Intercellular substance of cartilage tissue. Tissue cells: some features. Structure and functions of human cartilage tissue

23.09.2019

Cartilage tissue plays a supporting role. It does not work under tension, like dense connective tissue, but due to internal tension it resists compression well. This tissue forms the basis of the larynx

Nbrinlcho, serves for the immovable connection of bones, forming synchondrosis. Covering the articular surfaces of bones, it softens movement in the joints. Cartilage tissue is quite dense and at the same time quite elastic. Its intermediate substance is rich in dense amorphous matter. Cartilage develops from mesenchyme. At the site of the future cartilage, mesenchymal cells multiply intensively, their processes are shortened and the cells come into 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 - chondro-lasts. They multiply and produce ever new masses of intermediate substance.

The amount of the latter begins to prevail over the mass of cells. The rate of reproduction of cartilage cells by this time slows down, 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 isogeny (isos - equal, identical, genesis - emergence). Cells

Rice. 56. Various types cartilage:

A - hyaline cartilage of the trachea; B - elastic cartilage of the calf's auricle; B - fibrocartilage 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.

The isogenic group does not divide by mitosis and produces 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.

Thus, initially, the development of cartilage is accompanied by the growth of the entire mass of cartilage from the inside. Later, 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 are gradually walled up with it. Soon, 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. 56-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 (at different stages of differentiation) and chondrocytes. It differs from hyaline cartilage by the strong development of collagen fibers, which form bundles that lie almost parallel to each other, as 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.

Type of cartilage	INTERCELLULAR SUBSTANCE		Localization
	Fibers	Main substance
hyaline cartilage	collagen fibers (types II, VI, IX, X, XI collagen)	glycosaminoglycans and proteoglycans	trachea and bronchi, articular surfaces, larynx, connections of the ribs with the sternum
elastic cartilage	elastic and collagen fibers		auricle, corniculate and sphenoid cartilages of the larynx, nasal cartilages
fibrocartilage	parallel bundles of collagen fibers; the fiber content is higher than in other types of cartilage		places of transition of tendons and ligaments into hyaline cartilage, in intervertebral discs, semi-movable joints, symphysis
	in the intervertebral disc: the fibrous ring is located outside - it contains mainly fibers that have a circular course; and inside there is a nucleus pulposus - consists of glycosaminoglycans and proteoglycans and cartilage cells floating in them

Cartilage tissue

It consists of cells - chondrocytes and chondroblasts and a large amount of intercellular hydrophilic substance, characterized by elasticity and density.

Fresh cartilage tissue contains:

70-80% water,

10-15% organic matter

4-7% salts.

50-70% of the dry matter of cartilage tissue is collagen.

Cartilage tissue itself does not have blood vessels, and nutrients diffuse from the surrounding perichondrium.

Cells of cartilage tissue are represented by chondroblastic differentiation:

1. Stem cell

2. Semi-stem cell (prechondroblasts)

3. Chondroblast

4. Chondrocyte

5. Chondroclast

Stem and semi-stem cell- poorly differentiated cambial cells, mainly localized around the vessels in the perichondrium. By differentiating they turn into chondroblasts and chondrocytes, i.e. necessary for regeneration.

Chondroblasts- young cells are located in the deep layers of the perichondrium singly, without forming isogenic groups. Under a light microscope, chondroblasts are flattened, slightly elongated cells with basophilic cytoplasm. Under an electron microscope, the granular ER, Golgi complex, and mitochondria are well expressed in them, i.e. protein-synthesizing complex of organelles because main function of chondroblasts- production of the organic part of the intercellular substance: proteins collagen and elastin, glycosaminoglycans (GAG) and proteoglycans (PG). In addition, chondroblasts are capable of reproduction and subsequently turn into chondrocytes. In general, chondroblasts provide appositional (superficial, new growth from the outside) growth of cartilage from the perichondrium.

Chondrocytes- the main cells of cartilage tissue are located in the deeper layers of cartilage in cavities - lacunae. Chondrocytes can divide by mitosis, while the daughter cells do not separate, but remain together - so-called isogenic groups are formed. Initially they lie in one common lacuna, then a intercellular substance and each cell of a given isogenic group has its own capsule. Chondrocytes are oval-round cells with basophilic cytoplasm. Under an electron microscope, the granular ER, Golgi complex, and mitochondria are clearly visible. protein synthesizing apparatus, because main function of chondrocytes- production of the organic part of the intercellular substance of cartilage tissue. The growth of cartilage due to the division of chondrocytes and their production of intercellular substance ensures interstitial (internal) growth of cartilage.

In isogenic groups, three types of chondrocytes are distinguished:

1. Type I chondrocytes predominate in young, developing cartilage. They are characterized by a high nuclear-cytoplasmic ratio, the development of vacuolar elements of the lamellar complex, and the presence of mitochondria and free ribosomes in the cytoplasm. Division patterns are often observed in these cells, which allows them to be considered as a source of reproduction of isogenic groups of cells.

2. Type II chondrocytes are characterized by a decrease in the nuclear-cytoplasmic ratio, weakening of DNA synthesis, preservation high level RNA, intensive development of the granular endoplasmic reticulum and all components of the Golgi apparatus, which ensure the formation and secretion of glycosaminoglycans and proteoglycans into the intercellular substance.

3. Type III chondrocytes are characterized by the lowest nuclear-cytoplasmic ratio, strong development and ordered arrangement of the granular endoplasmic reticulum. These cells retain the ability to form and secrete protein, but their synthesis of glycosaminoglycnes is reduced.

In cartilage tissue, in addition to the cells that form the intercellular substance, there are also their antagonists - destroyers of the intercellular substance - these are chondroclasts(can be attributed to the macrophage system): quite large cells, in the cytoplasm there are many lysosomes and mitochondria. Chondroclast function- destruction of damaged or worn areas of cartilage.

Intercellular substance of cartilage tissue contains collagen, elastic fibers and ground substance. The main substance consists of tissue fluid and organic substances:

GAGs (chondroethinsulfates, keratosulfates, hyaluronic acid);

10% - PG (10-20% - protein + 80-90% GAG);

The intercellular substance is highly hydrophilic, the water content reaches 75% of the cartilage mass, this determines the high density and turgor of the cartilage. Cartilaginous tissues in the deep layers do not have blood vessels; nutrition is diffuse through the vessels of the perichondrium.

Perichondrium is a layer of connective tissue covering the surface of cartilage. In the perichondrium they secrete external fibrous(from dense, unformed CT with a large number of blood vessels) layer And inner cell layer, containing a large number of stem, semi-stem cells and chondroblasts.

Many human organs have cartilage tissue in their structure, which performs a number of important functions. This special type of connective tissue has a different structure depending on its location in the body, and this explains its different purposes.

The structure and functions of cartilage tissue are closely interrelated, each type plays a specific role.

Cartilage tissue under a microscope

Like any tissue in the body, cartilage contains two main components. This is the main intercellular substance, or matrix, and the cells themselves. The structural features of human cartilage tissue are that the mass fraction of the matrix is much greater than the total cellular weight. This means that during histological examination (examination of a tissue sample under a microscope), cartilage cells occupy a small space, and the main area of the field of view is the intercellular substance. In addition, despite the high density and hardness of cartilage tissue, the matrix contains up to 80% water.

The structure of the intercellular substance of cartilage

The matrix has a heterogeneous structure and is divided into two components: the main, or amorphous, substance, with a mass fraction of 60%, and chondrin fibers, or fibrils, occupying 40% of the total weight of the matrix. These fibers are similar in structure to the collagen formations that make up, for example, human skin. But they differ from it in the diffuse, disordered arrangement of fibrils. Many cartilaginous formations have a kind of capsule called perichondrium. It plays a leading role in the restoration (regeneration) of cartilage.

Composition of cartilage

The chemical composition of cartilage tissue is represented by various protein compounds, mucopolysaccharides, glycosaminoglycans, complexes of hyaluronic acid with proteins and glycosaminoglycans. These substances are the basis of cartilage tissue, the reason for its high density and strength. But at the same time they provide penetration into it various connections And nutrients, necessary for metabolism and cartilage regeneration. With age, the production and content of hyaluronic acid and glycosaminoglycans decreases, as a result, degenerative-dystrophic changes begin in the cartilage tissue. To slow the progression of this process, replacement therapy is necessary, which ensures the normal functioning of cartilage tissue.

Cellular composition of cartilage

The structure of human cartilage tissue is such that cartilage cells, or chondrocytes, do not have a clear and ordered structure. Their localization in the intercellular substance is more reminiscent of single islands, consisting of one or several cellular units. Chondrocytes can vary in age, and are divided into young and undifferentiated cells (chondroblasts), and fully mature ones, called chondrocytes.

Chondroblasts are produced by the perichondrium and, gradually moving into the deeper layers of cartilage tissue, differentiate and mature. At the beginning of their development, they are not located in groups, but singly, have a round or oval shape and have a huge nucleus compared to the cytoplasm. Already on initial stage During their existence, chondroblasts undergo active metabolism aimed at producing components of the intercellular substance. New proteins, glycosaminoglycans, and proteoglycans are formed, which then diffusely penetrate into the matrix.

Hyaline and elastic cartilage

The most important distinguishing feature chondroblasts, located immediately under the perichondrium, lies in their ability to divide and form their own kind. This feature is being actively studied by scientists, as it provides enormous opportunities for implementation. the newest way treatment of joint pathologies. By accelerating and regulating the division of chondroblasts, it is possible to completely restore cartilage tissue damaged by disease or injury.

Adult differentiated cartilage cells, or chondrocytes, are localized in the deep layers of cartilage. They are located in groups of 2-8 cells, and are called “isogenic groups”. The structure of chondrocytes is different from that of chondroblasts; they have a small nucleus and massive cytoplasm, and no longer know how to divide and form other chondrocytes. Their metabolic activity is also much reduced. They are capable of supporting metabolic processes in the cartilage tissue matrix only at a very moderate level.

Arrangement of elements in cartilage

Histological examination shows that the isogenic group is located in the cartilaginous lacuna and is surrounded by a capsule of interwoven collagen fibers. The chondrocytes in it are close to each other, separated only by protein molecules, and can have a variety of shapes: triangular, oval, round.

In diseases of cartilage tissue appears new look cells: chondroclasts. They are much larger than chondroblasts and chondrocytes, as they are multinucleated. These cells are not involved in either metabolism or cartilage regeneration. They are destroyers and “devourers” of normal cells and provide destruction and lysis of cartilage tissue during inflammatory or dystrophic processes in it.

Types of cartilage tissue

The intercellular substance of cartilage can have a different structure, depending on the type and location of the fibers. Therefore, there are 3 types of cartilage:

Hyaline or glassy.
Elastic or mesh.
Fibrous or connective tissue.

Types of cartilage

Each type is characterized by a certain degree of density, hardness and elasticity, as well as localization in the body. Hyaline cartilaginous tissue lines the articular surfaces of bones, connects the ribs to the sternum, and is found in the trachea, bronchi, and larynx. Elastic cartilage is a component of the small and medium bronchi, the larynx, and the human auricles are made from it. Connective cartilaginous tissue, or fibrous tissue, is so called because it connects ligaments or tendons of muscles with hyaline cartilage (for example, at the points of attachment of tendons to the bodies or processes of the vertebrae).

Blood supply and innervation of cartilage tissue

The structure of cartilage is very dense; it is not penetrated by even the smallest blood vessels (capillaries). All nutrients and oxygen necessary for the functioning of cartilage tissue enter it from the outside. In a diffuse manner, they penetrate from nearby blood vessels, from the perichondrium or bone tissue, and from the synovial fluid. Decay products are also removed diffusely and are removed from the cartilage through venous vessels.

Young and mature cartilage

Nerve fibers penetrate into the superficial layers of cartilage from the perichondrium only in separate single branches. This explains the fact that nerve impulses from cartilage tissue do not arrive during diseases, and pain syndrome appears during the reaction of bone structures, when the cartilage is practically destroyed.

Functions of cartilage tissue

The main function of cartilage tissue is musculoskeletal, which is to ensure strong connections various parts skeleton and various movements. Thus, hyaline cartilage, which is the most important structural part of the joints and lines the bone surfaces, makes possible the entire range of human movements. Thanks to its physiological sliding, they occur smoothly, comfortably and painlessly, with appropriate amplitude.

Cartilage of the knee joint

Other connections between bones that do not involve active movements in them are also made using durable cartilage tissue, in particular the hyaline type. These may be low-moving bone fusions that perform a supporting function. For example, in the places where the ribs meet the sternum.

The functions of connective cartilage tissue are explained by its localization and consist in ensuring the mobility of various parts of the skeleton. It makes possible a strong and elastic connection of muscle tendons with bone surfaces covered with hyaline cartilage.

Other functions of human cartilage tissue are also important, as they form the appearance, voice, and ensure normal breathing. First of all, this applies to the cartilage tissue that forms the basis of the ears and the tip of the nose. The cartilage that makes up the trachea and bronchi makes them mobile and functional, and the cartilaginous structures of the larynx are involved in the formation of the individual timbre of the human voice.

Nasal cartilages

Cartilage tissue without pathological changes is of great importance for human health and normal quality life.

They perform mechanical, support, and 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. The cellular composition of all types of cartilage tissue is the same and includes chondroblasts - poorly differentiated, flattened cells with basophilic cytoplasm; they are capable of proliferating and producing 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 chondroitin 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 and 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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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, formed by a cell or an isogenic group of cells, a pericellular matrix and a 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 substances – 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, which indicates the high synthetic activity of these cells. Osteoblasts synthesize collagen and glycosaminoglycans, which are then released into the 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 decreases, and remains functional activity characteristic of osteocytes. Osteoblasts, localized in the cambial layer of the periosteum, are in an inactive state, and their synthetic and transport organelles are poorly developed. 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 (bone 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 local processes of bone tissue restructuring are continuously carried out during ontogenesis, osteoclasts are also necessarily present in these places. In the process of embryonic osteohistogenesis, these cells play a very important role and are present in large quantities. Osteoclasts have a characteristic morphology: these cells are multinucleated (3 - 5 or more nuclei), have a fairly large size (about 90 μm) and a 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 is an organ whose main structural component is 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) by the complete absence of blood vessels and nerves. The shell of cartilage is the perichondrium, which is also called the perichondrium. Cartilaginous connective tissue (CCT) can act 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 an inner layer of loose fibrous connective tissue (LFC) and an outer layer of dense fibrous connective tissue (DIC). 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 the total mass of cartilaginous connective tissue. Most of all, CST contains intercellular substance, which is characterized by a rather 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 differential 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 material, 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 can take place in 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 a significant amount of 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)– found in the dense parts of the auricles, larynx (Santorin, Wrisberg, 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 activity 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 medicines quickly find themselves directly at the site of the disease.

Cartilaginous and bone tissues develop from sclerotomal mesenchyme; they belong to the tissues of the internal environment and, like all 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 (textus cartilagineus) is classified into hyaline, elastic and fibrous. The classification is based on the peculiarities of the organization of intercellular substance. The composition of cartilage tissue includes 80% water, 10-15% organic substances and 5-7% inorganic substances.

DEVELOPMENT OF CARTILAGE TISSUE or CHONDROGENESIS consists of 3 stages:

ü formation of chondrogenic islets;

ü formation of primary cartilage tissue;

ü differentiation of cartilage tissue.

During STAGE 1, 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.

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

With the onset of STAGE 3, granular EPS develops more intensively in chondrocytes, which produces both fibrillar proteins and chondriatine sulfates (chondriatin sulfuric acid), 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 TISSUE CELLS(chondrocytus) constitute the differential of chondrocytes: stem cell, semi-stem cell (prechondroblast), chondroblast, chondrocyte.

CHONDROBLASTS(chondroblastocytus) are located in the inner layer of the perichondrium, have organelles general meaning: granular ER, Golgi complex, mitochondria. FUNCTION 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. are formed. cells. 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.

CHONDROCYTES TYPE I 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 are located in mature cartilage, their nuclear-cytoplasmic ratio decreases somewhat, as the volume of the cytoplasm increases, they lose the ability to mitosis. Granular EPS is well developed in their cytoplasm; they secrete proteins and glycosaminoglycans (chondriatin sulfates). Therefore, 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 3 chondrocytes, a basophilic-stained ring is visible outside this ring), (glycosaminoglycans are secreted by type 2 chondrocytes) and the outermost ring is again oxyphilic-stained (proteins are secreted while there were only young type 1 chondrocytes in the cartilage). 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 it is and the more 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 (an immune rejection reaction does not occur).

The main substance of cartilage contains collagen fibers consisting of type II collagen. The orientation of these fibers depends on the force lines, and the direction of the force lines depends on the mechanical force 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.

HYALINE CARTILAGE TISSUE has a bluish-whitish color, translucent, fragile, in the body it is found at the junction of the ribs with the sternum, in the walls of the trachea and bronchi, larynx, and on the articular surfaces. Depending on where the hyaline cartilage is located, it has a different structure. If there is a malnutrition, the hyaline cartilage undergoes calcification.

HYALINE CARTILAGE AT THE ENDS OF THE RIBS covered with perichondrium, under which there is a zone of young cartilage. Here are young spindle-shaped chondrocytes, located in cartilaginous lacunae, and capable of producing only fibrillar proteins. Therefore, the intercellular substance around them is oxyphilic colored. The deeper chondrocytes become rounder. Even deeper, isogenic groups of chondrocytes are formed, capable of producing proteins and chondriatic sulfuric acid, which stains basophilically. Therefore, the intercellular substance around them is stained with basic dyes. Even deeper are isogenic groups containing even more mature chondrocytes that secrete only proteins. Therefore, the ground substance around them is colored oxyphilic.

HYALINE CARTILAGE OF ARTICULAR SURFACES does not have perichondrium and consists of 3 zones that are not clearly demarcated from each other. The outer zone includes spindle-shaped chondrocytes located in lacunae parallel to the surface of the cartilage. Deeper is the columnar zone, the cells of which continuously divide and form columns, and the inner zone is divided by the basophilic line into non-calcified and calcified parts. The calcified part adjacent to the bone tissue contains matrix vesicles and blood vessels.

NUTRITION This cartilage is produced from 2 sources: 1) due to nutrients found in the synovial fluid of the joint and 2) due to blood vessels passing through the calcified cartilage.

ELASTIC CARTILAGE TISSUE has a whitish-yellowish color, is located in the auricle, the wall of the external auditory canal, the arytenoid and cornicular cartilages of the larynx, the epiglottis, and in the bronchi of medium caliber. It differs from hyaline cartilage in that, firstly, it is elastic, since in addition to collagen, it contains elastic fibers that go into various directions and interwoven into the perichondrium, and stained brown with orcein; secondly, it contains less chondriatic sulfuric acid, lipids and glycogen; thirdly, it never undergoes calcification. At the same time general plan The structure of elastic cartilage tissue is similar to hyaline cartilage.

FIBER CARTILAGE(cortilago fibrosa) is located in the intervertebral discs, pubic fusion, sites of attachment of tendons to hyaline cartilage and in the maxillary joints. This cartilage is characterized by the presence of 3 sections: 1) tendon part; 2) fibrocartilage itself; 3) hyaline cartilage. Where there is a tendon, bundles of collagen fibers run parallel to each other, fibrocytes are located between them; in fibrous cartilage tissue the parallel arrangement of fibers is maintained, chondrocytes are located in the lacunae of the cartilaginous substance; hyaline cartilage has a normal structure.

AGE 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, weakening the permeability of cartilage and the supply of nutrients. This leads to calcification of the cartilage, penetration of blood vessels into it and the formation of bone substance inside the cartilage.