The musculoskeletal system unites bones, bone joints and muscles.

The main function of the apparatus is not only support, but also the movement of the body and its parts in space. The musculoskeletal system is divided into passive and active parts. TO passive parts that make up 1/3 of body weight are bones and bone joints. Active part (2/3 of body weight) are muscles, which, due to their ability to contract, set in motion the bones of the skeleton.

Consider the anatomical structure of the human skeleton. Skeleton (from the Greek. skeleton - dried) is a complex of bones, different in shape and size. In the skeleton, bones of the trunk, upper and lower extremities are distinguished. The bones are connected to each other using various types of connections and perform the functions of support, movement, protection, depot of various salts. The bone skeleton is also called a hard, rigid skeleton. Skeleton functions are subdivided into mechanical (support, spring, protective, locomotive, anti-gravity) and biological .

Support the function of the skeleton is that the bones, together with their joints, constitute the support of the whole body, to which soft tissues and organs are attached. Soft tissues in the form of ligaments, fasciae, capsules and stroma of organs are called the soft skeleton, since they also perform mechanical functions (attach organs to the hard skeleton, support the stroma of organs, and protect them).

The functions of support and movement of the skeleton are combined with spring the function of articular cartilage and other structures (arches of the foot), softening shocks and concussions.

Protective the function is expressed in the formation of bone receptacles for vital organs: the skull protects the brain, the spinal column protects the spinal cord, the chest protects the heart, lungs and large blood vessels. The organs of reproduction are located in the pelvic cavity. Inside the bones is the bone marrow, which gives rise to blood cells and the immune system.

Locomotor function, i.e. movement in space is possible due to the structure of bones in the form of long and short levers, movably connected to each other and set in motion by muscles, controlled by the nervous system. In addition, the bones determine the direction of the course of blood vessels, nerves, as well as the shape of the body and its dimensions ( formative function). The bones of the skeleton overcome the force of gravity ( antigravity function), create a support for the stability of the body, which rises above the ground. Leaf springs the function of the skeleton is that due to the bends of the bones and cartilaginous layers, shocks and concussions are extinguished. Thanks to the bones of the skeleton, each organ has its own location, this is topographic skeleton function. It should not be forgotten that the features of the bones of the skeleton (their size, thickness, dimensions) largely determine the external ( aesthetic) kind of person.

Biological the functions of the skeleton are associated with the participation of bones in mineral metabolism and hematopoiesis. Bones are a depot for mineral salts of phosphorus, calcium, iron, magnesium, copper and other elements, they maintain the constancy of the mineral composition of the fluids of the internal environment of the body. Hematopoietic and immunological the function of the skeleton is that in the red bone marrow (the central hematopoietic organ containing hematopoietic stem cells) of tubular, flat bones, the process of hematopoiesis is carried out, i.e. formation of all blood cells, including cells of the immune system - lymphocytes.

The skeleton includes 206 bones (85 paired and 36 unpaired). 29 bones form the skull, 26- the vertebral column, 25- form the ribs and sternum, 64- form the skeleton of the upper limbs and 62- the skeleton of the lower limbs. The mass of the "living" skeleton in newborns is about 11% of body weight, in children of different ages - from 9 to 18%. In adults, the ratio of skeletal mass to body mass until the elderly, senile age remains at the level of up to 20%, then decreases slightly.

The skeleton includes cartilaginous joints, bones and bone joints, bone marrow. Cartilage tissue precedes bone tissue, in this regard, we will consider the main structural features and types of cartilage tissue.

Cartilage tissue is a type of connective tissue, consists of cells (chondrocytes) and intercellular substance, it does not have blood, lymphatic vessels, nerves. The cartilage tissue does not have independent nutrition; it is carried out due to the diffusion of nutrients from the surrounding tissues. The cartilage tissue contains 10-15% organic matter, 70-80% water, 4-7% salts. Cartilage cells are rounded, located singly or in groups, scattered loosely. The intercellular substance contains many fibers and is flexible. By the type of fibers, three types of cartilage are distinguished: 1) elastic; 2) hyaline; 3) fibrous. Consider all three types of cartilage.

Hyaline cartilage ("hyalos" - transparent, bluish) covers the surfaces of bones, is the basis of ossification, has great elasticity. The airways (bones of the larynx, trachea, bronchi) are lined with it, rib cartilage and nose are built from it. By old age, hyaline cartilage can become fibrous.

Fibrous cartilage is characterized by the presence of a large number of densely lying fibers, the intercellular substance is also dense, there are few cells, 90% consists of type I collagen. This type of cartilage is found in the intervertebral discs, menisci, in the areas of attachment of tendons and ligaments to bones and cartilage.

Elastic cartilage is yellowish in color, contains a network of elastic fibers that permeate the entire intercellular substance, salts are never deposited in it. The body of this type of cartilage contains little: the outer ear (external auditory canal, auditory tube), the epiglottis are built from it.

Each bone as an organ consists of all types of tissues, but the main place is occupied by bone tissue, which is a type of connective tissue.

Bone.

Bone tissue is a special type of connective tissue with a calcified intercellular substance. The intercellular substance consists of a basic substance in which fibers are located and inorganic salts are contained. Fibers, called ossein, are no different from collagen fibers of loose fibrous connective tissue, they contain a protein called ossein. The basic substance of the bone in comparison with cartilage contains a relatively small amount of chondroitinsulfuric acid. Among the organic substances of the bone, proteins, fats, carbohydrates (mucopolysaccharides), citric acid should be noted. Organic substances give the bones elasticity, firmness, prevail in childhood.

Thus, the chemical composition of bones is complex. In addition to organic bones, it also contains inorganic substances that give it hardness and strength. In a living organism, bone contains 50% water, 28.15% organic matter, including 15.75% fat and 21.85% inorganic substances, represented by compounds of phosphorus, calcium, magnesium. In small quantities, bone contains more than 30 other various elements. Chemical analysis shows that fresh bone tissue contains 60% Ca 3 (PO 4) 2, 5.9% CaCO 3, 1.4% Mg 3 (PO 4). After removal of organic substances (in ash), the ratio of these salts is as follows: 87%: 10%: 2%. Salts contained in bone tissue form very complex compounds, which consist of submicroscopic crystals of the hydroxyapatite type, having the following composition [Ca 3 (PO 4) 2] 3 · Ca (OH) 2. Fat-free, bleached and dried bone (macerated) consists of 1/3 organic substances, called ossein, and 2/3 of inorganic substances. The elasticity, firmness of the bone depends on its organic substances, and the hardness - on mineral salts. Bone strength (mechanical properties) is provided by the physicochemical unity of organic and inorganic substances, as well as the structure of bone tissue. The combination of inorganic and organic substances in living bone gives it extraordinary strength and elasticity. In terms of hardness and elasticity, bone can be compared with copper, bronze, cast iron. At a young age, in children, bones are more elastic, resilient, they contain more organic matter and less inorganic. In elderly, old people, inorganic substances predominate in the bones. Bones become more brittle.

The following cells are isolated in the bone tissue: osteoblasts, osteocytes, osteoclasts. Osteoblasts- These are cells that form bone tissue, which have many processes for contact. In the formed bone, they are found only in areas of destruction and restoration of bone tissue. In the resulting bone, they cover with an almost continuous layer all surfaces of the developing intercellular substance. Osteoblasts come in various shapes: cubic, pyramidal, angular; the nucleus is round or oval, contains one or more nucleoli; in the cytoplasm under an electron microscope, mitochondria, intracellular mesh apparatus and other organelles are visible. After bone fractures, a callus is formed at the site of fusion due to the fact that the osteoblasts of the inner layer of the periosteum form a layer connecting the ends of the fractured bone, restoring its integrity. Osteoblasts synthesize components of the intercellular substance (procollagen → type I collagen; glycosaminoglycans; proteoglycans). Osteocytes- these are bone cells formed from osteoblasts, which, as the intercellular substance of the bone is formed, become enclosed in it, gradually change and turn into osteocytes. Osteocytes have an elliptical shape; the cytoplasm contains mitochondria, a nucleus, and a poorly developed intracellular mesh apparatus. Mitoses are not observed in osteocytes, their bodies are located in the bone cavities, and the processes penetrate into the bone tubules. The deposition of calcium salts in the intercellular substance of the bone excludes the possibility of diffusion of nutrients and metabolic products, as is the case in cartilage. Therefore, for the vital activity of osteocytes, a connection with the perivascular spaces inside the bone or with tissue fluid outside the bone is necessary. The bony tubule system provides a pathway for metabolism between osteocytes and tissue fluid. Osteoclasts- These are cells that take an active part in the destruction of calcified cartilage and bone. In the place where the osteoclast comes into contact with the bone substance, a cove or lacuna is formed in the latter, in which the osteoclast is located. It is possible that osteoclasts secrete enzymes, under the influence of which the calcified substance dissolves. Osteoclasts are multinucleated cells containing from 6 to 50 or less chromatin-poor nuclei; their cytoplasm has branched processes with jagged edges, sometimes it can contain different grain sizes. Where the cytoplasm of the osteoclast is adjacent to the bone, parallel stripes are visible in it, which are collagen fibers. Osteoclasts belong to the macrophage system and predominate in old age.

There are two main types of bone tissue - coarse fibrous and lamellar, some researchers distinguish the third type - dentin.

In coarse-fibrous bone tissue, collagen fibers form powerful bundles that can be located in different ways: parallel, at an angle to each other, or form a complex connection. Osteocytes lie between the fibers without a specific orientation, they are flattened, and the bone cavities have an elongated-oval shape. Rough-fibrous bone tissue predominates during embryonic development and in the first year of a child's life. Lamellar bone tissue is characterized by the fact that thin collagen fibers are arranged in it in the form of parallel bundles either in one direction, or in the form of overlapping plates (for example, in osteons of the tubular bone). Osteocytes lie between the plates or inside them. In addition to osteocytes, lamellar bone tissue includes a fine-fibrous base substance. This type of bone tissue is much stronger than coarse-fibered, and prevails after the first year of human life. Dentin is characterized by the fact that there are no bone cells, but there are tubules in which the processes of cells lie, the bodies of the cells themselves are located outside the dentin (these are cells resembling osteoblasts, called odontoblasts).

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% inorganic compounds, mainly calcium phosphates. Organic compounds are represented mainly by proteins and lipids that make up the matrix. Organic and inorganic compounds combine to provide a very strong supporting fabric.

Functions

1. support-mechanical- due to the significant strength of the bone tissue, it ensures 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;

Bone classification

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

1. Reticulofibrous (coarse-fibrous)

2. Lamellar

Reticularly 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 skeleton of the embryo; in adults, it is found only in the areas of the seams of the skull and in the places of attachment of the tendons to the bones.

Lamellar bone tissue- strictly parallel arrangement of collagen fiber bundles and the formation of bone plates are characteristic.

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

Compact- characterized by the absence of cavities. Shafts 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. The cancellous bone tissue forms the flat bones of the epiphyses of the tubular bones.

Bone tissue histogenesis

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

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

Yo Second row- hematogenous origin - hematopoietic stem cell, half-stem hematopoietic cell (precursor 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 the development of bone tissue can occur in two ways:

1. Directly from the mesenchyme - direct osteohistogenesis.

2. Indirect osteohistogenesis from the mesenchyme at the site of the previously developed cartilaginous bone model.

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

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.

During direct osteogenesis, 4 stages are noted:

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 bone) - At the site of development of the future bone, focal multiplication of mesenchymal cells occurs, as a result, a skeletal islet is formed and its vascularization occurs.

Yo Second stage(osteoid) - Islet cells differentiate, an oxyphilic intercellular substance with collagone fibrils is formed - organic bone matrix... Collagen fibers grow and move 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 solid mass. Some cells differentiate into osteocytes and some of them may be included in the stock. 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 appear on the other sides, separating osteoblasts from each other, gradually bricking 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 bone from the outside (appositional growth).

ET third stage- calcification of the intercellular substance.

Osteoblasts secrete an enzyme called phosphatase, which breaks down blood glycerophosphate into sugar and phosphoric acid. The acid reacts with calcium salts, which is contained in the basic substance and fibers, forming first 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 build calcium on the inner surface of the membrane. An important place in the concentration processes is occupied by osteinectin, a glycoprotein that binds calcium and phosphorus salts with collagen.

Calcification results in formation bone bars or beams, from which the outgrowths branch off, interconnecting and forming a wide network. The space between the bars is occupied by connective fibrous tissue with blood vessels passing through it.

At the time of the completion of histogenesis along the periphery of the bone primordium, a large number of fibers and osteogenic cells appear in the embryonic connective tissue. The part of the fibrous connective tissue that is directly adjacent to the bone bars 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 a lining of reticulofibrous bone tissue, is called primary cancellous bone.

Yo Fourth stage- the formation of secondary cancellous 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, they take part 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 consequence of this, a semblance of bone cylinders inserted into each other (primary osteon) appears around the vessel. From this point on, reticulofibrous tissue ceases to develop and is replaced by lamellar bone tissue.

From the side of the periosteum, general or general plates are formed, which cover the entire bone from the outside. According to this mechanism, development takes place flat bone... The bone formed in the embryonic period undergoes further restructuring, the destruction of the primary osteons and the development of new ones occur. This process continues almost all life.

Indirect osteohistogenesis

Bone development by indirect histogenesis occurs in 4 stages:

1. Formation of a cartilaginous model.

2. Perichondrial ossification.

3.Enchondral ossification.

4. Epiphyseal ossification.

Cartilage model formation - occurs in the second month of embryonic development. In the places of the future tubular bones, a cartilaginous primordium is laid from the mesenchyme, which very quickly takes the shape of the future bone. The anlage consists of the embryonic hyaline cartilage covered with the perichondrium. For some time it grows, both due to the cells formed from the side of 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 the 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 diaphysis of the cartilage, it is called perichondral.

The formation of a bone cuff disrupts the nutrition of the cartilage, which leads to dystrophic changes in the center of the cartilaginous primordium. Chondrocytes are vacuolated, their nuclei are pyknoted, and the so-called vesicular chondrocytes... The cartilage in this place stops growing. The unchanged distal parts of the diaphysis continue their growth, while chondrocytes at the border of the pineal gland and the 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 diaphysis;

2) dystrophic processes in the proximal section;

In parallel with this, the deposition of mineral salts occurs between the swollen cells, which causes the appearance of a sharp basophilia and fragility of the cartilage. From the moment of proliferation of the vasculature and the appearance of osteoblasts, the perichondrium is rebuilt and turns into the periosteum. Blood vessels and the surrounding mesenchyme, osteogenic cells and osteoclasts grow through the openings of the bone cuff and come into contact with the 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 areas of calcified cartilage.

Enchondral ossification- the process of bone formation inside the cartilaginous primordium (diaphyseal center of ossification).

As a result of the destruction of the enchondral bone by osteoclasts, large cavities and spaces (cavities of resorption) are formed, and finally a bone marrow cavity appears. From the penetrated mesenchyme, a bone marrow stroma is formed, in which stem cells of blood and connective tissue settle. In parallel, new and 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. Concentric bone plates are formed around the vessels, and primary osteons are laid.

Epiphyseal ossification - the process of the appearance of centers of ossification in the pineal glands. This is first preceded by the differentiation of chondrocytes, their hypertrophy, followed by a deterioration in nutrition, dystrophy and calcification. In the future, the process of ossification occurs.

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

a) the area of ​​unchanged cartilage;

b) the area of ​​columnar cartilage;

c) the zone of vesicle cells;

When the epiphyseal and diaphyseal centers of ossification are connected, bone growth in length stops. In humans, it 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 - otrochaty, elongated, size 15 by 45 microns.

The core is compact, 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 µm, the width is from 6 to 14 µm.

Osteoblasts- young cells that create bone tissue.

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

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

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

Osteoclasts(osteoclastocytes) cells of a hemotogenic nature, capable of destroying calcified cartilage and bone.

The shape is irregular, round.

Dimensions - diameter up to 90 microns.

The core is from 3 to several dozen.

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

a) corrugated border;

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

Corrugated hem- area of ​​absorption and secretion of hydrolytic enzymes.

Snug fit area osteoclast to the bone surface, surrounds, the first, as it were, seals the area of ​​action 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 from it the acid H 2 CO 3, 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 lacuna is formed.

Osteoclast differentiation depends on the effects of lymphokines, which are produced by T-lymphocytes.

Intercellular substance

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

Main substance contains small amounts of chondroitinsulfuric acid, a lot of citric acid, which form complexes with calcium, impregnating the organic matrix of the bone. The basic substance of the bone contains crystals of hydroxyapatite arranged in an orderly manner in relation to the fibrils of the organic matrix, as well as ammophoric calcium phosphate. Bone tissue contains more than 30 microelements (copper, strontium, zinc, barium, magnesium and others).

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

The structure of tubular bones

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

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

The diaphysis of the bone is formed by three layers:

1) the periosteum (periosteum);

2) the actual bone osteon layer;

3) endostomy (inner layer);

*Periosteum 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, the bone tissue is nourished. The osteogenic layer ensures bone growth in thickness, physiological and reparative regeneration.

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

Outdoor general plates do not form full rings around the diaphysis of the bone, overlap on the surface by the following layers of plates. External general plates have perforating canals, along which vessels enter the bone from the periosteum, in addition, collagen fibers penetrate into the bone from the side of the periosteum at different angles ( perforating fibers).

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

Osteon layer. In this layer, 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 a supply vessel is located and osteoblasts and osteoclasts are localized. From 5 to 20 bone plates are concentrically located around the central canal, collagen fibers in the bone plates of each layer have a strictly parallel direction. The direction of collagen fibers in adjacent plates does not coincide, 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, the bodies of osteocytes are located, which anastamose 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.

*Bone epiphysis- formed by cancellous bone tissue. 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 pineal gland, bone plates form a system trabeculus, which are located at an angle to each other. The cavities between the trabeculae are filled with reticular tissue and hematopoietic cells.

Growth of tubular bones.

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

1) destruction of the epiphyseal plate;

2) incessant replenishment of cartilaginous tissue by cell neoplasm.

In the metaepiphyseal plate, 3 zones are distinguished:

a) border zone;

b) the area 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 pineal gland bone. Blood capillaries are located between bone and cartilage.

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

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

When the centers of ossification in the diaphysis and pineal gland merge, the growth in length stops. In humans, this occurs at the age of 20-25.

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 characteristic mainly of embryos. In adults, it occurs at the site of overgrown cranial sutures, at the points of attachment of tendons to bones.

Collagen fibers are irregularly directed and form thick bundles.

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

Outside, the coarse-fibrous bone is covered with the 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, a high strength of the lamellar bone is achieved.

Bone tissue

Bone tissue ( textus ossei) is a specialized type of connective tissue with high mineralization intercellular organic matter containing about 70% inorganic compounds, mainly calcium phosphates. More than 30 microelements (copper, strontium, zinc, barium, magnesium, etc.) have been found in bone tissue, which play an important role in metabolic processes in the body.

Organic matter - bone matrix - is represented mainly by collagen-type proteins and lipids. Compared to cartilage tissue, it contains a relatively small amount of water, chondroitinsulfuric acid, but a lot of citric and other acids that form complexes with calcium, which impregnates the organic matrix of the bone.

Thus, the solid intercellular substance of the bone tissue (in comparison with the cartilage tissue) gives the bones a higher strength, and at the same time - fragility. Organic and inorganic components in combination with each other determine the mechanical properties of bone tissue - the ability to resist stretching and compression.

Despite the high degree of mineralization, in the bone tissues there is a constant renewal of their constituent substances, constant destruction and creation, adaptive restructuring to changing conditions of functioning. The morphological and functional properties of bone tissue change depending on age, physical activity, nutritional conditions, as well as under the influence of the activity of the endocrine glands, innervation and other factors.

Classification

There are two main types of bone:

Reticulofibrous (coarse-fibrous),

· Lamellar.

These types of bone tissue differ in structural and physical properties, which are mainly due to the structure of the intercellular substance. In coarse-fibrous tissue, collagen fibers form thick bundles going in different directions, and in lamellar tissue, bone substance (cells, fibers, matrix) form systems of plates.

Bone tissue also includes dentin and cementum of the tooth, which are similar to bone tissue in terms of a high degree of mineralization of the intercellular substance and supporting, mechanical function.

Bone cells: osteoblasts, osteocytes and osteoclasts. They all develop from the mesenchyme, like cartilage cells. More precisely, from the mesenchymal cells of the mesoderm sclerotome. However, osteoblasts and osteocytes are linked in their diferon in the same way as fibroblasts and fibrocytes (or chondroblasts and hodrocytes). And osteoclasts have a different - hematogenous origin.

Bone Differon and Osteohistogenesis

The development of bone tissue in the embryo is carried out in two ways:

1) directly from the mesenchyme - direct osteogenesis;

2) from the mesenchyme at the site of the previously developed cartilaginous bone model - this is indirect osteogenesis.

Postembryonic development of bone tissue occurs during its physiological and reparative regeneration.

In the process of development of bone tissue, a bone differon is formed:

Stem cells,

Half-stem cells (preosteoblasts),

Osteoblasts (a type of fibroblasts),

· Osteocytes.

The second structural element is osteoclasts (a type of macrophage), which develop from blood stem cells.

Stem and semi-stem osteogenic cells are not morphologically identified.

Osteoblasts(from the Greek. osteon-- bone, blastos- the rudiment) - these are young cells that create bone tissue. In the bone, they are found only in the periosteum. They are capable of proliferation. In the resulting bone, osteoblasts cover the entire surface of the developing bone tract with an almost continuous layer.

The shape of osteoblasts is different: cubic, pyramidal or angular. Their body size is about 15-20 microns. The nucleus is round or oval, often located eccentrically, and contains one or more nucleoli. In the cytoplasm of osteoblasts, the granular endoplasmic reticulum, mitochondria and the Golgi apparatus are well developed. It contains significant amounts of RNA and high activity of alkaline phosphatase.

Osteocytes(see Fig. 4, 5 Appendix)(from the Greek. osteon-- bone, cytus- cell) - this is the prevailing number of mature (definitive) cells of bone tissue that have lost the ability to divide. They have a process-like shape, a compact, relatively large nucleus and a weakly basophilic cytoplasm. Organelles are poorly developed. The presence of centrioles in osteocytes has not been established.

Bone cells lie in bone lacunae that follow the contours of the osteocyte. The length of the cavities ranges from 22 to 55 microns, the width - from 6 to 14 microns. Tubules bone lacunae are filled with tissue fluid, anastomosed with each other and with the perivascular spaces of the vessels entering the bone. The exchange of substances between osteocytes and blood is carried out through the tissue fluid of these tubules.

Osteoclasts(from the Greek. osteon- bone and clastos- crushed), are cells of a hematogenous nature, capable of destroying calcified cartilage and bone. Their diameter reaches 90 microns and more, and they contain from 3 to several tens of nuclei. The cytoplasm is weakly basophilic, sometimes oxyphilic. Osteoclasts are usually located on the surface of the bone bars. The side of the osteoclast, which is adjacent to the destroyed surface, is rich in cytoplasmic outgrowths ( corrugated hem); it is the area of ​​synthesis and secretion of hydrolytic enzymes. On the periphery of the osteoclast there is snug fit cells to the bone surface, which, as it were, seals the area of ​​enzyme action. This zone of the cytoplasm is light, contains few organelles, with the exception of microfilaments, consisting of actin.

The peripheral layer of the cytoplasm above the corrugated edge contains numerous small vesicles and larger ones - vacuoles.

It is believed that osteoclasts release CO2 into the environment, and the enzyme carbonic anhydrase promotes the formation of carbonic acid (H 2 CO 3) and the dissolution of calcium compounds. Osteoclast is rich in mitochondria and lysosomes, whose enzymes (collagenase and other proteases) break down collagen and proteoglycans of the bone matrix.

It is believed that one osteoclast can destroy as many bones as 100 osteoblasts create in the same time. The functions of osteoblasts and osteoclasts are interrelated and regulated by hormones, prostaglandins, functional load, vitamins, etc.

Intercellular substance (substantia intercellularis) consists of a basic amorphous substance impregnated with inorganic salts, in which collagen fibers are located, forming small bundles. They contain mainly protein - collagen types I and V... Fibers can have an irregular direction - in reticulofibrous bone tissue, or strictly oriented direction - in lamellar bone tissue.

The main substance of bone tissue, in comparison with cartilage, contains a relatively small amount of chondroitinsulfuric acid, but a lot of citric and other acids that form complexes with calcium, which impregnates the organic matrix of the bone. In addition to collagen protein, non-collagen proteins (osteocalcin, sialoprotein, osteonectin, various phosphoproteins, proteolipids involved in mineralization processes), as well as glycosaminoglycans, are found in the main substance of bone tissue. The basic substance of the bone contains crystals of hydroxyapatite, ordered in relation to the fibrils of the organic matrix of the bone, as well as amorphous calcium phosphate. More than 30 microelements (copper, strontium, zinc, barium, magnesium, etc.) have been found in bone tissue, which play an important role in metabolic processes in the body. A systematic increase in physical activity leads to an increase in bone mass from 10 to 50% due to high mineralization.

Skeletal tissue is a type of connective tissue with a pronounced supporting, mechanical function due to the presence of dense intercellular substance. Skeletal tissues include: cartilage, bone, dentin and cementum.

In addition to the main supporting function, these tissues are involved in water-salt metabolism, mainly of calcium and phosphate salts.

Skeletal tissues develop from the mesenchyme.

Cartilage tissue differ in elasticity and strength, are part of the respiratory system, joints, intervertebral discs.

They consist of cells (chondroblasts and chondrocytes) and intercellular substance, which is more in the cartilage tissue than cells.

Chondroblasts- young small flattened cells capable of dividing and synthesizing intercellular substance. Allocating the components of the intercellular substance, chondroblasts, as it were, "walled up" themselves in it and turn into chondrocytes.

Chondrocytes- the main type of cells of cartilage tissue, have a larger size and oval shape. They are located in special cavities (lacunae) in the intercellular substance, singly or in groups. Groups of cells lying in a common cavity are called isogenic. At the same time, some chondrocytes retain the ability to divide, while others actively synthesize components of the intercellular substance. Due to the activity of chondrocytes, there is an increase in the mass of cartilage from the inside.

The intercellular substance consists of fibers and a basic, or amorphous substance. In hyaline cartilage, most of the fibers are collagen, in elastic cartilage, elastic. The base substance contains water, organic matter and minerals.

Based on the structural features of the intercellular substance, cartilaginous tissues are divided into three types - hyaline, elastic and fibrous, or fibrous.

Hyaline cartilage- transparent, bluish-white, found on the articular surfaces of the bones, at the junction of the ribs with the sternum, in the larynx and airways.

Most of the hyaline cartilage tissue found in the body is covered by the perichondrium, in which two layers are distinguished: the outer one, consisting of fibrous connective tissue with blood vessels; and internal, containing chondroblasts. Under the perichondrium, in the surface layer of the cartilage, chondrocytes of a fusiform flattened shape are located. In deeper layers, cartilage cells acquire an oval or round shape, forming isogenic groups of 2 to 4 (less often up to 6) chondrocytes.

Elastic cartilage tissue found in the auricle, laryngeal cartilage, etc. In a non-fixed state, elastic cartilage tissue is yellowish and not as transparent as hyaline. According to the general plan of the structure, elastic cartilage is similar to hyaline. Outside, it is covered with the perichondrium. Cartilage cells are located in lacunae singly or form isogenic groups.

One of the main distinguishing features of elastic cartilage is the presence of elastic fibers in its intercellular substance, along with collagen fibers. Elastic fibers penetrate the intercellular substance in all directions.

In the layers adjacent to the perichondrium, the elastic fibers pass without interruption into the elastic fibers of the perichondrium.

Fibrous cartilage is located in the intervertebral discs, semi-movable joints, in the places of transition of dense fibrous connective tissue of tendons and ligaments into hyaline cartilage, where limited movements are accompanied by strong tensions. The intercellular substance contains parallel directed collagen bundles. Cartilage contains cavities that contain cartilage cells. Chondrocytes are located singly or form small isogenic groups.

Bone tissue is a specialized type of connective tissue with a high mineralization of the intercellular substance, containing about 70% of inorganic compounds, mainly calcium phosphates. More than 30 trace elements were found in the bone tissue.

The intercellular substance of bone tissue gives bones a higher strength, and at the same time - fragility. Organic and inorganic components in combination with each other determine the mechanical properties of bone tissue - the ability to resist stretching and compression.

Bone cells: osteoblasts, osteocytes and osteoclasts.

Osteoblasts- these are young cells of a cubic shape, form the intercellular substance. In the bone, they are found only in the periosteum.

Osteocytes- These are mature cells of bone tissue that have lost the ability to divide and are formed from osteoclasts. They have a process-like shape, a large nucleus. They lie in bone gaps that follow the contours of the osteocyte. The tubules of the bone lacunae are filled with tissue fluid. The exchange of substances between osteocytes and blood is carried out through the tissue fluid of these tubules.

Osteoclasts- macrophages of bone tissue, formed from blood monocytes, these are cells capable of destroying calcified cartilage and bone. Osteoclasts are usually located on the surface of the bone bars. The osteoclast side adjacent to the destroyed surface is rich in cytoplasmic outgrowths; it is the area of ​​synthesis and secretion of hydrolytic enzymes.

The intercellular substance consists of a basic amorphous substance, in which collagen fibers are located, forming small bundles. Fibers can have an irregular direction - in fibrous bone tissue, or strictly oriented direction - in lamellar bone tissue.

There are two main types of bone: coarse-fibrous (immature) and lamellar.

Rough-fibrous bone tissue occurs mainly in embryos. In adults, it can be found at the site of overgrown cranial sutures, in the places where tendons attach to bones. Randomly arranged collagen fibers form thick bundles in it. In the main substance of the bone tissue there are elongated-oval bone lacunae with long anastomosing tubules, in which osteocytes with their processes lie. From the surface, the coarse-fibrous bone is covered with the periosteum.

Lamellar bone tissue is the most common type of bone in the adult body. The structural units of the compact substance of the tubular bone are osteons. They are cylinders of different diameters, as if inserted into each other. The cylinders are composed of bone plates. Bone plates are composed of cells and intercellular substance. The intercellular substance consists of an amorphous substance and ossein fibers. Ossein fibers have a strictly ordered arrangement. In each bone plate, the fibers have the same arrangement. In adjacent bone plates, the fibers are located at right angles to each other. A blood vessel passes in the center of the osteon; circular bone plates are located around the vessel, between which there are cells. The bony canal, in which the blood vessel passes, is called the Havers canal.

The tubular bone as an organ is mainly built of lamellar bone tissue. Outside, the bone is covered with the periosteum, with the exception of the articular surfaces of the epiphyses, covered with hyaline cartilage.

Two layers are distinguished in the periosteum:

external (fibrous) - formed by dense fibrous loose connective tissue;

internal (cellular) - formed by loose connective tissue containing many osteoblasts, osteoclasts, many vessels.

The periosteum connects the bone with the surrounding tissues and takes part in its trophism, development, growth and regeneration.

Connective tissue.

1. General characteristics of bony fish

Bony fish are primary aquatic vertebrates with ossified or fully bony skeletons. The waters of Russia are inhabited by representatives of one subclass of Ray-finned fish Actinopterygii, which accounts for more than 99 living species in total, according to various estimates, 22-23 thousand species.

Bony fish first appeared on our planet about 400 million years ago. They reached the greatest diversity by the beginning of our era, far ahead of all other fish and fish, as well as terrestrial vertebrates. It is the most prosperous group of vertebrates today, distributed in all waters of our planet from the poles to the equator. They are found in fresh waters, in brackish seas and oceans, in mountain lakes and streams, in the depths of ocean depressions, in sunlit coral reefs, in lightless caves in the ocean.

In terms of the number of species, this is the most numerous class of vertebrates. Among the bony fish there are giants and dwarfs - from reaching 5-7 m in length and 500-1500 kg in weight of freshwater beluga, kaluga, catfish, Brazilian arapaima and sea swordfish and marlins to tiny Filipino gobies, 7-11 mm in length. The body shape of good swimmers, inhabitants of the water column, torpedo (mackerel, salmon, tuna). Fish that do not make large movements (bream, carp, crucian carp) compressed and lateral body. In bottom fish (anglerfish, stingray), the body is compressed, which provides great contact with the bottom, where the food is. With all the variety of conditions in the aquatic environment, fish can be divided into several ecological groups:

Marine - fish permanently living in marine waters

Freshwater - fish constantly living in fresh water

Anadromous - fish that make long spawning migrations from sea water bodies to fresh water and vice versa.

Fish also differ in the nature of their distribution in the reservoir:

Inhabiting the water column (silver carp, whale shark, pike perch).

Inhabiting the bottom of reservoirs (rays, flounders, gobies, carp, crucian carp, catfish, tench).

Inhabiting the coastal area (gobies, blend dogs).

Fish that live in rivers, especially in large ones, are divided into five groups.

Species inhabiting the mountainous part of the river (trout, minnow)

Inhabitants in the foothill part (grayling, dace)

In the flat part (chub, catfish)

Downstream (ide, rudd)

Inhabiting the estuary (bream, gobies).

By way of life, fish are distinguished into pelagic fish that keep in the upper layers of the open sea (herring, sardines, garfish, mackerel, pollock, tuna), on bottom and bottom fish that live on the bottom or at the bottom (cod, haddock, flounder, slabs, gobies, etc.), as well as schooling and solitary fish. A special group is made up of deep-sea fish, among which there are bathypelagic and benthic ones.

By the nature of their diet, planktivorous fish are distinguished, consuming plankton (small crustaceans and other organisms that "soar" in the water column), benthivorous (benthos - organisms that live on the bottom) and predatory fish. The weight of food consumed by fish during the year (annual ration) is usually from 4-7 to 23-25 ​​(for predators) the fish's own weights. Many fish stop feeding in winter. Some species congregate in the bottom depressions, plunging into winter torpor, such as sturgeon, carp, catfish, which lie on "pits" in the Volga delta, or flounder, which overwinter in the waters of Kamchatka. Winter cessation of feeding causes the annual winter suspension of growth, which is imprinted on the bones of fish, including scales, in the form of compacted zones of bone matter - "winter rings". Fish usually stop eating during the spawning (breeding) period, often severely depleted during this period.

In freshwater fish, the back is usually brown or greenish, corresponding to the yellowish tint of fresh water. Fish of the open sea, such as tuna, flying fish, ocean herring, have a dark blue or violet blue back. At a depth of 100 to 200 m, silvery fish are common. Deeper, from 200 to 500 m, many fish are reddish or red in color. Deeper they are replaced by brown, violet-black and black fish. Finally, in benthic fish of very great depths, the skin is often not colored at all. And also the blind fish of the cave waters have no color at all. On the contrary, the coloration of benthic fish of shallow depths is very diverse: from monotonous gray or brown, to the brightest and most unusual combinations of colors and patterns. Usually, if there are spots and stripes on the body of a fish, they make it less noticeable against the background of stones and algae, among which it lives. This protective coloration is sometimes remarkably accurate: among the granite rocks there are fish with a granite-like pattern, black fish among lava pieces, olive yellow among brown algae, and red ones among red algae and corals. Some bottom fish are capable of rapid pattern and color changes to match the nature of the surrounding bottom. Many flounders are especially remarkable in this respect.

In addition to coloring to match the color of the background surrounding the fish, there is also a fundamentally different color, characterized by sharp stripes, bright spots on the body and eye-like round spots on the tail. This color distorts the shape of the fish's body, breaking the body contour into parts and disorienting the enemy and prey. The colorful world of these fish, shining with all colors, is not inferior in its beauty to the world of butterflies and birds. In many deep-sea fish, the role of color is played by photophore light organs. Their location on the body of the fish and the color of the light they emit are specific for each species and also have characteristic sex differences that distinguish the male from the female.

On the sides of the body and on the head, pores of the lateral line are usually noticeable - a special organ characteristic only of aquatic animals, the sense of perception of the movements of water. Thanks to the lateral line, even blinded fish do not bump into obstacles and are able to catch moving prey.

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