The classification of cartilage tissue is based on the structural features of its intercellular substance - the matrix. This classification of types of cartilage tissue is far from perfect, since it does not contain a general unified principle. Thus, the term “fibrous” indicates the content of fibrous structures, and the term “elastic” already indicates a certain specific characteristic of the protein - elastin, which is part of the cartilage. The term “hyaline” only informs that the cartilage matrix is ​​externally homogeneous, and there is no mention at all about the structure and nature of the proteins that make up its structure.
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Cartilaginous tissue is present in extraskeletal structures - the larynx, nasal septum, bronchi, and stromal components of the heart.

The extracellular matrix of cartilage tissue differs from the matrix of other varieties connective tissue essential features of their structural macromolecular components. These features determine the pronounced originality of the architectonics of the matrix and its unique functional (biomechanical) characteristics.

The fibrous structures of the matrix are formed by special collagen proteins specific to cartilage tissue - “large” fibrillar collagen type II and accompanying “small” (minor) collagens IX, XI, as well as X and some other types. The main component of the interstitial matrix is ​​also the “large” proteoglycan aggrecan, specific for cartilage tissue, whose macromolecules form huge aggregates (their size exceeds the size of cells), occupying a large space. The composition of aggrecan macromolecules, making up a significant part of their mass, includes sulfated glycosaminoglycans - chondroitin sulfates and keratan sulfate.

Cartilage cells

The differential of cartilage tissue can be represented as follows: prechondroblasts-chondroblasts-chondrocytes. Based on the description of the differentiation of cartilage tissue cells, as well as for didactic reasons, we will describe three forms of chondrocytes: prechondroblasts, chondroblasts and chondrocytes.

Prechondroblasts

In the differential of cartilage cells, the precursor cells of chondroblasts, prechondroblasts, are isolated. The identification of prechondroblasts is to a certain extent conditional, since it is assumed that cartilage and bone have single semi-stem cells - common to chondroblasts and osteoblasts.

Chondroblasts

The main processes of cartilage tissue formation occur during embryogenesis, where the chondrocyte functions as its blast form and is called a chondroblast. Apparently, it is advisable to talk about a single population of chondroblast-chondrocyte cells, which ensures both the formation of cartilage tissue and its functioning in a mature state. The source of replenishment of the population of such cells are prechondroblasts.

A chondroblast can be defined as a cell in the transition stage from a prechondroblast to a mature chondrocyte. Such a cell has the secretory potencies necessary for the synthesis of matrix components, but still retains the ability to proliferate. Many researchers note that chondroblast and chondrocyte do not have distinct morphological differences, i.e. V morphological characteristics chondroblasts and chondrocytes, it has not yet been possible to determine the measure of specificity that would allow one to confidently distinguish between these two types of cells.

The role of chondroblasts-chondrocytes as perhaps the only cell in the life of cartilage is so important that they have been called “architects of cartilage.” This name reflects the fact that it is the sole producer of all macromolecular components of the cartilage tissue matrix. The formation of cartilage occurs primarily during embryogenesis and ends at a very young age. Thus, this process occurs almost entirely at the chondroblastic stage of cell differentiation.

Chondrocytes

Chondrocytes are highly specialized and metabolically active cells. The synthetic activity of the chondrocyte is specific and differentiated in the direction of production and secretion of type II collagen, minor collagens, aggrecan, glycoproteins characteristic of cartilage tissue, elastin (in elastic cartilages). The ultrastructure of a mature chondrocyte corresponds to high level its metabolic activity.

The fact that chondrocytes serve as a source of collagen in cartilage tissue is documented by both biochemical and morphological methods. Chondrocytes in monolayer cell culture give intracellular immunofluorescence with serum labeled for type II collagen. Using the same method, it was possible to localize type II collagen inside the cells of the cartilaginous metaphyseal plate in children using biopsy material.

No less convincing are the data related to the synthesis of proteoglycans. In chondrocytes, TEM reveals granules stained with ruthenium red, which fill the entire extracellular matrix of cartilage tissue and are nothing more than aggregates of proteoglycans compacted during fixation. These granules are found in vesicles of the Golgi complex, but they are absent from the GES. This means that aggrecan acquires its polyanionic character (ruthenium red stains polyanionic macromolecules selectively) when passing through the Golgi complex. These data are consistent with autoradiographic studies showing that S35 is selectively concentrated in the Golgi complex. Thus, not only was the fact of aggrecan biosynthesis by chondrocytes established, but also the exact intracellular localization of the central link in the process of its biosynthesis was revealed.

A comparison of the dimensions of the chondrocyte and the aggrecan aggregate (the former is significantly smaller in volume than the latter) allowed us to conclude that only the synthesis of monomeric aggrecan macromolecules occurs inside the chondrocyte, which are secreted outside the cell into the matrix, where the assembly of aggrecan aggregates occurs.

The synthesis of tissue structural glycoproteins of cartilage tissue by chondrocytes has been proven by biochemical methods. It is difficult to obtain morphological confirmation of this synthesis. It is believed that it is masked by pronounced processes of collagen and proteoglycan synthesis. The ability of chondrocytes to synthesize the protein elastin was demonstrated in a study of cultured chondrocytes from the rabbit ear.

According to modern ideas, the process of calcification of cartilage occurs with the active participation of chondrocytes in it. Mineralization is preceded by changes - both in the matrix and in the cells of cartilage.

Heterogeneity of chondrocytes

Chondrocytes of normal cartilage tissue are phenotypically a heterogeneous population of cells.

In hyaline cartilage, chondrocytes differing in their morphological and functional characteristics are detected. There are three main types.

Type I chondrocytes- relatively few cells with uneven process edges, a large nucleus, and a relatively weakly expressed GES. Cells of this type, for example, in articular cartilage, are attributed the possibility of mitotic division, i.e. a function necessary for the implementation of physiological regeneration in the process of natural change in the chondrocyte population.

Type II chondrocytes make up the bulk of cells and are characteristic of any type of hyaline cartilage. Such a chondrocyte is a cell (15-20 microns in diameter) with a large nucleus and many small processes, the so-called cytoplasmic “legs”. Nuclear chromatin is partially condensed and concentrated mainly on inner surface nuclear membrane. The hydroelectric power station is well developed in the cytoplasm; its channels are in some places expanded and filled with synthesis products. The Golgi complex is always well developed. Mitochondria are few in number.

Chondrocytes III type - these are also highly differentiated cells.

Chondrocyte phenotype and patterns of its maintenance

The question is what are the possibilities and the necessary conditions to maintain the chondrocyte phenotype in mature cartilage under normal and extreme situations, has been the subject of both study and debate in recent years. The chondrocyte and the matrix surrounding it are a single functional whole - the chondrocyte produces the matrix, the matrix ensures the maintenance of the chondrocyte phenotype. Accordingly, in normal cartilage in vivo there are conditions that ensure the maintenance of the stability of the chondrocyte phenotype.

It is believed that the chondrocyte phenotype is more labile than the phenotype of other connective tissue cells. It is acquired at a certain stage of chondrogenic differentiation of mesenchymal cells and is lost under pathological conditions, which undoubtedly has pathogenetic significance. The loss of the chondrocyte phenotype also occurs after their isolation from cartilage tissue for subsequent cultivation in monolayer cell culture conditions. In this case, against the background of pronounced proliferation of chondrocytes, inhibition of the biosynthesis of the cartilage matrix is ​​observed. This phenomenon is usually called the process of dedifferentiation.

However, under certain conditions, the chondrocyte phenotype (for example, after transferring cells from a monolayer to a suspension culture) can quickly be restored. Redifferentiation occurs, during which a number of genes involved in the process of cell differentiation are activated, including genes encoding components of the signaling system of one of the cytokines, IL-6. On the contrary, the expression of some other genes is suppressed. In particular, the suppression affects the connective tissue growth factor (CTGF) gene. The main sign of redifferentiation is the resumption of expression of specific components of the extracellular matrix, although at the same time, both the expression of nonspecific biosynthesis products that appeared during dedifferentiation, in particular type I collagen, and the altered structure of the chondrocyte may be partially preserved.

To maintain the mature chondrocyte phenotype, the presence of a normal, complete cartilage matrix is ​​necessary. Normally exactly structural features matrix stabilize the cell phenotype. This conclusion is supported by the fact that when culturing cartilage sections, i.e. while maintaining the matrix, the phenotype of chondrocytes does not change over a long period of cultivation (up to 9 weeks). Under pathological conditions, the chondrocyte phenotype changes, and the goal of therapy is its restoration.

Metabolic processes in cartilage tissue cells

Chondrocytes, as mentioned above, are the only type of cells present in mature cartilage tissue, and that is why only they can serve as a source for the formation of the extracellular matrix. The production of matrix and the maintenance of its structural integrity throughout the life of the organism are the main functions of chondrocytes. It is chondrocytes that carry out the biosynthesis of all specific matrix components. In addition, chondrocytes control the processes of assembly of supramolecular structures occurring in the matrix (for example, aggrecan aggregates and collagen fibrils) and the course of catabolic reactions.

As we have already emphasized, the number of chondrocytes is relatively small. They can ensure the formation of the matrix only due to the high metabolic (anabolic and catabolic) activity of each cell. This activity, most pronounced in embryonic and early postnatal ontogenesis, is one of characteristic properties chondrocytes.

The metabolic activity of chondrocytes, with the exception of processes common to all cells that ensure their own vital functions, is aimed at building and maintaining the matrix. It is advisable to consider it after the characteristics of the structural components of the matrix and the enzymes operating in it are presented. Here we will only pay attention to the conditions under which the metabolic functions of cartilage cells are carried out.

Relatively few cells of cartilage tissue (chondroblasts-chondrocytes) must ensure the formation and subsequent maintenance in a state of dynamic equilibrium large masses extracellular matrix. Cartilage cells perform their task in special conditions: They function in tissue poor in blood vessels, and in articular cartilage of adult organisms - in avascular tissue. If cartilages of other localizations, for example, intercostal cartilage, receive the materials necessary for metabolism from the capillaries of the perichondrium (perichondrium), then in articular cartilage, devoid of perichondrium and separated by a boundary line from the subchondral bone, there is no possibility of obtaining these materials from the blood.

This means that in mature articular cartilage, chondrocytes, distant from blood vessels, receive starting materials for metabolic processes only from the fluid washing the articular surface due to their penetration through the thickness of the matrix. The physical mechanism that carries out such penetration is diffusion - the movement of molecules in a solution from an area of ​​​​higher concentration to an area of ​​lower concentration until a uniform distribution of solute molecules among solvent molecules is achieved.

The rate of diffusion between polar and non-polar molecules is distinctly different. But the intensity of diffusion of all low-molecular substances is quite sufficient to meet the metabolic needs of chondrocytes throughout the entire thickness of the articular cartilage, even in the most massive areas of the cartilage of the human hip joint, where the thickness of the cartilage reaches 3.5-5 mm. The exception is oxygen; its concentration in the fluid is very low. With the oxygen concentration actually existing in the synovium (3-10 x 10-8 mol/ml), diffusion ensures the penetration of oxygen only to a depth of about 1.8 mm. Cells located in layers of cartilage more distant from the articular surface find themselves in conditions of oxygen deficiency. As a result, metabolic processes in chondrocytes of different layers of cartilage proceed with unequal activity. This is another manifestation of the metabolic heterogeneity of articular cartilage.

The metabolism of chondrocytes is predominantly anaerobic in nature, because it is carried out through glycolysis. This feature of the energy supply of cartilage tissue is an adaptive mechanism that allows cells to function in conditions of very low oxygen concentrations. If in the intercellular spaces of soft tissues the partial pressure of oxygen is 15-20 mm Hg. Art., then in the articular cartilage it does not exceed 5-8 mm Hg. Art. Moreover, in the basal zone of cartilage it is approximately 10 times lower than in the superficial zone. The lower the oxygen concentration in the cartilage matrix, the higher the intensity of glycolysis and, accordingly, the production of lactic acid.

Chondrocytes are phenotypically adapted to anaerobic operating conditions. In vitro experiments have shown that as the degree of hypoxia increases, anabolic processes are not only not inhibited, but are even activated. The efficiency of glucose utilization increases, which ensures more economical energy consumption. However, when tissue hypoxia is too pronounced (this condition is observed in RA, when the oxygen content in the fluid drops very sharply), the expression of a number of genes by chondrocytes is suppressed. The levels of mRNA encoding structural macromolecules of the matrix (type II collagen), the amount of some cytokines and integrins in chondrocytes decrease.

At the same time, unlike cells of other tissues, chondrocytes give a paradoxical response to an increase in the partial pressure of oxygen: inhibition of biosynthetic processes, in particular a decrease in the biosynthesis of DNA and proteoglycans. With age, oxygen consumption by chondrocytes decreases even more. Oxygen consumption by chondrocytes, especially the superficial layer of cartilage, decreases with excess glucose concentration in the SF.

Biomechanical properties of cartilage

Articular cartilage performs two main biomechanical functions:

1. take on the action of compression forces caused by gravity and loads developing during movements, contributing to them uniform distribution and the translation of axially directed forces into tangential ones;
2. form wear-resistant surfaces of the articulating elements of the skeleton.

Because the cartilage tissue contains very few cells - about 1% of the tissue mass; these properties depend almost entirely on the extracellular matrix.

From a biomechanical point of view, the cartilage tissue matrix is ​​a material consisting of two different phases - solid and liquid. The solid phase includes non-fibrous structural macromolecules, among which aggrecan aggregates predominate and fibrous structural macromolecules, among which type II collagen predominates. Liquid phase makes up approximately 80% of the tissue mass.

Collagen fibers form a strong network that fixes aggrecan aggregates and, limiting negatively charged aggrecan macromolecules in space, does not allow them to spread to the maximum extent. This network (framework) has little extensibility and provides tensile strength to the cartilage.

The composite solid phase matrix functions as a porous, permeable, fiber-bound, water-swollen material. Water molecules are located inside the spaces occupied by diffuse aggregates of aggrecan, and it is water, as an incompressible liquid, that provides the compressive strength of cartilage. The proteoglycan component of the matrix, due to its polyanionic properties, is responsible for the hyperhydrated state of cartilage and, therefore, plays a decisive role in the formation of strength to compressive loads. There is a pronounced positive correlation between the concentration of aggrecan in cartilage and its compressive strength.

Only less than 1% of water molecules are firmly held by collagen fibers. The remaining (more than 99%) water molecules located in the interfibrous substance of the matrix are quite free and mobile. Under compression loads, these free molecules, together with low molecular weight substances dissolved in water, can move through the matrix and “squeeze” out of the cartilage into the SF. When the pressure decreases, movement occurs in the opposite direction - from the fluid into the matrix. This explains the ability of cartilage to undergo reversible deformation (elasticity).

When water moves in a porous material, such as a matrix, friction arises, which, in combination with some features of the solid phase (mainly we are talking about complex system intermolecular bonds of matrix components) determines a certain viscosity of cartilage tissue.

Thus, the two-phase model generally explains the viscoelastic biomechanical properties of cartilage. At the same time, it also encounters objections. The main one is the illegality of combining all solid components into one phase. Experiments N.D. Broom, N. Silyn-Roberts showed that the destruction of a significant part of aggrecan aggregates (using hyaluronidase) has virtually no effect on the tensile strength of cartilage and, therefore, collagen fibers are independent of aggrecan in this biomechanical function. Probably, the strengthening of collagen fibers due to the interaction of different types of collagens is more significant than the connections between collagens and aggrecan, therefore there are reasons to consider aggrecan and collagens as two separate phases, which means a transition to a three-phase biomechanical model of cartilage (collagens-aggrecan-water).

It is possible that the biomechanical properties of cartilage are affected by the influence of glycoproteins. This means that the three-phase model does not sufficiently take into account the entire multicomponent nature of the cartilage matrix. But regardless of which biomechanical model turns out to be final, it is obvious that normal functioning of cartilage is possible only with optimal quantitative and structural relationships of all matrix components.

70.Cartilage tissue. Classification, development, structure, histochemical characteristics and function. Cartilage growth, regeneration and age-related changes.

Cartilaginous And bone tissue develop from sclerotomal mesenchyme, belong to the tissues of the internal environment and, like all other tissues of the internal environment, consist of cells and intercellular substance. The intercellular substance here is dense, so these tissues perform a support-mechanical function.

Cartilage tissue(textuscartilagineus). They are classified into hyaline, elastic and fibrous. The classification is based on the peculiarities of the organization of the intercellular substance. The composition of cartilage tissue includes 80% water, 10-15% organic matter and 5-7% inorganic substances.

Development of cartilage tissue, or chondrogenesis, consists of 3 stages: 1) formation of chondrogenic islets; 2) formation of primary cartilaginous tissue: 3) differentiation of cartilaginous tissue.

During 1st stage mesenchymal cells unite into chondrogenic islands, the cells of which multiply and differentiate into chondroblasts. The resulting chondroblasts contain granular ER, Golgi complex, and mitochondria. Chondroblasts then differentiate into chondrocytes.

During 2nd stage In chondrocytes, granular ER, Golgi complex, and mitochondria are well developed. Chondrocytes actively synthesize fibrillar protein (type II collagen), from which the intercellular substance is formed, which stains oxyphilic.

When advancing 3rd stage in chondrocytes, granular ER develops more intensively, on which fibrillar proteins and chondroitin sulfates (chondroitinsulfuric acid) are produced, which are stained with basic dyes. Therefore, the main intercellular substance of the cartilage tissue around these chondrocytes is stained basophilic.

Around the cartilaginous rudiment, a perichondrium is formed from mesenchymal cells, consisting of 2 layers: 1) the outer, more dense, or fibrous, and 2) the inner, more loose, or chondrogenic, which contains prechondroblasts and chondroblasts.

Appositional growth of cartilage, or growth by superposition, is characterized by the fact that chondroblasts are released from the perichondrium, which superimpose on the main substance of the cartilage, differentiate into chondrocytes and begin to produce the intercellular substance of cartilage tissue.

Interstitial growth cartilage tissue is produced by chondrocytes located inside the cartilage, which, firstly, divide by mitosis and, secondly, produce intercellular substance, due to which the volume of cartilage tissue increases.

Cartilage cells(chondrocytus). The chondrocyte differential consists of: stem cell, semi-stem cell (prechondroblast), chondroblast, chondrocyte.

Chondroblasts (chondroblastus) are located in the inner layer of the perichondrium, have organelles of general importance: granular ER, Golgi complex, mitochondria. Functions of chondroblasts:

1) secrete intercellular substance (fibrillar proteins);

2) in the process of differentiation they turn into chondrocytes;

3) have the ability to undergo mitotic division.

Chondrocytes located in cartilaginous lacunae. In the lacuna there is initially 1 chondrocyte, then, during its mitotic division, 2, 4, 6, etc. cells are formed. All of them are located in the same lacuna and form an isogenic group of chondrocytes.

Chondrocytes of the isogenic group are divided into 3 types: I, II, III.

Type I chondrocytes have the ability to undergo mitotic division, contain the Golgi complex, mitochondria, granular EPS and free ribosomes, have a large nucleus and a small amount of cytoplasm (large nuclear-cytoplasmic ratio). These chondrocytes are located in young cartilage.

Type II chondrocytes located in mature cartilage, their nuclear-cytoplasmic ratio decreases somewhat as the volume of the cytoplasm increases; they lose the ability to undergo mitosis. Granular EPS is well developed in their cytoplasm; they secrete proteins and glycosaminoglycans (chondroitin sulfates), so the main intercellular substance around them is stained basophilic.

Type III chondrocytes are located in old cartilage, lose the ability to synthesize glycosaminoglycans and produce only proteins, therefore the intercellular substance around them is stained oxyphilic. Consequently, around such an isogenic group one can see an oxyphilic-stained ring (proteins are secreted by type III chondrocytes), outside of this ring a basophilic-stained ring is visible (glycosaminoglycans are secreted by type II chondrocytes) and the outer ring itself is again oxyphilic-stained (proteins are secreted at a time when cartilage contained only young type I chondrocytes). Thus, these 3 differently colored rings around isogenic groups characterize the process of formation and function of 3 types of chondrocytes.

Intercellular substance of cartilage tissue. Contains organic substances (mainly type II collagen), glycosaminoglycans, proteoglycans and non-collagen type proteins. The more proteoglycans, the more hydrophilic the intercellular substance, the more elastic and permeable it is. Gases, water molecules, salt ions and micromolecules diffusely penetrate through the ground substance from the side of the perichondrium. However, macromolecules do not penetrate. Macromolecules have antigenic properties, but since they do not penetrate the cartilage, cartilage transplanted from one person to another takes root well (no immune rejection reaction occurs).

The main substance of cartilage contains collagen fibers consisting of type II collagen. The orientation of these fibers depends on power lines, and the direction of the latter depends on the mechanical effect on the cartilage. In the intercellular substance of cartilage tissue there are no blood and lymphatic vessels, therefore the nutrition of the cartilage tissue is carried out through the diffuse supply of substances from the vessels of the perichondrium.

Age-related changes in cartilage tissue. The greatest changes are observed in old age, when the number of chondroblasts in the perichondrium and the number of dividing cartilage cells decrease. In chondrocytes, the amount of granular ER, Golgi complex and mitochondria decreases, and the ability of chondrocytes to synthesize glycosaminoglycans and proteoglycans is lost. A decrease in the amount of proteoglycans leads to a decrease in the hydrophilicity of cartilage tissue, a weakening of cartilage permeability and nutrients. This leads to calcification of the cartilage, penetration of blood vessels into it and the formation of bone substance inside the cartilage.

Consisting of cartilage cells (chondrocytes) and a large amount of dense intercellular substance. Serves as a support. Chondrocytes have a variety of shapes and lie singly or in groups within cartilaginous cavities. The intercellular substance contains chondrinic fibers, similar in composition to collagen fibers, and the ground substance, rich in chondromucoid.

Depending on the structure of the fibrous component of the intercellular substance, three types of cartilage are distinguished: hyaline (vitreous), elastic (mesh) and fibrous (connective tissue).

Cartilaginous tissue (tela cartilaginea) is a type of connective tissue characterized by the presence of a dense intercellular substance. In the latter, a basic amorphous substance is distinguished, which contains compounds of chondroitinsulfuric acid with proteins (chondromucoids) and chondrinum fibers, similar in composition to collagen fibers. Fibrils of cartilage tissue belong to the type of primary fibers and have a thickness of 100-150 Å. Electron microscopy in the fibers of cartilage tissue, in contrast to the collagen fibers themselves, reveals only a vague alternation of light and dark areas without a clear periodicity. Cartilage cells (chondrocytes) are located in the cavities of the ground substance individually or in small groups (isogenic groups).

The free surface of the cartilage is covered with dense fibrous connective tissue - perichondrium, in the inner layer of which poorly differentiated cells - chondroblasts - are located. The cartilaginous tissue covering the articular surfaces of the bones does not have perichondrium. The growth of cartilage tissue is carried out due to the proliferation of chondroblasts, which produce the ground substance and subsequently turn into chondrocytes (appositional growth) and due to the development of a new ground substance around the chondrocytes (interstitial, intussusceptive growth). During regeneration, the development of cartilage tissue can also occur by homogenizing the ground substance of fibrous connective tissue and converting its fibroblasts into cartilage cells.

Nutrition cartilaginous fabric goes by diffusion of substances from the blood vessels of the perichondrium. Nutrients penetrate into the tissue of articular cartilage from the synovial fluid or from the vessels of the adjacent bone. Nerve fibers are also localized in the perichondrium, from where individual branches of the soft nerve fibers can penetrate into the cartilage tissue.

In embryogenesis, cartilaginous tissue develops from mesenchyme (see), between the contiguous elements of which layers of the main substance appear (Fig. 1). In such a skeletogenic rudiment, hyaline cartilage is first formed, temporarily representing all the main parts of the human skeleton. Subsequently, this cartilage can be replaced by bone tissue or differentiate into other types of cartilage tissue.

The following types of cartilage tissue are known.

Hyaline cartilage(Fig. 2), from which in humans the cartilages of the respiratory tract, thoracic ends of the ribs and articular surfaces of bones are formed. In a light microscope, its main substance appears homogeneous. Cartilage cells or isogenic groups of them are surrounded by an oxyphilic capsule. In differentiated areas of cartilage, a basophilic zone adjacent to the capsule and an oxyphilic zone located outside it are distinguished; Collectively, these zones form the cellular territory, or chondrin ball. The complex of chondrocytes with the chondrinic ball is usually taken to be the functional unit of cartilage tissue - the chondrone. The main substance between chondrons is called interterritorial spaces (Fig. 3).

Elastic cartilage(synonym: reticular, elastic) differs from hyaline in the presence of branching networks of elastic fibers in the ground substance (Fig. 4). The cartilage of the auricle, epiglottis, Wrisberg and Santorini cartilages of the larynx are built from it.

Fibrous cartilage(synonym for connective tissue) is located in the places of transition of dense fibrous connective tissue into hyaline cartilage and differs from the latter in the presence of real collagen fibers in the ground substance (Fig. 5).

Pathology of cartilage tissue - see Chondritis, Chondrodystrophy, Chondroma.

Rice. 1-5. The structure of cartilage tissue.
Rice. 1. Histogenesis of cartilage:
1 - mesenchymal syncytium;
2 - young cartilage cells;
3 - layers of the main substance.
Rice. 2. Hyaline cartilage (low magnification):
1 - perichondrium;
2 - cartilage cells;
3 - main substance.
Rice. 3. Hyaline cartilage (high magnification):
1 - isogenic group of cells;
2 - cartilaginous capsule;
3 - basophilic zone of the chondrin ball;
4 - oxyphilic zone of the chondrin ball;
5 - interterritorial space.
Rice. 4. Elastic cartilage:
1 - elastic fibers.
Rice. 5. Fibrous cartilage.

Cartilage tissue has a functional supporting role. It does not work by stretching, like dense connective tissue, but thanks to internal tension resists compression well and serves as a shock absorber for the bone apparatus.

This special tissue serves to immovably connect bones, forming synchondrosis. Covering the articular surfaces of bones, it softens movement and friction in the joints.

Cartilage tissue is very dense and at the same time quite elastic. Its biochemical composition is rich in dense amorphous substance. Cartilage develops from intermediate mesenchyme.

At the site of the future cartilage, mesenchymal cells multiply rapidly, their processes are shortened and the cells are in close contact with each other.

Then an intermediate substance appears, due to which mononuclear areas are clearly visible in the rudiment, which are the primary cartilaginous cells - chondrobe flippers. They multiply and produce ever new masses of intermediate substance.

The rate of reproduction of cartilage cells by this period slows down greatly, and due to the large amount of intermediate substance, they find themselves far apart from each other. Soon the cells lose the ability to divide through mitosis, but still retain the ability to divide amitotically.

However, now the daughter cells do not diverge far, since the intermediate substance surrounding them has become denser.

Therefore, cartilage cells are located in the mass of the ground substance in groups of 2-5 or more cells. They all come from the same initial cell.

Such a group of cells is called isogenic (isos - equal, identical, genesis - occurrence).

Rice. 1.

A - hyaline cartilage of the trachea;

B - elastic cartilage of the calf's auricle;

B -- fibrous cartilage of the calf intervertebral disc;

a - perichondrium; b ~ cartilage; c -- older section of cartilage;

• 1 - chondroblast; 2 - chondrocyte;
• 3 -- isogenic group of chondrocytes; 4 -- elastic fibers;
• 5 -- bundles of collagen fibers; 6 -- main substance;
• 7 -- chondrocyte capsule; 8 - basophilic and 9 - oxyphilic zone of the main substance around the isogenic group.

Cells of the isogenic group do not divide by mitosis and produce little intermediate substance of a slightly different chemical composition, which forms cartilaginous capsules around individual cells, and fields around the isogenic group.

The cartilage capsule, as revealed by electron microscopy, is formed by thin fibrils concentrically located around the cell.

Consequently, at the beginning of the development of cartilage tissue in animals, its growth occurs by an increase in the mass of cartilage from the inside.

Then the oldest part of the cartilage, where cells do not multiply and the intermediate substance is not formed, stops increasing in size, and the cartilage cells even degenerate.

However, the growth of cartilage as a whole does not stop. Around the obsolete cartilage, a layer of cells separates from the surrounding mesenchyme and becomes chondroblasts. They secrete an intermediate substance of cartilage around themselves and gradually become denser with it.

However, as they develop, chondroblasts lose the ability to divide by mitosis, form less intermediate substance and become chondrocytes. On top of the layer of cartilage formed in this way, due to the surrounding mesenchyme, more and more layers of it are layered. Consequently, cartilage grows not only from the inside, but also from the outside.

In mammals there are: hyaline (vitreous), elastic and fibrous cartilage.

Hyaline cartilage (Fig. 1-A) is the most common, milky white in color and somewhat translucent, so it is often called vitreous.

It covers the articular surfaces of all bones and forms the costal cartilages, tracheal cartilages, and some laryngeal cartilages. Hyaline cartilage consists, like all tissues of the internal environment, of cells and intermediate substance.

Cartilage cells are represented by chondroblasts and chondrocytes. Different from hyaline cartilage strong development collagen fibers that form bundles that lie almost parallel to each other, like in tendons!

There is less amorphous substance in fibrous cartilage than in hyaline cartilage. Round, light-colored cells of fibrocartilage lie between the fibers in parallel rows.

In places where fibrous cartilage is located between hyaline cartilage and dense connective tissue, a gradual transition from one type of tissue to another is observed in its structure. Thus, closer to the connective tissue, collagen fibers in cartilage form rough parallel bundles, and cartilage cells lie in rows between them, like fibrocytes of dense connective tissue. Closer to the hyaline cartilage, the bundles are divided into individual collagen fibers, forming a delicate network, and the cells lose their correct location.

They perform mechanical, support, protective functions. They contain elastic, dense intercellular substance. The water content is up to 70-80%, minerals up to 4-7%, organic matter up to 10-15%, and they are dominated by proteins, carbohydrates and very few lipids. They contain cells and intercellular substance. Cellular composition All types of cartilage tissue are the same and include chondroblasts - poorly differentiated, flattened cells with basophilic cytoplasm, they are able to proliferate and produce intercellular substance. Chondroblasts differentiate into young chondrocytes and acquire an oval shape. They retain the ability to proliferate and produce intercellular substance. The small ones then differentiate into larger, round mature chondrocytes. They lose the ability to proliferate and produce intercellular substance. Mature chondrocytes deep in the cartilage accumulate in one cavity and are called isogenic groups of cells.

Cartilaginous tissues differ in the structure of the intercellular substance and fibrous structures. There are hyaline, elastic and fibrous cartilage tissues. They participate in the formation of cartilage and form hyaline, elastic and fibrous cartilage.

Hyaline cartilage lines the articular surfaces, is located in the area where the ribs join the sternum and in the wall of the airways. The outside is covered with perichondrium - perichondrium, which contains blood vessels. E the peripheral part consists of denser connective tissue, and inner part loose, contains fibroblasts and chondroblasts. Chondroblasts produce and secrete intercellular substance and cause appositional growth of cartilage. In the peripheral part of the cartilage itself there are young chondrocytes. They proliferate, produce and secrete chondromitin sulfates + proteoglycans, allowing cartilage to grow from the inside.

In the middle part of the cartilage there are mature chondrocytes and isogenic groups of cells. Between the cells is the intercellular substance. It contains ground substance and collagen fibers. There are no vessels; it feeds diffusely from the vessels of the periosteum. In young cartilage, the intercellular substance is oxyphilic and gradually becomes basophilic. With age, starting from the central part, calcium salts are deposited in the cartilage, the cartilage calcifies, becomes brittle and brittle.

Elastic cartilage - forms the basis of the auricle, in the wall of the airways. It is similar in structure to hyaline cartilage, but contains elastic rather than collagen fibers, and normally it never calcifies.

Fibrous cartilage - it is located in the transition zone of ligaments, tendons with bone tissue, in the area where the bones are covered with hyaline cartilage and in the area of ​​intervertebral joints. In it, coarse bundles of collagen fibers run along the tension axis, being a continuation of the tendon threads. Fibrous cartilage in the area of ​​attachment to the bone is more similar to hyaline cartilage, and in the area of ​​transition to the tendon it is more like a tendon.

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Nutrition of cartilage tissue goes the way diffusion of substances from the blood vessels of the perichondrium. Nutrients penetrate into the tissue of articular cartilage from the synovial fluid or from the vessels of the adjacent bone.

Cartilage tissue: functions, structural features, types, restoration

Nerve fibers are also localized in the perichondrium, from where individual branches of the soft nerve fibers can penetrate into the cartilage tissue.

Hyaline cartilage
Elastic cartilage
Fibrous cartilage

Functions of bone tissue:

1) supporting;

2) mechanical;

osteocytes. These are process-shaped cells with a large nucleus and weakly expressed cytoplasm (nuclear-type cells). Cell bodies are localized in bone cavities (lacunae), and processes are located in bone tubules. Numerous bone tubules, anastomosing with each other, penetrate the bone tissue, communicating with the perivascular space, forming a drainage system of the bone tissue. This drainage system contains tissue fluid, through which metabolism is ensured not only between cells and tissue fluid, but also in the intercellular substance.

Osteoblasts

Osteoclasts

Intercellular substance

Bone

Classification of bone tissue

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Cartilage tissue - structure, types, location in the body.

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Cartilaginous tissue (textus cartilaginus) forms articular cartilage, intervertebral discs, cartilage of the larynx, trachea, bronchi, and external nose. Cartilage tissue consists of cartilage cells (chondroblasts and chondrocytes) and dense, elastic intercellular substance.

Cartilage tissue contains about 70-80% water, 10-15% organic substances, 4-7% salts. About 50-70% of the dry matter of cartilage tissue is collagen. The intercellular substance (matrix), produced by cartilage cells, consists of complex compounds that include proteoglycans. hyaluronic acid, glycosaminoglycan molecules. Cartilage tissue contains two types of cells: chondroblasts (from the Greek chondros - cartilage) and chondrocytes.

Chondroblasts are young round or ovoid cells capable of mitotic division. They produce components of the intercellular substance of cartilage: proteoglycans, glycoproteins, collagen, elastin. The cytolemma of chondroblasts forms many microvilli. The cytoplasm is rich in RNA, a well-developed endoplasmic reticulum (granular and non-granular), Golgi complex, mitochondria, lysosomes, and glycogen granules. The chondroblast nucleus, rich in active chromatin, has 1-2 nucleoli.

Chondrocytes are mature large cells of cartilage tissue. They are round, oval or polygonal, with processes and developed organelles. Chondrocytes are located in cavities - lacunae, surrounded by intercellular substance. If there is one cell in a lacuna, then such a lacuna is called primary. Most often, the cells are located in the form of isogenic groups (2-3 cells) occupying the cavity of the secondary lacuna. The walls of the lacuna consist of two layers: the outer layer, formed by collagen fibers, and the inner layer, consisting of aggregates of proteoglycans that come into contact with the glycocalyx of cartilage cells.

The structural and functional unit of cartilage is the chondrone, cell-derived or isogenic group of cells, pericellular matrix and lacuna capsule.

Nutrition of cartilage tissue occurs through the diffusion of substances from the blood vessels of the perichondrium. Nutrients penetrate into the tissue of articular cartilage from the synovial fluid or from the vessels of the adjacent bone. Nerve fibers are also localized in the perichondrium, from where individual branches of the soft nerve fibers can penetrate into the cartilage tissue.

In accordance with the structural features of cartilage tissue, three types of cartilage are distinguished: hyaline, fibrous and elastic cartilage.

Hyaline cartilage, from which in humans the cartilage of the respiratory tract, thoracic ends of the ribs and articular surfaces of bones is formed. In a light microscope, its main substance appears homogeneous. Cartilage cells or isogenic groups of them are surrounded by an oxyphilic capsule. In differentiated areas of cartilage, a basophilic zone adjacent to the capsule and an oxyphilic zone located outside it are distinguished; Collectively, these zones form the cellular territory, or chondrin ball. The complex of chondrocytes with the chondrinic ball is usually taken to be the functional unit of cartilage tissue - the chondrone. The main substance between chondrons is called interterritorial spaces.
Elastic cartilage(synonym: reticular, elastic) differs from hyaline in the presence of branching networks of elastic fibers in the ground substance. The cartilage of the auricle, epiglottis, Wrisberg and Santorini cartilages of the larynx are built from it.
Fibrous cartilage(synonym for connective tissue) is located in the places of transition of dense fibrous connective tissue into hyaline cartilage and differs from the latter in the presence of real collagen fibers in the main substance.

7. Bone tissue - location, structure, functions

Bone tissue is a type of connective tissue and consists of cells and intercellular substance, which contains a large amount of mineral salts, mainly calcium phosphate. Minerals make up 70% of bone tissue, organic – 30%.

Functions of bone tissue:

1) supporting;

2) mechanical;

3) protective (mechanical protection);

4) participation in the mineral metabolism of the body (calcium and phosphorus depot).

Bone cells - osteoblasts, osteocytes, osteoclasts. The main cells in formed bone tissue are osteocytes. These are process-shaped cells with a large nucleus and weakly expressed cytoplasm (nuclear-type cells).

Functions of cartilage tissue

Cell bodies are localized in bone cavities (lacunae), and processes are located in bone tubules. Numerous bone tubules, anastomosing with each other, penetrate the bone tissue, communicating with the perivascular space, forming a drainage system of the bone tissue. This drainage system contains tissue fluid, through which metabolism is ensured not only between cells and tissue fluid, but also in the intercellular substance.

Osteocytes are the definitive cell form and do not divide. They are formed from osteoblasts.

Osteoblasts found only in developing bone tissue. In formed bone tissue they are usually contained in an inactive form in the periosteum. In developing bone tissue, osteoblasts cover the periphery of each bone plate, tightly adjacent to each other.

The shape of these cells can be cubic, prismatic and angular. The cytoplasm of osteoblasts contains a well-developed endoplasmic reticulum, lamellar Golgi complex, many mitochondria, indicating high synthetic activity these cells. Osteoblasts synthesize collagen and glycosaminoglycans, which are then secreted into intercellular space. Due to these components, the organic matrix of bone tissue is formed.

These cells provide mineralization of the intercellular substance by secreting calcium salts. Gradually releasing intercellular substance, they become immured and turn into osteocytes. In this case, intracellular organelles are significantly reduced, synthetic and secretory activity is reduced, and the functional activity characteristic of osteocytes is preserved. Osteoblasts, localized in the cambial layer of the periosteum, are located in inactive state, synthetic and transport organelles are poorly developed in them. When these cells are irritated (in case of injuries, bone fractures, etc.), granular EPS and lamellar complex quickly develop in the cytoplasm, active synthesis and release of collagen and glycosaminoglycans occurs, the formation of an organic matrix (callus), and then the formation of definitive bone fabrics. In this way, due to the activity of osteoblasts of the periosteum, bone regeneration occurs when they are damaged.

Osteoclasts– bone-destructive cells are absent in formed bone tissue, but are contained in the periosteum and in places of destruction and restructuring of bone tissue. Since ontogenesis is continuously carried out local processes restructuring of bone tissue, then osteoclasts are necessarily present in these places. During embryonic osteohistogenesis, these cells play a very important role important role and are present in large quantities. Osteoclasts have a characteristic morphology: these cells are multinucleated (3 - 5 or more nuclei), have quite large size(about 90 µm) and characteristic shape– oval, but the part of the cell adjacent to the bone tissue has a flat shape. In the flat part, two zones can be distinguished: the central (corrugated part, containing numerous folds and processes, and the peripheral part (transparent) in close contact with the bone tissue. In the cytoplasm of the cell, under the nuclei, there are numerous lysosomes and vacuoles of various sizes.

The functional activity of the osteoclast is manifested as follows: in the central (corrugated) zone of the cell base, carbonic acid and proteolytic enzymes are released from the cytoplasm. The released carbonic acid causes demineralization of bone tissue, and proteolytic enzymes destroy the organic matrix of the intercellular substance. Fragments of collagen fibers are phagocytosed by osteoclasts and destroyed intracellularly. Through these mechanisms, resorption (destruction) of bone tissue occurs, and therefore osteoclasts are usually localized in the recesses of bone tissue. After the destruction of bone tissue, due to the activity of osteoblasts moving out of the connective tissue of blood vessels, new bone tissue is built.

Intercellular substance bone tissue consists of a basic (amorphous) substance and fibers that contain calcium salts. The fibers consist of collagen and are folded into bundles, which can be arranged in parallel (ordered) or disorderly, on the basis of which the histological classification of bone tissue is based. The main substance of bone tissue, like other types of connective tissues, consists of glycosaminergic and proteoglycans.

Bone tissue contains less chondroitinsulfuric acids, but more citric acids and others, which form complexes with calcium salts. During the development of bone tissue, an organic matrix is ​​first formed - the main substance and collagen fibers, and then calcium salts are deposited in them. They form crystals - hydroxyapatites, which are deposited both in the amorphous substance and in the fibers. Providing bone strength, calcium phosphate salts are also a depot of calcium and phosphorus in the body. Thus, bone tissue takes part in the mineral metabolism of the body.

When studying bone tissue, the concepts of “bone tissue” and “bone” should also be clearly distinguished.

Bone- this is the organ that is the main structural component which are bone tissue.

Classification of bone tissue

There are two types of bone tissue:

1) reticulofibrous (coarse fibrous);

2) lamellar (parallel fibrous).

The classification is based on the nature of the arrangement of collagen fibers. In reticulofibrous bone tissue, the bundles of collagen fibers are thick, tortuous, and arranged in a disorderly manner. In the mineralized intercellular substance, osteocytes are randomly located in the lacunae. Lamellar bone tissue consists of bone plates in which collagen fibers or their bundles are located parallel in each plate, but at right angles to the course of the fibers of adjacent plates. Osteocytes are located between the plates in the lacunae, while their processes pass through the plates in the tubules.

In the human body, bone tissue is presented almost exclusively in the lamellar form. Reticulofibrous bone tissue occurs only as a stage in the development of some bones (parietal, frontal). In adults, it is located in the area of ​​attachment of tendons to bones, as well as at the site of ossified sutures of the skull (sagittal suture, scales of the frontal bone).

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Human cartilaginous connective tissue

One of the types of connective tissue present in the human body is cartilage. Cartilaginous connective tissue is distinguished by its relatively high density and elasticity of the intercellular substance that envelops groups of chondrocytes and individual cells. Cartilage differs from bone tissue (as well as from a number of other tissues) complete absence blood vessels and nerves. The shell of cartilage is the perichondrium, which is also called the perichondrium. Cartilaginous connective tissue (CCT) can serve as a rigid skeletal base in some animals or forms elastic parts of the skeleton, covering the edges of bones and forming special shock-absorbing layers (such as intervertebral discs). In a word, the main functions of cartilaginous connective tissue are: supporting and joint-forming functions.

The structure of cartilage tissue

As noted above, cartilage tissue consists not only of the cartilage itself, but also of the perichondrium (perichondrium), which in turn includes inner layer loose fibrous connective tissue (LFCT) and an outer layer of dense fibrous connective tissue (PVCT). The PBST (along with chondrocytes and intercellular substance consisting of fibers, interstitial water and amorphous substance) also includes semi-stem and stem cells, a system of blood vessels, nerves and chondroblasts. The volume of chondrocytes is approximately up to 10% of total mass cartilaginous connective tissue. Most of all, CST contains intercellular substance, which is characterized by a fairly high hydrophilicity, and accordingly provides the possibility of delivering the necessary nutrients to the cells from the blood capillaries of the perichondrium due to diffusion processes. Cartilage can be glassy (if the intercellular substance is homogeneous), fibrous or mesh.

Chondrocytes

The diversity of chondrocytes that make up cartilaginous connective tissue includes chondroblasts, stem and semi-stem cells, and also includes mature and young chondrocytes. Chondrocytes are derivatives of chondroblasts, and in addition, these are cells that are the only cell populations present in cartilage tissue that are found in lacunae. There are young and mature chondrocytes. The former are in many ways identical to chondroblasts. They have an oblong shape, a fairly large Golgi apparatus, and in addition they can produce glycoproteins and protein for elastic and collagen fibers. Mature chondrocyte cells are oval in shape and less capable of synthesis when compared with young chondrocytes. Chondrocytes can divide and form separate cell groups framed by a single capsule. In vitreous cartilage, cell groups of up to 12 cells each may be present, but in other types of cartilage tissue, isogenic groups usually contain fewer cells.

Cartilage tissue: classification and histogenesis

Cartilaginous connective tissue develops not only at the embryonic level, but also in adults (tissue regeneration). During the development of cartilage, the so-called cartilaginous differon is formed, in which stem and semi-stem cells, and then chondroblasts and chondrocytes, successively replace each other. At the initial stage of cartilaginous embryogenesis, a small chondrogenic island is formed. Next, differentiation of chondroblasts occurs with the subsequent appearance of cartilage matrix and fibers. At the final stage of embryogenesis, the cartilaginous anlage experiences interstitial or appositional growth.

Cartilage tissue

In the first, the tissue increases from the inside (characteristic of both the embryonic period and regeneration processes), and in the second, the tissue is layered with the supply of chondroblasts acting in the perichondrium.

Regeneration and age-related changes

Cartilage is restored due to glucosamine and chondroitin sulfate. These components are building materials, thanks to which the elasticity and structure of the joints are restored, arthrosis pain is eliminated, the missing tissue volume is replenished, and the effect of anti-inflammatory drugs is enhanced. Regeneration of cartilage tissue is carried out from the cambial cells of the perichondrium (new cartilaginous layers grow). This process may leak into full force only in childhood, and in adults, cartilage regeneration, unfortunately, does not occur completely. In particular, PVNST is formed in place of the lost cartilage tissue. As a person ages, his fibrous and elastic cartilaginous tissues undergo virtually no changes. At the same time, vitreous cartilage (hyaline cartilage tissue) is prone to transformation into bone tissue and calcification.

Hyaline cartilage tissue

Vitreous tissue is localized mainly in the cartilage of the larynx, nose, bronchi, trachea, ribs, joints, as well as in cartilaginous growth plates present in tubular bones. Hyaline cartilage consists of chondrocytes and, accordingly, intercellular substance, which in turn includes collagen fibers, interstitial water and proteoglycans. Approximately 20-25% of the total volume is collagen fibers, and 5-10% is proteoglycans. The latter do not allow mineralization of vitreous cartilage tissue, and interstitial water, the volume of which reaches 65-85%, promotes depreciation of cartilage and normal metabolism in connective tissue, transporting nutritional components, metabolites and salts. A type of vitreous cartilage is articular cartilage. However, it does not have perichondrium, but receives the necessary nutrients from the synovial fluid. In articular cartilage, the following can be distinguished: acellular zone (superficial), intermediate zone and the so-called deep zone, i.e. zone of interaction of cartilage tissue with bone.

Elastic and fibrous cartilage tissue

Cartilaginous connective tissue, called elastic, is localized in the corniculate, epiglottic, arytenoid (vocal processes) and sphenoid cartilages of the larynx. In addition, elastic cartilaginous tissue is found in the auricle and eustachian tube. This type of tissue is especially needed where the ability of organ areas to change shape and volume, as well as reverse deformation, is required. The composition of elastic tissue includes chondrocytes and an intercellular substance consisting of an amorphous substance (and fibers).

Cartilaginous tissue, called fibrous tissue, is localized in articular menisci and discs, intervertebral discs (in their fibrous rings), in the pubic symphysis (symphysis), in areas of tendon attachment to hyaline cartilage and bones, and also on the surfaces of the sternoclavicular and temporo- mandibular joints. Fibrous cartilaginous connective tissue consists of elongated single chondrocytes and intercellular substance. The latter includes significant amount collagen fibers and a fairly small volume of amorphous substance. Typically, collagen fibers are located in the intercellular substance in the form of bundles, arranged in parallel and in an orderly manner.

Types of cartilage tissue and its structure

Cartilage tissue– a type of elastic, dense connective tissue that has a support-mechanical function.

Predominant composition of cartilage tissue: chondrocytes, chondroblasts.

Types of cartilage tissue

— Hyaline (vitreous)– found in the respiratory tract, at the ends of the rib bones and in the joints.

— Fibrous (connective tissue)– serves to connect dense tissue with the fibrous structure of hyaline cartilage.

— Elastic (has a mesh structure)– contained in dense parts ears, larynx (Santorini, Wriesberg, arytenoid, thyroid, cricoid cartilages), epiglottis.

Functions of cartilage tissue

— Ensuring a reliable connection while maintaining mobility between individual elements of the musculoskeletal system (for example, between the bony parts of the spine);

— Involvement in carbohydrate metabolism processes.

Complete regeneration of cartilage tissue observed in humans during childhood. With age, 100% recovery is impossible: damaged cartilage tissue is partially restored, with parallel formation of PVNST at the site of injury.

If there is mechanical damage to the joint or if the destruction is caused by a disease, it is possible to replace the joint with an artificial one.

The natural functions of cartilage tissue are supported by preparations with chondroitin sodium sulfate and glucosamine.

Good therapeutic effect in the initial stages of problems with cartilage tissue, moderate physical exercise and a course of anti-inflammatory treatment with the simultaneous use of drugs with easily digestible calcium are helpful.

The development of problems is caused by:
- injuries,
- infectious diseases,
- excessive physical exercise over a long period,
- hypothermia,
- heredity.

The positive effect of anti-inflammatory therapy is observed both when taking the drugs orally and when used externally. The effectiveness of the latter method of exposure is based on the high hydrophilicity of cartilage tissue. Due to this, they penetrate the skin medications quickly find themselves directly at the site of the disease.