Cancellous bones are long and short. General osteology

AT skeleton the following parts are distinguished: the skeleton of the body (vertebrae, ribs, sternum), the skeleton of the head (bones of the skull and face), the bones of the girdles of the limbs - the upper (scapula, collarbone) and lower (pelvic) and the bones of the free limbs - the upper (shoulder, bones of the forearm and brush) and lower (femur, bones of the lower leg and foot).

Number of individual bones, which are part of the skeleton of an adult, more than 200, of which 36 - 40 are located along the midline of the body and are unpaired, the rest are paired bones.

According to external form Distinguish bones long, short, flat and mixed.

However, such a division established back in the time of Galen only in one sign(external form) turns out to be one-sided and serves as an example of the formalism of the old descriptive anatomy, as a result of which bones that are completely heterogeneous in structure, function and origin fall into one group. So, the group of flat bones includes the parietal bone, which is a typical integumentary bone that ossifies endesmally, and the scapula, which serves for support and movement, ossifies on the basis of cartilage and is built from ordinary spongy substance.

Pathological processes also proceed quite differently in the phalanges and bones the wrists, although both belong to the short bones, or in the thigh and rib, enrolled in the same group of long bones.

Therefore, it is more correct distinguish bones on the basis of 3 principles on which any anatomical classification should be built: forms (structures), functions and development.

From this point of view, the following classification of bones(M. G. Prives):

I. Tubular bones. They are built from a spongy and compact substance that forms a tube with a bone marrow cavity; perform all 3 functions of the skeleton (support, protection and movement).

Of these, long tubular bones (shoulder and bones of the forearm, femur and bones of the lower leg) are resistant and long levers of movement and, in addition to the diaphysis, have endochondral foci of ossification in both epiphyses (biepiphyseal bones); short tubular bones (carpal bones, metatarsus, phalanges) represent short levers of movement; of the epiphyses, the endochondral focus of ossification is present in only one (true) epiphysis (monoepiphyseal bones).

II. Spongy bones. They are built mainly of spongy substance, covered with a thin layer of compact. Among them, long spongy bones (ribs and sternum) and short ones (vertebrae, carpal bones, tarsals) are distinguished. Spongy bones include sesamoid bones, that is, sesame plants similar to sesame grains, hence their name (patella, pisiform bone, sesamoid bones of the fingers and toes); their function is auxiliary devices for the work of muscles; development - endochondral in the thickness of the tendons. Sesamoid bones are located near the joints, participating in their formation and facilitating movements in them, but they are not directly connected with the bones of the skeleton.

III. Flat bones:
a) flat bones of the skull(frontal and parietal) perform a predominantly protective function. They are built of 2 thin plates of compact matter, between which there is diploe, diploe, - a spongy substance containing channels for veins. These bones develop on the basis of connective tissue (integumentary bones);

b) flat bones of the belts(scapula, pelvic bones) perform the functions of support and protection, built mainly from spongy substance; develop on the basis of cartilage tissue.

IV. Mixed bones (bones of the base of the skull). These include bones that merge from several parts that have different functions, structure and development. The clavicle, which develops partly endosmally, partly endochondral, can also be attributed to mixed bones.

Video lesson: Bone as an organ. Development and growth of bones. Classification of bones according to M.G. weight gain

Each human bone is a complex organ: it occupies a certain position in the body, has its own shape and structure, and performs its own function. All types of tissues take part in bone formation, but bone tissue predominates.

General characteristics of human bones

Cartilage covers only the articular surfaces of the bone, the outside of the bone is covered with periosteum, and the bone marrow is located inside. Bone contains adipose tissue, blood and lymphatic vessels, and nerves.

Bone has high mechanical properties, its strength can be compared with the strength of metal. The chemical composition of a living human bone contains: 50% water, 12.5% organic substances of a protein nature (ossein), 21.8% inorganic substances (mainly calcium phosphate) and 15.7% fat.

Types of bones by shape divided into:

Tubular (long - shoulder, femoral, etc.; short - phalanges of the fingers);
flat (frontal, parietal, scapula, etc.);
spongy (ribs, vertebrae);
mixed (wedge-shaped, zygomatic, lower jaw).

The structure of human bones

The basic structural unit of bone tissue is osteon, which is visible under a microscope at low magnification. Each osteon includes from 5 to 20 concentrically arranged bone plates. They resemble cylinders inserted into each other. Each plate consists of intercellular substance and cells (osteoblasts, osteocytes, osteoclasts). In the center of the osteon there is a channel - the channel of the osteon; blood vessels run through it. Intercalated bone plates are located between adjacent osteons.

Bone is formed by osteoblasts, releasing the intercellular substance and immuring in it, they turn into osteocytes - cells of a process form, incapable of mitosis, with weakly expressed organelles. Accordingly, the formed bone contains mainly osteocytes, and osteoblasts are found only in areas of growth and regeneration of bone tissue.

The largest number of osteoblasts is located in the periosteum - a thin but dense connective tissue plate containing many blood vessels, nerve and lymph endings. The periosteum provides bone growth in thickness and nutrition of the bone.

osteoclasts contain a large number of lysosomes and are able to secrete enzymes, which can explain the dissolution of bone substance by them. These cells take part in the destruction of the bone. In pathological conditions in the bone tissue, their number increases sharply.

Osteoclasts are also important in the process of bone development: in the process of building the final shape of the bone, they destroy calcified cartilage and even newly formed bone, “correcting” its primary shape.

Bone structure: compact and spongy substance

On the cut, sections of the bone, two of its structures are distinguished - compact matter(bone plates are located densely and in an orderly manner), located superficially, and spongy substance(bone elements are located loosely), lying inside the bone.

Such a structure of bones fully corresponds to the basic principle of structural mechanics - to ensure maximum strength of the structure with the least amount of material and great ease. This is also confirmed by the fact that the location of the tubular systems and the main bone beams corresponds to the direction of action of the forces of compression, tension and twisting.

The structure of bones is a dynamic reactive system that changes throughout a person's life. It is known that in people engaged in heavy physical labor, the compact layer of bone reaches a relatively large development. Depending on the change in the load on individual parts of the body, the location of the bone beams and the structure of the bone as a whole may change.

Connection of human bones

All bone joints can be divided into two groups:

Continuous connections, earlier in development in phylogenesis, immobile or inactive in function;
intermittent connections, later in development and more mobile in function.

Between these forms there is a transition - from continuous to discontinuous or vice versa - semi-joint.

The continuous connection of the bones is carried out through connective tissue, cartilage and bone tissue (the bones of the skull itself). A discontinuous connection of bones, or a joint, is a younger formation of a connection between bones. All joints have a common structural plan, including the articular cavity, articular bag and articular surfaces.

Articular cavity it is allocated conditionally, since normally there is no void between the articular bag and the articular ends of the bones, but there is liquid.

Articular bag covers the articular surfaces of the bones, forming a hermetic capsule. The articular bag consists of two layers, the outer layer of which passes into the periosteum. The inner layer secretes a fluid into the joint cavity, which plays the role of a lubricant, ensuring the free sliding of the articular surfaces.

Types of joints

The articular surfaces of the articulating bones are covered with articular cartilage. The smooth surface of the articular cartilage promotes movement in the joints. The articular surfaces are very diverse in shape and size, they are usually compared with geometric figures. Hence and names of joints according to shape: spherical (shoulder), elliptical (radio-carpal), cylindrical (radio-ulnar), etc.

Since the movements of the articulating links are made around one, two or many axes, joints are also usually divided by the number of axes of rotation into multiaxial (spherical), biaxial (elliptical, saddle) and uniaxial (cylindrical, block-shaped).

Depending on the number of articulating bones joints are divided into simple, in which two bones are connected, and complex, in which more than two bones are articulated.

A 10-year-old child was admitted to the traumatology department with a hand injury, crush injury, soft tissue defect, and fragmentation of the bones of the hand and wrist joint.

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Involuntary mobility of the sacrum, relative to the iliac bones.

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Bone classification

There are various classifications that cover all types of bones of the human skeleton, depending on their location, structure and functions.

1. By location : cranial bones; body bones; limb bones.

2. By development distinguish the following types of bones : primary (appear from connective tissue); secondary (formed from cartilage); mixed.

3. The following types of human bones are distinguished by structure: tubular; spongy; flat; mixed.

tubular bones

Tubular long bones are composed of both dense and spongy matter. They can be divided into several parts. The middle of the bone is formed by a compact substance and has an elongated tubular shape. This area is called the diaphysis. Its cavities first contain red bone marrow, which is gradually replaced by yellow, containing fat cells. At the ends of the tubular bone is the epiphysis - this is the area formed by the spongy substance. Red bone marrow is placed inside it. The area between the diaphysis and the epiphysis is called the metaphysis. During the period of active growth of children and adolescents, it contains cartilage, due to which the bone grows. Over time, the anatomy of the bone changes, the metaphysis completely turns into bone tissue. The long tubular bones include the thigh, shoulder, bones of the forearm. Tubular small bones have a slightly different structure. They have only one true epiphysis and, accordingly, one metaphysis. These bones include the phalanges of the fingers, the bones of the metatarsus. They function as short levers of movement.

Spongy types of bones

The name of the bones often indicates their structure. For example, spongy bones are formed from a spongy substance covered with a thin layer of compact. They do not have developed cavities, so the red bone marrow is placed in small cells. Spongy bones are also long and short. The former include, for example, the sternum and ribs. Short spongy bones are involved in the work of muscles and are a kind of auxiliary mechanism. These include the bones of the wrist, vertebrae.

flat bones

These types of human bones, depending on their location, have a different structure and perform certain functions. The bones of the skull are primarily protection for the brain. They are formed by two thin plates of dense substance, between which is located spongy. It has openings for veins. The flat bones of the skull develop from connective tissue. The scapula and pelvic bones also belong to the type of flat bones. They are formed almost entirely from a spongy substance that develops from cartilage tissue. These types of bones perform the function of not only protection, but also support.

mixed dice

Mixed bones are a combination of flat and short spongy or tubular bones. They develop in various ways and perform the functions that are necessary in a particular part of the human skeleton. Such types of bones as mixed are found in the body of the temporal bone, vertebrae. These include, for example, the clavicle.

cartilage tissue

Cartilage has an elastic structure. It forms the auricles, nose, some parts of the ribs. Cartilaginous tissue is also located between the vertebrae, as it perfectly resists the deforming force of loads. It has high strength, excellent resistance to abrasion and crushing.

BONE CLASSIFICATION

The following parts are distinguished in the skeleton: the bones of the body (vertebrae, ribs, sternum), the bones of the skull (cerebral and facial), the bones of the limb belts - the shoulder (scapula, clavicle) and pelvic (iliac, pubic, ischial) and the bones of the free limbs - the upper ( shoulder, bones of the forearm and hand) and lower (thigh, bones of the lower leg and foot).

The number of individual bones that make up the skeleton of an adult is more than 200, of which 36-40 are located along the midline of the body and are unpaired, the rest are paired bones.

According to the external shape, the bones are long, short, wide and mixed.

However, such a division, established back in the time of Galen, according to only one sign (external form) turns out to be one-sided and serves as an example of the formalism of the old descriptive anatomy, as a result of which bones that are completely heterogeneous in structure, function and origin fall into one group. So, the group of flat bones includes the parietal bone, which is a typical integumentary bone that ossifies endesmally, and the scapula, which serves for support and movement, ossifies on the basis of cartilage and is built from ordinary spongy substance.

Pathological processes also proceed quite differently in the phalanges and bones of the wrist, although both of them belong to short bones, or in the thigh and rib, enrolled in the same group of long bones.

Therefore, it is more correct to distinguish bones on the basis of 3 principles on which any anatomical classification should be built - forms (structures), functions and development.

From this point of view, the following classification of bones can be outlined:

I. Tubular bones: 1. Long; 2. Short

II. Spongy bones: 1. Long; 2. Short; 3. Sesamoid;

III. Flat bones: 1. Skull bones; 2.Bone belts

I. Tubular bones. They are built from a spongy and compact substance that forms a tube with a bone marrow cavity: they perform all 3 functions of the skeleton (support, protection and movement). Of these, long tubular bones (shoulder and bones of the forearm, femur and bones of the lower leg) are resistant and long levers of movement and, in addition to the diaphysis, have enchondral foci of ossification in both epiphyses (biepiphyseal bones); short tubular bones (metacarpus, metatarsus, phalanges) represent short levers of movement; of the epiphyses, the enchondral ossification focus is present in only one (true) epiphysis (monoepiphyseal bones).

II. Spongy bones. They are built mainly of spongy substance, covered with a thin layer of compact. Among them, long spongy bones (ribs and sternum) and short ones (vertebrae, wrist, tarsus) are distinguished. Spongy bones include sesamoid bones, that is, sesame plants similar to sesame grains, from where their name comes from (patella, pisiform bone, sesamoid bones of the fingers and toes); their function is auxiliary devices for the work of muscles; development - enchondral in the thickness of the tendons, which they strengthen. Sesamoid bones are located near the joints, participating in their formation and contributing to their movements, but are not directly connected with the bones of the skeleton.

III. Flat bones:

a) flat bones of the skull (frontal and parietal). Function - mainly protection (integumentary bones); structure - diploe; ossification - based on connective tissue;

b) flat bones of the belts (scapula, pelvic bones), function - support and protection; structure - mainly from a spongy substance; ossification - on the basis of cartilaginous tissue.

IV. Mixed bones (bones of the base of the skull) - this includes bones that merge from several parts that have different functions, structure and development. The clavicle, which develops partly endesmally and partly enchondrally, can also be attributed to mixed bones.

Number of individual bones, which are part of the skeleton of an adult, more than 200, of which 36 - 40 are located along the midline of the body and are unpaired, the rest are paired bones.

According to external form Distinguish bones long, short, flat and mixed.

Therefore, it is more correct distinguish bones on the basis of 3 principles on which any anatomical classification should be built: forms (structures), functions and development.

From this point of view, the following classification of bones(M. G. Prives):

I. Tubular bones. They are built from a spongy and compact substance that forms a tube with a bone marrow cavity; perform all 3 functions of the skeleton (support, protection and movement).

b) flat bones of the belts(scapula, pelvic bones) perform the functions of support and protection, built mainly from spongy substance; develop on the basis of cartilage tissue.

The bones form a solid skeleton, which consists of the vertebral column (spine), sternum and ribs (trunk bones), skull, bones of the upper and lower extremities (Fig. 1). Skeleton (skeleton) performs the functions of support, movement, protection, and is also a depot of various salts (mineral substances). The red bone marrow, located inside the bones, produces blood cells (erythrocytes, leukocytes, etc.) and the immune system (lymphocytes).

The human skeleton consists of 206 bones. Of these: 36 unpaired and 85 paired.

Bone classification

Taking into account the shape and structure, there are long (tubular) bones, short (spongy), flat (wide), mixed and air bones (Fig. 2).

long bones have an elongated bone body - the diaphysis, and thickened ends - the epiphyses. On the epiphyses are articular surfaces for connection with adjacent bones. The part of a long bone located between the diaphysis and the epiphysis is called the metaphysis. Among tubular bones, long tubular bones (humerus, femur, etc.) and short tubular bones (metacarpal, metatarsal, etc.) are distinguished.

short bones, or spongy, have a cubic or polygonal shape. Such bones are located in those parts of the body where greater mobility is combined with increased mechanical load (carpal and tarsal bones).

flat bones form the walls of cavities, perform protective functions (bones of the skull roof, pelvis, sternum, ribs, scapula).

Rice. one. Human skeleton. Front view.

1 - skull, 2 - spinal column, 3 - clavicle, 4 - scapula, 5 - humerus, 6 - bones of the forearm, 7 - bones of the wrist, 8 - metacarpal bones, 9 - phalanges of the fingers, 10 - femur, 11 - patella, 12 - fibula, 13 - tibia, 14 - tarsal bones, 15 - phalanges of the toes, 16 - metatarsal bones, 17 - lower leg bones, 18 - sacrum, 19 - pelvic bone, 20 - radius, 21 - ulna bone, 22 - ribs, 23 - sternum.

Rice. 2. Bones of various shapes.

1 - airy bone, 2 - long (tubular) bone, 3 - flat bone, 4 - spongy (short) bones, 5 - mixed bone.

mixed dice have a complex shape, their parts look like flat, spongy bones (for example, vertebrae, sphenoid bone of the skull).

air bones contain cavities lined with mucous membrane and filled with air. Such cavities have some bones of the skull (frontal, sphenoid, ethmoid, temporal, maxillary bones). The presence of cavities in the bones facilitates the mass of the head. These cavities also serve as voice resonators.

On the surface of each bone there are elevations (processes, tubercles), which are called apophyses. These places are places of attachment of muscles, fascia, ligaments. In places where blood vessels and nerves adjoin, there are grooves and notches on the surface of the bones. On the surface of each bone there are small nutrient holes(foramina nutritia), through which blood vessels and nerve fibers pass.

The structure of the bone

In the structure of the bone, a compact and spongy substance is distinguished (Fig. 3).

Compact substance (substantia compacta) forms the diaphysis of tubular bones, covers the outside of their epiphyses, as well as short (spongy) and flat bones. The compact substance of the bone is permeated with thin channels, the walls of which are formed by concentric plates (from 4 to 20). Each central channel, together with the plates surrounding it, is called osteon, or Haversian system (Fig. 4). The osteon is the structural and functional unit of the bone. Between the osteons are intercalary, intermediate plates. The outer layer of the compact substance is formed by the outer surrounding plates (Fig. 5). The inner layer that bounds the medullary cavity is formed

Rice. 3. Compact and spongy bone. 1 - spongy (trabecular) substance, 2 - compact substance, 3 - nutrient canal, 4 - nutrient opening.

Rice. 4. The structure of the osteon.

1 - osteon plates, 2 - osteocytes (bone cells), 3 - central canal.

Rice. 5. Microscopic structure of the bone (small magnification).

1 - periosteum, 2 - outer surrounding plates, 3 - osteon plates, 4 - central canals (osteonal canals), 5 - bone cells, 6 - insertion plates.

Rice. 6. A bone cell (osteocyte) in a bone lacuna.

1 - bone cell, 2 - bone gap, 3 - wall of the bone gap.

internal surrounding plates. Bone plates are built from bone cells (osteocytes) and intercellular substance impregnated with salts of calcium, phosphorus, magnesium and other chemical elements. There are connective tissue fibers in the bone, which have different orientations in neighboring plates. Processed bone cells are located in miniature lacunae containing bone (tissue) fluid (Fig. 6).

Due to the presence in the bone tissue of a significant amount of salts of various chemical elements that delay x-rays, the bone is clearly visible on x-rays.

Spongy substance (substantia spongiosa) built of bone plates (beams) with cells between them (Fig. 7). The bone beams are directed towards the pressure forces and tensile forces (Fig. 8). This arrangement of the bone beams contributes to the uniform transfer of pressure to the bone, which gives the bone greater strength.

Rice. 7. The spongy substance of the body and the alveolar part of the lower jaw in a longitudinal section. Right view. 1 - dental alveoli, 2 - spongy substance of the alveolar part of the lower jaw, 3 - compact substance of the dental alveolus, 4 - spongy substance of the body of the lower jaw, 5 - compact substance of the body of the lower jaw, 6 - angle of the lower jaw, 7 - branch of the lower jaw, 8 - condylar process, 9 - head of the lower jaw, 10 - notch of the lower jaw, 11 - coronoid process of the lower jaw.

Rice. eight. Scheme of the location of the bony crossbars in the spongy substance of the tubular bone. 1 - line of compression (pressure), 2 - line of tension.

All bones, except for their articular surfaces, are covered with a connective tissue sheath - periosteum(periosteum), which is firmly fused with the bone (Fig. 9). The walls of the bone marrow cavities, as well as the cells of the spongy substance, are lined with a thin connective tissue plate - endosteum, which, like the periosteum, performs a bone-forming function. From the osteogenic cells of the endosteum, the inner surrounding plates of compact bone substance are formed.

Skeleton structure

Taking into account the structure of bones and their functions, an axial skeleton and an additional skeleton are distinguished. The axial skeleton consists of the trunk skeleton (vertebral column and chest bones) and the head skeleton (skull). The accessory skeleton includes the bones of the upper and lower extremities.

One of the most important acts of adaptation of the organism to the environment is movement. It is carried out by a system of organs, which include bones, their joints and muscles, which together make up the apparatus of movement. All bones, interconnected by connective, cartilaginous and bone tissue, together make up the skeleton. The skeleton and its joints are the passive part of the apparatus of movement, and the skeletal muscles attached to the bones are its active part.

The doctrine of the bones is called osteology, the doctrine of the joints of bones - arthrology, about muscles - myology.

The skeleton (skeleton) of an adult is more than 200 interconnected bones (Fig. 23); it forms the solid foundation of the body.

The value of the skeleton is great. Not only the shape of the whole body, but also the internal structure of the body depends on the features of its structure. The skeleton has two main functions: mechanical and biological. The manifestations of the mechanical function are support, protection, movement. The supporting function is carried out by attaching soft tissues and organs to different parts of the skeleton. The protective function is achieved by the formation of cavities by some parts of the skeleton, in which vital organs are located. So, in the cranial cavity is the brain, in the chest cavity are the lungs and heart, in the pelvic cavity - the genitourinary organs.

The function of movement is due to the movable connection of most bones, which act as levers and are set in motion by muscles.

A manifestation of the biological function of the skeleton is its participation in the metabolism, especially mineral salts (mainly calcium and phosphorus), and participation in hematopoiesis.

The human skeleton is divided into four main sections: the skeleton of the body, the skeleton of the upper limbs, the skeleton of the lower limbs and the skeleton of the head - the skull.

The structure of the bones

Each bone (os) is an independent organ with a complex structure. The basis of the bone is a compact and spongy (trabecular) substance. Outside, the bone is covered with periosteum (periosteum). The exception is the articular surfaces of the bones, which do not have a periosteum, but are covered with cartilage. Inside the bone is the marrow. Bones, like all organs, are equipped with blood vessels and nerves.

Compact matter(substantia compacta) makes up the outer layer of all bones (Fig. 24) and is a dense formation. It consists of strictly oriented, usually parallel bone plates. In the compact substance of many bones, the bone plates form osteons. Each osteon (see Fig. 8) includes from 5 to 20 concentrically arranged bone plates. They resemble cylinders inserted into each other. The bone plate consists of calcified intercellular substance and cells (osteocytes). In the center of the osteon there is a canal through which the vessels pass. Intercalated bone plates are located between adjacent osteons. In the surface layer of the compact substance, under the periosteum, there are external general, or common, bone plates, and in its inner layer from the side of the bone marrow cavity, there are internal general bone plates. Intercalated and general plates are not part of osteons. In the outer common plates there are channels that perforate them, along which vessels pass from the periosteum into the bone. In different bones and even in different parts of the same bone, the thickness of the compact substance is not the same.

spongy substance(substantia spongiosa) is located under a compact substance and looks like thin bone crossbars that intertwine in different directions and form a kind of network. The basis of these crossbars is lamellar bone tissue. The crossbars of the spongy substance are arranged in a certain order. Their direction corresponds to the action of compressive and tensile forces on the bone. The compression force is due to the pressure on the bone of the weight of the human body. The tensile force depends on the active traction of the muscles acting on the bone. Since both forces act on one bone at the same time, the spongy substance crossbars form a single beam system that ensures uniform expansion of these forces on the entire bone.

periosteum(periosteum) (periosteum) is a thin, but strong enough connective tissue plate (Fig. 25). It consists of two layers: inner and outer (fibrous). The inner (cambial) layer is represented by loose fibrous connective tissue with a large number of collagen and elastic fibers. Vessels and nerves pass through it, as well as bone-forming cells - osteoblasts. The outer (fibrous) layer consists of dense connective tissue. The periosteum is involved in the nutrition of the bone: vessels penetrate from it through holes in the compact substance. Due to the periosteum, the developing bone grows in thickness. In case of bone fractures, osteoblasts of the periosteum are activated and participate in the formation of new bone tissue (a callus is formed at the site of the fracture). The periosteum is tightly fused to the bone by means of bundles of collagen fibers penetrating from the periosteum into the bone.

Bone marrow(medulla ossium) is a hematopoietic organ, as well as a depot of nutrients. It is located in the bone cells of the spongy substance of all bones (between the bone crossbars) and in the canals of tubular bones. There are two types of bone marrow: red and yellow.

red bone marrow- delicate reticular tissue, horned with blood vessels and nerves, in the loops of which there are hematopoietic elements and mature blood cells, as well as bone tissue cells involved in the process of bone formation. Mature blood cells, as they form, penetrate into the bloodstream through the walls of relatively wide blood capillaries with slit-like pores located in the bone marrow (they are called sinusoidal capillaries).

yellow bone marrow consists mainly of adipose tissue, which determines its color. During the period of growth and development of the organism, red bone marrow predominates in the bones, with age it is partially replaced by yellow. In an adult, red bone marrow is located in the spongy substance, and yellow - in the canals of tubular bones.

According to modern concepts, the red bone marrow, as well as the thymus gland, are considered the central organs of hematopoiesis (and immunological protection). In the red bone marrow, erythrocytes, granulocytes (granular leukocytes), platelets (platelets), as well as B-lymphocytes and precursors of T-lymphocytes are formed from hematopoietic cells. The precursors of T-lymphocytes with the blood flow enter the thymus gland, where they turn into T-lymphocytes. B- and T-lymphocytes from the red bone marrow and the thymus gland enter the peripheral organs of hematopoiesis (lymph nodes, spleen), in which they multiply and turn under the influence of antigens into active cells involved in protective reactions.

The chemical composition of bones. The composition of bones includes water, organic and inorganic substances. Organic substances (ossein, etc.) determine the elasticity of the bone, and inorganic (mainly calcium salts) - its hardness. The combination of these two types of substances determines the strength and elasticity of bones. The ratio of organic and inorganic substances in the bones changes with age, which is reflected in their properties. So, in old age, the content of organic substances in the bones decreases, and inorganic increases. As a result, the bones become more brittle and more easily fractured.

Bone Development

Bones develop from embryonic connective tissue - mesenchyme, which is a derivative of the middle germ layer - Mesoderm. In their development, they go through three stages: 1) connective tissue (membranous), 2) cartilaginous, 3) bone. The exceptions are the clavicle, the bones of the roof of the skull and most of the bones of the facial section of the skull, which in their development bypass the cartilaginous stage. Bones that go through two stages of development are called primary, and three stages are called secondary.

The process of ossification (Fig. 26) can proceed in different ways: endesmal, enchondral, perichondral, periosteal.

Endesmal ossification occurs in the connective tissue anlage of the future bone due to the action of osteoblasts. In the center of the anlage, an ossification nucleus appears, from which the ossification process spreads radially over the entire plane of the bone. In this case, the surface layers of the connective tissue are preserved in the form of a periosteum (periosteum). In such a bone, one can detect the location of this primary ossification nucleus in the form of a tubercle (for example, the tubercle of the parietal bone).

Endochondral ossification occurs in the thickness of the cartilaginous anlage of the future bone in the form of an ossification focus, and the cartilage tissue is preliminarily calcified and is not replaced by bone, but is destroyed. The process spreads from the center to the periphery and leads to the formation of a spongy substance. If a similar process goes the other way around, from the outer surface of the cartilaginous bone rudiment to the center, then it is called perichondral ossification, while the osteoblasts of the perichondrium play an active role.

As soon as the process of ossification of the cartilaginous laying of the bone is completed, further deposition of bone tissue along the periphery and its growth in thickness are carried out due to the periosteum (periosteal ossification).

The process of ossification of the cartilaginous anlages of some bones begins at the end of the 2nd month of intrauterine life, and in all bones it is completed only by the end of the second decade of human life. It should be noted that different parts of the bones ossify non-simultaneously. Later, other cartilaginous tissue is replaced by bone in the area of the metaphyses of the tubular bones, where the bones grow in length, as well as in the places of attachment of muscles and ligaments.

Bone shape

The shape distinguishes between long, short, flat and mixed bones. Long and short bones, depending on the internal structure, as well as developmental features (ossification process), can be divided into tubular (long and short) and spongy (long, short and sesamoid).

tubular bones built of compact and spongy substance and have a bone marrow cavity (canal). Of these, the long ones are the levers of movement and make up the skeleton of the proximal and middle sections of the limbs (shoulder, forearm, thigh, lower leg). In each long tubular bone, the middle part is distinguished - diaphysis, or body, and two ends - epiphyses(areas of bone between the diaphysis and epiphyses are called metaphyses). Short tubular bones are also levers of movement, making up the skeleton of the distal parts of the limbs (metacarpus, metatarsus, fingers). Unlike long tubular bones, they are monoepiphyseal bones - only one of the epiphyses has its own ossification nucleus, and the second epiphysis (the base of the bone) ossifies due to the spread of this process from the body of the bone.

spongy bones have a predominantly spongy structure and are covered on the outside with a thin layer of compact substance (they do not have a channel inside). The long spongy bones include the ribs and sternum, and the short ones include the vertebrae, wrist bones, etc. This group may also include sesamoid bones that develop in the tendons of the muscles near some joints.

flat bones consist of a thin layer of spongy substance located between two plates of compact substance. These include part of the bones of the skull, as well as the shoulder blades and pelvic bones.

mixed dice- these are bones that lasted from several parts, having a different shape and development (bones of the base of the skull).

Bone joints

Bone connections are divided into two main groups: continuous connections - synarthroses and discontinuous connections - diarthroses (Fig. 27).

Synarthrosis- this is the connection of bones by means of a continuous layer of tissue that completely occupies the gaps between the bones or their parts. These joints, as a rule, are inactive and occur where the angle of displacement of one bone relative to another is small. In some synarthroses, there is no mobility. Depending on the tissue connecting the bones, all synarthroses are divided into three types: syndesmosis, synchondrosis and synostosis.

Syndesmoses, or fibrous connections, are continuous connections with the help of fibrous connective tissue. The most common type of syndesmosis are ligaments. Syndesmoses also include membranes (webs) and sutures. Ligaments and membranes are usually built from dense connective tissue and are solid fibrous formations. Sutures are relatively thin layers of connective tissue, through which almost all the bones of the skull are interconnected.

Synchondrosis, or cartilaginous connections, - connections of bones with the help of cartilage. These are elastic adhesions, which, on the one hand, allow mobility, and on the other hand, they absorb shocks during movements.

Synostoses- immovable connections with the help of bone tissue. An example of such a connection is the fusion of the sacral vertebrae into a monolithic bone - the sacrum.

Throughout a person's life, one type of continuous connection can be replaced by another. So, some syndesmoses and synchondroses undergo ossification. With age, for example, there is an ossification of the sutures between the bones of the skull; synchondroses present in childhood between the sacral vertebrae pass into synostoses, etc.

Between synarthosis and diarthrosis there is a transitional form - hemiarthrosis (half-joint). In this case, there is a narrow gap in the center of the cartilage connecting the bones. The hemiarthrosis includes the pubic symphysis - the connection between the pubic bones.

diarthrosis, or joints(holistic, or synovial joints), - discontinuous movable joints, which are characterized by the presence of four main elements: the articular capsule, articular cavity, synovial fluid and articular surfaces (Fig. 28). Joints (articulationes) are the most common type of connection in the human skeleton; they make precise dosed movements in certain directions.

joint capsule surrounds the articular cavity and ensures its tightness. It consists of outer - fibrous and inner - synovial membranes. The fibrous membrane fuses with the periosteum (periosteum) of the articulating bones, and the synovial membrane fuses with the edges of the articular cartilage. The synovial membrane is lined from the inside with endothelial cells, which makes it smooth and shiny.

In some joints, the fibrous membrane of the capsule becomes thinner in places, and the synovial membrane forms a protrusion in these places, which are called synovial bags, or bursae. They are usually located near the joints under the muscles or their tendons.

Articular cavity- this is a gap limited by the articular surfaces and the synovial membrane, hermetically isolated from the tissues surrounding the joint. The pressure in the joint cavity is negative, which contributes to the convergence of the articular surfaces.

synovial fluid(synovia) is a product of the exchange of the synovial membrane and articular cartilage. It is a clear, sticky liquid, similar in composition to blood plasma. It fills the articular cavity, moisturizes and lubricates the articular surfaces of the bones, which reduces friction between them and contributes to their better adhesion.

Articular surfaces of bones covered with cartilage. Due to the presence of articular cartilage, the articulating surfaces are smoother, which contributes to better glide, and the elasticity of the cartilage softens possible shocks during movements.

The articular surfaces are compared in shape with geometric figures and are considered as surfaces resulting from the rotation of a straight or curved line around a conditional axis. When a straight line rotates around a parallel axis, a cylinder is obtained, and when a curved line is rotated, depending on the shape of the curvature, a ball, ellipse or block is formed, etc. According to the shape of the articular surfaces, spherical, elliptical, cylindrical, block-shaped, saddle-shaped, flat and other joints are distinguished (Fig. 29). In many joints, one articular surface is shaped like a head and the other is shaped like a cavity. The range of motion in the joint depends on the difference in the length of the arc of the head and the arc of the cavity: the greater the difference, the greater the range of motion. Articular surfaces that correspond to each other are called congruent.

In some joints, in addition to the main elements, there are additional ones: articular lips, articular discs and menisci, articular ligaments.

articular lip consists of cartilage, is located in the form of a rim around the articular cavity, which increases its size. Articular lip have shoulder and hip joints.

Articular discs and menisci built from fibrous cartilage. Located in the duplication of the synovial membrane, they are introduced into the joint cavity. The articular disc at the same time divides the joint cavity into two sections that do not communicate with each other; the meniscus does not completely separate the joint cavity. Along their outer circumference, the discs and menisci are fused with the fibrous membrane of the capsule. The disc is present in the temporomandibular joint and the menisci are present in the knee joint. Thanks to the articular disc, the volume and direction of movement in the joint change.

Articular ligaments divided into intracapsular and extra-capsular. Intracapsular ligaments, covered with a synovial membrane, are located inside the joint and are attached to the articulating bones. Extracapsular ligaments strengthen the joint capsule. At the same time, they affect the nature of movements in the joint: they contribute to the movement of the bone in a certain direction and can limit the range of motion. In addition to ligaments, muscles are involved in strengthening the joints.

In the ligaments and capsules of the joints there are a large number of sensitive nerve endings (proprioreceptors) that perceive irritation caused by a change in the tension of the ligaments and the capsule during movement of the joints.

To determine the nature of movements in the joints, conditionally three mutually perpendicular axes are carried out: frontal, sagittal and vertical. Flexion (flexio) and extension (extensio) are performed around the frontal axis, abduction (abductio) and adduction (adductio) around the sagittal axis, and rotation (rotatio) around the vertical axis. In some joints, circular motion (circumductio) is also possible, in which the bone describes a cone.

Depending on the number of axes around which movement can occur, the joints are divided into uniaxial, biaxial and triaxial. Uniaxial joints include cylindrical and block-shaped, biaxial - ellipsoid and saddle-shaped, triaxial - spherical. In triaxial joints, as a rule, a large range of motion is possible.

Flat joints are characterized by low mobility, which has the nature of sliding. The articular surfaces of flat joints are considered as segments of a ball with a large radius.

Depending on the number of articulating bones, the joints are divided into simple, in which two bones are connected, and complex, in which more than two bones are connected. Joints that are anatomically separate from each other, but movements in which can only occur simultaneously, are called combined. An example of such joints are the two temporomandibular joints.

tubular bones They consist of a tube (diaphysis) and two heads (epiphyses), moreover, the spongy substance is present only in the heads, and the tubes have a cavity filled with yellow bone marrow in adults. Until the end of puberty, between the diaphysis and the epiphyses there is a layer of epiphyseal cartilage, due to which the bone grows in length. The heads have articular surfaces covered with cartilage. Tubular bones are divided into long (humerus, radius, femur) and short (carpus bones, metatarsus, phalanges).

spongy bones built primarily of spongy matter. They are also divided into long (ribs, collarbones) and short (vertebrae, wrist bones, tarsals).

flat bones formed by the outer and inner plates of a compact substance, between which there is a spongy substance (occipital, parietal, scapula, pelvic).

Bones of a complex structure - vertebrae, wedge-shaped (located under the brain) - are sometimes distinguished into a separate group mixed bones.

Tests

1. The shoulder blade refers to
A) cancellous bones
B) flat bones
B) mixed bones
D) tubular bones

2. Ribs refer to
A) cancellous bones
B) flat bones
B) mixed bones
D) tubular bones

3) The bone grows in length due to
A) periosteum
B) spongy bone tissue
B) dense bone tissue
D) cartilage

4. At the end of the tubular bone is
A) diaphysis
B) red bone marrow
B) epiphysis
D) epiphyseal cartilage