Nursing care for patients with neoplasms. Features of the organization of nursing care for cancer patients

Bone tissue forms the basis of the skeleton. It is responsible for the protection of internal organs, movement, and is involved in metabolism. Bone tissue also includes dental tissue. Bone is a hard and flexible organ. Its features continue to be studied. There are more than 270 bones in the human body, each of which performs its own function.

Bone tissue is a type of connective tissue. One is both ductile and resistant to deformation, durable.

There are 2 main types of bone tissue depending on its structure:

1. Coarse fiber. This is a denser, but less elastic bone tissue. In the body of an adult, it is very small. It is mainly found at the junction of bone with cartilage, at the junction of cranial sutures, as well as at the fusion of fractures. Coarse-fibrous bone tissue is found in large quantities during the period of human embryonic development. It acts as the rudiment of the skeleton, and then gradually degenerates into a lamellar one. The peculiarity of this type of tissue is that its cells are arranged randomly, which makes it denser.
2. Lamellar. Lamellar bone tissue is the main one in the human skeleton. It is part of all the bones of the human body. A feature of this tissue is the arrangement of cells. They form fibers, which in turn form plates. The fibers that make up the plates can be located at different angles, which makes the fabric strong and elastic at the same time, but the plates themselves are parallel to each other.

In turn, lamellar bone tissue is divided into 2 types - spongy and compact. Spongy tissue has the appearance of cells and is looser. However, despite the reduced strength, spongy tissue is more voluminous, lighter, and less dense.

It is the spongy tissue that contains the bone marrow involved in the hematopoietic process.

Compact bone tissue performs a protective function, so it is denser, stronger and heavier. Most often, this tissue is located outside the bone, covering and protecting it from damage, cracks, and fractures. Compact bone tissue makes up the majority of the skeleton (about 80%).

Bone(textus osseus) is a specialized type of connective tissue that has a high degree of mineralization of the intercellular substance.

Bone tissue consists of cellular elements (osteoblasts, osteocytes and osteoclasts) and intercellular substance (ossein and osseomucoid).

The intercellular substance contains about 70% of inorganic compounds, mainly calcium phosphates. Organic compounds are represented mainly by proteins and lipids that make up the matrix. Organic and inorganic compounds in combination give a very strong supporting tissue.

Functions

1. musculoskeletal- due to the significant strength of the bone tissue, it provides the movement of the body in space and its support.

2. protective- bone tissue protects vital organs from damage;

3. depot calcium and phosphorus in the body;

Classification of bone tissue

Depending on the structure and physical properties, two types of bone tissue are distinguished:

1. Reticulofibrous (coarse fibrous)

2. Plate

Reticular - fibrous bone tissue- has a multidirectional arrangement of bundles of ossein fibers (type I collagen), surrounded by calcified osseomucoid. Osteocytes lie between the bundles of ossein fibers in the lacunae of the osteomucoid. This tissue is characteristic of the fetal skeleton; in adults, it is found only in the areas of the sutures of the skull and in the places where the tendons are attached to the bones.

lamellar bone tissue- characteristic is a strictly parallel arrangement of bundles of collagen fibers and the formation of bone plates.

Depending on the orientation of these plates in space, this tissue, in turn, is divided into: 1) compact; 2) spongy;

compact- characterized by the absence of cavities. The diaphyses of tubular bones are built from it.

Spongy- characterized by the fact that the bone plates form trabeculae located at an angle to one another. As a result, a spongy structure is formed. Spongy bone tissue forms flat bones epiphyses of tubular bones.

Bone histogenesis

The source of bone tissue development is the mesenchyme. With the development of bone tissue, two differons of cells (histogenetic series) are formed.

Yo First row- stem osteogenic cells, semi-stem stromal cells, osteoblasts, osteocytes.

Yo Second row- hematogenous origin - stem hematopoietic cell, semi-stem hematopoietic cell (predecessor of myeloid cells and macrophages), unipotent colony-forming monocytic cell (monoblast), promonocyte, monocyte, osteoclast (macrophages).

Distinguish between embryonic and postembryonic development of bone tissue.

Embryonic Bone development can occur in two ways:

1. Directly from the mesenchyme - direct osteohistogenesis.

2. From the mesenchyme in place of the previously developed cartilaginous bone model, indirect osteohistogenesis.

Postembryonic development bone is carried out during regeneration and ectopic osteogenesis.

Embryonic osteohistogenesis

Direct osteohistogenesis is characteristic of the development of coarse fibrous bone tissue during the formation of flat bones (skull bones) and occurs during the first month of development and is characterized at the beginning primary membranous osteoid bone tissue, which is then impregnated with calcium and phosphorus salts.

There are 4 stages during direct osteogenesis:

1) Formation of a skeletal island,

2) Osteoid stage,

3) Calcification of the intercellular substance, the formation of coarse fibrous bone,

4) Formation of secondary cancellous bone,

Yo First stage(formation of a skeletal island) - At the site of the development of the future bone, focal reproduction of mesenchymal cells occurs, as a result, a skeletal island is formed and its vascularization occurs.

Yo Second stage(osteoid) - Islet cells differentiate, an oxyphilic intercellular substance with collagen fibrils is formed - organic matrix of bone tissue. Collagen fibers grow and push the cells apart, but they do not lose their processes and remain connected to each other. Mucoproteins (osseomucoid) appear in the main substance, which cements the fibers into one strong mass. Some cells differentiate into osteocytes and some of them may be included in the thickness of the fibrous mass. Others are located on the surface, differentiate into osteoblasts and for some time they are located on one side of the fibrous mass, but soon collagen fibers also appear on the other sides, separating osteoblasts from each other, gradually immuring them into the intercellular substance, while they lose their ability to reproduce and turn into osteocytes. In parallel with this, new generations of osteoblasts are formed from the surrounding mesenchyme, which build up the bone from the outside (appositional growth).

YOT third stage- calcification of the intercellular substance.

Osteoblasts secrete the enzyme phosphatase, which breaks down blood glycerophosphate into sugar and phosphoric acid. The acid reacts with calcium salts, which is contained in the base substance and fibers, first forming calcium compounds, then crystals - hydroxysitamites.

A significant role in the concentration of the osseoid is played by matrix vesicles of the lysosome type, up to 1 μm in diameter, which have a high activity of alkaline phosphatase and pyrophosphatase, contain lipids and establish calcium on the inner surface of the membrane. Osteinectin, a glycoprotein that binds calcium and phosphorus salts to collagen, occupies an important place in the processes of concentration.

The result of calcification is the formation bone bars or beams, from which outgrowths branch off, connecting with each other and forming a wide network. The space between the crossbars is occupied by a connective fibrous tissue with blood vessels passing through it.

At the time of completion of histogenesis along the periphery of the bone rudiment, a large number of fibers and osteogenic cells appear in the embryonic connective tissue. Part of the fibrous connective tissue that is directly adjacent to the bony crossbars turns into periosteum, which provides trophism and bone regeneration. Such a bone, which is formed in the early stages of embryonic development and consists of an overlay of reticulofibrous bone tissue, is called primary spongy bone.

Yo Fourth stage- formation of secondary spongy bone (lamellar)

The formation of this bone is accompanied by the destruction of individual sections of the primary bone and the ingrowth of blood vessels into the thickness of the reticulofibrous bone. In this process, both in the embryonic period and after birth, osteoclasts.

As a result of the differentiation of the mesenchyme adjacent to the blood vessels, bone plates are formed on which a layer of new osteoblasts is superimposed, and a new plate appears. Collagen fibers in each plate are oriented at an angle to the fibers to the previous plate. As a result, around the vessel there is a similarity of bone cylinders inserted into each other (primary osteon). From this point on, reticulofibrous tissue ceases to develop and is replaced by lamellar bone.

From the side of the periosteum, common or general plates are formed, which cover the entire bone from the outside. This mechanism leads to the development flat bone. The bone formed in the embryonic period undergoes further restructuring, destruction of primary osteons and development of new ones. This process continues throughout life.

indirect osteohistogenesis

Bone development by indirect histogenesis occurs in 4 stages:

1.Formation of cartilage model.

2. Perichondrial ossifications.

3.Enchondral ossifications.

4. Epiphyseal ossifications.

Formation of cartilage model - occurs in the second month of embryonic development. In places of future tubular bones, a cartilage germ is laid from the mesenchyme, which very quickly takes the form of a future bone. The rudiment consists of embryonic hyaline cartilage covered with perichondrium. For some time, it grows, both due to the cells formed from the perichondrium, and due to the multiplication of cells in the internal areas.

Perichondral ossification- the process of osteohistogenesis begins in the area of ​​the diaphysis, while the skeletal cells of the perichondrium differentiate towards osteoblasts, which are between the perichondrium and cartilage, i.e. perichondral, form reticulofibrous bone tissue, which is then rebuilt into lamellar. Due to the fact that this bone in the form of an openwork cuff surrounds the cartilage diaphysis, it is called perichondral.

The formation of a bone cuff disrupts the nutrition of the cartilage, which leads to degenerative changes in the center of the cartilage bud. Chondrocytes vacuolize, their nuclei pyknotezize, and the so-called vesicular chondrocytes. The cartilage in this place stops growing. Unaltered distal parts of the diaphysis continue their growth, while chondrocytes at the border of the epiphysis and diaphysis are collected in columns, the direction of which coincides with the long axis of the future bone.

It should be emphasized that two oppositely directed processes occur in the chondrocyte column:

1) reproduction and growth in the distal parts of the diaphysis;

2) dystrophic processes in the proximal section;

In parallel with this, mineral salts are deposited between the swollen cells, which causes the appearance of a sharp basophilia and cartilage fragility. Since the growth of the vasculature and the appearance of osteoblasts, the perichondrium is rebuilt and turns into the periosteum. Blood vessels and their surrounding mesenchyme, osteogenic cells and osteoclasts grow through the openings of the bony cuff and come into contact with calcified cartilage. Osteoclasts secrete hydrolytic enzymes that carry out chondrolysis of the calcified intercellular substance. As a result, the diaphyseal cartilage is destroyed and spaces appear in it, in which osteocytes settle, forming bone tissue on the surface of the remaining sections of the calcified cartilage.

Endochondral ossification- the process of bone formation inside the cartilaginous rudiment (diaphyseal ossification center).

As a result of the destruction of the endochondral bone by osteoclasts, large cavities and spaces (cavities of resorption) are formed, and finally a medullary cavity appears. From the penetrated mesenchyme, the stroma of the bone marrow is formed, in which stem cells of blood and connective tissue settle. In parallel with this, more and more new crossbars of bone tissue grow from the side of the periosteum. Growing in length towards the epiphyses, and increasing in thickness, they form a dense layer of bone. Around the vessels, concentric bone plates are formed, and primary osteons are formed.

Epiphyseal ossification - the process of the appearance of ossification centers in the epiphyses. This is first preceded by differentiation of chondrocytes, their hypertrophy, followed by malnutrition, dystrophy and calcification. Subsequently, the process of ossification takes place.

It should be noted that between the epiphyseal and diaphyseal centers of ossification are formed metaepiphyseal plate, consisting of 3 zones:

a) zone of unchanged cartilage;

b) zone of columnar cartilage;

c) bubble cell zone;

When the epiphyseal and diaphyseal centers of ossification are connected, the growth of the bone in length stops. In humans, this is about 20-25 years old.

bone cells

Bone tissue contains three types of cells:

a) osteocytes; b) osteoblasts; c) osteoclasts;

Osteocytes these are the predominant, definitive cells of bone tissue that have lost the ability to divide.

Form - process, elongated, dimensions 15 by 45 microns.

The nucleus is compact and relatively round.

The cytoplasm is weakly basophilic, with underdeveloped organelles.

Localization - in bone cavities or lacunae. The length of the cavities is from 22 to 55 microns, the width is from 6 to 14 microns.

osteoblasts- young cells that create bone tissue.

Shape - cubic, pyramidal, angular, about 15 - 20 microns in size.

The nucleus is round or oval, located eccentrically, contains one or more nucleoli.

Cytoplasm - contains a well-developed agranular endoplasmic reticulum, mitochondria, the Golgi complex, a significant amount of RNA, high activity of alkaline phosphatase.

osteoclasts(osteoclastocytes) cells of a hematogenous nature, capable of destroying calcified cartilage and bone.

The shape is irregular, rounded.

Dimensions - diameter up to 90 microns.

Core - number from 3 to several tens.

The cytoplasm is weakly basophilic, sometimes oxyphilic, contains a large number of lysosomes, mitochondria. On the side of the osteoclast adhering to the destroyed surface, two zones are distinguished:

a) corrugated border;

b) a zone of tight fit of the osteoclast to the bone surface.

corrugated border- area of ​​absorption and secretion of hydrolytic enzymes.

Tight zone osteoclast to the bone surface, surrounds, the first, as it were, seals the area of ​​\u200b\u200baction of enzymes. This zone of the cytoplasm is light, contains few organelles, with the exception of microfilaments consisting of actin.

The peripheral layer of the cytoplasm contains numerous small vesicles and larger vacuoles, many mitochondria, lysosomes, and the granular endoplasmic reticulum is poorly developed. There are suggestions that osteoclasts secrete CO 2, and the enzyme carbonic anhydrase- synthesizes acid H 2 CO 3 from it, which destroys the organic matrix of the bone and dissolves calcium salts. In the place where the osteoclast comes into contact with the bone substance, a gap is formed.

Differentiation of osteoclasts depends on the action of lymphokines, which are produced by T-lymphocytes.

intercellular substance

The intercellular substance is formed by the main substance impregnated with inorganic layers and bundles of collagen fibers located in it.

Base substance contains small amounts of chondroitin sulfuric acid, a lot of citric acid, which form complexes with calcium, impregnating the organic matrix of the bone. The ground substance of the bone contains hydroxyapatite crystals ordered in relation to the fibrils of the organic matrix, as well as ammophic calcium phosphate. Bone tissue contains more than 30 trace elements (copper, strontium, zinc, barium, magnesium and others).

Collagen fibers form small bundles. The fibers contain the protein type I collagen. In reticulofibrous bone tissue, the fibers have a random direction and are strictly oriented in lamellar bone tissue.

The structure of tubular bones

The tubular bone is built mainly from lamellar bone tissue, with the exception of tubercles.

In the tubular bone, the central part is distinguished - diaphysis and its peripheral ending - epiphysis.

The diaphysis of the bone is formed by three layers:

1) periosteum (periosteum);

2) the actual bone osteon layer;

3) endosteum (inner layer);

*Periosteum It consists of a superficial fibrous layer formed by bundles of collagen fibers and a deep osteogenic layer consisting of osteoblasts and osteoclasts. Due to the periosteum, which is permeated with blood vessels, bone tissue is nourished. The osteogenic layer ensures bone growth in thickness, physiological and reparative regeneration.

*Bone proper ( osteon layer) is separated from the periosteum by a layer of external general plates, and from the endosteum, by a layer of internal general plates.

External general plates do not form complete rings around the diaphysis of the bone, overlap on the surface with the following layers of plates. The outer general plates have perforating channels, along which vessels enter the bone from the periosteum, in addition, collagen fibers penetrate into the bone from the periosteum at different angles ( perforating fibers).

Internal general plates well developed only where the compact substance of the bone directly borders the medullary cavity. In those places where the compact substance passes into the spongy one, its internal general plates continue into the plates of the spongy substance.

osteon layer. In this layer, the bone plates are located in osteons, forming osteon plates and insert plates, the latter are localized between osteons.

*Osteon the main structural unit of the compact substance of the tubular bone. Each osteon is a bone tube with a diameter of 20 to 300 microns, in the central canal of which there is a feeding vessel and osteoblasts and osteoclasts are localized. Around the central canal, from 5 to 20 bone plates are concentrically located, collagen fibers in the bone plates of each layer have a strictly parallel direction. The direction of collagen fibers in adjacent plates does not match, and therefore they are located at an angle to each other, which helps to strengthen the osteon, as a structural element of the bone. Between the bone plates in the bone lacunae are the bodies of osteocytes, which anastomose with each other with their processes located in the bone tubules.

*Osteon layer is a system of parallel cylinders (osteons), the spaces between which are filled with intercalated bone plates.

*Endostom- fine-fibrous connective tissue that lines the bone from the side of the medullary canal. Fibrous connective tissue contains osteoblasts and osteoclasts.

*Pineal bone- Made up of spongy bone. Outside it is covered with a periosteum, under which there is a layer of general plates and a layer of osteons. In the thickness of the epiphysis, bone plates form a system trabeculae which are at an angle to each other. The cavities between the trabeculae are filled with reticular tissue and hematopoietic cells.

The growth of tubular bones.

The growth of tubular bones in length is provided by the presence of metaepiphyseal cartilaginous plate growth, in which 2 opposite histogenetic processes appear:

1) destruction of the epiphyseal plate;

2) continuous replenishment of cartilaginous tissue by neoplasm of cells.

In the metaepiphyseal plate, 3 zones are distinguished:

a) border zone;

b) zone of columnar cells;

c) zone of vesicular cells;

*border zone - consists of rounded and oval cells and single isogenic groups, some provide a connection between the cartilaginous plate and the bone of the epiphysis. Between bone and cartilage are blood capillaries.

*Columnar cell zone - consists of actively proliferating cells that form columns located along the axis of the bone.

*Bubble cell zone - characterized by hydration and destruction of chondrocytes, followed by endochondral ossification. The distal part of this zone borders on the diaphysis, from where osteogenic cells and blood capillaries penetrate into it. Longitudinally arranged columns of cells are essentially bone tubules, in place of which osteons are formed.

When the centers of ossification in the diaphysis and epiphysis merge, growth in length stops. In humans, this happens at 20-25 years.

The growth of the tubular bone in thickness is carried out due to the proliferation of cells of the deep osteogenic layer of the periosteum.

Reticulofibrous bone tissue

This type of bone tissue is typical mainly for embryos. In adults, it occurs at the site of overgrown cranial sutures, at the points of attachment of tendons to bones.

Collagen fibers have a random direction and form thick bundles.

The ground substance contains elongated-oval bone cavities (lacunae) with long anastomosing tubules, in which bone cells lie - osteocytes with their processes.

Outside, the coarse fibrous bone is covered with periosteum.

lamellar bone tissue

This tissue consists of bone plates formed by bone cells and a mineralized amorphous substance with collagen fibers. In different bone plates, the direction of collagen fibers is different.

Due to this, greater strength of the lamellar bone is achieved.

Cartilaginous tissue (textus cartilaginus) forms articular cartilages, intervertebral discs, cartilages of the larynx, trachea, bronchi, external nose. Cartilage tissue consists of cartilage cells (chondroblasts and chondrocytes) and a dense, elastic intercellular substance.

Cartilaginous tissue contains about 70-80% water, 10-15% organic matter, 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, which include proteoglycans. hyaluronic acid, glycosaminoglycan molecules. There are two types of cells in the cartilaginous tissue: chondroblasts (from the Greek chondros - cartilage) and chondrocytes.

Chondroblasts are young, capable of mitotic division, rounded or ovoid cells. 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), the Golgi complex, mitochondria, lysosomes, and glycogen granules. The chondroblast nucleus, rich in active chromatin, has 1-2 nucleoli.

Chondrocytes are mature large cartilage cells. They are round, oval or polygonal, with processes, developed organelles. Chondrocytes are located in cavities - lacunae, surrounded by intercellular substance. If there is one cell in the gap, then such a gap 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 lacunae consist of two layers: the outer one, formed by collagen fibers, and the inner one, consisting of aggregates of proteoglycans that come into contact with the glycocalyx of cartilage cells.

The structural and functional unit of cartilage is the chondron, formed by a cell or an isogenic group of cells, a pericellular matrix, and a lacuna capsule.

Cartilage tissue is nourished by diffusion of substances from the blood vessels of the perichondrium. Nutrients enter the articular cartilage tissue from the synovial fluid or from the vessels of the adjacent bone. Nerve fibers are also localized in the perichondrium, from where individual branches of amyopiatic nerve fibers can penetrate into the cartilaginous tissue.

In accordance with the structural features of the cartilage tissue, there are three types of cartilage: hyaline, fibrous and elastic cartilage.

hyaline cartilage, from which the cartilages of the respiratory tract, the thoracic ends of the ribs and the articular surfaces of the bones are formed in humans. In a light microscope, its main substance appears to be homogeneous. Cartilage cells or their isogenic groups are surrounded by an oxyphilic capsule. In differentiated areas of cartilage, a basophilic zone adjacent to the capsule and an oxyphilic zone located outward from it are distinguished; Together, these zones form a cellular territory, or chondrin ball. A complex of chondrocytes with a chondrin ball is usually taken as a functional unit of cartilage tissue - a chondron. The ground substance between chondrons is called interterritorial spaces.
Elastic cartilage(synonym: mesh, elastic) differs from hyaline by the presence of branching networks of elastic fibers in the main substance. The cartilage of the auricle, epiglottis, vrisberg and santorin cartilages of the larynx are built from it.
fibrocartilage(a synonym for connective tissue) is located at the transition points of dense fibrous connective tissue into hyaline cartilage and differs from the latter by the presence of real collagen fibers in the ground substance.

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 - 30%.

Functions of bone tissue:

1) support;

2) mechanical;

3) protective (mechanical protection);

4) participation in the mineral metabolism of the body (depot of calcium and phosphorus).

Bone cells - osteoblasts, osteocytes, osteoclasts. The main cells in the formed bone tissue are osteocytes. These are process-shaped cells with a large nucleus and weakly expressed cytoplasm (nuclear-type cells). The cell bodies are localized in the bone cavities (lacunae), and the processes are located in the bone tubules. Numerous bone tubules, anastomosing with each other, penetrate the bone tissue, communicating with the perivascular space, form the drainage system of the 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 in the intercellular substance.

Osteocytes are definitive forms of cells and do not divide. They are formed from osteoblasts.

osteoblasts found only in developing bone tissue. In the formed bone tissue, they are usually contained in an inactive form in the periosteum. In developing bone tissue, osteoblasts surround each bone plate along the periphery, tightly adhering to each other.

The shape of these cells can be cubic, prismatic and angular. The cytoplasm of osteoblasts contains a well-developed endoplasmic reticulum, the Golgi lamellar complex, many mitochondria, which indicates a high synthetic activity of these cells. Osteoblasts synthesize collagen and glycosaminoglycans, which are then released into the extracellular space. Due to these components, an organic matrix of bone tissue is formed.

These cells provide mineralization of the intercellular substance through the release of calcium salts. Gradually releasing the intercellular substance, they seem to be walled up and turn into osteocytes. At the same time, intracellular organelles are significantly reduced, synthetic and secretory activity is reduced, and the functional activity characteristic of osteocytes is preserved. Osteoblasts localized in the cambial layer of the periosteum are in an inactive state; synthetic and transport organelles are poorly developed in them. When these cells are irritated (in case of injuries, bone fractures, etc.), a granular EPS and a lamellar complex rapidly develop in the cytoplasm, active synthesis and release of collagen and glycosaminoglycans, the formation of an organic matrix (bone callus), and then the formation of definitive bone fabrics. In this way, due to the activity of osteoblasts of the periosteum, bones regenerate when they are damaged.

osteoclasts- bone-destroying cells are absent in the 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 in ontogeny, osteoclasts are also necessarily present in these places. In 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 rather large size (about 90 microns) and a characteristic shape - oval, but the part of the cell adjacent to the bone tissue has a flat shape. 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 depressions of bone tissue. After the destruction of bone tissue due to the activity of osteoblasts, which are evicted from the connective tissue of the vessels, a new bone tissue is built.

intercellular substance bone tissue consists of the main (amorphous) substance and fibers, which contain calcium salts. The fibers consist of collagen and are folded into bundles, which can be arranged in parallel (orderly) or randomly, on the basis of which the histological classification of bone tissues is built. The main substance of bone tissue, as well as other types of connective tissues, consists of glycosamino- and proteoglycans.

The bone tissue contains less chondroitin sulfuric acids, but more citric and others, which form complexes with calcium salts. In the process of bone tissue development, 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 an amorphous substance and in fibers. Providing bone strength, calcium phosphate salts are also both 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, one should also clearly separate the concepts of “bone tissue” and “bone”.

Bone is an organ whose main structural component is bone tissue.