Functions of fibrous connective tissues. Fibrous connective tissue: what it is, functions, structure, types The structure and function of dense connective tissue

It is characterized by a predominance of densely spaced 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 loose connective tissue characterized by a disordered arrangement of fibers. It forms capsules, perichondrium, periosteum, reticular layer of the dermis of the skin.

Densely formed connective tissue contains strictly ordered fibers, the thickness of which corresponds to those mechanical loads in which the organ functions. Shaped connective tissue is found, for example, in tendons, which are composed of thick, parallel bundles of collagen fibers. In this case, each bundle delimited from the adjacent layer of fibrocytes is called bundleI-th order... Several bundles of the first order, separated by layers of loose fibrous connective tissue, are called bundleII-th order... Layers of loose fibrous connective tissue are called endothenonia... The beams of the II order are combined into thicker bundlesIII-th order surrounded by thicker layers of loose fibrous connective tissue called peritenonium... Tufts of the III order can be a tendon, and in larger tendons they can combine into bundlesIV-th order, which are also surrounded by peritenonium. Endotenonium and peritenonium contain blood vessels, nerves and proprioceptive nerve endings feeding the tendon.

Connective tissue with special properties

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

Reticular tissue

Consists of dendritic reticular cells and reticular fibers. Most of the 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 an accumulation of fat cells and is divided into two types: white and brown adipose tissue.

White adipose tissue is widespread 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 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 to generate heat. 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)

include all the basic functions inherent in connective tissues, the most important of which are: (1) trophic, (2) regulatory, (3) protective and (4) supporting (mechanical).

Classification of fibrous connective tissue based on the ratio of cells and intercellular substance, as well as the properties and characteristics of the organization (degree of order) of the latter. In accordance with the classification, loose fibrous connective tissue is distinguished (see Fig. 69 and 71) and dense fibrous connective tissue (Fig. 71-73).

1. It is characterized by a relatively low fiber content in the intercellular substance, a relatively large volume of the basic amorphous substance, and a numerous and varied cellular composition.

2. differs in the predominance of fibers in the intercellular substance with an insignificant volume occupied by the main amorphous substance, a relatively small and uniform cellular composition. Dense fibrous connective tissue, in turn, is subdivided into:

(a) formalized(in which all fibers are oriented in the same direction);

(b) unformed(with different fiber orientation).

Loose fibrous connective tissue is the most common type of connective tissue (see Fig. 69) and performs all the functions inherent in connective tissues, interacting with other tissues, linking them together (which justifies the general name of this group of tissues) and contributing to the maintenance of homeostasis in the body. This tissue is found everywhere, in all organs - it forms them stroma(base), in particular, interlobular layers and layers between layers and membranes, fills the spaces between functional elements of other tissues, accompanies nerves and blood vessels, and is part of the skin and mucous membranes. Loose fibrous connective tissue contains a variety of cells and intercellular substance, including fibers of various types and a basic amorphous substance.

Loose fibrous connective tissue cells represent a complex heterogeneous population of functionally diverse and interacting with each other and with the components of the intercellular substance of the elements.

Fibroblasts- the most common and functionally leading cells of loose fibrous connective tissue. They produce (and partially destroy) all components of the intercellular substance (fibers and the main amorphous substance), regulate the activity of other cells of connective tissues. Mature

fibroblast is a large process cell with unsharp boundaries and a light nucleus containing fine chromatin and 1-2 nucleoli (see Fig. 69). The cytoplasm is weakly basophilic and is characterized by diplasmic differentiation- unsharp division into endoplasm(the inner, denser part surrounding the core) and ectoplasm(peripheral, relatively light part, forming processes). The endoplasm contains most of the organelles of a powerfully developed synthetic apparatus, as well as lysosomes, mitochondria; ectoplasm is filled mainly with elements of the cytoskeleton (Fig. 70). Precursors of fibroblasts in tissue are considered adventitial cells- small, poorly differentiated, fusiform flattened cells located along the capillaries (see Fig. 69).

The final form of fibroblast development is fibrocyte- a narrow, fusiform cell, incapable of proliferation, with long thin processes, a dense nucleus and a poorly developed synthetic apparatus. Fibrocytes predominate in dense fibrous connective tissue (see Fig. 71-73).

Macrophages (histiocytes)- the second largest (after fibroblasts) cells of loose fibrous connective tissue - are formed from monocytes after their migration into the connective tissue from the lumen of blood vessels (see Fig. 56 and 62). The morphological features of histiocytes depend on their functional activity. Resting histiocytes look like small cells with clear contours, a small dark nucleus and dense cytoplasm. Activated histiocytes have a variable shape (see Fig. 69). Their nucleus is lighter than in resting cells, but darker than in fibroblasts. The cytoplasm with uneven edges contains numerous large phagolysosomes, which in the form of vacuoles are clearly visible under a light microscope, giving it a foamed appearance. (see fig. 69). The ultrastructural organization of the activated histiocyte is characterized by numerous outgrowths of the cytoplasm and pseudopodia, a significant number of lysosomes, and a moderately developed Golgi complex (see Fig. 70). Functions of histiocytes: absorption and digestion damaged, infected, tumor and dead cells, components of the intercellular substance, as well as exogenous materials and microorganisms; induction of immune responses(as antigen-presenting cells); regulation of the activity of other types of cells due to the secretion of cytokines, growth factors, enzymes.

Fat cells (adipocytes), according to accepted concepts, they are formed from precursors common with fibroblasts by accumulation of lipid inclusions. Adipocytes- large spherical cells (in clusters they are deformed, becoming multifaceted) with a flattened and displaced to the periphery nucleus and almost entirely filling the cytoplasm, one large, fatty drop (for this reason, adipocytes of white adipose tissue are called single-drop). The rest of the cytoplasm forms the thinnest rim surrounding the fat drop and expanding to a flattened half moon in the area around the nucleus (see Fig. 69 and 71). With standard methods of processing histological material, the lipids in the fat droplet dissolve, as a result of which the adipocyte takes the form of an empty vesicle with the thinnest layer of cytoplasm and a flattened nucleus. To identify lipids on histological preparations, special methods of fixation and posting of the material are used, ensuring their safety, as well as staining the sections (most often with Sudan Black or Sudan III) - see Fig. 7. Fat cells are a normal component of loose fibrous connective tissue and are ubiquitous in small numbers. The tissue in which adipocytes are structurally and functionally leading cellular elements is called fatty and belong to one of the types of connective tissues with special properties (see Fig. 71).

Fat cells store lipids, which serve as a source of energy in the body (trophic function), they also release a number of cytokines and other biologically active peptides - adipokines, affecting other cells (regulatory function). Adipose tissue provides a number of additional functions, which include: supporting, protective and plastic- it surrounds various organs and fills the spaces between them, protecting them from mechanical injury, serves as a supporting and fixing element; heat insulating- it prevents excessive loss of body heat; depositing- adipose tissue accumulates fat-soluble vitamins and steroid hormones (especially estrogens); endocrine- adipose tissue synthesizes estrogens and a hormone that regulates food intake - leptin.

Mast cells develop in tissues from a precursor with bone marrow origin. These are cells of an elongated or rounded shape, with an oval or rounded nucleus, which at the light-optical level is often traced from

hard, as it is disguised metachromatic granules, lying in the cytoplasm (see Fig. 69). Electron microscopy reveals outgrowths of the cytoplasm and microvilli, moderately developed synthetic apparatus and elements of the cytoskeleton, lipid droplets, as well as granules with morphologically variable contents (see Fig. 70). Mast cell granules are similar in structure and composition to basophil granules, but not identical to them; they contain: heparin, histamine, dopamine, chemotactic factors, hyaluronic acid, glycoproteins, phospholipids and enzymes. When activated, these cells also produce prostaglandins, thromboxane, prostacyclin, and leukotrienes. With the gradual release of small doses of these biologically active substances, mast cells (like basophils) perform regulatory functions, aimed at maintaining homeostasis. The regulatory function of mast cells is also associated with their production of cytokines and growth factors. With rapid massive (anaphylactic) degranulation of mast cells in response to an antigen (allergen), allergic reactions, proceeding with a spasm of smooth muscle cells, vasodilatation, an increase in their permeability, tissue damage. The clinical manifestations of massive degranulation of mast cells depend on its prevalence and localization in the body and have varying degrees of severity up to anaphylactic shock and death. In tissues, mast cells are located mainly near small vessels - perivascular(see Fig. 69), which is probably due to their regulatory function and influence on vascular permeability.

Plasma cells (plasma cells) and their precursors - B-lymphocytes - are constantly contained in small quantities in various areas of loose fibrous connective tissue (see Fig. 69). They are small in size, located singly or in groups, and (as in lymphoid tissue) produce and secrete antibodies (immunoglobulins), thereby providing humoral immunity. Typical morphological and functional signs of plasmocytes have been described earlier and shown in Fig. 65 and 66.

Dendritic antigen-presenting cells develop from precursors of bone marrow origin. They are found in loose fibrous connective tissue, epithelium, lymphoid tissue (see Fig. 67), lymph and blood. These cells have a high activity of capture, processing and presentation of antigens to lymphocytes, morphologically they are characterized by a processional form.

Leukocytes(granulocytes and agranulocytes) are normal cellular components of loose fibrous connective tissue (see Fig. 69), into which they migrate from small vessels, but their content in it is normally insignificant. By releasing cytokines, these cells affect each other, the rest of the connective tissue cells and the cells of neighboring tissues. A local increase in the number of leukocytes in loose fibrous connective tissue is detected when inflammation.

Pigment cells are of neural origin and are the descendants of cells that evolved in the embryonic period from the neural crest. They have a process shape; their cytoplasm contains the pigment melanin. In the loose fibrous connective tissue of humans and other mammals, pigment cells are relatively rare. The numerical predominance of these cells over other cellular elements of the connective tissue is characteristic of the iris and choroid. This fabric is called pigmented and belong to one of the types of connective tissues with special properties (see above).

Intercellular substance of loose fibrous connective tissue consists of three types of fibers (collagen, reticular and elastic) and the main amorphous substance.

Collagen fibers are formed by type I collagen and consist of fibrils that are detected only under an electron microscope. On histological preparations, collagen fibers have the form of oxyphilic longitudinally striated convoluted strands running in different directions one by one and often forming bundles of variable thickness (see Fig. 71). They are well detected when stained with iron hematoxylin (see Fig. 69). Collagen fibers provide high mechanical properties of the connective tissue, determine its architectonics, connect cells with the intercellular substance and the individual components of the latter among themselves; affect the properties of cells.

Reticular fibers have a small diameter and, as a rule, form thin, stretchable three-dimensional networks. They are formed by type III collagen, are not detected in standard histological stains and require special staining methods (silver salts, PIC reaction). The main function of the reticular fibers is supporting. They are found in loose fibrous connective tissue (especially in newly formed or undergoing restructuring), as well as in all other types of connective tissue.

fabrics. Reticular fibers are especially abundant in hematopoietic (myeloid and lymphoid) tissues.

Elastic fibers formed by proteins elastin(dominates and forms the backbone of the fiber) and fibrillin(located on the periphery of the mature fiber). They are capable of reversible deformation, imparting elastic properties to the fabric. Elastic fibers are thinner than collagen ones, they branch and anastomose with each other, forming three-dimensional networks (see Fig. 69); unlike collagen fibers, they usually do not form bundles. At the light-optical level, they are not detected by standard staining methods and are detected using selective methods (most often - orsein, rice. 154), but stained with iron hematoxylin (see Fig. 69).

Basic amorphous substance fills the gaps between the fibrous components of the intercellular substance and surrounds the cells. When examined under light-optical and electron microscopes, it has an amorphous structure, transparent, characterized by weak basophilia (see Fig. 69) and low electron density. At the molecular level, it has a complex organization and consists of hydrated macromolecular complexes of proteoglycans and structural glycoproteins.

Dense fibrous connective tissue characterized by (1) a very high content of fibers (mainly collagen), forming thick bundles and occupying the bulk of the tissue volume, (2) a small amount of the main amorphous substance in the composition of the intercellular substance, (3) a relatively low content of cellular elements and (4) the predominance of one (main) type of cells - fibrocytes - above the rest (especially in densely formed tissue).

The main property of dense fibrous connective tissue - very high mechanical strength - is due to the presence of powerful bundles of collagen fibers. The orientation of these fibers corresponds to the direction of action of the forces that cause deformation of the tissue.

Dense fibrous loose connective tissue characterized by the location in three different planes of bundles of collagen fibers, which are intertwined with each other, forming a three-dimensional network (see Fig. 71). The content of the main amorphous substance is small, the cells are few. Such tissue forms capsules of various organs and deep (reticular) layer of the dermis(see Fig. 71), in which

this fabric occupies the main volume (see also fig. 177). In the dermis, between the layer of dense fibrous connective tissue and the epidermis, there is a loose fibrous connective tissue, and deeper than the dense fibrous tissue is adipose tissue, which forms the hypodermis (see Fig. 71 and 177).

Dense fibrous formed connective tissue contains thick collagen fiber bundles, located parallel to each other (in the direction of the load), and a small amount of the main amorphous substance (Fig. 72 and 73). The cell content is low; among them the overwhelming majority are fibrocytes. The described structure has a tissue that forms tendons, ligaments, fascia and aponeuroses.

Tendon as an organ includes bundles of collagen fibers of various orders with fibrocytes located between them and surrounding bundles of shell (interlayers) of loose and dense unformed connective tissues. In the tendon, primary, secondary and tertiary tendon bundles are distinguished (see Fig. 72 and 73). Primary tendon (collagen) bundles are located between the rows of fibrocytes. Secondary tendon (collagen) bundles formed by a group of primary bundles surrounded on the outside by a sheath of loose fibrous unformed connective tissue - endothendinium. Tertiary tendon (collagen) bundles consist of several secondary bundles, which are surrounded from the outside by a sheath of dense fibrous loose connective tissue - peritendinium, extending deep into the tendon of the endothendinium layer. The tendon as a whole can be a tertiary bundle, in some cases it consists of several tertiary bundles, surrounded by a common sheath - epithendinium.

There are several types of different tissues in the human body. All of them play a role in our life. Connective tissue is one of the most important. Its specific gravity is about 50% of the human mass. It is a connecting link that connects all the tissues of our body. Many functions of the human body depend on its condition. Different types of connective tissue are discussed below.

General information

Connective tissue, the structure and function of which has been studied for many centuries, is responsible for the work of many organs and their systems. Its specific gravity ranges from 60 to 90% of their mass. It forms a supporting frame called the stroma and the outer layers of organs called the dermis. Main features of connective tissue:

common origin from the mesenchyme;
structural similarity;
performance of support functions.

The bulk of the hard connective tissue is of the fibrous type. It is composed of elastin and collagen fibers. Together with the epithelium, connective tissue is an integral part of the skin. In doing so, she combines it with

Connective tissue is strikingly different from others in that it is represented in the body by 4 different conditions:

fibrous (ligaments, tendons, fascia);
hard (bones);
gel-like (cartilage, joints);
liquid (lymph, blood; intercellular, synovial, cerebrospinal fluid).

Also, representatives of this type of tissue are: sarcolemma, fat, extracellular matrix, iris, sclera, microglia.

Connective tissue structure

It includes immobile cells (fibrocytes, fibroblasts) that make up the main substance. It also has fibrous formations. They represent the intercellular substance. In addition, it contains various free cells (fat, wandering, obese, etc.). Connective tissue is composed of an extracellular matrix (base). The jelly-like consistency of this substance is due to its composition. The matrix is a highly hydrated gel formed by high molecular weight compounds. They make up about 30% of the weight of the intercellular substance. At the same time, the remaining 70% is water.

Classification of connective tissues

The classification of this type of fabric is complicated by their variety. So, its main types are subdivided, in turn, into several more separate groups. There are such types:

The connective tissue itself, from which the fibrous and specific tissue is isolated, characterized by special properties. The first is divided into: loose and dense (unformed and shaped), and the second - into fatty, reticular, mucous, pigmented.
Skeletal, which is subdivided into cartilaginous and bone.
Trophic, which includes blood and lymph.

Any connective tissue determines the functional and morphological integrity of the organism. She has such characteristic features:

tissue specialization;
versatility;
polyfunctionality;
ability to adapt;
polymorphism and multicomponent.

General functions of connective tissue

Various types of connective tissue perform the following functions:

structural;
ensuring water-salt balance;
trophic;
mechanical protection of the bones of the skull;
shape-generating (for example, the shape of the eyes is determined by the sclera);
ensuring the constancy of tissue permeability;
musculoskeletal (cartilage and bone tissue, aponeuroses and tendons);
protective (immunology and phagocytosis);
plastic (adaptation to new environmental conditions, wound healing);
homeostatic (participation in this important process of the body).

In a general sense, the functions of connective tissue:

giving the human body shape, stability, strength;
protection, covering and connection of internal organs to each other.

The main function of the intercellular substance contained in the connective tissue is supporting. Its base ensures a normal metabolism. Nervous and connective tissue ensures the interaction of organs and various systems of the body, as well as their regulation.

The structure of various types of fabrics

The extracellular substance, called the extracellular matrix, contains many different compounds (inorganic and organic). It is from their composition and quantity that the consistency of the connective tissue depends. Substances such as blood and lymph contain an intercellular substance in liquid form called plasma. The matrix is in the form of a gel. The intercellular substance of bones and tendon fibers are solid insoluble substances.

The intercellular matrix is represented by such proteins as elastin and collagen, glycoproteins and proteoglycans, glycosaminoglycans (GAGs). It may include structural proteins laminin and fibronectin.

Loose and dense connective tissue

These types of connective tissue contain cells and an extracellular matrix. In a loose one there are much more of them than in a dense one. The latter is dominated by various fibers. The functions of these tissues are determined by the ratio of cells and intercellular substance. Loose connective tissue performs mainly at the same time, it also participates in the musculoskeletal activity. Cartilaginous, bone and dense fibrous connective tissue perform a musculoskeletal function in the body. The rest are trophic and protective.

Loose fibrous connective tissue

Loose loose fibrous connective tissue, the structure and functions of which are determined by its cells, is found in all organs. In many of them, it forms the base (stroma). It includes collagen and elastic fibers, fibroblasts, macrophages, and a plasma cell. This tissue accompanies the vessels of the circulatory system. Through its loose fibers, the process of metabolism of blood with cells takes place, during which the transfer of nutrients from it to tissues occurs.

There are 3 kinds of fibers in the intercellular substance:

Collagenous ones that go in different directions. These fibers have the form of straight and wavy strands (constrictions). Their thickness is 1-4 microns.
Elastic, which is slightly thicker than collagen fibers. They are connected (anastomosed) with each other, forming a broad-plaited network.
Reticular, distinguished by their subtlety. They are woven into a mesh.

Cellular elements of loose fibrous tissue are:

Fibroblasts are the most numerous. They are spindle-shaped. Many of them are equipped with processes. Fibroblasts are capable of multiplying. They take part in the formation of the basic substance of this type of tissue, being the basis of its fibers. These cells produce elastin and collagen, as well as other substances related to the extracellular matrix. Inactive fibroblasts are called fibrocytes. Fibroclasts are cells that can digest and absorb the extracellular matrix. They are mature fibroblasts.
Macrophages, which can be round, elongated and irregular. These cells can absorb and digest pathogenic microorganisms and dead tissue, and neutralize toxins. They are directly involved in the formation of immunity. They are subdivided into histocytes (in a quiescent state) and free (wandering) cells. Macrophages are distinguished by their ability to move amoeba. By their origin, they belong to blood monocytes.
Fat cells capable of accumulating a reserve supply in the cytoplasm in the form of drops. They have a spherical shape and are able to displace other structural units of tissues. In this case, dense adipose connective tissue is formed. It protects the body from heat loss. In humans, it is mainly located under the skin, between the internal organs, in the omentum. It is subdivided into white and brown.
located in the tissues of the intestines, and lymph nodes. These small structural units are distinguished by their round or oval shape. They play an important role in the activity of the body's defense systems. For example, in the synthesis of antibodies. Plasma cells produce blood globulins, which play an important role in the normal functioning of the body.
Mast cells, often called tissue basophils, are characterized by their granularity. Their cytoplasm contains special granules. They come in a variety of forms. Such cells are located in the tissues of all organs with an interlayer of loose loose connective tissue. They include substances such as heparin, hyaluronic acid, histamine. Their direct purpose is the secretion of these substances and the regulation of microcirculation in tissues. They are considered immune cells of this type of tissue and respond to any inflammation and allergic reactions. Tissue basophils are concentrated around blood vessels and lymph nodes, under the skin, in the red bone marrow, and in the spleen.
Pigment cells (melanocytes) with a highly branched form. They contain melanin. These cells are found in the skin and the iris of the eyes. By origin, ectodermal cells are isolated, as well as derivatives of the so-called neural crest.
Adveptic cells located along the blood vessels (capillaries). They are distinguished by their elongated shape and have a core in the center. These structural units can multiply and transform into other forms. It is at their expense that the dead cells of this tissue are replenished.

Dense fibrous connective tissue

Connective tissue includes tissue:

Dense, loose, which consists of a significant number of densely spaced fibers. It also includes a small number of cells located between them.
Densely shaped, characterized by a special arrangement of connective tissue fibers. It is the main building material for ligaments and other formations in the body. So, for example, tendons are formed by densely spaced parallel bundles of collagen fibers, the spaces between which are filled with a basic substance and a thin elastic network. Densely fibrous connective tissue of this type contains only fibrocyte cells.

From it, an elastic fibrous is also isolated, of which some ligaments (vocal) are composed. The shells of round vessels, the walls of the trachea and bronchi are formed from them. In them, flattened or thick rounded elastic fibers are directed parallel, while many of them have branches. The space between them is occupied by loose unformed connective tissue.

Cartilage tissue

The connective is formed by cells and a large volume of intercellular substance. It is designed to perform a mechanical function. There are 2 types of cells that form this tissue:

Chondrocytes with an oval shape and a nucleus. They are located in capsules around which the intercellular substance is distributed.
Chondroblasts, which are flattened young cells. They are found on the periphery of the cartilage.

Specialists divide cartilaginous tissue into 3 types:

Hyaline, found in various organs such as ribs, joints, airways. The intercellular substance of such cartilage is translucent. It has a uniform consistency. The hyaline cartilage is covered by the perichondrium. It has a bluish white tint. The skeleton of the embryo consists of it.
Elastic, which is the building material of the larynx, epiglottis, the walls of the external auditory canals, the cartilaginous part of the auricle, small bronchi. In its intercellular substance there are developed elastic fibers. There is no calcium in such cartilage.
Collagen, which is the basis of intervertebral discs, menisci, pubic articulation, sternoclavicular and mandibular joints. Its extracellular matrix includes dense fibrous connective tissue composed of parallel bundles of collagen fibers.

This type of connective tissue, regardless of its location in the body, has the same coverage. It is called the perichondrium. It consists of dense fibrous tissue, which includes elastic and collagen fibers. It contains a large number of nerves and blood vessels. Cartilage grows due to the transformation of the structural elements of the perichondrium. However, they are able to quickly transform. These building blocks are converted into cartilage cells. This fabric has its own characteristics. Thus, the extracellular matrix of mature cartilage does not have vessels, therefore, its nutrition is carried out using the diffusion of substances from the perichondrium. This fabric is distinguished by its flexibility, it is resistant to pressure and has sufficient softness.

Bone connective tissue

The connective bone tissue is particularly hard. This is due to the calcification of its intercellular substance. The main function of connective bone tissue is musculoskeletal. All the bones of the skeleton are built from it. The main structural elements of the fabric:

Osteocytes (bone cells), which have a complex process shape. They have a compact dark core. These cells are located in bone cavities that follow the contours of osteocytes. The intercellular substance is located between them. These cells are unable to reproduce.
Osteoblasts, which are a structural element of the bone. They are rounded. Some of them have multiple cores. Osteoblasts are located in the periosteum.
Osteoclasts, which are large multinucleated cells involved in the destruction of calcified bone and cartilage. Throughout a person's life, there is a change in the structure of this tissue. In this case, simultaneously with the decay process, the formation of new elements arising at the site of destruction and in the periosteum is carried out. Osteoclasts and osteoblasts are involved in this complex cell replacement.

Bone tissue contains an intercellular substance, consisting of a basic amorphous substance. It contains ossein fibers that are not found in other organs. Connective tissue includes tissue:

coarse fibrous, present in embryos;
lamellar, available in children and adults.

This type of tissue consists of such a structural unit as a bone plate. It is formed by cells in special capsules. Between them there is a fine-fibrous intercellular substance, which contains calcium salts. Ossein fibers, which have a significant thickness, are parallel to each other in the bone plates. They lie in a certain direction. At the same time, in adjacent bone plates, the fibers have a direction perpendicular to other elements. This ensures that this fabric is more durable.

Bone plates located in different parts of the body are arranged in a certain order. They are the building blocks of all flat, tubular and mixed bones. In each of them, the plates are the basis of complex systems. For example, tubular bone consists of 3 layers:

Outer, in which the plates on the surface are overlapped by the next layer of these structural units. However, they do not form complete rings.
The middle is formed by osteons, in which the bony plates are formed around the blood vessels. Moreover, they are located concentrically.
Internal, in which the layer of bone plates limits the space where the bone marrow is located.

Bones grow and regenerate due to the periosteum covering the outer surface, which consists of connective tissue and osteoblasts. Mineral salts determine their strength. With a lack of vitamins or hormonal disorders, the calcium content decreases significantly. The bones form the skeleton. Together with the joints, they represent the musculoskeletal system.

Diseases caused by weakness of connective tissue

Insufficient strength of collagen fibers, weakness of the ligamentous apparatus can cause such serious diseases as scoliosis, flat feet, joint hypermobility, prolapse of organs, retinal detachment, blood diseases, sepsis, osteoporosis, osteochondrosis, gangrene, edema, rheumatism, cellulitis. Many experts attribute a weakening of immunity to the pathological state of connective tissue, since the circulatory and lymphatic systems are responsible for it.

Classification. The 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 ratio of cells and intercellular structures, as well as the degree of orderliness of the arrangement of connective tissue fibers.

Fibrous connective tissue

Loose fibrous connective tissue

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

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

Distinguish the followingcells loose fibrous connective tissue:

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

stem cells;

semi-stem progenitor cells;

low-specialized fibroblasts- small-process cells with a rounded 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 cells (40-50 microns and more). Their nuclei are light, contain 1-2 large nucleoli. The boundaries of the cells are indistinct, 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 basic substances 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 the intercellular substance.

Rice. 6-1. Loose connective tissue. 1. Collagen fibers. 2. Elastic fibers. 3. Fibroblast. 4. Fibrocyte. 5. Macrophage. 6. Plasmacyte. 7. Fat cell. 8. Tissue basophil (mast cell). 9. Pericite. 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 cells that are flattened, round, elongated and irregular in shape. Their borders are always clearly delineated, and the edges are uneven. . The cytolemma of macrophages forms deep folds and long micro outgrowths, with the help of which these cells capture foreign particles. They usually have one core. The cytoplasm is basophilic, rich in lysosomes, phagosomes and pinocytic vesicles, contains a moderate amount of mitochondria, granular endoplasmic reticulum, Golgi complex, glycogen inclusions, lipids, etc.

Function: phagocytosis, secrete biologically active factors and enzymes into the intercellular substance (interferon, lysozyme, pyrogens, proteases, acid hydrolases, etc.), 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 (plasma cells). Their size ranges from 7 to 10 microns. The shape of the cells is round or oval. The nuclei are relatively small, round or oval, and located eccentrically. The cytoplasm is sharply basophilic, contains a well-developed granular endoplasmic reticulum, in which proteins (antibodies) are synthesized. Basophilia is deprived only of a small light zone near the nucleus, which forms the so-called sphere, or courtyard. Centrioles and the Golgi complex are found here.

Functions: These cells provide humoral immunity. They synthesize antibodies - gamma globulins (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. Mast cell organelles are poorly developed.

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

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

Function: they have the ability to accumulate in large quantities reserve fat, which is involved in trophism, energy production and water metabolism.

6. Pigment cells- have short, irregularly shaped processes. These cells contain in their cytoplasm the pigment melanin, which is capable of absorbing UV light.

Function: protection of cells from the action of ultraviolet irradiation.

7. Adventitious cells - low-specialized cells accompanying blood vessels. They have a flattened or fusiform shape with a weakly basophilic cytoplasm, an oval nucleus, and underdeveloped organelles.

Function: serves as a cambium.

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

Function: regulate changes in the lumen of blood capillaries.

9. Leukocytes migrate to connective tissue from the blood.

Function: see blood cells.

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

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

- The first is the molecular level - is 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 spiral. Each procollagen chain contains sets of three different amino acids, which are repeatedly and regularly repeated throughout its length. The first amino acid in such a set can be any, the second - proline or lysine, the third - glycine.

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

A. I. Polypeptide chain.

II. Collagen molecules (tropocollagen).

III. Protofibrils (microfibrils).

IV. Fibril of minimum thickness, in which transverse striation becomes visible.

V. Collagen fiber.

B. Spiral structure of 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 in length and cross-linked by means of hydrogen bonds. First formed protoftsbrill, and 5-b protofibrils, fastened together by lateral bonds, are microfibrils, about 10 nm thick. They are distinguishable in an electron microscope in the form of weakly sinuous filaments.

- Third, fibrillar level. With the participation of glycosamine-glycans and glycoproteins, microfibrils form bundles of fibrils. They are transversely 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 tens .

Function: determine the strength of connective tissues.

Elastic fibers - their shape is round or flattened, widely anastomosed with each other. The thickness of elastic fibers is usually less than collagen fibers. The main chemical component of elastic fibers is globular protein elastin, synthesized by fibroblasts. Electron microscopy made it possible to establish that the elastic fibers in the center contain amorphous component, and along the periphery - microfibrillary. In terms of strength, elastic fibers are inferior to collagen ones.

Function: determines the elasticity and extensibility of the connective tissue.

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

Basic substance Is a gelatinous hydrophilic medium, 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 composition of the main substance includes lipids, albumins and blood globulins, minerals (sodium, potassium, calcium, etc.).

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

Dense fibrous connective tissue

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

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

Dense loose connective tissue.

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

Densely 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, densely lying parallel bundles of collagen fibers, separated by fibrocytes, a small number of fibroblasts, and a base substance. Each bundle of collagen fibers is called beam of the first order. Several bundles of the first order, surrounded by thin layers of loose fibrous connective tissue (endothenonium), make up second order beams... The second-order beams add beams of the third order, separated by thicker layers of loose connective tissue (peritenonium). In large tendons, there may be bundles of the fourth order. In peritenonia and endotenonia, blood vessels and nerves pass.

Distinguish between collagen and elastic dense formed connective tissues. These include tendons, ligaments, fascia, etc.

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

Orderly (Fig. 111) in the tendons distinguish three orders of collagen fibers. Bundles of the first order 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, constitutes the bundles of the second order. The set of beams of the second order is 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.

The densely formed elastic connective tissue mainly consists of elastic fibers and layers of loose connective tissue containing collagen fibers and fibroblasts. The elastic tissue is located mainly in the 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 loose 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 feed the skin and rare fat cells.

Dense tissues include cartilage and skin tissue.

Cartilage tissue. Cartilaginous tissue is characterized by a dense main intermediate substance, in which cartilaginous cells without processes (chondrocytes) are located in groups and singly. Cartilage tissue performs a supporting function and is the basis for laying the skeleton of an animal. In adult animals, cartilage is found on the articular surfaces, the tips of the ribs, in the walls of the trachea and bronchi, the auricle and other places. Cartilage is composed of a large amount of intercellular substance and cellular elements. The main intermediate substance is not so dense that vessels and nerves do not grow into it. Therefore, the cartilage is nourished from the surface through their perichondrium by the diffusion of substances. According to 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, being watered, turn into chondrocytes, increasing the total mass of developing cartilage or filling places after its damage.

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

In addition to collagen fibers, elastic cartilage in the basic substance contains a network of elastic fibers that 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. The cells and isogenic groups in the elastic cartilage are arranged in columns (see Figure 113, b). elastic cartilage is present in the auricle, in the epiglottis, in the external auditory canal, in the windpipe of the reindeer. Calcification processes are always absent in elastic cartilage.

Fibrous cartilage is a type of hyaline cartilage that contains ordered bundles of collagen fibers of considerable diameter. A striped structure is created in which stripes of hyaline cartilage alternate with bundles of collagen fibers (see Figure 113, c). Fibrous cartilage is intermediate between hyaline cartilage, tendons and fascia. It is constantly moving from hyaline cartilage to formed connective tissue. Intervertebral discs (menisci) and transitions from tendons to bones are made of fibrous cartilage. Cartilage tissue, in addition to supporting function, takes part in the metabolism of carbohydrates.