Cartilage tissue is a type of connective tissue consisting of cartilage cells (chondrocytes) and large quantity 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).
Pathology of cartilage tissue - see Chondritis, Chondrodystrophy.
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 main substance of fibrous connective tissue and converting its fibroblasts into cartilage cells.
Nutrition of cartilage tissue occurs through the diffusion of substances from the blood vessels of the perichondrium. In the tissue of articular cartilage nutrients penetrate 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 of 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.
The bone marrow that fills the bone marrow cavities contains mainly fats (up to 98% of the dry yellow marrow) and smaller amounts of choline phosphatides, cholesterol, proteins and minerals. The composition of fats is dominated by palmitic, oleic, and stearic acids.
In accordance with the characteristics of the chemical composition, bone is used for the production of semi-finished products, jellies, brawn, bone fat, gelatin, glue, and bone meal.
Cartilage tissue. Cartilage tissue performs supporting and mechanical functions. It consists of a dense ground substance in which round-shaped cells, collagen and elastin fibers are located (Fig. 5.14). Depending on the composition of the intercellular substance, hyaline, fibrous and elastic cartilages are distinguished. Hyaline cartilage covers the articular surfaces of bones, and the costal cartilages and trachea are built from it. Calcium salts are deposited in the intercellular substance of such cartilage with age. Hyaline cartilage is translucent and has a bluish tint. 
Fibrous cartilage makes up the ligaments between the vertebrae, as well as the tendons and ligaments at their attachment to the bones. Fibrous cartilage contains many collagen fibers and a small amount of amorphous substance. It has the appearance of a translucent mass.
Elastic cartilage is cream-colored, the intercellular substance of which is dominated by elastin fibers. Lime is never deposited in elastic cartilage.
Cartilage tissue
It is part of the auricle and larynx.
The average chemical composition of cartilage tissue includes: 40-70% water, 19-20% proteins, 3.5% fats, 2-10% minerals, about 1% glycogen.
Cartilage tissue is characterized by a high content of mucoprotein - chondromucoid and mucogylisaccharide - chondroitinsulfuric acid in the main intercellular substance. An important property of this acid is its ability to form salt-like compounds with various proteins: collagen, albumin, etc. This apparently explains the “cementing” role of mucopolysaccharides in cartilage tissue.
Cartilage tissue is used for food purposes, and gelatin and glue are also produced from it. However, the quality of gelatin and glue is often not high enough, since mucopolysaccharides and glucoproteins pass into solution from the tissue along with gelatin, reducing the viscosity and strength of the jelly.
Cartilaginous tissue is a type of supporting tissue characterized by the strength and elasticity of the matrix. This is due to their position in the body: in the joints, in the intervertebral discs, in the wall of the respiratory tract (larynx, trachea, bronchi).
Cartilaginous
○ Hyaline
○ Elastic
○ Fibrous
However, the general plan of their structure is similar.
1. Presence of cells (chondrocytes and chondroblasts).
2. Formation of isogenic groups of cells.
3. The presence of a large amount of intercellular substance (amorphous, fibers), which provides strength and elasticity - that is, the ability to undergo reversible deformation.
4. Lack of blood vessels - nutrients diffuse from the perichondrium, thanks to high content water (up to 70–80%) in the matrix.
5. Characterized by a relatively low level of metabolism.
Cartilage tissue
They have the ability for continuous growth.
During the development of cartilage tissue, a differentiation of cartilage cells is formed from the mesenchyme. This includes:
1. Stem cells - characterized by a round shape, a high nuclear-cytoplasmic ratio, a diffuse arrangement of chromatin and a small nucleolus. The organelles of the cytoplasm are poorly developed.
2. Semi-stem cells (prechondroblasts) – in them the number of free ribs increases, grEPS appears, the cells become elongated, and the nuclear-cytoplasmic ratio decreases. Like stem cells, they exhibit low
proliferative activity.
3. Chondroblasts are young cells located on the periphery of cartilage. They are small flattened cells capable of proliferation and synthesis of components of the intercellular substance. In the basophilic cytoplasm, grEPS is well developed and
agrEPS, Golgi apparatus. During development they turn into chondrocytes.
4. Chondrocytes are the main (definitive) type of cartilage tissue cells. They come in oval, round or polygonal shapes. Located in special cavities
– lacunae – intercellular substance, singly or in groups. These groups are called isogenic cell groups.
Isogenic groups of cells - (from the Greek isos - equal, genesis - development) - groups of cells (chondrocytes) formed by the division of one cell. They lie in a common cavity (lacuna) and are surrounded by a capsule formed by the intercellular substance of cartilaginous tissue.
The main amorphous substance (cartilage matrix) contains:
1. Water – 70–80%
2. Inorganic compounds – 4–7%.
3. Organic matter – 10–15%
– Glycosaminoglycans:
Ø chondroitin sulfates (chondroitin-6-sulfate, chondroitin-4-sulfate,
Ø hyaluronic acid;
– Proteoglycans.
– Chondronectin – this glycoprotein connects cells to each other and to various substrates (cell connection with type I collagen).
There are many fibers in the intercellular substance:
1. Collagen (types I, II, VI)
2. And in elastic cartilage - elastic.
Ways of cartilage growth.
Interstitial growth of cartilage is an increase in the volume of cartilage tissue (cartilage) due to an increase in the number of dividing chondrocytes and the accumulation of intercellular substance components secreted by these cells.
Appositional growth of cartilage is an increase in the volume of cartilaginous tissue (cartilage) due to the replenishment of cells located on the periphery (mesenchymal cells - during embryonic chondrogenesis, perichondrium chondroblasts - during the postembryonic period of ontogenesis).
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The structure of individual human tissues, types of cartilage
Tendons and ligaments. Strength (muscle pulling or external forces) acts on tendons and ligaments in one direction. Therefore, the fibrous plates of tendons, consisting of fibroblasts (fibrocytes), ground substance and collagen fibers, are located parallel to each other. Bundles (from 10 to 1000) of fibrous plates are separated from each other by layers of unformed connective tissue. Small bundles are combined into larger ones, etc. The entire tendon is covered by a thicker layer of unformed tissue called the peritendon. It carries vessels and nerves to the tendon, ligament; There are also germ cells there.
Fascia, muscle aponeuroses, capsules of joints and organs, etc. The forces acting on them are directed in different directions. The bundles of fibrous plates are located at an angle to each other, so the fascia and capsules are difficult to stretch and separate into separate layers.
Cartilage tissue. It can be permanent (for example, cartilage of the ribs, trachea, intervertebral discs, menisci, etc.) and temporary (for example, in bone growth zones - metaphyses). Temporary cartilage is subsequently replaced by bone tissue. Cartilage tissue does not have connective tissue layers, vessels or nerves. Its trophism is provided only from the side of the perichondrium (a layer of fibrous connective tissue covering the cartilage) or from the side of the bone. The growth layer of cartilage is located in the lower layer of the perichondrium. When damaged, cartilage does not recover well.
There are three types of cartilage:
1. Hyaline cartilage. Covers the articular surfaces of bones, forms the cartilaginous ends of the ribs, rings of the trachea and bronchi. The elastic ground substance (chondromucoid) of the cartilaginous plates contains individual collagen fibers.
2. Elastic cartilage.
Structure and functions of human cartilage tissue
Forms the auricle, wings of the nose, epiglottis, and cartilages of the larynx. The main substance of the cartilaginous plates contains predominantly elastic fibers.
3. Fibrous cartilage. Forms intervertebral and articular discs, menisci, articular lips. The cartilaginous plates are penetrated by a large number of collagen fibers.
Bone tissue forms individual bones - the skeleton. Makes up about 17% of a person's total weight. Bones have strength with low mass. The strength and hardness of bone is provided by collagen fibers, a special basic substance (ossein) impregnated with minerals (mainly hydroxyapatite-phosphoric lime) and the orderly arrangement of bone plates. Bone plates form the outer layer of any bone and the inner layer of the medullary cavity; The middle layer of the tubular bone is made up of special, so-called osteon systems - multi-row, concentrically located plates around a canal in which there are vessels, nerves, and loose connective tissue. The spaces between the osteons (tubes) are filled with intercalated bone plates. Osteons are located along the length of the bone or in accordance with the load. Very thin tubules extend to the sides from the osteon canal, connecting the separated osteocytes.
There are two types of bone - cortical(compact or dense), up to 80% and trabecular(spongy or porous), constituting up to 20% of the total bone mass. If osteons and intercalary plates lie tightly, a compact substance is formed. It forms the diaphyses of long bones, the top layer of flat bones and covers the spongy part of the bone. At the ends of the bones, where a large volume is needed for joint articulation while maintaining lightness and strength, a spongy substance is formed. It consists of crossbars, beams (trabeculae), forming bone cells (like a sponge). Trabeculae are composed of osteons and intercalated bone plates, which are positioned in accordance with the pressure on the bone and the pull of the muscles.
On the outside, the bone, with the exception of the articular surfaces, is covered with periosteum (a layer of connective tissue, dense on top and loose closer to the bone). The latter contains many vessels, nerves, and contains bone-like cells - osteoblasts, which contribute to the growth of bones in width and the healing of fractures.
The rate of renewal of cortical and trabecular bone in an adult is from 2.5 to 16% per year.
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
Cartilage tissue chemical composition 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 provide 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. Cartilage, which is part of the trachea and bronchi, makes them mobile and functional, and cartilaginous structures The larynx is 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.
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. There are two types of cells in cartilage tissue: 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 of 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). 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 bone tissue drainage system. 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 forms 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 is reduced, and the functional activity characteristic of osteocytes is preserved. 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. During the process of embryonic osteohistogenesis, these cells play a very important role and are present in large numbers. Osteoclasts have a characteristic morphology: these cells are multinucleated (3 - 5 or more nuclei), have a fairly large size (about 90 microns) and a characteristic shape - oval, but the part of the cell adjacent to the bone tissue is flat. 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.
Functional activity The osteoclast manifests itself 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
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 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 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 of 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.
36. Skeletal tissues. general characteristics. Cartilage tissues, localization in the body. Cellular composition, features of the organization of intercellular substance in different types of cartilage. Structural and functional characteristics of cells and intercellular substance. concept of an isogenic group of cells.
Skeletalfabrics
GeneralcharacteristicboneAndcartilaginousfabrics
Skeletal tissues (textus skeletales) are a type of connective tissue with a pronounced supporting, mechanical function due to the presence of dense intercellular substance. Skeletal tissues include:
cartilaginousfabrics,
bonefabrics,
dentinetooth
cementtooth.
In addition to the main supporting function, these tissues take part in water-salt metabolism, mainly calcium and phosphate salts.
Like all other tissues of the internal environment of the body, skeletal tissues develop from mesenchyme, or more precisely from the mesenchyme that is evicted from the sclerotomes of the mesoderm.
Cartilaginousfabrics
Cartilaginous tissue (textus cartilaginei) is characterized by elasticity and strength, which is associated with the position of this tissue in the body. Cartilage tissue is part of the organs of the respiratory system, joints, and intervertebral discs.
As in other tissues, cartilage tissue contains cells and intercellular substance. The main cellular elements are chondroblasts and chondrocytes. There is more intercellular substance in cartilage tissue than cells. It is characterized by hydrophilicity and elasticity. The supporting function of cartilage tissue is associated with the elasticity of the intercellular substance.
Cartilage tissue is significantly hydrated - fresh tissue contains up to 80% water. More than half of the volume of “dry” matter of cartilage tissue is fibrillar protein collagen. There are no blood vessels in the cartilage tissue - nutrients diffuse from the surrounding tissues.
Classification
Distinguishthreekindcartilaginousfabrics:
hyaline,
elastic,
fibrous.
This division of cartilage tissue is based on the structural and functional features of the structure of their intercellular substance, the degree of content and ratio of collagen and elastic fibers.
Briefcharacteristiccellscartilaginousfabrics
Chondroblasts are small flattened cells capable of dividing and synthesizing intercellular substance. By releasing the components of the intercellular substance, hodroblasts, as it were, “immune” themselves in it and turn into chondrocytes. The growth of cartilage that occurs is called peripheral, or appositional, i.e. by “layering” new layers of cartilage.
Chondrocytes are larger and oval in shape. They lie in special cavities of the intercellular substance - lacunae. Chondrocytes often form the so-called. isogenic groups of 2-6 cells that originate from a single cell. At the same time, some chondrocytes retain the ability to divide, while others actively synthesize components of the intercellular substance. Due to the activity of chondrocytes, the mass of cartilage increases from the inside - interstitial growth.
types of cartilage tissue, age-related changes and cartilage regeneration
Based on the structural features of the intercellular substance, cartilage tissue is divided into three types - hyaline, elastic and fibrous or fibrous.
Hyaline cartilage tissue
Hyaline cartilaginous tissue (textus cartilaginous hyalinus), also called vitreous (from the Greek hyalos - glass) - due to its transparency and bluish-white color, is the most common type of cartilage tissue. In the adult body, hyaline tissue is found on the articular surfaces of bones, at the junction of the ribs with the sternum, in the larynx and airways.
Most of the hyaline cartilage tissue found in the human body is covered with perichondrium and, together with the plate of cartilaginous tissue, represents anatomical formations - cartilage.
The perichondrium has two layers: the outer layer, consisting of fibrous connective tissue with blood vessels; and internal, predominantly cellular, containing chondroblasts and their precursors - prechondroblasts. Under the perichondrium in the superficial layer of cartilage there are young chondrocytes of a spindle-shaped flattened shape. In the deeper layers, cartilage cells acquire an oval or round shape. Due to the fact that the synthetic and secretory processes in these cells are weakened, after division they do not diverge far, but lie compactly, forming isogenic groups of 2 to 4 (less often up to 6) chondrocytes.
Elastic cartilage tissue
The second type of cartilage tissue - elastic cartilage tissue (textus cartilagineus elasticus) is found in those organs where the cartilaginous base is subject to bending (in the auricle, corniculate and wedge-shaped cartilages of the larynx, etc.). In a fresh, unfixed state, elastic cartilaginous tissue is yellowish in color and not as transparent as hyaline tissue. By overall plan The structure of elastic cartilage is similar to hyaline cartilage. On the outside it is covered with perichondrium. Cartilage cells (young and specialized chondrocytes) are located in the lacunae singly or form isogenic groups.
One of the main distinguishing features of elastic cartilage is the presence of elastic fibers in its intercellular substance, along with collagen fibers. Elastic fibers penetrate the intercellular substance in all directions.
In the layers adjacent to the perichondrium, elastic fibers without interruption pass into the elastic fibers of the perichondrium. There are less lipids, glycogen and chondroitin sulfates in elastic cartilage than in hyaline cartilage.
Fibrous cartilage tissue
The third type of cartilage tissue - fibrous, or fibrous, cartilaginous tissue (textus cartilaginous fibrosa) is found in the intervertebral discs, semi-movable joints, in the places where the dense fibrous connective tissue of tendons and ligaments transitions into hyaline cartilage, where limited movements are accompanied by strong tensions. The intercellular substance contains parallel-directed collagen bundles, which gradually loosen and transform into hyaline cartilage. Cartilage has cavities in which cartilage cells are enclosed. Chondrocytes are located singly or form small isogenic groups. The cytoplasm of cells is often vacuolated. From the hyaline cartilage toward the tendon, the fibrocartilage becomes more and more tendon-like. At the border of cartilage and tendon, between the collagen bundles, compressed cartilage cells lie in columns, which, without any border, pass into tendon cells located in the dense fibrous connective tissue of the tendon.
Age-related changes and regeneration
As the body ages, the concentration of proteoglycans in cartilage tissue and the associated hydrophilicity of the tissue decrease. The processes of reproduction of chondroblasts and young chondrocytes are weakened.
Chondroclasts participate in the resorption of dystrophically altered cells and intercellular substance. After the death of chondrocytes, some of the gaps are filled with an amorphous substance and collagen fibrils. In some places, deposits of calcium salts are found in the intercellular substance (“chalking of cartilage”), as a result of which the cartilage becomes cloudy, opaque, becomes hard and brittle. As a result, the resulting disturbance in the trophism of the central areas of cartilage can lead to the ingrowth of blood vessels into them, followed by bone formation.
Physiological regeneration of cartilage tissue is carried out due to poorly specialized cells of the perichondrium and cartilage through the reproduction and differentiation of prechondroblasts and chondroblasts. However, this process is very slow. Post-traumatic regeneration of cartilage tissue of extra-articular localization is carried out due to the perichondrium. Recovery can occur due to cells of the surrounding connective tissue that have not lost the ability to undergo metaplasia (i.e., the transformation of fibroblasts into chondroblasts).
In articular cartilage, depending on the depth of the injury, regeneration occurs both due to the proliferation of cells in isogenic groups (with shallow damage), and due to the second source of regeneration - cambial cells of subchondral bone tissue (with deep damage to the cartilage).