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Connective tissue functions, structure, significance in the body. Dense fibrous connective tissue (dense fibrous connective tissue)

Classification. Connective tissue itself is divided into:

1) fibrous connective tissues:

    loose fibrous connective tissue;

    dense fibrous connective tissue:

a) dense, unformed connective tissue;

b) densely formed connective tissue;

2) connective tissues with special properties.

This classification is based on the principle of the relationship between cells and intercellular structures, as well as the degree of orderliness in the arrangement of connective tissue fibers.

Fibrous connective tissues

Loose fibrous connective tissue

This type of connective tissue is found in all organs, as it accompanies blood and lymphatic vessels and forms the stroma of many organs.

Structure. It consists of cells and intercellular substance (Fig. 6-1).

The following are distinguished:cells loose fibrous connective tissue:

1. Fibroblasts- the most numerous group of cells, varying in degree of differentiation, characterized primarily by the ability to synthesize fibrillar proteins (collagen, elastin) and glycosaminoglycans with their subsequent release into the intercellular substance. During the process of differentiation, a number of cells are formed:

    stem cells;

    semi-stem progenitor cells;

    unspecialized fibroblasts– small-processed cells with a round or oval nucleus and a small nucleolus, basophilic cytoplasm, rich in RNA.

Function: have a very low level of protein synthesis and secretion.

    differentiated fibroblasts(mature) - large-sized cells (40-50 microns or more). Their nuclei are light and contain 1-2 large nucleoli. Cell boundaries are unclear and blurred. The cytoplasm contains a well-developed granular endoplasmic reticulum.

Function: Intensive biosynthesis of RNA, collagen and elastic proteins, as well as glycosminoglycans and proteoglycans necessary for the formation of the ground substance and fibers.

    fibrocytes- definitive forms of fibroblast development. They have a fusiform shape and pterygoid processes. They contain a small number of organelles, vacuoles, lipids and glycogen.

Function: the synthesis of collagen and other substances in these cells is sharply reduced.

- myofibroblasts- functionally similar to smooth muscle cells, but unlike the latter, they have a well-developed endoplasmic reticulum.

Function: these cells are observed in the granulation tissue of the wound process and in the uterus during the development of pregnancy.

- fibroclasts.- cells with high phagocytic and hydrolytic activity; they contain a large number of lysosomes.

Function: take part in the resorption of intercellular substance.

Rice. 6-1. Loose connective tissue. 1. Collagen fibers. 2. Elastic fibers. 3. Fibroblast. 4. Fibrocyte. 5. Macrophage. 6. Plasmocyte. 7. Fat cell. 8. Tissue basophil (mast cell). 9. Pericyte. 10. Pigment cell. 11. Adventitial cell. 12. Basic substance. 13. Blood cells (leukocytes). 14. Reticular cell.

2. Macrophages– wandering, actively phagocytic cells. The shape of macrophages is different: there are flattened, round, elongated and irregularly shaped cells. Their boundaries are always clearly defined and the edges are jagged . The cytolemma of macrophages forms deep folds and long microprotrusions, with the help of which these cells capture foreign particles. As a rule, they have one core. The cytoplasm is basophilic, rich in lysosomes, phagosomes and pinocytotic vesicles, contains a moderate amount of mitochondria, granular endoplasmic reticulum, Golgi complex, glycogen inclusions, lipids, etc.

Function: phagocytosis, secrete biologically active factors and enzymes (interferon, lysozyme, pyrogens, proteases, acid hydrolases, etc.) into the intercellular substance, which ensures their various protective functions; produce monokine mediators, interleukin I, which activates DNA synthesis in lymphocytes; factors that activate the production of immunoglobulins, stimulate the differentiation of T- and B-lymphocytes, as well as cytolytic factors; provide processing and presentation of antigens.

3. Plasma cells (plasmocytes). Their size ranges from 7 to 10 microns. The shape of the cells is round or oval. The kernels are relatively small, round or oval in shape, and located eccentrically. The cytoplasm is strongly basophilic and contains a well-developed granular endoplasmic reticulum in which proteins (antibodies) are synthesized. Only a small light zone near the nucleus, forming a so-called sphere, or courtyard, is devoid of basophilia. Centrioles and the Golgi complex are found here.

Functions: These cells provide humoral immunity. They synthesize antibodies - gammaglobulins (proteins), which are produced when an antigen appears in the body and neutralize it.

4. Tissue basophils (mast cells). Their cells have a varied shape, sometimes with short, wide processes, which is due to their ability to amoeboid movements. In the cytoplasm there is a specific granularity (blue), reminiscent of granules of basophilic leukocytes. It contains heparin, hyaluronic acid, histamine and serotonin. The organelles of mast cells are poorly developed.

Function: tissue basophils are regulators of local connective tissue homeostasis. In particular, heparin reduces the permeability of intercellular substances, blood clotting, and has an anti-inflammatory effect. Histamine acts as its antagonist.

5. Adipocytes (fat cells) – are located in groups, less often – singly. Accumulating in large quantities, these cells form adipose tissue. The shape of single fat cells is spherical; they contain one large drop of neutral fat (triglycerides), occupying the entire central part of the cell and surrounded by a thin cytoplasmic rim, in the thickened part of which lies the nucleus. In this regard, adipocytes have a signet ring shape. In addition, the cytoplasm of adipocytes contains a small amount of cholesterol, phospholipids, free fatty acids, etc.

Function: have the ability to accumulate large quantities of reserve fat, which takes part in trophism, energy formation and water metabolism.

6. Pigment cells– have short, irregularly shaped processes. These cells contain in their cytoplasm the pigment melanin, which can absorb UV rays.

Function: protection of cells from the effects of ultraviolet radiation.

7. Adventitial cells - poorly specialized cells accompanying blood vessels. They have a flattened or spindle-shaped shape with weakly basophilic cytoplasm, an oval nucleus and poorly developed organelles.

Function: acts as a cambium.

8. Pericytes They have a branched shape and surround the blood capillaries in the form of a basket, located in the crevices of their basement membrane.

Function: regulate changes in the lumen of blood capillaries.

9. Leukocytes migrate into connective tissue from the blood.

Function: see blood cells.

Intercellular substance consists of the main substance and the fibers located in them - collagen, elastic and reticular.

TO collagen fibers in loose, unformed fibrous connective tissue are located in different directions in the form of twisted round or flattened strands 1-3 microns or more thick. Their length is indefinite. The internal structure of collagen fiber is determined by fibrillar protein - collagen, which is synthesized in the ribosomes of the granular endoplasmic reticulum of fibroblasts. There are several levels of organization in the structure of these fibers (Fig. 6-2):

- First – molecular level – represented by collagen protein molecules having a length of about 280 nm and a width of 1.4 nm. They are built from triplets - three polypeptide chains of the collagen precursor - procollagen, twisted into a single helix. Each procollagen chain contains sets of three different amino acids, repeated many times and regularly throughout its length. The first amino acid in such a set can be any, the second can be proline or lysine, and the third can be glycine.

Rice. 6-2. Levels of structural organization of collagen fiber (diagram).

A. I. Polypeptide chain.

II. Collagen molecules (tropocollagen).

III. Protofibrils (microfibrils).

IV. A fibril of minimal thickness in which transverse striations become visible.

V. Collagen fiber.

B. Helical structure of the collagen macromolecule (according to Rich); small light circles – glycine, large light circles – proline, shaded circles – hydroxyproline. (According to Yu. I. Afanasyev, N. A. Yurina).

- Second – supramolecular, extracellular level – represents collagen molecules connected lengthwise and cross-linked via hydrogen bonds. First are formed protofcbrilla, and 5-b protofibrils, held together by lateral bonds, make up microfibrils with a thickness of about 10 nm. They are distinguishable in an electron microscope in the form of slightly sinuous threads.

- Third, fibrillar level. With the participation of glycosaminoglycans and glycoproteins, microfibrils form fibril bundles. They are cross-striated structures with an average thickness of 50–100 nm. The repetition period of dark and light areas is 64 nm.

- Fourth, fiber level. The composition of collagen fiber (1-10 microns thick), depending on the topography, includes from several fibrils to several dozen .

Function: determine the strength of connective tissues.

Elastic fibers – their shape is round or flattened, widely anastomosing with each other. The thickness of elastic fibers is usually less than collagen. The main chemical component of elastic fibers is globular protein elastin, synthesized by fibroblasts. Electron microscopy revealed that the elastic fibers in the center contain amorphous component, and on the periphery - microfibrillar. Elastic fibers are inferior in strength to collagen fibers.

Function: determines the elasticity and extensibility of connective tissue.

Reticular fibers belong to the type of collagen fibers, but are distinguished by their smaller thickness, branching and anastomoses. They contain an increased amount of carbohydrates, which are synthesized by reticular cells and lipids. Resistant to acids and alkalis. They form a three-dimensional network (reticulum), which is where they get their name.

Main substance is a gelatinous hydrophilic environment, in the formation of which fibroblasts play an important role. It contains sulfated (chondroitinsulfuric acid, keratin sulfate, etc.) and non-sulfated (hyaluronic acid) glycosaminoglycans, which determine the consistency and functional characteristics of the main substance. In addition to these components, the main substance includes lipids, albumins and blood globulins, minerals (sodium, potassium, calcium salts, etc.).

Function: transport of metabolites between cells and blood; mechanical (binding of cells and fibers, cell adhesion, etc.); supporting; protective; water metabolism; regulation of ionic composition.

Dense fibrous connective tissue

It is characterized by a relatively large number of densely located fibers (collagen), a small amount of cellular elements (fibrocytes, fibroblasts) and the ground substance between them.

Depending on the nature of the location of the fibrous structures, this tissue is divided into:

    Dense, unformed connective tissue.

It is located in the dermis of the skin and is characterized by a disordered arrangement of fibers.

    Dense formed connective tissue.

It is found in tendons, ligaments, fibrous membranes and is characterized by a strictly ordered arrangement of fibers.

Tendon consists of thick, tightly packed parallel bundles of collagen fibers separated by fibrocytes, a small number of fibroblasts, and ground substance. Each bundle of collagen fibers is called a first order beam. Several bundles of the first order, surrounded by thin layers of loose fibrous connective tissue (endotenonium), make up second order beams. From beams of the second order they are composed third order beams, separated by thicker layers of loose connective tissue (peritenonium). Large tendons may also have fourth-order bundles. The peritenonium and endotenonium contain blood vessels and nerves.

Connective tissue is the most common tissue in the body, accounting for more than half of a person’s weight. By itself, it is not responsible for the functioning of the body's systems, but has an auxiliary effect in all organs.

Features of the structure of connective tissue

There are three main types of connective tissue, which have different structures and perform specific functions: connective tissue itself, cartilage and bone.

Types of connective tissue
Type Characteristic
Dense fibrous- Shaped, where the chondrinic fibers run parallel;
- unshaped, where fibrous structures form a network.
Loose fibrousRelative to cells, there is more intercellular substance, including collagen, elastic and reticular fibers.
Fabrics with special properties- Reticular - forms the basis of hematopoietic organs, surrounding maturing cells;
fatty – located in the abdominal region, on the hips, buttocks, storing energy resources;
- pigmented - found in the iris of the eye, the skin of the nipples of the mammary glands;
- mucous membrane is one of the components of the umbilical cord.
Bone connectiveConsists of osteoblasts, they are located inside the lacunae, between which lie blood vessels. The intercellular space is filled with mineral compounds and chondrinic fibers.
Cartilaginous connectiveDurable, built from chondroblasts and chondroitin. It is surrounded by perichondrium, where new cells are formed. There are hyaline cartilages, elastic and fibrous.

Types of connective tissue cells

Fibroblasts– cells that produce an intermediate substance. They are engaged in the synthesis of fibrous formations and other components of connective tissue. Thanks to them, wounds heal, scars form, and foreign bodies encapsulate. Still undifferentiated oval-shaped fibroblasts with a large number of ribosomes. Other organelles are poorly developed. Mature fibroblasts have large sizes and processes.

Fibrocytes- This is the final form of fibroblast development. They have a wing-shaped structure, the cytoplasm includes a limited number of organelles, and synthesis processes are reduced.

Myofibroblasts during differentiation they become fibroblasts. They are similar to myocytes, but unlike the latter, they have a developed ER. These cells are often found in granulation tissue as cuts heal.

Macrophages— body size varies from 10 to 20 micrometers, oval shape. Among the organelles there are the largest number of lysosomes. The plasmalem forms long processes, thanks to which it captures foreign bodies. Macrophages serve to form innate and acquired immunity. Plasmocytes have an oval body, sometimes polygonal. The endoplasmic reticulum is developed and is responsible for the synthesis of antibodies.

Tissue basophils, or mast cells, are located in the wall of the digestive tract, uterus, mammary glands, tonsils. The body shape is different, sizes from 20 to 35, sometimes reaching 100 microns. They are surrounded by a dense shell; inside they contain specific substances that are of great importance - heparin and histamine. Heparin prevents blood clotting, histamine acts on the capillary membrane and increases its permeability, this leads to plasma leakage through the walls of the bloodstream. As a result, blisters form under the epidermis. This phenomenon is often observed with anaphylaxis or allergies.

Adipocytes- cells that store lipids necessary for nutrition and energy processes. The fat cell is completely filled with fat, which stretches the cytoplasm into a thin ball, and the nucleus takes on a flattened shape.

Melanocytes contain the pigment melanin, but they do not produce it themselves, but only capture what has already been synthesized by epithelial cells.

Adventitial cells undifferentiated, can later transform into fibroblasts or adipocytes. They are found near capillaries, arteries, in the form of flat-bodied cells.

The appearance of cells and nuclei of connective tissue differs among its subtypes. So, in a cross section, an adipocyte looks like a signet ring, where the nucleus acts as a signet, and the ring is a thin cytoplasm. The nucleus of a plasma cell is small in size, located on the periphery of the cell, and the chromatin inside forms a characteristic pattern - a wheel with spokes.

Where is connective tissue located?

Connective tissue has a varied location in the body. Thus, collagen fibrous structures form tendons, aponeuroses and fascial sheaths.

Unformed connective tissue is one of the components of the dura mate (dura mater of the brain), joint capsules, and heart valves. Elastic fibers that make up the vascular adventitia.

Brown adipose tissue is most developed in one-month-old infants and provides effective thermoregulation. Cartilaginous tissue forms the nasal cartilage, laryngeal cartilage, and external auditory canal. Bone tissue forms the internal skeleton. Blood is a liquid form of connective tissue that circulates through a closed circulatory system.

Functions of connective tissue:

  • Support— forms the internal skeleton of a person, as well as the structure of organs;
  • nutritious— delivers O2, lipids, amino acids, glucose through the bloodstream;
  • protective– responsible for immune reactions through the formation of antibodies;
  • restorative- ensures wound healing.

Difference between connective tissue and epithelial tissue

  1. The epithelium covers muscle tissue, the main component of the mucous membranes, forms the outer covering and provides a protective function. Connective tissue forms the parenchyma of organs, provides a supporting function, is responsible for the transport of nutrients, and plays an important role in metabolic processes.
  2. Non-cellular structures of connective tissue are more developed.
  3. The appearance of the epithelium is similar to cells, and the connective tissue cells have an oblong shape.
  4. Different tissue origins: epithelium comes from ectoderm and endoderm, and connective tissue comes from mesoderm.

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 µm, with 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 weakly 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.

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 They 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 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, contains 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 there is a need for energy in the body, 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 Their main feature is 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, connecting, 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 characterized 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 appear, 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 long-term 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 of the mammary glands, the anus and in the scrotum. The main cells of this tissue are pigment cells that develop from the neural crest.

characterized by a high content of intercellular substance, consisting of fibers And basic amorphous substance, filling the space between the fibers.

Classification based on the ratio of cells and intercellular substance, as well as the degree of ordering of the fibrous component.

1. Loose fibrous connective tissue (FCT) characterized by:

A) relatively low fiber content in the intercellular substance;

b) a relatively large volume of basic amorphous substance;

V) numerous and varied cellular composition.

2. Dense fibrous connective tissue characterized by:

a) predominance of fibers in the intercellular substance;

b) an insignificant volume of the main amorphous substance;

c) small and uniform cellular composition.

Types of Dense Connective Tissue:

A) formalized(all fibers are oriented in the same direction - they form parallel bundles, as in tendons, or intertwine in the same plane, as in aponeuroses);

b) unformed(the fibers are randomly oriented).

LOOS FIBROUS CONNECTIVE TISSUE (LOAF CONNECTIVE TISSUE)– the most common type of connective tissue (part of the mucous and serous membranes, skin, forms the stroma of organs, layers, fills the spaces between functional elements in other tissues, accompanies blood vessels and nerves . “Binds”, “connects” tissues together.

PBCT cells are a complex heterogeneous population of cells interacting with each other:

1. FIBROBLASTS – most common, functional leading cells.

Origin: Stem Cell line of mechanocytes (a special stem cell of mesenchymal nature). Self-sustaining population, rarely divides, resistant to damaging factors. Morphologically – apparently corresponds adventitial cells - small spindle-shaped cell with a dark nucleus. basophilic cytoplasm and poorly developed organelles.

Functions:

1) products all components intercellular substance (glycosaminoglycans, collagen, elastin, fibronectin, laminin and other proteins and glycoproteins);

2) maintaining the structural organization of the intercellular substance

(balance of production and destruction - collagenase);

3) regulation of the activity of other connective tissue cells and influence on other tissues (humoral factors are identified that affect the growth, differentiation, functional activity of macrophages, lymphocytes, smooth muscle cells, epithelium - cytokines: colony-stimulating factor of granulocytes and macrophages, interleukins-3 and -7).

Differenton: SC→PSC→ poorly differentiated (young) fibroblast → differentiated (mature) fibroblast → fibrocyte.



Poorly differentiated fibroblast– basophilic cytoplasm, with a small number of processes, moderately developed synthetic apparatus (mainly free ribosomes); ability. to proliferation and migration, which is important in reparative processes.

Mature fibroblast– the most numerous type, a large cell (40-50 µm in diameter), has processes, with blurred cell boundaries; light oval core; nucleoli; slightly basophilic cytoplasm. The peripheral part of the cytoplasm - ectoplasm - is lighter (mainly elements of the cytoskeleton). Powerful synthetic apparatus: synthesis (glycosaminoglycans, collagen, glycoproteins, actin) and release. Mobile, able to change shape, attach to other cells and fibers.

fibrocyte– the final form, inactive, long-lived, incapable of proliferation. Narrow, spindle-shaped, with thin branches. The core is dense. The synthetic apparatus is poorly developed, there are many lysosomes. Function– regulation of metabolism and maintaining the stability of the intercellular substance.

Fibroclasts- cells specialized in the destruction of intercellular substance. Provide tissue restructuring. Numerous in young connective tissue (granulation tissue) and scars. Cytoplasmic vacuoles with collagen fibrils at different stages of lysis are characteristic. Extra- and intracellular cleavage.

Myofibroblasts– more than half of their cytoplasm is occupied by elements of the contractile apparatus (actin microfilaments). Actively participate in reparative processes. Wound contraction: contracting, they tighten the edges of the wound and form collagen (type III), which fills the damaged area (in granulation tissue in wound healing conditions).

2. MACROPHAGES (histiocytes) – second in number , descendants of Blood Stem Cells, formed from monocytes; especially numerous in the lamina propria of the mucous and serous membranes; resting macrophages – inactive; wandering – with high functional activity.

Functions:

1. Phagocytosis - recognition, capture and digestion of damaged, infected, tumor and dead cells, components of the intercellular substance, exogenous microorganisms and substances (there are receptors for immunoglobulins, tumor cell antigens on the surface);

A) nonspecific phagocytosis characteristic of pulmonary macrophages that capture particles of dust, soot, etc.

b) specific phagocytosis– first, immunoglobulins and complement proteins of blood plasma (united under the name opsonins) surround (opsonize) the bacterium. The macrophage has receptors for opsonins and easily captures opsonized bacteria and forms phagosomes. Lysosomes contain lysozyme, which destroys the bacterial wall, and hydrolytic enzymes. They can also secrete the contents of lysosomes outside the cells in infected areas.

2.Induction of immune reactions – play the role of antigen-presenting cells; carry out processing (processing) of antigens: a sequence of 8-11 amino acids - epitopes of antigens - together with molecules of the major histocompatibility complex are released onto the cell surface - only after this can lymphocytes recognize the antigen (“genetically foreign”).

3. Regulation of the activity of other types of cells (fibroblasts, lymphocytes, mast cells, etc.) through the secretion of bioactive factors ( monokins): interleukin-1, neutrophil chemotaxis factor, endogenous pyrogens (through the thermoregulation center they cause an increase in temperature); tumor necrosis factor (cytotoxic effect on transformed cells)).

Morphology: Active ones have high mobility, changeable, usually process form (microgrowths, pseudopodia) with uneven, but clear edges. The nuclei are darker than those of fibroblasts, and invaginations are characteristic. Cytoplasm: numerous lysosomes and large phagolysosomes, pinocytotic vesicles, developed cytoskeletal elements. The remaining organelles are moderately developed.

At the site of damage, they can turn into special types - giant multinucleated cells and epithelioid cells.

3. MAST CELLS (mast cells, tissue basophils) – 10%.

Apparently, descendants of HSCs (blood stem cells). Relatively long life expectancy in contrast to blood basophils.

Functions:

1. regulatory - homeostasis (by slowly releasing small doses of bioactive substances that affect vascular permeability and tone and maintaining fluid balance in tissues);

2. protective– an important role in the development of the inflammatory response (rapid, local release of inflammatory mediators and chemotactic factors that attract neutrophils and eosinophils.

3.participation in allergic reactions: mast cells have receptors for class E immunoglobulins (IgE - formed in response to the penetration of certain allergen antigens) on the plasmalemma. →. Isolation of bioactive substances from granules and synthesis of a number of new substances (prostaglandins, thromboxane, etc.). They attract effector cells involved in the so-called late phase reactions ( long-term immune stimulation, which develops several hours after contact with the allergen).

Localization:

Perivascular (small vessels); very much in the dermis; in the lamina propria of the mucous membrane of the digestive, respiratory, excretory tracts, and the stroma of the thymus. Local growth in the stroma during functional activity (thyroid gland, mammary gland, uterus), near foci of inflammation. Possibly capable of fission (extremely rare).

Morphology:

Elongated or round in shape with an uneven surface, thin processes and outgrowths. (20-30 microns - 1.5 - 2 times larger than blood basophils). The nuclei are small, round, non-segmented, heterochromatin; at the light level - masked by granules. Cytoplasm – moderate development of organelles, lipid droplets and granules. The most typical ones are: granules.

Granules- similar, but not identical to blood basophil granules. Metachromasia (colored differently from the color of the dye), numerous, large, vary in size, density, composition; in humans they sometimes contain layered inclusions similar to a curl (“scrolls”). Composition of granules:

heparin (30% of the contents – a powerful anticoagulant, anti-inflammatory effect);

histamine (10% - heparin antagonist, the most important mediator of inflammation and immediate allergic reactions (causes swelling in allergic rhinitis, some forms of asthma, anaphylactic shock);

dopamine, chemotaxis factors of eosinophils and neutrophils, hyaluronic acid, glycoproteins, phospholipids, enzymes (proteases, acid hydrolases).

Yield of biogenic amines leads to a change in the state of the intercellular substance and the permeability of the blood-tissue barrier (an important role in the first stages of inflammation).

For anaphylactic degranulation [anaphylax And I – an immediate allergic reaction caused by repeated introduction of an allergen; characterized by a sharp contraction (spasm) of smooth muscles (bronchioles) and dilation of capillaries] granules merge into chains - an intracytoplasmic channel (complex exocytosis), massive release. → rapid vasodilating effect on capillaries and venules, increases their permeability and the release of plasma into tissues, spasm of smooth muscles of bronchioles, acute rhinitis, swelling, itching, diarrhea, drop in blood pressure.

Substances that inhibit mast cell degranulation with various mechanisms of pharmacological action (antihistamines) are widely used as prevention and treatment.

4. FAT CL. (adipocytes)

They are formed from young fibroblasts by the accumulation of small lipid droplets in the cytoplasm, which merge into one large one ( single-droplet adipocytes). They are found everywhere, in the form of clusters (lobules) or individually, along the vessels. Large cells, spherical in shape, with a flattened nucleus and a thin rim of cytoplasm with organelles along the periphery (signet ring cells). High metabolic activity: lipid metabolism, depot of fat-soluble vitamins and steroid hormones; regulatory function (produce the hormone leptin, which regulates food intake, and estrogens).