3. Bone structure
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 dense intercellular substance, consisting of amorphous and fibrous components. Chondroblasts located singly along the periphery cartilage tissue. They are elongated, flattened cells with basophilic cytoplasm containing a well-developed granular endoplasmic reticulum and 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 cartilage tissue - chondrocytes. Chondroblasts have the ability to undergo mitotic division. The perichondrium surrounding the cartilaginous tissue contains inactive, poorly differentiated forms of chondroblasts, which, under certain conditions, differentiate into chondroblasts that synthesize intercellular substance, and then into chondrocytes.
Chondrocytes by maturity, according to morphology and function, are divided into cells of type I, II and III. All types 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 lacuna 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 chondroitinsulfuric acids), as well as proteoglycans. Glycosoaminoglycans bind large number water and determine the density of the intercellular substance. In addition, the amorphous substance contains a significant amount of mineral substances that do not form crystals. Vessels are normally absent in cartilage tissue.
Depending on the structure of the intercellular substance, cartilage tissue is divided into hyaline, elastic and fibrous cartilage tissue.
Hyaline cartilage tissue characterized by the presence of only collagen fibers in the intercellular substance. In this case, 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 the cartilages, consisting of hyaline cartilaginous 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 cartilages 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 bones in the body pass through the hyaline cartilage stage during their development.
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 refractive index 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 tissue is opaque, elastic, less dense and less transparent than hyaline cartilage tissue. It is part of elastic cartilage: the auricle and the cartilaginous part of the external auditory canal, the cartilage 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 fiber bundles in the form of chains. According to its physical properties, it is characterized by high strength. In the body it is found only in limited places: it forms part of the intervertebral discs (fibrous ring), and is also localized in the places of attachment of ligaments and tendons to hyaline cartilage. In these cases, the gradual transition of fibrocytes of connective tissue into chondrocytes of cartilage tissue is clearly visible.
There are the following two concepts that should not be confused - cartilaginous tissue and cartilage. Cartilage tissue- this is a type of connective tissue, the structure of which is described above. Cartilage is an anatomical organ that consists of cartilage tissue and perichondrium. The perichondrium covers the cartilage tissue on the outside (with the exception of the cartilaginous tissue of the articular surfaces) and consists of fibrous connective tissue.
The perichondrium has two layers:
external - fibrous;
internal - cellular or cambial (germinal).
Poorly differentiated cells are localized in the inner layer - 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 a component of cartilage, performs the following functions: provides trophism to avascular cartilaginous tissue; protects cartilage tissue; ensures regeneration of cartilage tissue when damaged.
The trophism of the hyaline cartilaginous 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(chondrogistogenesis) is carried out from the mesenchyme. Initially, mesenchymal cells in places where cartilage tissue is formed intensively proliferate, become rounded and form focal clusters of cells - chondrogenic islets. Then these rounded cells differentiate into chondroblasts, synthesize and release 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 the intercellular substance. The next stage of cartilage tissue development is the stage of chondrocyte differentiation, during which type II and III chondrocytes appear and lacunae are formed. The perichondrium is formed from the mesenchyme surrounding the cartilaginous islands. During the development of cartilage, two types of cartilage growth are observed: interstitial growth - due to the proliferation of chondrocytes and their release of intercellular substance; oppositional growth - due to the activity of chondroblasts of the perichondrium and the overlay of cartilage tissue along the periphery of the cartilage.
Age-related changes in to a greater extent noted in hyaline cartilaginous tissue. In old and senile age, deposition of calcium salts is observed in the deep layers of hyaline cartilage (cartilage chalking), germination of blood vessels into this area, and then replacement of calcified cartilaginous tissue with bone tissue - ossification. Elastic cartilage tissue does not undergo calcification and ossification, but the elasticity of cartilage in old age also decreases.
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 substances - 30%.
Functions of bone tissue:
mechanical;
protective;
participation in the mineral metabolism of the body - a depot of calcium and phosphorus.
Bone cells: osteoblasts, osteocytes, osteoclasts. The main cells in 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 with intercellular substance. The ultrastructural organization of osteocytes is characterized by the presence in the cytoplasm of a weakly defined granular endoplasmic reticulum, a small number of mitochondria and lysosomes, and no centrioles. Heterochromatin predominates in the nucleus. All these data indicate that osteocytes have insignificant functional activity, which consists in maintaining metabolism between cells and 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. They are absent in formed bone tissue, but are usually contained in an inactive form in the periosteum. In developing bone tissue, they cover the periphery of each bone plate, tightly adjacent to each other, forming a kind of epithelial layer. The shape of such actively functioning cells can be cubic, prismatic, or angular. The cytoplasm of osteoblasts contains a well-developed granular endoplasmic reticulum and 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, the organic matrix of bone tissue is formed. Then these same cells provide mineralization of the intercellular substance by secreting calcium salts. Gradually, releasing intercellular substance, they become walled up 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, synthetic and transport organelles are poorly developed. When these cells are irritated (in the case of injuries, bone fractures, and so on), a granular endoplasmic reticulum and lamellar complex quickly develop in the cytoplasm, active synthesis and release of collagen and glycosaminoglycans occurs, and the formation of an organic matrix (bone callus), and then the formation of definitive bone tissue. In this way, due to the activity of osteoblasts of the periosteum, bone regeneration occurs when they are damaged.
Oteoclasts- bone-destructive cells are absent in 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 during ontogenesis, osteoclasts are necessarily present in these places. During the process of embryonic osteohistogenesis, 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 quite large cells (about 90 microns in diameter), thirdly, they have a characteristic shape - the cell is oval in shape , but the part of it adjacent to the bone tissue is flat. In this case, two zones are distinguished in the flat part:
the central part is corrugated and 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 different 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 there is resorption(destruction) of bone tissue 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 ground substance and fibers that contain calcium salts. The fibers consist of type I collagen and are folded into bundles, which can be arranged in parallel (ordered) or disordered, 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 glycosaminoglycans and proteoglycans, but the chemical composition of these substances differs. In particular, bone tissue contains less chondroitinsulfuric acids, but more citric and other acids that form complexes with calcium salts. In the process of bone tissue development, organic matrix substance and collagen (ossein, type II collagen) fibers are first formed, and then calcium salts (mainly phosphates) are deposited in them. Calcium salts form hydroxyapatite crystals, 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 also 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).
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 in 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 represented almost exclusively in the 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 tendons to bones, as well as at the site of ossified sutures of the skull (sagittal suture of the squama of the frontal bone).
When studying bone tissue, the concepts of bone tissue and bone should be differentiated.
3. Bone is an anatomical organ whose main structural component is bone tissue. Bone as an organ consists of the following elements:
bone tissue;
periosteum;
bone marrow (red, yellow);
vessels and nerves.
Periosteum (periosteum) surrounds bone tissue along the periphery (with the exception of articular surfaces) and has a structure similar to the perichondrium. The periosteum is divided into outer fibrous and inner cellular or cambial layers. 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 tissue in formed bones it is represented only in a lamellar form, however, in different bones, in different parts of the same bone, it has a different structure. In flat bones and epiphyses of tubular bones, bone plates form crossbars (trabeculae), making up the cancellous bone. In the diaphyses 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 a cross section of the diaphysis of the tubular bone, next layers:
periosteum (periosteum);
outer layer of common or general plates;
osteon layer;
inner layer of general or general plates;
internal fibrous lamina endosteum.
External common plates are located under the periosteum in several layers, but do not form complete rings. Osteocytes are located between the plates in the lacunae. 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, trophism is ensured in bone tissue, and perforating fibers connect the periosteum with bone tissue.
Osteon layer consists of two components: osteons and insertion plates between them. Osteon- is a structural unit of the compact substance of tubular bone. Each osteon consists of:
5-20 concentrically layered plates;
osteon channel, in which vessels pass (arterioles, capillaries, venules).
Between channels 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, according to the lines of force and gravity, and provide a supporting function. When the direction of the force lines changes as a result of a fracture or curvature of 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 are preserved and such remaining parts of osteons are called insert plates. During postnatal ontogenesis, bone tissue is constantly restructured - some osteons are destroyed (resorbed), others are formed, and therefore there are always intercalary plates between the osteons, as remnants of previous osteons.
Inner layer common records has a structure similar to the outer one, but it is less pronounced, and in the area of the transition of the diaphysis into the epiphyses, the common plates continue into trabeculae.
Endosteum - a thin connective tissue plate lining the cavity of the diaphysis canal. The layers in the endosteum are not clearly defined, but among the cellular elements there are osteoblasts and osteoclasts.
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. 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 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) located in the places where dense fibrous connective tissue transitions into hyaline cartilage and differs from the latter by 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 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, a lamellar Golgi complex, and 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.
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
The basis of the musculoskeletal system is cartilage tissue. It is also part of the facial structures, becoming the site of attachment of muscles and ligaments. The histology of cartilage is represented by a small number of cellular structures, fibrous formations and nutrients. This ensures sufficient shock-absorbing function.
What does it represent?
Cartilage is a type of connective tissue. The structural features are increased elasticity and density, due to which it is able to perform a supporting and mechanical function. Articular cartilage consists of cells called chondrocytes and a ground substance containing fibers that provide the elasticity of the cartilage. Cells in the thickness of these structures form groups or are located separately. The location is usually near bones.
Types of cartilage
Depending on the characteristics of the structure and localization in the human body, there is the following classification of cartilage tissue:
- Hyaline cartilage contains chondrocytes arranged in the form of rosettes. The intercellular substance is larger in volume than the fibrous substance, and the threads are represented only by collagen.
- Elastic cartilage contains two types of fibers - collagen and elastic, and the cells are arranged in columns or columns. This type of fabric has less density and transparency, but has sufficient elasticity. This matter makes up the cartilage of the face, as well as the structures of the secondary formations in the bronchi.
- Fibrous cartilage is a connective tissue that functions as strong shock-absorbing elements and contains a significant amount of fibers. The localization of the fibrous substance is throughout the musculoskeletal system.
Properties and structural features of cartilage tissue
The histological specimen shows that the tissue cells are loosely located, surrounded by an abundance of intercellular substance. All types of cartilage tissue are capable of absorbing and counteracting the compressive forces that arise during movement and load. This ensures an even distribution of gravity and reduces the load on the bone, which stops its destruction. Skeletal areas where friction processes constantly occur are also covered with cartilage, which helps protect their surfaces from excessive wear. The histology of this type of tissue differs from other structures in the large amount of intercellular substance, and the cells are loosely located in it, form clusters or are found separately. The main substance of the cartilage structure is involved in the processes of carbohydrate metabolism in the body.
This type of material in the human body, like others, contains cells and intercellular substance of cartilage. The peculiarity is in a small number of cellular structures, due to which the properties of the tissue are ensured. Mature cartilage is a loose structure. Elastic and collagen fibers perform a supporting function in it. The general structural plan includes only 20% of cells, and the rest is fibers and amorphous matter. This is due to the fact that, due to dynamic load, the vascular bed of the tissue is weakly expressed and therefore it is forced to feed from the main substance of the cartilaginous tissue. In addition, the amount of moisture contained in it performs shock-absorbing functions, smoothly relieving tension in bone tissue.
What are they made of?
The trachea and bronchi are composed of hyaline cartilage. Each type of cartilage has unique properties due to differences in location. The structure of hyaline cartilage differs from the rest in the smaller number of fibers and greater filling with amorphous substance. In this regard, it is not able to withstand heavy loads, since its tissues are destroyed by the friction of bones, however, it has a rather dense and solid structure. Therefore, it is characteristic that the bronchi, trachea and larynx consist of this type of cartilage. Skeletal and musculoskeletal structures are formed predominantly by fibrous matter. Its variety includes part of the ligaments connected to hyaline cartilage. The elastic structure occupies an intermediate location relative to these two tissues.
Cellular composition
Chondrocytes do not have a clear and ordered structure, but are more often located completely chaotically. Sometimes their clusters resemble islands with large areas of absence of cellular elements. In this case, a mature type of cell and a young one, called chondroblasts, are located together. They are formed by the perichondrium and have interstitial growth, and during their development they produce various substances.
Chondrocytes are the source of components of the intercellular space, it is thanks to them that there is such a chemical table of elements in the composition of the amorphous substance:
Hyaluronic acid is contained in an amorphous substance. - proteins;
- glycosaminoglycans;
- proteoglycans;
- hyaluronic acid.
During the embryonic period, most bones are hyaline tissue.
The structure of the intercellular substance
It consists of two parts - fibers and an amorphous substance. In this case, fibrillar structures are located chaotically in the tissue. The histology of cartilage is influenced by its production by cells chemicals, responsible for density, transparency and elasticity. The structural features of hyaline cartilage consist in the presence of only collagen fibers in its composition. If an insufficient amount of hyaluronic acid is released, it destroys tissues due to degenerative processes in them.
Blood flow and nerves
The structures of cartilage tissue do not have nerve endings. Pain reactions in them are represented only with the help of bone elements, while the cartilage will already be destroyed. This causes a large number of untreated diseases of this tissue. There are few nerve fibers on the surface of the perichondrium. The blood supply is poor and the vessels do not penetrate deep into the cartilage. Therefore, nutrients enter the cells through the ground substance.
Functions of structures
The auricle is formed from this tissue. Cartilage is the connecting part of the human musculoskeletal system, but is sometimes found in other parts of the body. The histogenesis of cartilage tissue goes through several stages of development, due to which it is able to provide support while at the same time being completely elastic. They are also part of the external formations of the body such as the cartilage of the nose and ears. Ligaments and tendons are attached to them to the bone.
Age-related changes and diseases
The structure of cartilage tissue changes with age. The reasons for this lie in the insufficient supply of nutrients to it; as a result of disturbances in trophism, diseases arise that can destroy fibrous structures and cause cell degeneration. A young body has a much larger supply of fluid, so these cells have sufficient nutrition. However, age-related changes cause “drying out” and ossification. Inflammation due to bacterial or viral agents can cause cartilage degeneration. Such changes are called “chondrosis”. At the same time, it becomes less smooth and is unable to perform its functions, as its nature changes.
Signs that the tissue has been destroyed are visible during histology analysis.
How to eliminate inflammatory and age-related changes?
To cure cartilage, drugs are used that can restore the independent development of cartilage tissue. These include chondroprotectors, vitamins and products that contain hyaluronic acid. Important proper diet with a sufficient amount of protein, because it is a stimulator of body regeneration. It is shown to keep the body in good shape, because overweight body and insufficient physical activity cause destruction of structures.
Cartilage tissue, like bone, refers to skeletal tissues with a support-mechanical function. According to the classification, there are three types of cartilage tissue - hyaline, elastic and fibrous. Structural features various types cartilage tissue depends 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 widely used in humanshyaline cartilage tissue.
It is part of the trachea, some cartilages of the larynx, large bronchi, themaphyses of bones, and is found at the junction of the ribs with the sternum and in some other areas of the body. Elastic cartilaginous tissue is part of the auricle, medium-caliber bronchi, and some cartilages of the larynx. Fibrous cartilage is commonly found where tendons and ligaments meet hyaline cartilage, such as intervertebral discs.
The structure of all types of cartilage tissue in general outline similar: they contain cells and intercellular substance (matrix). One of the features of the intercellular substance of cartilage tissue is its high water content: the water content normally ranges from 60 to 80%. The area occupied by the intercellular substance is significantly larger than the area occupied by cells. The intercellular substance of cartilage tissue is produced by cells (chondroblasts and young chondrocytes) and has a complex chemical composition. It is divided 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 hyaline cartilage tissue by collagen fibrils formed by type II collagen, running diffusely in different directions. On histological preparations, fibrils are invisible, since they have the same refractive index as the amorphous substance. In elastic cartilage tissue, along with collagen fibrils, there are numerous elastic fibers consisting of the protein elastin, which is also produced by cartilage cells. Fibrous cartilage tissue contains a large number of bundles of collagen fibers consisting of collagen types I and II.
The leading chemical compounds that form the main amorphous substance of cartilage tissue (chondromucoid) are sulfated glycosaminoglycans (keratosulfates and chondroitin sulfates A and C) and neutral mucopolysaccharides, most of which are represented by complex supramolecular complexes. In cartilage, compounds of hyaluronic acid molecules with proteoglycans and specific sulfated glycosaminoglycans are widespread. This ensures the special properties of cartilage tissue - 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 to the intercellular substance of cartilage are keratosulfates and certain types of chondroitin sulfates. They make up about 30% of the dry mass of cartilage.
The main cells of cartilage tissue arechondroblasts and chondrocytes.
Chondroblastsare young, poorly differentiated cells. They are located near the perichondrium, lie alone and are characterized by a round or oval shape with uneven edges. The large nucleus occupies a significant part of the cytoplasm. Among the cellular organelles, synthesis organelles predominate - ribosomes and polysomes, granular endoplasmic reticulum, Golgi complex, mitochondria; Characteristic inclusions of glycogen. In general histological staining of preparations with hematoxylin and eosin, chondroblasts are weakly basophilic. The structure of chondroblasts indicates that these cells exhibit 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 chondroblasts in humans 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 poor development synthetic apparatus. In addition, some of the chondroblasts located immediately under the perichondrium have not lost their ability to divide.
Chondrocytes- mature cells of cartilage tissue - occupy mainly the central areas of the cartilage. The synthetic abilities of these cells are significantly lower than those of chondroblasts. Differentiated chondrocytes most often lie in cartilage tissues not singly, but in groups of 2, 4, 8 cells. These are so-called isogenic groups of cells that 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 significant 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 metabolic processes in cartilage tissue at a certain level.
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, spindle-shaped, triangular - depending on the position on a particular section of the cartilage. The cartilaginous cavities are surrounded by a narrow strip, lighter than the main substance, which forms, as it were, the shell of the cartilaginous cavity. This shell, characterized by oxyphilicity, is called the cellular territory, or territorial matrix. More distant areas 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. Interweavings of collagen fibrils form the wall of the lacunae. The spaces between cells inside the lacunae are filled with proteoglycans. The interstitial matrix is characterized by a weakly basophilic or oxyphilic color and corresponds to the oldest areas of the intercellular substance.
Thus, definitive cartilaginous tissue is characterized by a strictly polarized distribution of cells depending on the degree of their differentiation. Near the perichondrium there are the least differentiated cells - chondroblasts, which look like cells elongated parallel to the perichondrium. They actively synthesize intercellular substance and retain mitotic ability. The closer to the center of the cartilage, the more differentiated the cells are, they are arranged 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 cell has been described -chondroclasts. They occur only when cartilage tissue is destroyed, and are not detected under normal conditions. 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 components of the cartilage matrix. In other words, chondroclasts are macrophages of cartilage tissue that are part of a single macrophage-phagocytic system of the body.
Joint diseases
V.I. Mazurov
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 little 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 of which 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, which 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 cartilage
Cartilage tissue without pathological changes is of great importance for human health and normal quality life.