unformed dense connective tissue forms a reticular layer of the dermis and capsules of various organs. Performs a mechanical and protective function.

Formed dense connective tissue differs in that the collagen bundles in it lie parallel to each other (in the direction of the load). Forms tendons, ligaments, fascia and aponeuroses (in the form of plates). Between the fibers there are fibroblasts and fibrocytes. In addition to collagen, there are elastic ligaments (vocal, yellow, connecting the vertebrae), formed by bundles of elastic fibers.

INFLAMMATION

Inflammation is a protective-adaptive reaction to local damage, developed during evolution. Factors that cause inflammation can be exogenous (infection, injury, burn, hypoxia) or endogenous (focus of necrosis, salt deposition). The biological meaning of this protective reaction is the elimination or restriction of the source of damage from healthy tissue, and tissue regeneration. Although this is a protective reaction, in some cases the manifestations of this reaction, especially chronic inflammation, can cause severe tissue damage.

Phases of inflammation:

I. alteration phase– tissue damage and discharge inflammatory mediators, a complex of bioactive substances responsible for the occurrence and maintenance of inflammatory phenomena.

Inflammatory mediators:

humoral(from blood plasma) – kinins, coagulation factors, etc.;

cellular mediators secreted by cells in response to damage; produced by monocytes, macrophages, mast cells, granulocytes, lymphocytes, platelets. These mediators: bioamines (histamine, serotonin), eicosanoids (arachid derivatives O new acid: prostaglandins, leukotri e us), and others.

II. exudation phase includes:

· changes in microcirculation I thoracic bed: spasm of arterioles, then dilatation of arterioles, capillary and venules - hyperemia occurs And I – redness and fever.

· formation of liquid (cell-free) exudate - due to increased vascular permeability, changes in osmotic pressure at the site of inflammation (due to damage) and hydrostatic pressure in the vessels. Outflow disturbance leads to the emergence edema.

· formation of cellular exudate (migration of leukocytes through the endothelium).

Cellular composition phases of inflammation:

1 phase : in the initial stages, evictions are most active neutrophil granulocytes, which perform phagocytic and microbicidal functions; as a result of their activity, decay products are formed that attract monocytes to the site of inflammation, evicting them from the blood;

2 phase : monocytes in connective tissue turn into macrophages. Macrophages phagocytose dead neutrophils, cellular detritus, microorganisms and can initiate an immune response.

IN focus of chronic inflammation microphages and lymphocytes predominate, which form clusters - granulomas. By merging, macrophages form giant multinucleated cells.

III. proliferation phase (repair) – Macrophages, lymphocytes and other cells cause: chemotaxis, proliferation and stimulation of synthetic activity fibroblasts; activation of the formation and growth of blood vessels. Young granulation tissue is formed, collagen is deposited, and a scar is formed.

CONNECTIVE TISSUE WITH SPECIAL PROPERTIES

ADIAT TISSUE

Adipose tissue is a special type of connective tissue, in which the main volume is occupied by fat cells - adipocytes. Adipose tissue is ubiquitous in the body, accounting for 15-20% of body weight in men and 20-25% in women (i.e. 10-20 kg in a healthy person). With obesity (and in developed countries this is about 50% of the adult population), the mass of adipose tissue increases to 40-100 kg. Abnormalities in the content and distribution of adipose tissue are associated with a number of genetic disorders and endocrine disorders.

Mammals, including humans, have two types of adipose tissue: white And brown, which differ in color, distribution in the body, metabolic activity, the structure of the cells that form them (adipocytes) and the degree of blood supply.

White adipose tissue – the predominant type of adipose tissue. Forms superficial (hypodermis - a layer of subcutaneous fatty tissue) and deep - visceral - accumulations, forms soft elastic layers between internal organs.

During embryogenesis, adipose tissue develops from mesenchyme. The precursors of adipocytes are poorly differentiated fibroblasts (lipoblasts) lying along the course of small blood vessels. During differentiation, small lipid droplets are first formed in the cytoplasm, the droplets merge with each other, forming one large drop (95-98% of the cell volume), and the cytoplasm and nucleus shift to the periphery. These fat cells are called single-droplet adipocytes. Cells lose their processes, acquire a spherical shape, and during development their size increases 7-10 times (up to 120 microns in diameter). The cytoplasm is characterized by a developed agranular ER, a small Golgi complex, and a small number of mitochondria.

White adipose tissue consists of lobules (compact clusters of adipocytes) separated by thin layers of loose fibrous connective tissue carrying blood and lymphatic vessels and nerves. In the lobules, the cells take on the shape of polyhedra.

Functions of white adipose tissue:

· energetic (trophic): adipocytes have high metabolic activity: lipogenesis (deposition of fats) - lipolysis (mobilization of fats) - providing the body with reserve sources;

· supporting, protective, plastic– completely or partially surrounds various organs (kidneys, eyeball, etc.). Sudden weight loss can lead to kidney displacement;

· heat insulating;

· regulatory– in the process of myeloid hematopoiesis, adipocytes are part of the stromal component of the red brain, which creates a microenvironment for proliferating and differentiating blood cells;

· depositing ( vitamins, steroid hormones, water )

· endocrine– synthesizes estrogens (the main source in men and

elderly women) and a hormone that regulates food intake - leptin Leptin inhibits the secretion of a special neuropeptide NPY by the hypothalamus, which increases food intake. During fasting, leptin secretion decreases, and during saturation, it increases. Insufficient leptin production (or lack of leptin receptors in the hypothalamus) leads to obesity.

Obesity

In 80% of cases, the increase in adipose tissue mass occurs due to an increase in the volume (hypertrophy) of adipocytes. In 20% (with the most severe forms of obesity developing at a young age) there is an increase in the number of adipocytes (hyperplasia): the number of adipocytes can increase 3-4 times.

Starvation

A decrease in body weight as a result of therapeutic or forced fasting is accompanied by a decrease in adipose tissue mass - increased lipolysis and inhibition of lipogenesis - a sharp decrease in adipocyte volumes with maintaining their total number. When normal nutrition is resumed, cells quickly accumulate lipids, the cells increase in size and turn into typical adipocytes, resulting in rapid restoration of body weight after discontinuation of the diet. Adipose tissue on the palms, soles and retro-orbital areas is very resistant to lipolysis processes. A decrease in adipose tissue mass by more than a third of the norm causes dysfunction of the hypothalamic-pituitary-ovarian system - suppression of the menstrual cycle and infertility. Anorexia nervosa is a type of eating disorder in which the fat reserve is reduced to 3% of the normal level of adipose tissue mass, often resulting in death.

Brown adipose tissue

In an adult, brown adipose tissue is present in small quantities, only in a few clearly defined areas (between the shoulder blades, on the back of the neck, at the hilum of the kidneys). In newborns it makes up up to 5% of body weight. Its content changes little with insufficient or excess nutrition. Brown adipose tissue is most strongly developed in animals that hibernate.

Connective tissues- this is a complex of mesenchymal derivatives, consisting of cellular differons and a large amount of intercellular substance (fibrous structures and amorphous substance), involved in maintaining the homeostasis of the internal environment and differing from other tissues by a lesser need for aerobic oxidative processes.

Connective tissue makes up more than 50% of the human body weight. It participates in the formation of the stroma of organs, the layers between other tissues, the dermis of the skin, and the skeleton.

The concept of connective tissues (tissues of the internal environment, supporting-trophic tissues) combines tissues that are different in morphology and functions, but have some common properties and develop from a single source - mesenchyme.

Structural and functional features of 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:

mechanical;

supporting and form-building;

protective (mechanical, nonspecific and specific immunological);

reparative (plastic).

trophic (metabolic);

morphogenetic (structure-forming).

Connective tissues themselves:

Fibrous connective tissues:

Loose fibrous unformed connective tissue

Unformed

Dense fibrous connective tissue:

Unformed

Decorated

Connective tissues with special properties:

Reticular tissue

Adipose tissue:

Mucous

Pigmented

Loose fibrous unformed connective tissue

Peculiarities:

many cells, little intercellular substance (fibers and amorphous substance)

Localization:

forms the stroma of many organs, the adventitia of the vessels, located under the epithelia - forms its own lamina of mucous membranes, submucosa, located between muscle cells and fibers

Functions:

1. Trophic function: located around the vessels, pvst 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 pvst. 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.

Cells (10 types)

1. Fibroblasts

Fibroblastic differon cells: stem and semi-stem cell, low-specialized fibroblast, differentiated fibroblast, fibrocyte, myofibroblast, fibroclast.

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

Unspecialized fibroblast- small, weakly branched cells 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- the most functionally active cells of this series: they synthesize fiber proteins (proelastin, procollagen) and organic components of the main substance (glycosaminoglycans, proteoglycans). In accordance with their function, these cells have all the morphological characteristics of a protein-synthesizing cell - in the nucleus: clearly defined nucleoli, often several; euchromatin predominates; in the cytoplasm: the protein synthesizing apparatus is well expressed (granular EPS, lamellar complex, mitochondria). At the light-optical level - weakly branched cells with unclear boundaries, with basophilic cytoplasm; the nucleus is light, with nucleoli.

There are 2 populations of fibroblasts:

Short-lived (several weeks) Function: protective.

Long-lived (several months) Function: musculoskeletal.

fibrocyte- mature and aging cell of this series; spindle-shaped, weakly branched cells with slightly basophilic cytoplasm. They have all the morphological characteristics and functions of differentiated fibroblasts, but expressed to a lesser extent.

Cells of the fibroblastic series are the most numerous pvst cells (up to 75% of all cells) and produce most of the intercellular substance.

The antagonist is fibroclast- a cell with a large content of lysosomes with a set of hydrolytic enzymes, ensures the destruction of the intercellular substance. Cells with high phagocytic and hydrolytic activity take part in the “resorption” of intercellular substance during the period of organ involution (for example, the uterus after pregnancy). They combine the structural features of fibril-forming cells (developed granular endoplasmic reticulum, Golgi apparatus, relatively large but few mitochondria), as well as lysosomes with their characteristic hydrolytic enzymes.

Myofibroblast- a cell containing contractile actomyosin proteins in the cytoplasm, therefore capable of contracting. Cells that are morphologically similar to fibroblasts, combining the ability to synthesize not only collagen, but also contractile proteins in significant quantities. It has been established that fibroblasts can transform into myofibroblasts, which are functionally similar to smooth muscle cells, but unlike the latter they have a well-developed endoplasmic reticulum. Such cells are observed in granulation tissue during wound healing and in the uterus during pregnancy. They take part in wound healing, bringing the edges of the wound closer together during contraction.

2. Macrophages

The next pvst cells in number are tissue macrophages (synonym: histiocytes), making up 15-20% of pvst cells. They are formed from blood monocytes and belong to the macrophage system of the body. Large cells with a polymorphic (round or bean-shaped) nucleus and a large amount of cytoplasm. Of the organelles, lysosomes and mitochondria are well defined. Uneven contour of the cytomembrane, capable of active movement.

Functions: protective function through phagocytosis and digestion of foreign particles, microorganisms, tissue breakdown products; participation in cellular cooperation in humoral immunity; production of the antimicrobial protein lysozyme and the antiviral protein interferon, a factor stimulating the immigration of granulocytes.

3. Mast cells (synonyms: tissue basophil, mast cell, mast cell)

They make up 10% of all pvst cells. They are usually located around blood vessels. A round-oval, large, 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, serotonin, chymase, tryptase. When stained, mast cell granules have the property metachromasia- change in dye color. The precursors of tissue basophils originate from hematopoietic stem cells of the red bone marrow. The processes of mitotic division of mast cells are observed extremely rarely.

Functions: Heparin reduces the permeability of intercellular substances and blood clotting, and has an anti-inflammatory effect. Histamine acts as its antagonist. The number of tissue basophils varies depending on the physiological conditions of the body: it increases in the uterus and mammary glands during pregnancy, and in the stomach, intestines, and liver at the height of digestion. In general, mast cells regulate local homeostasis.

4. Plasmocytes

Formed from B lymphocytes. In morphology they are similar to lymphocytes, although they have their own characteristics. The nucleus is round and eccentrically located; 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 like a “wheel with spokes”. The cytoplasm is basophilic, with a light “yard” near the nucleus. Under an electron microscope, the protein synthesizing apparatus is clearly visible: granular EPS, lamellar complex (in the area of ​​the light “yard”) and mitochondria. Cell diameter is 7-10 microns. Function: are effector cells of humoral immunity - they produce specific antibodies (gamma globulins)

5. Leukocytes

Leukocytes released from the vessels are always present in the RVST.

6. Lipocytes (synonyms: adipocyte, fat cell).

1). White lipocytes- 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. When preparing histological preparations in the usual way, a drop of fat is dissolved in alcohol and washed away, so the remaining narrow ring-shaped strip of cytoplasm with an eccentrically located nucleus resembles a ring.

Function: white lipocytes store fat as a reserve (high-calorie energy material and water).

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

7. Adventitial cells

These are poorly specialized cells that accompany blood vessels. They have a flattened or spindle-shaped shape with slightly basophilic cytoplasm, an oval nucleus and a small number of organelles. During the process of differentiation, these cells can apparently turn into fibroblasts, myofibroblasts and adipocytes.

8. Pericytes

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

9. Vascular endothelial cells

They are formed from poorly differentiated mesenchymal cells and cover all blood and lymphatic vessels from the inside; produce a lot of biologically active substances.

10. Melanocytes (pigment cells, pigmentocytes)

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

It is characterized by a predominance of densely located fibers and an insignificant content of cellular elements, as well as the main amorphous substance. Depending on the nature of the location of the fibrous structures, it is divided into dense formed and dense unformed connective tissue (see table).

Dense, unformed connective tissue characterized by a disordered arrangement of fibers. It forms capsules, perichondrium, periosteum, and the reticular layer of the dermis of the skin.

Dense shaped connective tissue contains strictly ordered fibers, the thickness of which corresponds to the mechanical loads under which the organ functions. Formed connective tissue is found, for example, in tendons, which consist of thick, parallel bundles of collagen fibers. In this case, each bundle, delimited from the neighboring one by a layer of fibrocytes, is called in a bunI-th order. Several bundles of the first order, separated by layers of loose fibrous connective tissue, are called in a bunII-th order. Layers of loose fibrous connective tissue are called endotenonium. Beams of the second order are combined into thicker ones bunchesIII-th order, surrounded by thicker layers of loose fibrous connective tissue called peritenonium. Bundles of the third order can be a tendon, and in larger tendons they can be combined into bunchesIV-th order, which are also surrounded by peritenonium. The endotenonium and peritenonium contain blood vessels, nerves, and proprioceptive nerve endings that supply the tendon.

Connective tissues with special properties

Connective tissues with special properties include reticular, adipose, pigment and mucous. These tissues are characterized by a predominance of homogeneous cells.

Reticular tissue

Consists of branched reticular cells and reticular fibers. Most reticular cells are associated with reticular fibers and contact each other with processes, forming a three-dimensional network. This tissue forms the stroma of the hematopoietic organs and the microenvironment for the blood cells developing in them, and carries out phagocytosis of antigens.

Adipose tissue

It consists of a collection of fat cells and is divided into two types: white and brown adipose tissue.

White adipose tissue is widely distributed in the body and performs the following functions: 1) depot of energy and water; 2) depot of fat-soluble vitamins; 3) mechanical protection of organs. Fat cells are located quite close to each other, have a rounded shape due to the content of a large accumulation of fat in the cytoplasm, which pushes the nucleus and a few organelles to the periphery of the cell (Fig. 4-a).

Brown adipose tissue is found only in newborns (behind the sternum, in the area of ​​the shoulder blades, on the neck). The main function of brown adipose tissue is heat production. The cytoplasm of brown fat cells contains a large number of small liposomes that do not fuse with each other. The nucleus is located in the center of the cell (Fig. 4-b). The cytoplasm also contains a large number of mitochondria containing cytochromes, which give it a brown color. Oxidative processes in brown fat cells are 20 times more intense than in white ones.

Rice. 4. Diagram of the structure of adipose tissue: a – ultramicroscopic structure of white adipose tissue, b – ultramicroscopic structure of brown adipose tissue. 1 – adipocyte nucleus, 2 – lipid inclusions, 3 – blood capillaries (according to Yu.I. Afanasyev)

There are collagen and elastic dense formed connective tissues. These include tendons, ligaments, fascia, etc.

Tendons firmly connect the muscles of the skeleton. They are built from different bundles of collagen fibers going in the same direction, i.e.

In an orderly manner (Fig. 111), three orders of collagen fibers are distinguished in tendons. First order bundles are collagen fibers separated from each other by tendon cells. The set of bundles of the first order, united by a thin layer of loose connective tissue, makes up the bundles of the second order. The set of beams of the second order makes up the beams of the third order. They are surrounded by a much thicker layer of connective tissue (see Fig. 111) in the layers between the bundles of the II and III orders there are blood vessels and nerve fibers that feed and innervate the tendons.

Dense formed elastic connective tissue mainly consists of elastic fibers and layers of loose connective tissue containing collagen fibers and fibroblasts. Elastic tissue is located mainly in ligaments. Elastic tissue is also represented by extensive membranes, for example, in the walls of large arteries and other organs.

The dermis of the skin is a representative of dense, unformed connective tissue. It also mainly consists of a dense network of collagen fibers located in different directions. The cells of the network contain small islands of loose connective tissue with blood vessels that nourish the skin and rare fat cells.

Dense tissues include cartilage and skin tissue.

Cartilage tissue. Cartilaginous tissue is characterized by a dense basic intermediate substance, in which cartilage cells without processes (chondrocytes) are located in groups and individually. Cartilaginous tissue performs a supporting function and is the basis for laying the animal’s skeleton. In adult animals, cartilage is found on the articular surfaces, tips of the ribs, in the walls of the trachea and bronchi, the auricle and other places. Cartilage consists of a large amount of intercellular substance and cellular elements. The main intermediate substance is not so dense that blood vessels and nerves do not grow into it. Therefore, cartilages are nourished from the surface through their perichondrium by diffusion of substances. Based on the structure of the intermediate substance, three types of cartilage are distinguished: hyaline, elastic and fibrous (Fig. 113). perichondrium cells, chondroblasts, multiply by mitosis and, becoming hydrated, turn into chondrocytes, increasing the total mass of developing cartilage or filling in places after its damage.

Hyaline (or vitreous) cartilage is characterized by its transparency and has a bluish tint. It is found on articular surfaces, rib tips, nasal septum, trachea and bronchi. The diameter of chondrocytes is 3-30 microns, their shape is round, oval, angular, disc-shaped. Chondrocytes are often located in groups of two to four - these are the so-called isogenic groups. Cartilage cells lying closer to the perichondrium are always located singly. The main intermediate substance of hyaline cartilage consists of amorphous and fibrous (collagen) materials. The older the animal, the more pronounced the content of the main substance is, as a result, darker spots are created around groups and individual cells. With age, lime salts accumulate in cartilage, and the cartilage becomes more fragile.

Elastic cartilage in the main substance, in addition to collagen fibers, contains a network of elastic fibers, which give the entire cartilage greater elasticity and flexibility, as well as a yellowish color and less transparency. Chondrocytes and isogenic groups are surrounded by darker capsules. Cells and isogenic groups in elastic cartilage are arranged in columns (see Fig. 113, b). Elastic cartilage is present in the auricle, epiglottis, external auditory canal, and windpipe of reindeer. In elastic cartilage, calcification processes are always absent.

Fibrous cartilage is a type of hyaline cartilage that contains ordered bundles of collagen fibers of significant diameter. A striped structure is created in which strips of hyaline cartilage alternate with bundles of collagen fibers (see Fig. 113, c). Fibrous cartilage occupies an intermediate position between hyaline cartilage, tendons and fascia. It constantly passes from hyaline cartilage into formed connective tissue. Intervertebral discs (menisci), as well as the transition points from tendons to bones, are made of fibrocartilage. In addition to its supporting function, cartilage tissue takes part in carbohydrate metabolism.