cartilage tissue, like bone, refers to skeletal tissues with a musculoskeletal function. According to the classification, three types of cartilage tissue are distinguished - hyaline, elastic and fibrous. The structural features of various types of cartilage tissue depend on its location in the body, mechanical conditions, and the age of the individual.
Types of cartilage tissue: 1 - hyaline cartilage; 2 - elastic cartilage; 3 - fibrous cartilage
The most widespread in humans ishyaline cartilage tissue.
It is part of the trachea, some cartilages of the larynx, large bronchi, temaphyses of bones, is found at the junction of the ribs with the sternum and in some other areas of the body. Elastic cartilage tissue is part of the auricle, medium-sized bronchi, and some cartilages of the larynx. Fibrous cartilage is commonly found at the junction of tendons and ligaments with hyaline cartilage, such as intervertebral discs.
The structure of all types of cartilage tissue is broadly similar: they contain cells and an intercellular substance (matrix). One of the features of the intercellular substance of the cartilaginous tissue is its high water content: the water content normally ranges from 60 to 80%. The area occupied by the intercellular substance is much larger than the area occupied by the cells. The intercellular substance of cartilage tissue is produced by cells (chondroblasts and young chondrocytes) and has a complex chemical composition. It is subdivided into the main amorphous substance and the fibrillar component, which makes up approximately 40% of the dry mass of the intercellular substance and is represented in the hyaline cartilage tissue by collagen fibrils formed by type II collagen, which diffuse in different directions. On histological preparations, fibrils are invisible, since they have the same refractive index as an amorphous substance. In the elastic cartilage tissue, along with collagen fibrils, there are numerous elastic fibers consisting of elastin protein, which is also produced by cartilage cells. Fibrous cartilage contains a large number of bundles of collagen fibers, consisting of type I and type II collagen.
The leading chemical compounds that form the main amorphous substance of cartilaginous tissues (chondromucoid) are sulfated glycosaminoglycans (keratosulfates and chondroitin sulfates A and C) and neutral mucopolysaccharides, most of which are complex supramolecular complexes. In cartilage, compounds of hyaluronic acid molecules with proteoglycans and with specific sulfated glycosaminoglycans have become widespread. This ensures the special properties of cartilage tissues - mechanical strength and at the same time permeability to organic compounds, water and other substances necessary to ensure the vital activity of cellular elements. The marker compounds most specific for the intercellular substance of cartilage are keratosulfates and certain varieties of chondroitin sulfates. They make up about 30% of the dry mass of cartilage.
The main cells of cartilage tissue -chondroblasts and chondrocytes.
Chondroblastsare young, undifferentiated cells. They are located near the perichondrium, lie singly and are characterized by a round or oval shape with uneven edges. A large nucleus occupies a significant part of the cytoplasm. Synthesis organelles predominate among cell organelles - ribosomes and polysomes, granular endoplasmic reticulum, Golgi complex, mitochondria; characterized by inclusions of glycogen. With general histological staining of preparations with hematoxylin and eosin, chondroblasts are weakly basophilic. The structure of chondroblasts indicates that these cells show high metabolic activity, in particular, associated with the synthesis of intercellular substance. It has been shown that in chondroblasts the synthesis of collagen and non-collagen proteins is spatially separated. The entire cycle of synthesis and excretion of high-molecular components of the intercellular substance in functionally active human chondroblasts takes less than a day. Newly formed proteins, proteoglycans and glycosaminoglycans are not located directly near the cell surface, but spread diffusely at a considerable distance from the cell in the previously formed intercellular substance. Among chondroblasts, there are also functionally inactive cells, the structure of which is characterized by a weak development of the synthetic apparatus. In addition, part of the chondroblasts located immediately under the perichondrium did not lose the ability to divide.
Chondrocytes- Mature cells of cartilage tissue - occupy mainly the central parts of the cartilage. The synthetic ability of these cells is significantly lower than that of chondroblasts. Differentiated chondrocytes most often lie in cartilaginous tissues not singly, but in groups of 2, 4, 8 cells. These are the so-called isogenic groups of cells, which were formed as a result of the division of one cartilage cell. The structure of mature chondrocytes indicates that they are not capable of division and a noticeable synthesis of intercellular substance. But some researchers believe that under certain conditions, mitotic activity in these cells is still possible. The function of chondrocytes is to maintain at a certain level of metabolic metabolic processes in cartilage tissues.
Isogenic groups of cells are located in cartilaginous cavities surrounded by a matrix. The shape of cartilage cells in isogenic groups can be different - round, oval, fusiform, triangular - depending on the position on a particular area of cartilage. The cartilaginous cavities are surrounded by a narrow, lighter than the main substance, strip, forming, as it were, a shell of the cartilaginous cavity. This shell, which is characterized by oxyphilicity, is called the cellular territory, or territorial matrix. The more distant regions of the intercellular substance are called the interstitial matrix. Territorial and interstitial matrices are areas of intercellular substance with different structural and functional properties. Within the territorial matrix, collagen fibrils are oriented around the surface of isogenic cell groups. Weaves of collagen fibrils form a wall of lacunae. The spaces between cells within the lacunae are filled with proteoglycans. The interstitial matrix is characterized by weakly basophilic or oxyphilic coloration and corresponds to the oldest sections of the intercellular substance.
Thus, the definitive cartilage tissue is characterized by a strictly polarized distribution of cells depending on the degree of their differentiation. Near the perichondrium are the least differentiated cells - chondroblasts, which look like cells elongated parallel to the perichondrium. They actively synthesize the intercellular substance and retain the mitotic ability. The closer to the center of the cartilage, the more differentiated the cells are, they are located in isogenic groups and are characterized by a sharp decrease in the synthesis of components of the intercellular substance and the absence of mitotic activity.
In modern scientific literature, another type of cartilage tissue cells is described -chondroclasts. They occur only during the destruction of cartilaginous tissue, and in the conditions of its normal life are not detected. In size, chondroclasts are much larger than chondrocytes and chondroblasts, since they contain several nuclei in the cytoplasm. The function of chondroclasts is associated with the activation of cartilage degeneration processes and participation in phagocytosis and lysis of fragments of destroyed cartilage cells and cartilage matrix components. In other words, chondroclasts are macrophages of cartilaginous tissue that are part of a single macrophage-phagocytic system of the body.
Joint diseases
IN AND. Mazurov
Consisting of cartilage cells (chondrocytes) and a large amount of dense intercellular substance. Acts as a support. Chondrocytes have a variety of shapes and lie singly or in groups within cartilage cavities. The intercellular substance contains chondrin fibers, similar in composition to collagen fibers, and the main 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, the main amorphous substance is distinguished, which contains compounds of chondroitinsulfuric acid with proteins (chondromucoids) and chondrin fibers, similar in composition to collagen fibers. Fibrils of cartilaginous tissue belong to the type of primary fibers and have a thickness of 100-150 Å. Electron microscopy in the fibers of the cartilaginous tissue, in contrast to the actual collagen fibers, reveals only an indistinct alternation of light and dark areas without a clear periodicity. Cartilage cells (chondrocytes) are located in the cavities of the ground substance singly or in small groups (isogenic groups).
The free surface of the cartilage is covered with dense fibrous connective tissue - the perichondrium (perichondrium), in the inner layer of which there are poorly differentiated cells - chondroblasts. The cartilaginous tissue of the perichondrium that covers the articular surfaces of the bones does not have. The growth of cartilaginous tissue is carried out due to the reproduction of chondroblasts, which produce the ground substance and later turn into chondrocytes (appositional growth) and due to the development of a new ground substance around chondrocytes (interstitial, intussusceptive growth). During regeneration, the development of cartilage tissue can also occur by homogenizing the basic substance of the fibrous connective tissue and converting its fibroblasts into cartilage cells.
Cartilage tissue is nourished by diffusion of substances from the blood vessels of the perichondrium. Nutrients enter the articular cartilage tissue 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 amyopiatic nerve fibers can penetrate into the cartilaginous tissue.
In embryogenesis, cartilaginous tissue develops from mesenchyme (see), between the approaching elements of which layers of the main substance appear (Fig. 1). In such a skeletal rudiment, hyaline cartilage is first formed, temporarily representing all the main parts of the human skeleton. In the future, 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 the cartilages of the respiratory tract, the thoracic ends of the ribs and the articular surfaces of the bones are formed in humans. In a light microscope, its main substance appears to be homogeneous. Cartilage cells or their isogenic groups 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; Together, these zones form a cellular territory, or chondrin ball. A complex of chondrocytes with a chondrin ball is usually taken as a functional unit of cartilage tissue - a chondron. The ground substance between chondrons is called interterritorial spaces (Fig. 3).
Elastic cartilage(synonym: reticulate, elastic) differs from hyaline by the presence of branching networks of elastic fibers in the ground substance (Fig. 4). The cartilage of the auricle, epiglottis, vrisberg and santorin cartilages of the larynx are built from it.
fibrocartilage(a synonym for connective tissue) is located at the transition points of dense fibrous connective tissue into hyaline cartilage and differs from the latter by the presence of real collagen fibers in the ground substance (Fig. 5).
Cartilage pathology - see Chondritis, Chondrodystrophy, Chondroma.
Rice. 1-5. The structure of cartilage.
Rice. 1. Cartilage histogenesis:
1 - mesenchymal syncytium;
2 - young cartilage cells;
3 - layers of the main substance.
Rice. 2. Hyaline cartilage (small magnification):
1 - perichondrium;
2 - cartilage cells;
3 - the main substance.
Rice. 3. Hyaline cartilage (large magnification):
1 - isogenic group of cells;
2 - cartilaginous capsule;
3 - basophilic zone of the chondrin ball;
4 - oxyphilic zone of the chondrin ball;
5 - interterritorial space.
Rice. 4. Elastic cartilage:
1 - elastic fibers.
Rice. 5. Fibrous cartilage.
Cartilage is a type of hard connective tissue. From the name it is clear that it consists of cartilage cells and intercellular substance. The main function of cartilage tissue is support.
Cartilage tissue has high elasticity and elasticity. For joints, cartilage is very important - it eliminates friction due to the release of fluid and lubrication of the joints. Due to this, the load on the joints is significantly reduced.
Unfortunately, with age, cartilage tissue loses its properties. Often, cartilage tissue is damaged at a young age. This is because cartilage is very prone to destruction. It is very important to take care of your health in time, since damaged cartilage tissue is one of the main causes of diseases of the musculoskeletal system.
Types of cartilage
- hyaline cartilage
- Elastic cartilage
- fibrocartilage
hyaline cartilage tissue found in the composition of the cartilages of the larynx, bronchi, bone temafises, in the area of attachment of the ribs to the sternum.
Made from elastic cartilage consist of auricles, bronchi, larynx.
Fibrous cartilage tissue is located in the area of transition of ligaments and tendons to hyaline cartilage tissue.
However, all three types of cartilage tissue are similar in composition - they consist of cells (chondrocytes) and intercellular substance. The latter has a high bypass, approximately 60-80 percent of water. In addition, the intercellular substance occupies more space than cells. The chemical composition is quite complex. The intercellular substance of the cartilaginous tissue is divided into an amorphous substance and a fibrillar component, which includes about forty percent of the dry matter - collagen. The production of the matrix (intercellular substance) is carried out by chondroblasts and young chondrocytes.
Chondroblasts and chondrocytes
Chondroblasts are round or ovoid cells. The main task: the production of components of the intercellular substance, such as collagen, elastin, glycoproteins, proteoglycans.
Chondrocytes take into account mature cells of cartilage tissue of large size. The shape can be round, oval, polygonal. Where are chondrocytes located? In lacunae. The intercellular substance surrounds chondrocytes. The walls of the lacunae are two layers - the outer one (from collagen fibers) and the inner one (from aggregates of proteoglycans).
It combines not only collagen fibrils, but also elastic fibers, which consist of elastin protein. Its production is also the task of cartilage cells. Elastic cartilage tissue is characterized by increased flexibility.
The composition of fibrous cartilage tissue includes bundles of collagen fibers. Fibrous cartilage is very strong. Fibrous rings of intervertebral discs, intra-articular discs consist of fibrous cartilage tissue. In addition, fibrous cartilage covers the articular surfaces of the temporomandibular and sternoclavicular joints.
3. The structure of the bone
4. Osteohistogenesis
1. Skeletal connective tissues include cartilaginous and bone tissues that perform supporting, protective and mechanical functions, as well as taking part in the metabolism of minerals in the body.
cartilage tissue consists of cells - chondrocytes, chondroblasts and a dense intercellular substance, consisting of amorphous and fibrous components. Chondroblasts located singly along the periphery of the cartilaginous tissue. They are elongated flattened cells with basophilic cytoplasm containing a well-developed granular endoplasmic reticulum and the Golgi apparatus. These cells synthesize the components of the intercellular substance, release them into the intercellular environment and gradually differentiate into the definitive cells of the cartilage tissue - chondrocytes. Chondroblasts are capable of mitotic division. The perichondrium surrounding the cartilaginous tissue contains inactive, poorly differentiated forms of chondroblasts, which, under certain conditions, differentiate into chondroblasts that synthesize the intercellular substance, and then into chondrocytes.
Chondrocytes by degree of maturity, according to morphology and function are divided into cells of type I, II and III. All varieties of chondrocytes are localized in the deeper layers of cartilage tissue in special cavities - gaps. Young chondrocytes (type I) divide mitotically, but the daughter cells end up in the same gap and form a group of cells - an isogenic group. The isogenic group is a common structural and functional unit of cartilage tissue. The location of chondrocytes in isogenic groups in different cartilage tissues is not the same.
intercellular substance cartilage tissue consists of a fibrous component (collagen or elastic fibers) and an amorphous substance, which contains mainly sulfated glycosaminoglycans (primarily chondroitin sulfuric acids), as well as proteoglycans. Glycosaminoglycans bind a large amount of water and determine the density of the intercellular substance. In addition, the amorphous substance contains a significant amount of minerals that do not form crystals. Vessels in the cartilage tissue are normally absent.
Depending on the structure of the intercellular substance, cartilage tissues are divided into hyaline, elastic and fibrous cartilage tissue.
hyaline cartilage tissue characterized by the presence of only collagen fibers in the intercellular substance. At the same time, the refractive index of the fibers and the amorphous substance is the same, and therefore the fibers in the intercellular substance are not visible on histological preparations. This also explains a certain transparency of cartilage, consisting of hyaline cartilage tissue. Chondrocytes in isogenic groups of hyaline cartilage tissue are arranged in the form of rosettes. In terms of physical properties, hyaline cartilage tissue is characterized by transparency, density and low elasticity. In the human body, hyaline cartilage tissue is widespread and is part of the large cartilage of the larynx. (thyroid and cricoid), trachea and large bronchi, makes up the cartilaginous parts of the ribs, covers the articular surfaces of the bones. In addition, almost all the bones of the body in the process of their development pass through the stage of hyaline cartilage.
Elastic cartilage tissue characterized by the presence of both collagen and elastic fibers in the intercellular substance. In this case, the refractive index of elastic fibers differs from the refraction of an amorphous substance, and therefore elastic fibers are clearly visible in histological preparations. Chondrocytes in isogenic groups in elastic tissue are arranged in the form of columns or columns. In terms of physical properties, elastic cartilage is opaque, elastic, less dense, and less transparent than hyaline cartilage. She is part of elastic cartilage: auricle and cartilaginous part of the external auditory canal, cartilages of the external nose, small cartilages of the larynx and middle bronchi, and also forms the basis of the epiglottis.
Fibrous cartilage tissue characterized by the content in the intercellular substance of powerful bundles of parallel collagen fibers. In this case, chondrocytes are located between the bundles of fibers in the form of chains. According to physical properties, it is characterized by high strength. It is found only in limited places in the body: it is part of the intervertebral discs (annulus fibrosus) and also localized in the places of attachment of ligaments and tendons to hyaline cartilage. In these cases, a gradual transition of connective tissue fibrocytes into cartilage chondrocytes is clearly seen.
There are the following two concepts that should not be confused - cartilage tissue and cartilage. cartilage tissue- This is a type of connective tissue, the structure of which is described above. Cartilage is an anatomical organ made up of cartilage and perichondrium. The perichondrium covers the cartilaginous tissue from the outside (with the exception of the cartilaginous tissue of the articular surfaces) and consists of fibrous connective tissue.
There are two layers in the perichondrium:
external - fibrous;
internal - cellular or cambial (growth).
In the inner layer, poorly differentiated cells are localized - prechondroblasts and inactive chondroblasts, which, in the process of embryonic and regenerative histogenesis, first turn into chondroblasts, and then into chondrocytes. The fibrous layer contains a network of blood vessels. Consequently, the perichondrium, as an integral part of the cartilage, performs the following functions: provides trophic avascular cartilage tissue; protects cartilage; provides regeneration of cartilaginous tissue when it is damaged.
The trophism of the hyaline cartilage tissue of the articular surfaces is provided by the synovial fluid of the joints, as well as from the vessels of the bone tissue.
Development cartilage tissue and cartilage(chondrohistogenesis) is carried out from the mesenchyme. At first, mesenchymal cells in the places of cartilage tissue laying intensively proliferate, round and form focal accumulations of cells - chondrogenic islets. Then these rounded cells differentiate into chondroblasts, synthesize and secrete fibrillar proteins into the intercellular environment. Then chondroblasts differentiate into type I chondrocytes, which synthesize and secrete not only proteins, but also glycosaminoglycans and proteoglycans, that is, they form an intercellular substance. The next stage in the development of cartilage tissue is the stage of differentiation of chondrocytes, with the appearance of type II, III chondrocytes and the formation of lacunae. The perichondrium is formed from the mesenchyme surrounding the cartilaginous islands. In the process of cartilage development, two types of cartilage growth are noted: interstitial growth - due to the reproduction of chondrocytes and the release of intercellular substance by them; oppositional growth - due to the activity of chondroblasts of the perichondrium and the imposition of cartilaginous tissue along the periphery of the cartilage.
Age-related changes are more marked in hyaline cartilage tissue. In the elderly and senile age in the deep layers of hyaline cartilage, the deposition of calcium salts is noted. (shallowing of cartilage), sprouting into this area of the vessels, and then replacing the calcified cartilage tissue with bone tissue - ossification. Elastic cartilage tissue does not undergo calcification and ossification, however, the elasticity of cartilage also decreases in old age.
2. Bone tissue is a type of connective tissue and consists of cells and intercellular substance, which contains a large amount of mineral salts, mainly calcium phosphate. Minerals make up 70% of bone tissue, organic - 30%.
Functions of bone tissue:
mechanical;
protective;
participation in the mineral metabolism of the body - the depot of calcium and phosphorus.
bone cells: osteoblasts, osteocytes, osteoclasts. The main cells in the formed bone tissue are osteocytes. These are process-shaped cells with a large nucleus and weak cytoplasm (nuclear-type cells). Cell bodies are localized in bone cavities - lacunae, and processes - in bone tubules. Numerous bone tubules, anastomosing with each other, penetrate the entire bone tissue, communicating with the perivascular spaces, and form drainage system bone tissue. This drainage system contains tissue fluid, through which the exchange of substances is ensured not only between cells and tissue fluid, but also between the intercellular substance. The ultrastructural organization of osteocytes is characterized by the presence in the cytoplasm of a weakly expressed granular endoplasmic reticulum, a small number of mitochondria and lysosomes, and centrioles are absent. The nucleus is dominated by heterochromatin. All these data indicate that osteocytes have little functional activity, which is to maintain the metabolism between cells and intercellular substance. Osteocytes are definitive forms of cells and do not divide. They are formed from osteoblasts.
osteoblasts found only in developing bone tissue. They are absent in the formed bone tissue, but are usually contained in an inactive form in the periosteum. In developing bone tissue, they cover each bone plate along the periphery, tightly adhering to each other, forming a kind of epithelial layer. The shape of such actively functioning cells can be cubic, prismatic, angular. The cytoplasm of osteoblasts contains a well-developed granular endoplasmic reticulum and a lamellar Golgi complex, many mitochondria. This ultrastructural organization indicates that these cells are synthesizing and secreting. Indeed, osteoblasts synthesize collagen protein and glycosaminoglycans, which are then released into the intercellular space. Due to these components, an organic matrix of bone tissue is formed. Then these same cells provide the mineralization of the intercellular substance through the release of calcium salts. Gradually, releasing the intercellular substance, they seem to be immured and turn into osteocytes. At the same time, 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, synthetic and transport organelles are poorly developed. When these cells are irritated (in case of injuries, bone fractures, etc.), a granular endoplasmic reticulum and a lamellar complex rapidly develop in the cytoplasm, active synthesis and release of collagen and glycosaminoglycans, the formation of an organic matrix (bone callus) and then the formation of definitive bone tissue. In this way, due to the activity of periosteal osteoblasts, bones regenerate when they are damaged.
Oteoclasts- bone-destroying cells are absent in the formed bone tissue. But they 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 in ontogenesis, osteoclasts are necessarily present in these places. In the process of embryonic osteogenesis, these cells play an important role and are found in large numbers. Osteoclasts have a characteristic morphology: firstly, these cells are multinucleated (3-5 or more nuclei), secondly, they are rather large cells (about 90 microns in diameter), thirdly, they have a characteristic shape - the cell has an oval shape , but the part of it adjacent to the bone tissue is flat. At the same time, two zones are distinguished in the flat part:
the central part - corrugated contains numerous folds and islands;
the peripheral (transparent) part is 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 and therefore osteoclasts are usually localized in the depressions of bone tissue. After the destruction of bone tissue due to the activity of osteoblasts, which are evicted from the connective tissue of the vessels, a new bone tissue is built.
intercellular substance bone tissue consists of the ground substance and fibers, which contain calcium salts. The fibers consist of type I collagen and are folded into bundles that can be arranged in parallel (ordered) or disordered, on the basis of which the histological classification of bone tissues is built. The main substance of bone tissue, like other types of connective tissues, consists of glycosaminoglycans and proteoglycans, but the chemical composition of these substances is different. In particular, bone tissue contains less chondroitin sulfuric acids, but more citric and other acids that form complexes with calcium salts. In the process of development of bone tissue, an organic matrix, the main substance and collagen (ossein, type II collagen) fibers, are first formed, and then calcium salts (mainly phosphate) are deposited in them. Calcium salts form hydroxyapatite crystals, which are deposited both in the amorphous substance and in the fibers, but a small part of the salts is deposited amorphously. Providing bone strength, calcium phosphate salts are simultaneously a depot of calcium and phosphorus in the body. Therefore, bone tissue takes part in mineral metabolism.
Classification of bone tissue
There are two types of bone tissue:
reticulofibrous (coarse-fibrous);
lamellar (parallel fibrous).
AT reticulofibrous bone tissue bundles of collagen fibers are thick, tortuous and randomly arranged. 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 arranged parallel in each plate, but at right angles to the course of the fibers in adjacent plates. Between the plates in the gaps are osteocytes, while their processes pass through the tubules through the plates.
In the human body, bone tissue is represented almost exclusively by a lamellar form. Reticulofibrous bone tissue occurs only as a stage in the development of some bones (parietal, frontal). In adults, they are located in the area of attachment of the tendons to the bones, as well as in place of the ossified sutures of the skull (sagittal suture of the scales of the frontal bone).
When studying bone tissue, it is necessary to differentiate the concepts of bone tissue and bone.
3. Bone is an anatomical organ, the main structural component of which is bone. Bone as an organ is made up of the following items:
bone;
periosteum;
bone marrow (red, yellow);
vessels and nerves.
Periosteum (periosteum) surrounds the bone tissue along the periphery (with the exception of the articular surfaces) and has a structure similar to the perichondrium. In the periosteum, the outer fibrous and inner cellular or cambial layers are isolated. The inner layer contains osteoblasts and osteoclasts. A pronounced vascular network is localized in the periosteum, from which small vessels penetrate into the bone tissue through perforating channels. Red bone marrow is considered as an independent organ and belongs to the organs of hematopoiesis and immunogenesis.
Bone in the formed bones it is represented only by a lamellar form, however, in different bones, in different parts of one bone, it has a different structure. In flat bones and epiphyses of tubular bones, bone plates form crossbars (trabeculae) that make up the spongy bone. In the diaphysis of tubular bones, the plates are adjacent to each other and form a compact substance. However, even in a compact substance, some plates form osteons, while other plates are common.
The structure of the diaphysis of the tubular bone
On the transverse section of the diaphysis of the tubular bone, next layers:
periosteum (periosteum);
the outer layer of common or general plates;
layer of osteons;
inner layer of common or general plates;
internal fibrous plate endost.
External common plates located under the periosteum in several layers, but without forming complete rings. Osteocytes are located between the plates in the gaps. Perforating channels pass through the outer plates, through which perforating fibers and vessels penetrate from the periosteum into the bone tissue. With the help of perforating vessels in the bone tissue, trophism is provided, and the perforating fibers connect the periosteum with the bone tissue.
Osteon layer consists of two components: osteons and insertion plates between them. Osteon- is a structural unit of the compact substance of the tubular bone. Each osteon consists of:
5-20 concentrically layered plates;
osteon canal, in which the vessels (arterioles, capillaries, venules) pass.
Between canals of neighboring osteons there are anastomoses. Osteons make up the bulk of the bone tissue of the diaphysis of the tubular bone. They are located longitudinally along the tubular bone, respectively, along the force and gravity lines and provide a support function. When the direction of the lines of force changes as a result of a fracture or curvature of the bones, non-load-bearing osteons are destroyed by osteoclasts. However, such osteons are not completely destroyed, and part of the bone plates of the osteon along its length is preserved, and such remaining parts of osteons are called osteons. insert plates. During postnatal ontogenesis, there is a constant restructuring of the bone tissue - some osteons are destroyed (resorbed), others are formed, and therefore there are always intercalated plates between the osteons, like the remains of previous osteons.
The inner layer shared records has a structure similar to the outer one, but it is less pronounced, and in the area of the transition of the diaphysis to the epiphyses, the common plates continue into trabeculae.
Endost - a thin connective tissue plate lining the cavity of the diaphysis canal. The layers in the endosteum are not clearly expressed, but among the cellular elements there are osteoblasts and osteoclasts.
cartilage tissue
General characteristics: relatively low metabolic rate, absence of blood vessels, hydrophilicity, strength and elasticity.
Structure: chondrocyte cells and intercellular substance (fibers, amorphous substance, interstitial water).
Lecture: CARTILAGE TISSUE
Cells ( chondrocytes) make up no more than 10% of the cartilage mass. The bulk of the cartilage tissue is intercellular substance. The amorphous substance is quite hydrophilic, which allows nutrients to be delivered to the cells by diffusion from the capillaries of the perichondrium.
Differon chondrocytes: stem, semi-stem cells, chondroblasts, young chondrocytes, mature chondrocytes.
Chondrocytes are derivatives of chondroblasts and the only population of cells in cartilage, located in lacunae. Chondrocytes can be divided according to the degree of maturity into young and mature. Young retain the structural features of chondroblasts. They have an oblong shape, developed GREP, a large Golgi apparatus, are able to form proteins for collagen and elastic fibers and sulfated glycosaminoglycans, glycoproteins. Mature chondrocytes are oval or round in shape. The synthetic apparatus is less developed when compared with young chondrocytes. Glycogen and lipids accumulate in the cytoplasm.
Chondrocytes are capable of dividing and form isogenic groups of cells surrounded by a single capsule. In hyaline cartilage, isogenic groups can contain up to 12 cells, in elastic and fibrous cartilage - a smaller number of cells.
Functions cartilaginous tissues: supporting, formation and functioning of joints.
Classification of cartilage tissues
There are: 1) hyaline, 2) elastic and 3) fibrous cartilage tissue.
Histogenesis . In embryogenesis, cartilage is formed from mesenchyme.
1st stage. Formation of a chondrogenic island.
2nd stage. Differentiation of chondrroblasts and the beginning of the formation of fibers and cartilage matrix.
3rd stage. Cartilage growth in two ways:
1) Interstitial growth- due to an increase in tissue from the inside (formation of isogenic groups, accumulation of extracellular matrix), occurs during regeneration and in the embryonic period.
2) Apposition growth- due to tissue layering due to the activity of chondroblasts in the perichondrium.
Cartilage regeneration . When cartilage is damaged, regeneration occurs from the cambial cells in the perichondrium, with the formation of new layers of cartilage. Full regeneration occurs only in childhood. Adults are characterized by incomplete regeneration: PVNST is formed in place of the cartilage.
Age changes . Elastic and fibrocartilage are resistant to damage and change little with age. Hyaline cartilage tissue can undergo calcification, sometimes transforming into bone tissue.
Cartilage as an organ consists of several tissues: 1) cartilaginous tissue, 2) perichondrium: 2a) outer layer - PVNST, 2b) inner layer - RVST, with blood vessels and nerves, and also contains stem, semi-stem cells and chondroblasts.
1. Hyaline cartilage
Localization: cartilages of the nose, larynx (thyroid cartilage, cricoid cartilage, arytenoid, except for the vocal processes), trachea and bronchi; articular and costal cartilages, cartilaginous growth plates in tubular bones.
Structure: cartilage cells, chondrocytes (described above) and intercellular substance consisting of collagen fibers, proteoglycans and interstitial water. Collagen fibers(20-25%) consist of type II collagen, arranged randomly. proteoglycans, making up 5-10% of the mass of cartilage, are sulfated glycosaminoglycans, glycoproteins that bind water and fibers. Hyaline cartilage proteoglycans prevent its mineralization. interstitial water(65-85%) provides incompressibility of the cartilage, is a shock absorber. Water promotes efficient metabolism in cartilage, carries salts, nutrients, metabolites.
articular cartilage is a type of hyaline cartilage, does not have a perichondrium, receives nutrition from the synovial fluid. In articular cartilage, there are: 1) a superficial zone, which can be called acellular, 2) a middle (intermediate) zone containing columns of cartilage cells, and 3) a deep zone in which cartilage interacts with bone.
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2. ELASTIC CARTILAGE
Localization: auricle, cartilages of the larynx (epiglottic, corniculate, sphenoid, as well as the vocal process at each arytenoid cartilage), Eustachian tube. This type of tissue is necessary for those parts of organs that are able to change their volume, shape and have reversible deformation.
Structure: cartilage cells, chondrocytes (described above) and intercellular substance consisting of elastic fibers (up to 95%) fibers and amorphous substance. For visualization, dyes are used that reveal elastic fibers, such as orcein.
3. FIBROUS CARTILAGE
Localization: fibrous rings of intervertebral discs, articular discs and menisci, in the symphysis (pubic articulation), articular surfaces in the temporomandibular and sternoclavicular joints, at the points of attachment of tendons to bones or hyaline cartilage.
Structure: chondrocytes (often singly) of an elongated shape and an intercellular substance consisting of a small amount of amorphous substance and a large amount of collagen fibers. The fibers are arranged in orderly parallel bundles.
