BONE TISSUES
Structure: cells and intercellular substance.
Kinds bone tissue: 1) reticulofibrous, 2) lamellar.
Also, bone tissues include tissues specific to teeth: dentin, cementum.
in bone tissue 2 differenton cells: 1) osteocyte and its precursors, 2) osteoclast.
Differenton osteocyte : stem and semi-stem cells, osteogenic cells, osteoblasts, osteocytes.
Cells are formed from poorly differentiated mesenchymal cells; in adults, stem and semi-stem cells are found in the inner layer of the periosteum; during bone formation, they are located on its surface and around the intraosseous vessels.
osteoblasts capable of dividing, arranged in groups, have an uneven surface and short processes connecting them with neighboring cells. The synthetic apparatus is well developed in the cells, because osteoblasts are involved in the formation of intercellular substance: they synthesize matrix proteins (osteonectin, sialoprotein, osteocalcin), collagen fibers, enzymes (alkaline phosphatase, etc.).
The function of osteoblasts: the synthesis of intercellular substance, the provision of mineralization.
The main factors activating osteoblasts are: calcitonin, thyroxine (thyroid hormones); estrogens (ovarian hormones); vitamins C, D; piezo effects that occur in the bone when compressed.
Osteocytes - osteoblasts immured in mineralized intercellular substance. Cells are located in gaps - cavities of the intercellular substance. With their processes, osteocytes are in contact with each other; there is an intercellular fluid around the cells in the lacunae. The synthetic apparatus is less developed than in osteoblasts.
Function of osteocytes: maintenance of homeostasis in bone tissue.
Osteoclast. Differenton osteoclast includes monocyte differon (develops in the red bone marrow), then the monocyte leaves the bloodstream and transforms into a macrophage. Several macrophages fuse to form a multinucleated symplast osteoclast. The osteoclast contains many nuclei and a large volume of cytoplasm. Polarity is characteristic (the presence of functionally unequal surfaces): the cytoplasmic zone adjacent to the bone surface is called the corrugated border, there are many cytoplasmic outgrowths and lysosomes.
Functions of osteoclasts: destruction of fibers and amorphous bone substance.
Bone resorption osteoclast: the first stage is attachment to the bone with the help of proteins (integrins, vitronectins, etc.) to ensure sealing; the second stage is the acidification and dissolution of minerals in the area of destruction by pumping hydrogen ions with the participation of ATPases of the membranes of the corrugated edge; the third stage is the dissolution of the organic substrate of the bone with the help of lysosome enzymes (hydrolases, collagenases, etc.), which the osteoclast removes by exocytosis to the destruction zone.
Factors activating osteoclasts: parathyroid hormone parathyrin; piezo effects that occur in the bone when it is stretched; weightlessness; absence physical activity(immobilization), etc.
Factors that inhibit osteoclasts: thyroid hormone calciotonin, ovarian hormones estrogen.
intercellular substance of bone consists of collagen fibers (collagen I, V types) and the main (amorphous) substance, consisting of 30% organic and 70% inorganic substances. Organic bone substances: glycosaminoglycans, proteoglycans; inorganic substances: calcium phosphate, mainly in the form of hydroxyapatite crystals.
The largest volume in an adult is lamellar bone tissue, which is compact and spongy. On the surface of the lamellar bones in the area of attachment of the tendons, as well as in the sutures of the skull, there is reticulofibrous bone tissue.
Bone as an organ consists of several tissues: 1) bone tissue, 2) periosteum: 2a) outer layer - PVNST, 2b) inner layer - RVST, with blood vessels and nerves, as well as stem and semi-stem cells.
1. RETICULOFIBROSIS (COARSE FIBER) BONE TISSUE
This tissue is formed in human fetuses as the basis of bones. In adults, it is slightly represented and is located in the sutures of the skull at the points of attachment of the tendons to the bones.
Structure: osteocytes and intercellular substance in which bundles of collagen mineralized fibers are arranged randomly. Osteocytes are found in bone cavities. From the surface, parts of the bone are covered with periosteum, from which reticulofibrous bone tissue receives nutrients by diffusion.
LAMINATE (FINE) BONE TISSUE – the main type of bone tissue in the adult body. Structure: osteocytes and intercellular substance consisting of fibers (collagen or ossein) and amorphous substance. The intercellular substance is represented by plates with a thickness of 3-10 microns. In the plate, the fibers are arranged parallel to each other, the fibers of neighboring plates lie at an angle to each other. Between the plates are the bodies of osteocytes in the gaps, and the bone tubules with processes of osteocytes penetrate the plates at a right angle.
Types of lamellar bone tissue. Made of lamellar bone tissue compact and spongy substance most flat and tubular bones.
in spongy matter bone plates are straight, are part of trabeculae - a complex of 2-3 parallel plates. Trabeculae delimit cavities filled with red bone marrow.
AT compact bone along with straight plates there are concentric plates that form osteons.
Histological structure of the tubular bone as an organ. The tubular bone consists of a diaphysis - a hollow tube consisting of a strong compact bone, and epiphyses - the expanding ends of this tube, built of spongy substance.
Bone as an organ consists of lamellar bone tissue, outside and from the side of the bone marrow cavity, it is covered with connective tissue membranes (periosteum, endosteum). The bone cavity contains red and yellow bone marrow, blood and lymphatic vessels and nerves.
In the bones are distinguished compact (cortical) substance bones and spongy (trabecular) substance, which are formed by lamellar bone tissue. Periosteum, or periosteum, consists of an outer (PVNST or PVOST) and an inner layer (RVST). The inner layer contains osteogenic cambial cells, preosteoblasts, and osteoblasts. The periosteum takes part in bone tissue trophism, development, growth and regeneration. Endost- the membrane covering the bone from the side of the bone marrow is formed by loose fibrous connective tissue, where there are osteoblasts and osteoclasts, as well as other PBST cells. The articular surfaces of the epiphyses do not have periosteum and perichondrium. They are covered with a type of hyaline cartilage called articular cartilage.
The structure of the diaphysis . The diaphysis consists of a compact substance (cortical bone), in which three layers are distinguished: 1) the outer layer of common plates; 2) the middle layer is osteon; 3) the inner layer of common plates.
The outer and inner common plates are straight plates, in which osteocytes will receive nutrition from the periosteum and endosteum. In the outer common plates there are perforating (Volkmann) canals, through which vessels enter the bone from the periosteum into the bone. In the middle layer, most of the bone plates are located in osteons, and between the osteons lie insert plates- remnants of old osteons after bone remodeling.
Osteons are structural units of the compact substance of the tubular bone. They are cylindrical formations, consisting of concentric bone plates, as if inserted into each other. In the bone plates and between them are the bodies of bone cells and their processes, passing in the intercellular substance. Each osteon is delimited from the adjacent osteon by a cleavage line formed by the ground substance. At the center of each osteon is channel (haversian channel), where blood vessels with RVST and osteogenic cells pass. The vessels of the osteon channels communicate with each other and with the vessels of the bone marrow and periosteum. On the inner surface of the diaphysis, bordering the medullary cavity, there are bony crossbars of the cancellous bone.
The structure of the epiphysis. The epiphysis consists of a spongy substance, the bone trabeculae (beams) of which are oriented along the load lines of force, providing strength to the epiphysis. The spaces between the beams contain red bone marrow.
Bone vascularization . Blood vessels form a dense network in the inner layer of the periosteum. From here, thin arterial branches originate, which supply the osteons with blood, penetrate into the bone marrow through the nutrient holes and form a supply network of capillaries passing through the osteons.
bone tissue innervation . In the periosteum, myelinated and unmyelinated nerve fibers form plexuses. Some of the fibers accompany the blood vessels and penetrate with them through the nutrient holes into the osteon channels and then reach the bone marrow.
Bone remodeling and renewal . Throughout a person's life, restructuring and renewal of bone tissue occurs. Primary osteons are destroyed and at the same time new ones appear, both in place of old osteons, and from the side of the periosteum. Under the influence of osteoclasts, the bone plates of the osteon are destroyed, and a cavity forms in this place. This process is called resorption bone tissue. In the cavity around the remaining vessel, osteoblasts appear, which begin to build new plates, concentrically layering on each other. This is how secondary generations of osteons occur. Between the osteons are the remains of destroyed osteons of previous generations - insert plates.
It should be noted that in weightlessness (in the absence of gravity and the forces of attraction of the Earth) the destruction of bone tissue by osteoclasts occurs, which is prevented in astronauts by physical exercises.
Age changes . With age, the total mass of connective tissue formations increases, the ratio of collagen types, glycosaminoglycans changes, and sulfated compounds become more numerous. In the endosteum of aging bone, the population of osteoblasts decreases, but the activity of osteoclasts increases, which leads to thinning of the compact layer and restructuring of the cancellous bone.
In adults, the complete change of bone formations depends on its size and for the hip is 7-12 years, for the rib 1 year. In the elderly, in women in menopause, there is a pronounced decalcification of the bones - osteoporosis.
The development of bone tissue in embryogenesis and in the postnatal period
The human embryo has no bone tissue by the beginning of organogenesis (3-5 weeks). In place of future bones are osteogenic cells or cartilage formations (hyaline cartilage). At the 6th week of embryogenesis, the necessary conditions(active development of the chorion - the future placenta, and germination of blood vessels with oxygen supply), and the development of bone tissue begins in embryogenesis, and then after birth (postembryonic development).
The development of bone tissue in the embryo is carried out in two ways: 1) direct osteogenesis- directly from the mesenchyme; and 2) indirect osteogenesis- in place of the cartilaginous bone model previously developed from the mesenchyme. Postembryonic development of bone tissue occurs during physiological regeneration.
direct osteogenesis characteristic in the formation of flat bones (for example, the bones of the skull). It is observed already in the first month of embryogenesis and includes three main stages: 1) formation of osteogenic islets from proliferating mesenchymal cells; 2) differentiation of cells of osteogenic islets into osteoblasts and the formation of an organic bone matrix (osteoid), while some of the osteoblasts turn into osteocytes; the other part of the osteoblasts is not the surface of the intercellular substance, i.e. on the surface of the bone, these osteoblasts will become part of the periosteum; 3) calcification (calcification) of the osteoid - the intercellular substance is impregnated with calcium salts; reticulofibrous bone tissue is formed; 4) restructuring and growth of the bone - old areas of coarse fibrous bone are gradually destroyed and new areas of lamellar bone are formed in their place; due to the periosteum, common bone plates are formed, due to the osteogenic cells located in the adventitia of the vessels of the bone, osteons are formed.
Bone development in place of a previously formed cartilage model (indirect osteogenesis). This type of bone development is characteristic of most bones of the human skeleton (long and short tubular bones, vertebrae, pelvic bones). Initially, a cartilaginous model of the future bone is formed, which serves as the basis for its development, and later the cartilage is destroyed and replaced by bone tissue.
Indirect osteogenesis begins in the second month of embryonic development, ends by the age of 18-25 and includes the following stages:
1) education cartilaginous bone model from the mesenchyme in accordance with the patterns of cartilage histogenesis;
2) education perichondral bone cuff: in the inner layer of the perichondrium, osteoblasts differentiate, which begin to form bone tissue; the perichondrium is replaced by the periosteum;
3) education endochondral bone in the diaphysis: the perichondral bone disrupts the nutrition of the cartilage, as a result, osteogenic islands appear in the diaphysis from the mesenchyme growing here with blood vessels. In parallel, osteoclasts destroy the bone with the formation of a bone marrow cavity;
4) education endochondral bone in the epiphysis;
5) formation epiphyseal plate growth in cartilage (metaepiphyseal cartilage): at the border of the epiphysis and diaphysis, chondrocytes gather in columns, as the growth of unchanged distal cartilage continues. In the column of chondrocytes, there are two oppositely directed processes: on the one hand, the reproduction of chondrocytes and the growth of cartilage ( columnar cells) in its distal section and in the periosseous zone, dystrophic changes ( vesicular chondrocytes).
6) restructuring of reticulofibrous bone tissue into lamellar: the old parts of the bone are gradually destroyed and new ones are formed in their place; due to the periosteum, common bone plates are formed, due to the osteogenic cells located in the adventitia of the vessels of the bone, osteons are formed.
Over time, in the metaepiphyseal plate of cartilage, the processes of cell destruction begin to prevail over the process of neoplasm; the cartilaginous plate becomes thinner and disappears: the bone stops growing in length. The periosteum ensures the growth of tubular bones in thickness by appositional growth. The number of osteons after birth is small, but by the age of 25 their number increases significantly.
Bone regeneration. Physiological regeneration of bone tissues and their renewal occur slowly due to osteogenic cells of the periosteum and osteogenic cells in the osteon canal. Post-traumatic regeneration (reparative) is faster. The sequence of regeneration corresponds to the scheme of osteogenesis. The process of bone mineralization is preceded by the formation of an organic substrate (osteoid), in the thickness of which cartilage beams can form (in case of impaired blood supply). Ossification in this case will follow the type of indirect osteogenesis (see the diagram of indirect osteogenesis).
Compact substance of tubular bone. Under the periosteum is the external system of common bone plates. The main volume of the compact part of the bone is occupied by a layer of osteons. From the inside, the internal system of common bone plates adjoins the osteon layer. Inset on the left: osteon.
lamellar bone tissue(compact substance of the diaphysis of a tubular bone, transverse section). Osteons (1) and intercalated bone plates (6) are visible. In the osteon, the osteon channel (2), concentric bone plates (3), bone cavities or bodies (lacunae containing osteocytes) (4), and cleavage line (5) are clearly visible. Schmorl stain.
lamellar bone tissue(compact substance of the diaphysis of a tubular bone, transverse section). Concentric bone plates (5) form the osteon. Small blood vessels pass through the osteon canal (1). Between the plates there are bone bodies (lacunae) (2), from which bone tubules extend (3). The osteon is limited by the cleavage line (4). Intercalated bone plates (6) connect adjacent osteons. Schmorl stain.
lamellar bone tissue(compact substance of the diaphysis of a tubular bone, longitudinal section). Osteons are oriented along the long axis of the tubular bone. On a longitudinal section, the osteon channels 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). Schmorl stain.
lamellar bone tissue(compact substance of the diaphysis of a tubular bone, longitudinal section). The osteon channel (1) is surrounded by several layers of bone plates (4). The plates are separated by bone bodies (lacunae) (2) in which osteocytes are located. Numerous thin bone tubules (3) containing processes of osteocytes depart from each lacuna. The osteon canal, lacunae, and bone tubules make up the lacunar-tubular system. Schmorl stain.
Lecture 24. Topic: “Lamellar bone tissue”. 1. 2. Plan: The structure of lamellar bone tissue (on the example of the structure of a tubular bone). Histogenesis of bone tissue at the site of cartilage. Regeneration.
Lamellar bone tissue, adult organisms can be spongy and compact. Lamellar spongy bone tissue consists of bone plates that go in different directions, forming bone proteins, crossbars corresponding to the direction of deformation forces. This is typical for the epiphyses of tubular bones. Lamellar compact bone tissue consists of bone plates that are closely adjacent to each other. It is observed in the diaphysis of tubular bones.
Structure. The structure of the tubular bone The outer layer of the diaphysis consists of several layers of bone plates, located parallel to the outer perimeter of the bone. This is a system of common external bone plates (1 layer). Layer 2 is the osteon system. Osteon are concentric layers of bone plates located around the central canal of the osteon or Haversian canal, in which the vessels and nerves pass. Between the osteons are the remnants of the former osteons, these are the so-called intercalated bone plates.
3 layer. The system of common internal bone plates that limit the medullary canal of the tubular bone. This system of internal bone plates is covered by the inner shell of the bone - the endosteum, consisting of osteoblasts and thin collagen fibers. Outside, the tubular bone is covered with a connective tissue sheath called the periosteum or periosteum.
From the side of the periosteum, blood vessels and nerves pass through the transverse or perforating canals into the central canals of the osteons. The periosteum is rich in collagen fibers, vessels and nerves, as well as cells: fibroblasts, osteoblasts and pericytes.
1. 2. 3. The strength of bone tissue is due to: Collagen fibers of adjacent bone plates are located at different angles to each other and some of the fibers pass from one bone plate to another. Bundles of collagen fibers are cemented by an amorphous intercellular substance - osteomucoid. The intercellular substance contains hydroxyapatite crystals in the form of needle-shaped particles with a thickness of 1.5 to 7.5 nm.
Development (histogenesis) of bone in place of cartilage. 1. 2. 3. The tubular bones of the skeleton develop according to this type. In place of the cartilaginous bone model, blood vessels grow into its perichondrium (diaphase) and pericytes penetrate. From the surrounding mesenchyme in this area, osteoblasts are formed, which form an osteo-like tissue.
A - perichondral ossification B - endochondral ossification 4. This is how coarse fibrous bone tissue arises, which will form a bone ring (cuff) around the diaphysis. 5. This process is called perichondral or perichondral ossification. 6. With the help of osteoclast cells, the cartilage tissue inside the blank (model) is destroyed, which leads to the formation of cavities - lacunae. 7. In these gaps, osteoblasts are formed from mesenchymal cells and pericytes, which will take part in the formation of coarse fibrous bone tissue inside the cartilage. This is endochondral or intracartilaginous ossification.
8. Later, ossification occurs in the epiphyses of the tubular bones, except for the epiphyseal line, or the cartilaginous growth plate. 9. This line in a person does not ossify until the age of 23 - 25, and due to its bones grow in length. 10. In thickness, the bone grows until the advanced age of the body, since its growth is due to osteons, as well as the periosteum. 1 - ossification in the diaphysis 2 - formation of endochondral bone 3, 4 - ossification in the epiphase region
Regeneration (reparative). 1. 2. 3. In the periosteum and endosteum, 2 days after injury, mass reproduction of pericytes and the formation of osteoblasts are observed. Osteoblasts are young coarse-fibered bone tissue that connects bone fragments. Transformation of coarse fibrous to lamellar bone tissue.
It has a thinner and more complex structure. It is based on bone plates, consisting of dense bundles of collagen fibrils. The beams have approximately the same thickness and always go in a certain direction. Between the fiber bundles are osteocytes, strongly flattened and elongated. A characteristic feature of lamellar bone tissue is that the fibrils in two adjacent plates have a different direction and are located at an angle to each other. Part of the fibrils passes from one plate to another, which determines their tight connection. Such complex structure achieve greater bone strength.
Chemical analysis shows that the intermediate consists of organic and inorganic compounds. The latter are much larger in number. General analysis shows that it contains: water - 50%, fat - 15.7%, other organic substances - 12.45%, salts - 21.85%.
From inorganic compounds, not counting water, the highest percentage make up phosphorus and calcium carbonate salts, giving complex compounds - hydroxyapatite crystals. On electron micrographs, the crystals look like needle-shaped particles, the length of which reaches 150 nm and a thickness of 1.5–7.5 nm. Crystal sizes increase with age. It is they who determine the hardness of the bone tissue. Crystals permeate the entire intermediate substance, settling on collagen fibrils.
If the bone is carefully ignited, then organic substances burn out and inorganic compounds remain, fragile, but retaining its shape. When bone is etched with inorganic acids, calcium salts become soluble, and a base remains that has the shape and structure of the bone. Such decalcified bone loses its hardness, bends easily, and can be cut with a knife.
With age, the amount of inorganic salts increases, so the bones of older people are more fragile and more easily fractured. The microscopic structure of the intermediate substance of bone tissue is determined by the location of collagen fibrils in it. Accordingly, a spongy and dense intermediate substance is distinguished.
The spongy substance is built more simply. The plates in it form crossbars of unequal thickness, intersecting with each other in different directions. The location of the crossbars is determined by mechanical conditions: the thicker ones, consisting of a large number of plates, are arranged so that the greatest pressure falls on their ribs. With this structure of the bone substance, the greatest strength is achieved with the least weight. The gaps between the crossbars are filled with red bone marrow. From the spongy substance, for example, the epiphyses of long tubular bones are built.
The dense substance located in the diaphysis of tubular bones has a more complex structure. The distribution of the plates here is determined by the direction of the blood vessels, which penetrate the bone in large numbers and are located mainly along its length. Vessels run in cavities called haversian canals. Around the latter, the bone plates are arranged in regular, ever-expanding circles, forming, as it were, cylinders inserted one into the other.
The entire system of plates with a Haversian canal in the middle is called the Haversian system or osteon. The tubular bone, richly supplied with blood vessels, consists of a large number of closely adjacent osteons, which are located along its long axis. In flat bones, osteons run parallel to their surface, while in vertebral bodies, they run perpendicular to their axis.
The gaps remaining between the osteons are filled with plates, which are called intercalary. From the outer surface, the tubular bones are covered by a system of external general plates. The internal surfaces of the bone cavities are lined with internal general plates. The location of the general plates, as well as the intercalary ones, is not associated with blood vessels.
In the bone substance there are vessels that are not covered with bone plates. Some of them enter the bone through the general plates, others connect the Haversian canals to each other, i.e. go radially. The distribution of spongy and dense matter in various bones is not accidental and is determined by the functional significance of the bone, the conditions of pressure, tension, etc.
The most common type of bone tissue in an adult organism. It consists of bone plates that contain fibrils. The plates can delaminate, and the fibrils of one plate can continue into neighboring ones. Creating a single fibrous base of the bone. Compact and spongy substance is built from this tissue in most flat and tubular bones.
Tubular bone tissue as an organ is mainly built from lamellar bone tissue, except for tubercles. From the outside, the bone is covered with periosteum, with the exception of articular surfaces epipheses covered with a type of hyaline cartilage.
44. Direct osteohistogenesis. The method of osteogenesis is characteristic for the development of coarse fibrous tissue during the formation flat bones, such as the integumentary bones of the skull. The process is observed mainly during the first month of intrauterine development. In the first stage- skeletal island formation- in the places of development of the future bone, focal reproduction of mesenchymal cells and vascularization of the skeletal island occur. In the second stage, which consists in the differentiation of islet cells, is formed oxyphilic intercellular substance with collagen fibrils- organic matrix of bone tissue. In the main substance, mucoproteins appear, cementing the fibers into one strong mass. Some cells differentiate into osteocytes, while others, located on the surface, differentiate into osteoblasts. Osteoblasts separate from each other. Gradually, these cells become "immured" in the intercellular substance, lose their ability to multiply and turn into osteocytes.
Third stage- calcification of the intercellular substance. At the same time, osteoblasts secrete the enzyme alkaline phosphatase, which breaks down the glycerophosphates contained in the peripheral blood into carbohydrate compounds.
One of the mediators of calcification is osteonectin- a glycoprotein that selectively binds calcium and phosphorus salts to collagen. As a result of calcification, bone crossbars, or beams. Then outgrowths branch off from these crossbars, connecting with each other and forming a wide network. By the time histogenesis is completed, along the periphery of the bone rudiment in the embryonic connective tissue, a large number of fibers and osteogenic cells.
Part of this fibrous tissue, adjacent directly to the bone crossbars, turns into periosteum, which provides trophism and bone regeneration. Further in the process of development, it is replaced by the secondary spongy bone of adults, which differs from the first in that it is built from lamellar bone tissue. - the fourth stage of osteogenesis.Bone plates are formed around blood vessels by differentiation of the mesenchyme adjacent to them. Above such plates, a layer of new osteoblasts is formed and new plates arise. Thus, bone cylinders are formed around the vessel, inserted one into the other. Since the appearance of osteons, reticulofibrous bone tissue ceases to develop and is replaced by lamellar bone tissue. From the side of the periosteum, common, or general, plates are formed, covering the entire bone from the outside. This is how flat bones develop.
45. Indirect osteohistogenesis. Bone development in place of cartilage those. indirect osteogenesis, begins in the diaphysis. The formation of the perichondriaal bone cuff is preceded by the growth of blood vessels with differentiation in the perichondrium, adjacent to the middle part of the diaphysis, osteoblasts, forming in the form of a cuff, first reticulofibrous bone tissue, then replaced by a lamellar one.
The formation of a bone cuff disrupts the nutrition of the cartilage. As a result, dystrophic changes occur in the center of the diaphyseal part of the cartilaginous rudiment. Chondrocytes vacuolize, their nuclei pyknotize, form vesicular chondrocytes . Cartilage growth in this place stops. Elongation of the perichondral bone cuff is accompanied by an expansion of the cartilage destruction zone and the appearance of osteoclasts- this leads to the appearance of foci of endochondral ossification. Thus, in the column of chondrocytes, I have two oppositely directed processes - reproduction and growth in the distal parts of the diaphysis and dystrophic processes in its proximal part.
Since the growth of the vasculature and the appearance of osteoblasts, the perichondrium turns into the periosteum. The diaphyseal cartilage is destroyed, elongated spaces appear in it, in which osteocytes “settle”, forming bone tissue on the surface of the remaining sections of calcified cartilage.