Bone tissue. Bones

Bone develops from the mesenchyme and is a form of connective tissue in which the intercellular substance is calcified. The intercellular substance consists of a basic substance, in which fibers and inorganic salts are located. Fibers such as collagen fibers of connective tissue are called ossein. The fibers and the main substance between them are impregnated with calcium, phosphorus, magnesium, etc. salts, which form complex compounds.
In the intercellular substance there are cavities connected by the thinnest bone tubules. In these cavities lie osteocytes - process cells, incapable of mitosis, with weakly expressed organelles. The processes of osteocytes penetrate the tubules, which are of great importance in the delivery nutrients cells and the main substance. The tubules are connected to the channels that run inside the bone and contain blood vessels, which provides a pathway for metabolism between osteocytes and blood.
In addition to osteocytes, osteoblasts are found in bone tissue. Their cytoplasm is basophilic and contains a large amount of RNA. Organelles are well developed. Osteoblasts form bone tissue - by secreting the intercellular substance and walled up in it, they turn into osteocytes. Accordingly, in the formed bone, osteoblasts are found only in areas of growth and regeneration of bone tissue.
Another form of bone cells are osteoclasts - large multinucleated cells. Their cytoplasm contains a large number of lysosomes. These cells form microvilli directed towards the micro focus of bone or cartilage destruction.
Osteoclast secretes enzymes, which can explain the dissolution of bone substance. These cells are actively involved in bone destruction. With pathological processes in bone tissue, their number increases sharply. They are also important in the process of bone development: in the process of building the final shape of the bone, they destroy calcified cartilage and even newly formed bone: "correcting" its primary shape. In the process of bone formation, blood vessels are actively involved, providing the formation of an osteogenic site.
Bone tissue builds the skeleton and therefore has a supporting function. The skeletal material is strong only with a combination of organic and inorganic components of the bone (removal of organic matter makes the bone fragile, inorganic - softness). Bones also take part in metabolism, because they are a kind of depot of calcium, phosphorus and other substances.
Bone tissue, despite its strength and density, constantly renews its constituent substances, there is a restructuring of the internal structure of the bone and even a change in its external shape.
There are two types of bone tissue: coarse-fibrous and lamellar (Fig. 25, a, b).
Coarse bone... In this bone, in the main substance, powerful bundles of ossein fibers pass in different directions. Osteocytes are also located without a certain orientation. The bones of the skeleton of fish and amphibians are built from such tissue. In adult higher vertebrates, coarse-fibrous bone is found in places where the cranial sutures are overgrown and tendons are attached to the bone.
Lamellar bone... Of lamellar bone tissue is built most of skeleton of an adult. The diaphysis of the tubular bone consists of three layers - a layer of external general plates, a layer of Haversian systems (osteons) and a layer of internal general plates. The outer general plates are located under the periosteum; the inner ones are located on the side of the bone marrow. These plates cover the entire bone, forming a concentric lamination. Through the general plates, channels pass into the bone into which blood vessels pass. Each plate is a characteristic basic bone substance, in which bundles of ossein (collagen) fibers run in parallel rows. Osteocytes lie between the plates.

a - coarse-fibrous: I - bone cells (osteocytes) - 2 - intercellular substance - b - lamellar: I - osteon, 2 - internal general plates, 3 - external general plates, 4 - osteon (Haversian) canal.

Video: Histological preparation "Rough-fibrous bone tissue"

In the middle layer, the bony plates are arranged concentrically around the canal, where the blood vessels pass, forming an osteon (Haversian system). Osteon is like a system of cylinders inserted into one another. This construction gives the bone extreme strength. In two adjacent plates, bundles of ossein fibers run in different directions, almost at right angles to each other. Intercalated (intermediate) plates are located between the osteons. These are parts of the former osteons, evidence of active remodeling of bone tissue. The periosteum is a fibrous connective tissue containing osteoblasts, blood vessels, and nerve endings. Osteoblasts in bone fractures are activated and take part in bone formation.

Plan:

1. Sources of development, morphofunctional characteristic and structural features, blood supply, regeneration, age changes varieties of cartilage tissue.

2. Sources of development, morphofunctional characteristics of cells and intercellular substance, structural features, regeneration, age-related changes in the varieties of bone tissue.

Skeletal tissue - this is the 3rd group in the fuel assembly system and mainly perform a support-mechanical function.

Knowledge histological structure, the features of the regeneration of skeletal tissues are normally necessary for students to understand and master the mechanisms of pathological processes in various diseases skeletal tissues that you will study in other departments. Skeletal tissue diseases are quite common:

Mechanical damage - fractures;

Metabolic diseases (example: Ca ++ metabolic disorders;

Neoplasms emanating from skeletal tissues.

For you, as for future dentists, this topic is also of undoubted interest:

1. The main area of \u200b\u200byour medical activity - the dentoalveolar apparatus includes as a component - bone tissues, and pathological processes often affect these bone tissues.

2. Yes, and such hard tooth tissues as dentin and cement according to the classification are the 3rd subgroup of skeletal tissues called dentinoid tissues.

Cartilage and bone tissues form skeletal tissues that perform mainly a musculoskeletal function. In addition to the musculoskeletal, these tissues also perform the following functions:

1.protective (mechanical protection of the chest and abdominal cavity);

2. participation in mineral metabolism, especially in the exchange of Ca ++.

Skeletal tissue classification:

1. Cartilage tissue:

a) hyaline cartilage;

b) elastic cartilage;

c) collagen-fibrous cartilage.

2. Bone tissue:

a) fine-fibrous (lamellar) bone tissue;

b) reticulofibrous (coarse-fibrous) bone tissue.

General morphological and functional characteristics of cartilage tissues:

Cartilage tissue, like any connective tissue, consists of cells and intercellular substance. Cartilage cells are represented by chondroblastic differentials:

1. Stem cell

2. Half-stem cage

3. Chondroblast

4. Chondrocyte

5. Chondroclast

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

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

Chondrocytes - the main cells of cartilage tissue, located in the deeper layers of cartilage in cavities - lacunae. X / cytes can divide by mitosis, while the daughter cells do not diverge, remain together - so-called isogenic groups are formed. Initially, they lie in one common lacuna, then an intercellular substance is formed between them, and each cell of this isogenic group has its own capsule. X / cytes are oval-rounded cells with basophilic cytoplasm. Under an electron microscope, granular EPS, Golgi complex, mitochondria, i.e. protein-synthesizing apparatus, because the main function of x / cytes is the production of the organic part of the intercellular substance of the cartilage tissue. The growth of cartilage due to the division of x / cytes and the production of intercellular substance by them provides interstitial (internal) growth of cartilage.

In cartilage tissue, in addition to the cells that form the intercellular substance, there are also their antagonists - the destroyers of the intercellular substance - these are chondroclasts (can be attributed to the macrophagic system): rather large cells, there are many lysosomes and mitochondria in the cytoplasm. The function of x / clasts is the destruction of damaged or worn out areas of cartilage.

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

GAG (chondroetin sulfates, keratosulfates, hyaluronic acid);

PG (protein + GAG);

The intercellular substance is highly hydrophilic, the water content reaches 75% of the mass of the cartilage, which determines the high density and turgor of the cartilage. Cartilage tissues in the deep layers do not have blood vessels; nutrition is carried out diffusely due to the vessels of the perichondrium.

Perichondrium is the layer of connective tissue that covers the surface of the cartilage. In the perichondrium, the outer fibrous layer (from dense unformed SDM with a large number of blood vessels) and the inner cell layer are isolated, containing a large number of stem, semi-stem cells and f / blasts.

We considered general principle the structure of cartilage tissue. How do 3 types of cartilage differ from each other? The differences mainly relate to the structure of the intercellular substance:

Hyaline cartilage - covers all articular surfaces of bones, is contained in the sternal ends of the ribs, in the airways. The main difference between hyaline cartilage and other cartilage is in the structure of the intercellular substance: the intercellular substance of hyaline cartilage in preparations stained with hematoxylin-eosin seems homogeneous, without fibers. In fact, there is a large number of collagen fibers in the intercellular substance, whose refractive index is the same as the refractive index of the main substance; therefore, collagen fibers are not visible under a microscope, i.e. they are disguised. The second difference between hyaline cartilage is that there is a clearly defined basophilic zone around the isogenic groups - the so-called territorial matrix. This is due to the fact that x / cytes secrete a large amount of GAGs with an acidic reaction; therefore, this area is colored with basic paints, i.e. basophilic. Weakly oxyphilic areas between territorial matrices are called interterritorial matrix.

Elastic cartilage available in auricle, epiglottis, horn-shaped and wedge-shaped cartilages of the larynx. The main difference between elastic cartilage is that in the intercellular substance, in addition to collagen fibers, there is a large number of randomly located elastic fibers, which gives elasticity to the cartilage. Elastic cartilage has a lower content of lipids, chondroetin sulfates and glycogen. Elastic cartilage is not calcified.

Fibrous cartilagelocated in the places of attachment of tendons to bones and cartilage, in the symphysis and intervertebral discs. In structure, it occupies an intermediate position between the densely formed connective and cartilaginous tissue. Difference from other cartilage: in the intercellular substance there are much more collagen fibers, and the fibers are oriented in an oriented manner - they form thick bundles, clearly visible under a microscope. X / cytes more often lie singly along the fibers, without forming isogenic groups.

C O S T N Y E T K A N I

Bone tissue consists of cells and intercellular substance. Bone cells include osteogenic stem and semi-stem cells, osteoblasts, osteocytes and osteoclasts.

Stem cells - these are reserve cambial cells located in the periosteum. Semi-stem cells - cells with high proliferative activity, have a developed synthetic apparatus.

Osteoblasts - these are cells that form bone tissue, i.e. functionally, the main cells of bone tissue. Localized mainly in the periosteum. They have a polygonal shape, weakly processes cells can be found. The cytoplasm is basophilic; granular EPS, lamellar complex and mitochondria are well deposited under an electron microscope. Function: production of the organic part of the intercellular substance, i.e. proteins of ossein fibers and osseomucoid. During maturation, osteoblasts turn into osteocytes.

Osteocytes- in terms of quantitative composition, the most numerous cells of bone tissue... These are process cells that lie in bone cavities - lacunae. The cell diameter reaches 50 microns. The cytoplasm is weakly basophilic. Organoids are poorly developed (granular EPS, PC and mitochondria). Do not share. Function: take part in the physiological regeneration of bone tissue, produce the organic part of the intercellular substance. The thyroid hormone calcitonin has a stimulating effect on osteoblasts and osteocytes - the synthesis of the organic part of the intercellular substance increases and the deposition of calcium increases, while the concentration of calcium in the blood decreases.

Osteoclasts - these are large cells, almost 2 times larger than osteocytes, their diameter reaches 100 microns. Osteoclasts are specialized macrophages, formed by the fusion of many macrophages of hematogenous origin, therefore they contain 10 or more nuclei. In osteoclasts, lysosomes and mitochondria are well expressed. Function - bone destruction... Osteoclasts release CO2 and the enzyme carbonic anhydrase; CO2 is bound by H2O (the reaction is catalyzed by carbonic anhydrase) and carbonic acid H2CO3 is formed; carbonic acid reacts dissolves calcium salts, dissolved calcium is washed out into the blood. The organic part of the intercellular substance is lysed by the proteolytic enzymes of osteoclast lysosomes. Osteoclast function is stimulated by parathyriocalcitonin of the parathyroid gland.

The intercellular substance of bone tissue consists of:

1. Inorganic compounds (phosphate and carbonate calcium salts) - make up 70% of the intercellular substance.

2. The organic part of the intercellular substance is represented by collagen (synonym - ossein) fibers and an amorphous adhesive mass (osseomucoid) - is 30%.

The ratio of the organic and inorganic parts of the intercellular substance depends on age: in children, the organic part is slightly more than 30%, and the inorganic part is less than 70%, therefore their bones are less strong, but more flexible (not brittle); in old age, on the contrary, the proportion of the inorganic part increases, and the organic part decreases, so the bones become harder, but more brittle.

In contrast to cartilage tissue, there are more blood vessels in the bone tissue: available both in the periosteum and in the deep layers of the bone.

Bone as an organ is covered by the periosteum... It distinguishes between the outer fibrous and inner cell layers. In the periosteum there are a lot of blood vessels, stem and semi-stem osteogenic cells, osteoblasts. The function of the periosteum is nutrition and bone regeneration.

Histological difference tfibrous and reticulofibrous bones consists in the spatial organization (structure) of the intercellular substance, more precisely, in the arrangement of the ossein fibers:

1. In fine-fibered bone tissue, ossein fibers are located in the same plane parallel to each other and are glued together with an osseomucoid and calcium salts are deposited on them - ie. form plates, therefore, fine-fibrous bone tissue is otherwise called lamellar bone tissue. The direction of the ossein fibers in 2 adjacent plates are mutually perpendicular, which gives special strength to this fabric. Osteocytes lie between the bone plates in the lacunae cavities. If we consider the tubular bone as an organ, then it is distinguished:

1) Periosteum (periosteum).

2) Outdoor common (general) plates - bone plates surround the bone along the entire perimeter, and between them there are osteocytes.

3) Osteon layer... Osteon ( Haversian system) is a system of 5-20 cylinders of bone plates, concentrically inserted into each other. In the center of the osteon is a blood capillary. Osteocytes lie between the bony plate-cylinders in the lacunae. The gaps between adjacent osteons are filled with intercalation plates - these are the remnants of decaying old osteons that were here before these osteons.

4) Internal general (general) plates (similar to the outer ones).

5) Endoost - structurally similar to the periosteum.

Regeneration and growth of bone in thickness is carried out due to the periosteum and endosteum.

All tubular bones, as well as most of the flat bones, are histologically fine-fibrous bone.

2. Reticulofibrous bone tissue is present in the cranial sutures, in the places of attachment of tendons to the bones, in the embryonic period, at the beginning, at the site of the cartilaginous model of the future bone, reticulofibrous bone is formed, which then becomes fine-fibrous. Rough-fibrous (reticulofibrous) bone is also formed when bones are fused after a fracture, i.e. at callus... The main difference between reticulofibrous bone tissue is in the arrangement of ossein fibers in the intercellular substance - the fibers are arranged randomly, irregularly, stick together with an osseomucoid and calcium salts are deposited on them. Osteoblasts and osteocytes are also located in the lacunae. Reticulofibrous bone is less strong.

Regulation of calcium exchange between bone tissue and blood:

1. Hormonal regulation:

1) parathyriocalcitonin - washes out of the bones, increases in the blood;

2) calcitonin - Ca ++ decreases in the blood, it is deposited in the bones;

3) mineralocorticoids from the adrenal glands.

2. Vitamins:

1) vit. D - enhances absorption of Ca ++ in the intestine and enhances deposition in bones;

2) vit. C - reduces the content of Ca ++ in bones;

3) vit. A - calcium is washed out of the bones into the blood.

Bone tissue consists of cells and solid intercellular substance containing inorganic compounds; performs the function of support, participates in trophic and metabolic processes, provides mechanical protection of organs of the central nervous system and chest cavity. In the red bone marrow, hematopoiesis and cell differentiation are carried out immune system... Bone tissue contains three types of cells: osteoblasts, osteocytes, osteoclasts. Osteoblasts (from lat. os - bone; blastos - sprout) - poorly differentiated cells that produce organic elements of the intercellular substance of bone tissue. Osteocytes (from lat. os - bone; cytus - cell) are located in special cavities of the intercellular substance - lacunae (from lat. lacuna - cavity). The cells have the shape of a flattened oval corresponding to the lacuna, they are interconnected by numerous processes located in the bone tubules. Osteoclasts (from lat. os - bone; classis - divide, crush, destroy) - "bone crushers" - large, multinucleated cells, located on the surface of bone tissue in areas of resorption. The surface facing the destroyed bone has a large number of thin, densely spaced branching processes, which together form a corrugated structure. Here, the synthesis of hydrolytic enzymes involved in the processes of bone destruction takes place. The intercellular substance of bone tissue consists of osein (collagen) fibers and calcified amorphous substance, with mineral substances accounting for 65-70% of dry mass.

In accordance with the structural organization, coarse and fine fibrous bones are distinguished; the former develop from the mesenchyme at the site of the mesenchyme, the latter from the mesenchyme at the site of the cartilaginous tissue. Rough-fibrous bone tissue is characterized by the disordered orientation of coarse bundles of osein fibers. This tissue is characteristic of bones early stage ontogenesis, in the postembryonic period occurs in minor parts of the body - dental alveoli, skull bones near bone sutures, bone labyrinth inner ear, areas of attachment of tendons and ligaments. Thin-fibrous (lamellar) bones are characterized by the fact that thin axial fibers, located in parallel, form layers - bone plates, adjacent bone plates have different orientations of fibrils. In the plates, cell cavities are regularly located - lacunae, in which bone cells and processes present in the bone tubules are located. Depending on the position of the bone plates, a compact and cancellous substance is distinguished. In a compact, or dense substance, the bone plates are strongly pressed together. The spongy substance is found in the epiphyses of the tubular and in the inner regions of the flat bones. The spongy substance has a loose, but very strong structure, consists of bony plates arranged in strict accordance with the laws of mechanics, which provides this part of the bone with greater resistance to fracture and considerable lightness. In the cells between the beams of the spongy substance, the bone marrow and blood vessels are located.

The preparation "Bone cells of the herring gill cover" (no painting). The operculum bone of the fish is washed, dried and imprinted in balm without coloring. With this treatment, the structure of the intercellular substance on the preparation is not revealed and the cells are not preserved, but the bone cavities in which the cell bodies were located are clearly visible. Bone cells are connected to each other through processes located in the bone tubules, the cells have the shape of a flattened oval, corresponding to the bone cavity (lacuna) (Fig. 34).

Figure: 34

The drug "Decalcified thigh bone of a cat" (staining with thionine and picric acid). At low magnification of the microscope (x10), you can see and sketch the ordered structure of the compact substance of the tubular bone in a cross section. Outside, the bone is surrounded by the periosteum (periosteum) - a sheath of unformed connective tissue, with a predominance of dense fibrous material. The outer, denser layer is built from a binding of thick bundles of collagen fibers, here are blood vessels and nerves that are sent to the deep, inner parts of the bone. The inner layer of the periosteum contains thin bundles of collagen, elastic fibers and is characterized by the presence of a large number of cambial cells called osteoblasts, which carry out bone growth. From the periosteum, bundles of collagen fibers, called perforating (Sharpeevsky), penetrate deep into the bone tissue, such connecting fibers are especially abundant in the areas of tendon attachment. The perforating fibers provide the mechanical strength of the connection between the periosteum and the bone. Under the periosteum in the diaphysis, a compact substance is revealed, formed by three layers: the outer layer of the general general bone plates, the osteonic layer, the inner layer of the general general bone plates (Fig. 35).

Figure: 35and - compact substance; b - osteon structure

The outer layer of common general bone plates consists of osteocytes arranged in parallel rows and forming several thin-walled tubular plates, nested one inside the other. This layer surrounds, like a case, the bone from all sides; in some areas, the layer is pierced by Volkman canals, through which blood vessels enter the bone from the periosteum.

The osteonic layer is formed by numerous osteons. Osteon is a structural and functional unit of bone tissue. In the center of the osteon is the central Haversian blood canal, surrounded by bony plates arranged in concentric rows. In the spaces between the individual osteons, interstitial bone plate systems (or interstitial systems of bone plates) are found that are not directly connected to blood vessels or Haversian canals and are the remnants of destroyed osteons.

The inner layer of the common general bone plates has a structure similar to that of the outer layer of the common plates.

In the center of the tubular bone is the medullary cavity, lined with loose fibrous connective tissuecalled endoostom. In the bone marrow cavity is the red and yellow bone marrow.

Control questions

• 1. Give the structural and functional characteristics of the cells and intercellular substance of bone tissue.
• 2. Give the classification of the bone tissue.
• 3. How do bone cells differentiate?
• 4. What is the function of the basic substance of bone tissue?
• 5. What are the distinctive features of bone cells.
• 6. What are the main stages of bone tissue differentiation?
• 7. What are the features of osteoblasts, osteocytes, osteoclasts?
• 8. Describe the concepts of "osteon", "insertion bone plates", "Haversian canal".
• 9. What is the periosteum and endosteum?

Bone tissue is a specialized type of connective tissue with a high mineralization of the intercellular substance. The bones of the skeleton are built from these tissues.

Bone development (osteogenesis)

Distinguish:

A) Embryonic osteogenesis.

In the embryo, bone tissue develops from the mesenchyme in two ways:

1). Direct osteohistogenesis (directly from the mesenchyme). In this way, coarse-fibrous (reticulofibrous) bone tissue develops during the formation of flat bones. This process is observed mainly during the first month of intrauterine development and proceeds in four stages:

a) the stage of formation of an osteogenic island. There is a focal multiplication of mesenchymal cells and the formation of vessels in this focus (vascularization);

b) osteoid stage. Differentiation is carried out from the mesenchymal cells of osteoblasts located on the surface of the islet and osteocytes - in the depth of the islet. Osteoblasts form an oxyphilic intercellular substance with collagen fibrils;

c) stage osteoid calcification. At this stage, the impregnation of the intercellular substance with calcium salts (hydroxyapatite crystals). As a result of calcification, bone beams, or beams, are formed, the spaces between which are filled with fibrous connective tissue with blood vessels passing through it.

d) stages of restructuring of coarse-fibrous bone tissue into lamellar tissue, associated with the growth of capillaries and the formation of osteons.

2). Indirect osteohistogenesis (from the mesenchyme at the site of the previously developed cartilaginous model of the bone) - at the 2nd month of embryonic development in the places of the future tubular bones, a cartilaginous primordium (hyaline cartilage covered with perichondrium) is laid from the mesenchyme, which very quickly takes the shape of the future bone.

B) Postembryonic osteohistogenesis - carried out during regeneration.

Structure.Bone tissue consists of:

A. Cells:

1) Osteocytes - the predominant number of bone cells that have lost the ability to divide. They have a process-like shape and are poor in organelles. Are located in bone cavities, or lacunas, which follow the contours of the osteocyte. The processes of the osteocyte penetrate into the tubules of the bone and play a role in its trophism.

2) Osteoblasts -young cells that create bone tissue. In the bone, they are found in the deep layers of the periosteum, in the places of formation and regeneration of bone tissue. These cells are various shapes (cubic, pyramidal or angular), contain one nucleus, and in the cytoplasm there is a well-developed granular endoplasmic reticulum, mitochondria and the Golgi complex.

3) Osteoclasts - cells that can destroy calcified cartilage and bone. They are large (their diameter reaches 90 microns), contain from 3 to several tens of nuclei . The cytoplasm is weakly basophilic, rich in mitochondria and lysosomes. The granular endoplasmic reticulum is relatively poorly developed.

B. Intercellular substance,consisting of:

basic substance, which contains a relatively small amount of chondroitinsulfuric acid and a lot of citric and other acids that form complexes with calcium (amorphous calcium phosphate, hydroxyapatite crystals).

collagen fibersforming small beams.

Depending on the location of collagen fibers in the intercellular substance, bone tissue classified on:

1. Reticulofibrous bone tissue. In it, collagen fibers are disordered. Such tissue is found mainly in embryos. In adults, it can be found at the site of the cranial sutures and where the tendons attach to the bones.

2. Lamellar bone tissue. It is the most common type of bone in the adult body. It consists of bone platesformed by bone cells and a mineralized amorphous substance with collagen fibers oriented in a certain direction. In adjacent plates, the fibers usually have a different direction, due to which a greater strength of the lamellar bone tissue is achieved. The compact and spongy substance of most of the flat and tubular bones of the skeleton is built from this tissue.

Compact substance of tubular bone.The external system of common bone plates is located under the periosteum. The main volume of the compact part of the bone is occupied by the layer of osteons. From the inside to the layer of osteons, the internal system of common bone plates adjoins. Inset on the left is osteon.

Lamellar bone tissue(compact substance of the diaphysis of the tubular bone, cross section). Osteons (1) and intercalated bone plates (6) are visible. In the osteon, the osteon canal (2), concentric bone plates (3), bony cavities or bodies (lacunae containing osteocytes) (4), and the cleft line (5) are clearly visible. Staining according to Schmorl.

Lamellar bone tissue(compact substance of the diaphysis of the tubular bone, cross section). Concentric bone plates (5) form the osteon. Small blood vessels pass through the osteon canal (1). Bone corpuscles (lacunae) (2) are located between the plates, from which the bone tubules depart (3). Osteon is bounded by the cleavage line (4). Inserted bone plates (6) connect adjacent osteons. Staining according to Schmorl.

Lamellar bone tissue(compact substance of the diaphysis of the tubular bone, longitudinal section). Osteons are oriented along the long axis of the tubular bone. On a longitudinal section, the osteon canals are parallel. The characteristic organization of the compact substance is visible: bone bodies (lacunae) (1) are located between the bone plates (3); lacunae with bone tubules extending from them (2) communicate with the osteon canal (4). Staining according to Schmorl.

Lamellar bone tissue(compact substance of the diaphysis of the tubular bone, longitudinal section). The osteon canal (1) is surrounded by several layers of bone plates (4). The plates are separated by bone corpuscles (lacunae) (2), in which the osteocytes are located. Numerous thin bone tubules (3), containing processes of osteocytes, extend from each lacuna. The osteon canal, lacunae and bone tubules make up the lacunar-tubular system. Staining according to Schmorl.