66367 1
Bone tissue represents a very advanced specialized variety of tissues of the internal environment.
This system harmoniously combines such opposing properties as mechanical strength and functional plasticity, the processes of new formation and destruction.
Bone tissue consists of cells and intercellular substance, which are characterized by a certain histoarchitecture. The main cells of bone tissue are osteoblasts, osteocytes and osteoclasts.
Osteoblasts have an oval or cubic shape. The large light nucleus is not located in the center, it is somewhat shifted to the periphery of the cytoplasm. Often several nucleoli are found in the nucleus, which indicates the high synthetic activity of the cell.
Electron microscopic studies have shown that a significant part of the osteoblast cytoplasm is filled with numerous ribosomes and polysomes, tubules of the granular endoplasmic reticulum, the Golgi complex, mitochondria, and special matrix vesicles. Osteoblasts have proliferative activity, are producers of intercellular substance and play a major role in the mineralization of the bone matrix. They synthesize and secrete chemical compounds such as alkaline phosphatase, collagens, osteonectin, osteopontin, osteocalcin, bone morphogenetic proteins, etc. The matrix vesicles of osteoblasts contain numerous enzymes, which, released outside the cell, initiate bone mineralization processes.
The organic matrix of bone tissue synthesized by osteoblasts consists predominantly (90-95%) of type I collagen, III-V collagens and other types, as well as non-collagen proteins (osteocalcin, osteopontin, osteonectin, phosphoproteins, bone morphogenetic proteins) and glycosaminoglycan substances. Proteins of a non-collagenous nature have the properties of mineralization regulators, osteoinductive substances, mitogenic factors, and regulators of the rate of formation of collagen fibrils. Thrombospondin promotes the adhesion of osteoblasts to subperiosteal osteoid of human bone. Osteocalcin is considered a potential indicator of the function of these cells.
The ultrastructure of osteoblasts indicates that their functional activity is different. Along with functionally active osteoblasts with high synthetic activity, there are inactive cells. Most often they are localized on the periphery of the bone from the side of the medullary canal and are part of the periosteum. The structure of such cells is characterized by a low content of organelles in the cytoplasm.
Osteocytes are more differentiated cells than osteoblasts. They have a process shape.
Osteocyte processes are located in tubules that penetrate the mineralized bone matrix in various directions. The flattened bodies of osteocytes are located in special cavities - lacunae - and are surrounded on all sides by a mineralized bone matrix. A significant part of the osteocyte cytoplasm is occupied by the ovoid nucleus. Organelles of synthesis in the cytoplasm are poorly developed: there are a few polysomes, short tubules of the endoplasmic reticulum, and single mitochondria. Due to the fact that the tubules of neighboring lacunae anastomose with each other, the processes of osteocytes are interconnected using specialized gap junctions. IN small space tissue fluid circulates around the bodies and processes of osteocytes, containing a certain concentration of Ca 2+ and PO 4 3-, and may contain unmineralized or partially mineralized collagen fibrils.
The function of osteocytes is to maintain the integrity of the bone matrix by participating in the regulation of bone mineralization and providing a response to mechanical stimuli. Currently, more and more evidence is accumulating that these cells take an active part in the metabolic processes occurring in the intercellular substance of bone, in maintaining the constancy of the ion balance in the body. The functional activity of osteocytes largely depends on their stage life cycle and the actions of hormonal and cytokine factors.
Osteoclasts- These are large multinucleated cells with strongly oxyphilic cytoplasm. They are part of the body's phagocytic-macrophage system, derivatives of blood monocytes.
A corrugated brush border is defined at the periphery of the cell. The cytoplasm contains many ribosomes and polysomes, mitochondria, endoplasmic reticulum tubules, and the Golgi complex is well developed. Distinctive feature The ultrastructure of osteoclasts is the presence of a large number of lysosomes, phagosomes, vacuoles and vesicles.
Osteoclasts have the ability to create an acidic environment locally at their surface as a result of intensive glycolysis processes occurring in these cells. The acidic environment in the area of direct contact between the cytoplasm of osteoclasts and the intercellular substance promotes the dissolution of mineral salts and creates optimal conditions for the action of proteolytic and a number of other lysosome enzymes. A cytochemical marker of osteoclasts is the activity of the acid phosphatase isoenzyme, which is called acid nitrophenylphosphatase. The functions of osteoclasts include resorption (destruction) of bone tissue and participation in the process of remodeling bone structures during embryonic and postnatal development.
The intercellular substance of bone tissue consists of organic and inorganic components. Organic compounds are represented by collagens I, III, IV, V, IX, XIII types (about 95%), non-collagen proteins (bone morphogenetic proteins, osteocalcin, osteopontin, thrombospondin, bone sialoprotein, etc.), glycosaminoglycans and proteoglycans. The inorganic part of the bone matrix is represented by hydroxyapatite crystals containing large quantities of calcium and phosphorus ions; in much smaller quantities it contains magnesium and potassium salts, fluorides, and bicarbonates.
The intercellular substance of bone is constantly renewed. The destruction of old intercellular substance is a rather complex and not yet clear in many details process, in which all types of bone tissue cells and a number of humoral factors take part, but osteoclasts play a particularly noticeable and important role.
Types of bone tissue
Depending on the microscopic structure, there are two main types of bone tissue - reticulofibrous (coarse fibrous) and lamellar.Reticulofibrous bone tissue is widely represented in embryogenesis and early postnatal histogenesis of skeletal bones, and in adults it is found in the places of attachment of tendons to bones, along the line of healing of cranial sutures, as well as in the area of fractures.
Both in embryogenesis and during regeneration, reticulofibrous bone tissue is always replaced by lamellar tissue over time. A characteristic feature of the structure of reticulofibrous bone tissue is the disordered, diffuse arrangement of bone cells in the intercellular substance. Powerful bundles of collagen fibers are weakly mineralized and run in different directions. The density of osteocytes in reticulofibrous bone tissue is higher than in lamellar bone tissue, and they do not have a specific orientation in relation to collagen (ossein) fibers.
Lamellar bone tissue is the main tissue in almost all human bones. In this type of bone tissue, the mineralized intercellular substance forms special bone plates 5-7 microns thick.
Each bone plate is a collection of closely spaced parallel collagen fibers impregnated with hydroxyapatite crystals. In adjacent plates, the fibers are located at different angles, which gives the bone additional strength. Between the bone plates in the lacunae, bone cells - osteocytes - lie in an orderly manner. The processes of osteocytes penetrate through the bone canaliculi into the surrounding plates, entering intercellular contacts with other bone cells. There are three systems of bone plates: surrounding (general, there are external and internal), concentric (part of the osteon structure), intercalary (representing the remnants of collapsing osteons).
The composition of bone is divided into compact and spongy substance. Both of them are formed by lamellar bone tissue. Features of the histoarchitectonics of lamellar bone will be presented below when describing bone as an organ.
Joint diseases
V.I. Mazurov
Rice. 74. Hyaline cartilage tissue (a section of hyaline cartilage)
Staining: hematoxylin-eosin
1 - perichondrium: 1.1 - outer fibrous layer, 1.2 - inner (chondrogenic) cell layer, 1.3 - blood vessels; 2 - zone of young cartilage: 2.1 - chondrocytes, 2.2 - intercellular substance (cartilage matrix); 3 - zone of mature cartilage: 3.1 - cellular territory, 3.1.1 - isogenic group of chondrocytes, 3.1.2 - territorial matrix, 3.2 - interterritorial matrix
Rice. 75. Elastic cartilaginous tissue (section of elastic cartilage)
Staining: orcein-hematoxylin
1 - isogenic group of chondrocytes; 2 - intercellular substance (cartilage matrix): 2.1 - elastic fibers, 2.2 - ground substance
Rice. 76. Fibrous (fibrous) cartilage tissue (a section of fibrocartilage)
Staining: hematoxylin-eosin
1 - isogenic groups of chondrocytes; 2 - intercellular substance (cartilage matrix): 2.1 - collagen fibers
Rice. 77. Development of bone tissue directly from mesenchyme (direct osteogenesis)
Staining: hematoxylin-eosin
1 - bone trabecula: 1.1 - osteocyte lacunae, 1.2 - calcified intercellular substance, 1.3 - osteoblasts, 1.3.1 - active osteoblasts, 1.3.2 - inactive osteoblasts, 1.4 - osteoclasts, 1.5 - erosive lacuna; 2 - osteogenic cells (differentiating from mesenchyme) connective tissue; 3 - blood vessel
Rice. 78. Ultrastructural organization of bone tissue cells
Drawings with EMF
A - osteoblast; B - osteocyte; B - osteoclast
1 - core(s); 2 - cytoplasm: 2.1 - cisterns of granular endoplasmic reticulum, 2.2 - Golgi complex, 2.3 - mitochondria, 2.4 - microvilli, 2.5 - microfolded border (cytoplasmic processes); 3 - osteoid; 4 - calcified intercellular substance; 5 - osteocyte lacuna (contains the cell body); 6 - bone tubules with osteocyte processes; 7 - erosion lacuna: 7.1 - erosion front
Rice. 79. Development of bone in place of cartilage (indirect osteogenesis)
Staining: hematoxylin-eosin
1 - diaphysis: 1.1 - periosteum, 1.1.1 - osteogenic layer (inner layer of the periosteum), 1.2 - perichondral bone ring, 1.2.1 - hole, 1.3 - remains of calcified cartilage, 1.4 - endochondral bone, 1.5 - blood vessels, 1.6 - developing bone marrow; 2 - epiphyses: 2.1 - perichondrium, 2.2 - rest zone, 2.3 - proliferation zone (with columns of chondrocytes), 2.4 - hypertrophy zone, 2.5 - calcification zone; 3 - articular capsule
Rice. 80. Rough fibrous bone tissue (total planar preparation)
Not painted
1 - osteocyte lacuna (location of the cell body); 2 - bone tubules (containing processes of osteocytes); 3 - intercellular substance
Rice. 81. Lamellar bone tissue (cross section of the diaphysis of decalcified tubular bone)
1 - periosteum: 1.1 - perforating (Volkmann) canal, 1.1.1 - blood vessel;
2 - compact bone substance: 2.1 - external encircling plates, 2.2 - osteons, 2.3 - interstitial plates, 2.4 - internal encircling plates; 3 - cancellous bone: 3.1 - bone trabeculae, 3.2 - endosteum, 3.3 - intertrabecular spaces
Rice. 82. Transverse section of osteon
(diaphysis of decalcified tubular bone)
Staining: thionin-picric acid
1 - osteon channel: 1.1 - connective tissue, 1.2 - blood vessels; 2 - concentric bone plates; 3 - osteocyte lacuna containing its body; 4 - bone tubules with processes of osteocytes; 5 - cementing line
Rice. 83. Lamellar bone tissue. Area of spongy substance (diaphysis of decalcified tubular bone)
Staining: thionin-picric acid
1 - bone trabeculae; 2 - packages of bone plates; 3 - cementing lines; 4 - lacunae of osteocytes containing their bodies; 5 - bone tubules with processes of osteocytes; 6 - endosteum; 7 - intertrabecular spaces; 8 - bone marrow; 9 - adipose tissue; 10 - blood vessel
Rice. 84. Synovial joint (joint). General view
Staining: hematoxylin-eosin
1 - bone: 1.1 - periosteum; 2 - synovial joint (joint): 2.1 - articular capsule (bursa), 2.2 - articular cartilage (hyaline), 2.3 - articular cavity (contains synovial fluid)
Rice. 85. Area of synovial joint (joint)
Staining: hematoxylin-eosin
1 - joint capsule (bursa): 1.1 - fibrous layer, 1.2 - synovial layer forming synovial villi (shown by bold arrows), 1.2.1 - synovial intima (synoviocytes), 1.2.2 - deep part of the subintimal fibrovascular layer, 1.2.3 - superficial part of the subintimal fibrovascular layer; 2 - articular cartilage (hyaline): 2.1 - tangential zone, 2.1.1 - acellular plate, 2.1.2 - flattened chondrocytes, 2.2 - intermediate zone, 2.2.1 - round chondrocytes, 2.2.2 - isogenic groups of chondrocytes, 2.3 - radial zone, 2.3.1 - columns of chondrocytes, 2.3.2 - layer of hypertrophied (dystrophically changed) chondrocytes, 2.4 - border line (mineralization front), 2.5 - calcified hyaline cartilage; 3 - subchondral bone tissue
Rice. 86. Ultrastructural organization of synovial cells (synoviocytes)
Drawing with EMF
A - synoviocyte A (phagocytic synovial cell);
B - synoviocytes B (secretory synovial cells):
1 - nucleus, 2 - cytoplasm: 2.1 - mitochondria, 2.2 - cisterns of granular endoplasmic reticulum, 2.3 - lysosomes, 2.4 - secretory granules, 2.5 - microvilli, 2.6 - cytoplasmic process
Development of bone tissue in place of cartilage is somewhat more complicated than osteohistogenesis, which occurs directly in the mesenchyme. In this case, the development of bone tissue is preceded by the formation of a cartilaginous model of the tubular bone, which performs a supporting function at the pre-osseous stage of skeletal formation. The starting cells are the cambial cells of the perichondrium - adventitia. When blood vessels grow to the perichondrium and conditions of trophism and oxygenation improve, these cells differentiate not into chondroblasts, but into osteoblasts, which produce the intercellular substance of reticulofibrous bone tissue. They form a kind of bone cuff surrounding the cartilaginous model of the future tubular bone. This is how perichondral bone tissue and periosteum arises. Surrounded by bone tissue, cartilage cells that have lost contact with their nutritional source undergo degeneration. Blood vessels with cambial cells located around them grow into the resulting cavities of the degenerating cartilage from the periosteum. Some of them turn into osteoblasts, which determine the enchondral development of reticulofibrous bone tissue. Cells that are embedded in the intercellular substance differentiate into osteocytes, and peripherally located cells - osteoblasts - multiply and continue the synthesis and secretion of the components of the intercellular substance. All these processes initially occur in the middle of the cartilaginous model of the tubular bone (diaphysis) and spread in the proximal and distal directions.
In the area of contact between cartilage and bone tissue One can distinguish zones of unchanged cartilage, proliferating chondrocytes forming cell columns, a zone of degeneration and replacement of cartilage with bone tissue. The zone of proliferating cartilage cells determines the growth zone of future bone and is important for the formation of the bone growth vector.
Simultaneously with formation of reticulofibrous bone tissue, containing osteoblasts and osteocytes, another histogenetic type of cell appears - osteoclasts. These large multinucleate (up to 20-100 nuclei) cells up to 100 microns in diameter are derivatives of hematopoietic stem cells. The cytoplasm of osteoclasts is oxyphilic with a poorly developed endoplasmic reticulum. The Golgi complex is well developed. The cytoplasm contains many lysosomes containing acid phosphatase, collagenase, carbonic anhydrase and other enzymes. There are especially many lysosomes in that part of the osteoclast cytoplasm that faces the tissue being destroyed. On this surface there are numerous outgrowths of the cytoplasm, forming something like a “brush (corrugated) border.” Osteoclasts are specialized in the “extracellular work” of lysosomes: hydrolytic enzymes come out of them and resorb the intercellular substance. Using microcinema methods, it was shown that osteoclasts undergo demineralization and destruction of ossein fibers and amorphous substance, and then macrophages phagocytose the remains of the organic substrate. Osteoclasts destroy cartilage tissue and reticulofibrous bone tissue, forming channels for ingrowth vessels and the penetration of osteoblasts.
Subsequent stages of histogenesis consist of the processes of new bone tissue formation, its destruction by osteoclasts and restructuring - remodeling. An important factor in the histogenesis of lamellar bone tissue, which is part of the tubular bone, is the vector of bone growth. It determines the direction of movement of osteoclasts, therefore, the formation of channels and the ingrowth of blood vessels into them (along the growth vector). The blood vessel, in turn, determines the ordered (concentric) arrangement of osteoblasts around itself. In this case, osteoblasts synthesize an intercellular substance, the ossein fibers of which are ordered (in parallel) located near the osteoblast and, upon mineralization, form a bone plate 3-10 microns thick. The adjacent bone plate contains ossein fibrils, which are located at an angle relative to the first.
Throughout histogenesis and the entire age-related dynamics of bone tissue, a continuous restructuring occurs in it due to the coordinated activity of osteoblasts and osteocytes that form the intercellular substance, as well as osteoclasts that destroy bone tissue, which is necessary for the processes of its self-renewal. This is how a change in generations of bone plates and the forming structural and functional units - osteons occurs, an orderly arrangement of the latter is achieved, therefore, high mechanical strength of bone tissue and bone as an organ (see bone).
Dentinoid bone tissue characterized by the absence of bone cell bodies in the thickness of the intercellular substance. Dentin is a substance consisting of collagen fibers and a basic amorphous substance impregnated with mineral salts. The cells that form the dentin of the tooth - odontoblasts (more precisely, their nuclear-containing part) - are located outside the dentin in the dental pulp. Dentin is penetrated by dentinal tubules, in which the processes of odontoblasts pass. Dental cement has a similar structure.
Reticulofibrous (coarse fibrous) bone tissue characterized by a random arrangement of ossein fibrils in the form of thick, dense bundles of fibers and a basic amorphous substance. Such bone tissue forms bones in the embryonic and early postnatal periods. In an adult, it is preserved only at the site of attachment of the tendon to the bone, in the healing sutures of the skull, and also as part of the tissue regenerate at the site of bone fractures.
Lamellar bone tissue It is distinguished by the ordered arrangement of ossein fibrils in the composition of bone plates. The latter form one after another layers of fibrils impregnated with calcium salts, formed by osteoblasts. The layers have a thickness from 3-7 to several hundred micrometers. Each bone plate consists of parallel oriented thin ossein (collagen) fibers (type 1 collagen). But the collagen fibers of two bone plates adjacent to each other are oriented at different angles. The bone plate is connected to the adjacent plate by collagen fibrils. This creates a strong fibrous bone base. Bone plates are located concentrically around the vessels, that is, they form osteons - structural and functional units of lamellar bone as an organ. In addition, there are external and internal surrounding and intercalary plates of the tubular bone (see below).
Regeneration. Bone tissue regeneration involves deterministic osteogenic elements in the periosteum, bone marrow mechanocytes, which multiply and differentiate into osteoblasts. By producing intercellular substance, osteoblasts differentiate into osteocytes and form reticulofibrous bone tissue. In addition, adventitial cells of the fibrous connective tissue of the periosteum also take part in the regeneration of bone tissue. However, their differentiation largely depends on the microenvironment, extra-tissue and extra-organ factors (for example, on the reposition of fragments, immobility of fragments, oxygenation of the fracture site, etc.).
Differentiation of adventitial cells possible in three directions: osteogenic, chondrogenic, fibroblastic. This determines the ratio various types tissues in the regenerate. With predominantly osteoblastic histogenesis, reticulofibrous bone tissue is formed, which is gradually remodeled to form bone tissue resembling lamellar tissue in its structure.
Bone tissue contains cells that produce intercellular substance, in which collagen fibers predominate. A small volume is occupied by the main (adhesive) substance. Its cellular composition is the same, represented by osteoblasts - cells that form bone tissue. These are large, round-shaped cells with a round nucleus, with a well-developed protein synthesizing apparatus, and produce intercellular substance (collagen fibers). The number of these cells is large in a growing organism during regeneration. Osteocytes are also classified as bone tissue cells. They have a thin body and long thin processes that lie in the bone canaliculi, anastomose with the processes of other cells and transport tissue fluid through the bone canaliculi. There are also osteoclasts - cells that destroy bone tissue. They develop from blood monocytes and belong to the macrophage system. These are large, multinucleated cells with a well-developed lysosomal apparatus. There are microvilli on one surface of the cell. Lysosomal enzymes are secreted into the microvilli area and break down the protein matrix, which leads to the release of calcium and its leaching from the bone.
Bone tissues differ in the structure of the intercellular substance. In coarse bone tissue, collagen fibers form bundles that intertwine. Osteocytes are located between the fibers, but an adult has few thin bones. In lamellar bone tissue, collagen fibers run parallel to each other, are tightly glued together and form bone plates. The strength of bone tissue is ensured by the fact that the plates run at different angles. Osteocytes are located between the plates. Their processes penetrate the bone plates in all areas.
Lamellar bone tissue forms compact bone. It contains osteons and a spongy part where osteons are absent.
The diaphysis of the tubular bone is built of compact bone tissue. On the outside, the diaphysis is covered with periosteum (periosteum), its outer layer consists of denser fibrous tissue, and the inner layer is looser and contains fibroblasts and osteoblasts. Some of the collagen fibers go into the bone substance, so the periosteum is tightly connected to the bone. It contains a large number of receptors and blood vessels are located here.
The diaphysis is built of lamellar bone tissue. On the outside there is a layer of large bone plates that run concentrically along the diameter of the entire bone. Next, the inner layer of common plates is isolated, and from the inside lies the endosteum, consisting of loose connective tissue containing blood vessels. Between them there is a wide middle osteogenic layer. It contains osteons - the structural and functional units of bone. Osteons are located along the axis of the diaphysis and consist of concentric bone plates of different diameters. Inside each osteon there is an osteon canal, which contains a blood vessel. Between the osteons are the remains of bone plates - these are the remains of osteons. Normally, osteons in humans are gradually destroyed and new osteons are formed. Osteocytes are located between the bone plates of all layers, and their processes penetrate the bone plates and create a branched network of tubules. The blood vessels of the periosteum enter the osteons through perforating channels, go along their channels, anastomose with each other and deliver nutrients into the osteon canal. From there, calcium phosphates very quickly spread through the bone tubules to all parts of the bone.