Bone as an organ: structure, properties, functions. The structure of bone as an organ. Classification of bones Structure of bone as an organ sections of tubular bone

Human skeleton: functions, departments

The skeleton is a collection of bones, cartilage that belongs to them, and ligaments connecting the bones.

There are more than 200 bones in the human body. The skeleton weighs 7-10 kg, which is 1/8 the weight of a person.

The following are distinguished in the human skeleton: departments:

• head skeleton(scull), torso skeleton- axial skeleton;
• upper limb belt, lower limb belt- accessory skeleton.

Human skeleton front

Skeletal functions:

• Mechanical functions:

1. support and attachment of muscles (the skeleton supports all other organs, gives the body a certain shape and position in space);
2. protection - the formation of cavities (the skull protects the brain, the chest protects the heart and lungs, and the pelvis protects the bladder, rectum and other organs);
3. movement - a movable connection of bones (the skeleton together with the muscles makes up the motor apparatus, the bones in this apparatus play a passive role - they are levers that move as a result of muscle contraction).

1. mineral metabolism;
2. hematopoiesis;
3. blood deposition.

Classification of bones, features of their structure. Bone as an organ

Bone- a structural and functional unit of the skeleton and an independent organ. Each bone occupies a precise position in the body, has a certain shape and structure, and performs its characteristic function. All types of tissues take part in bone formation. Of course, the main place is occupied by bone tissue. 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 fatty tissue, blood and lymphatic vessels, and nerves. Bone tissue has high mechanical properties; its strength can be compared to the strength of metal. Relative bone density is about 2.0. Living bone contains 50% water, 12.5% ​​organic protein substances (ossein and osseomucoid), 21.8% inorganic mineral substances (mainly calcium phosphate) and 15.7% fat.

In dried bone, 2/3 consists of inorganic substances, on which the hardness of the bone depends, and 1/3 - organic substances, which determine its elasticity. The content of mineral (inorganic) substances in bone gradually increases with age, causing the bones of older and older people to become more fragile. For this reason, even minor injuries in old people are accompanied by bone fractures. The flexibility and elasticity of bones in children depend on the relatively higher content of organic substances in them.

Osteoporosis- a disease associated with damage (thinning) of bone tissue, leading to fractures and bone deformation. The reason is failure to absorb calcium.

The structural functional unit of bone is osteon. Typically, an osteon consists of 5-20 bone plates. Osteon diameter is 0.3 - 0.4 mm.

If the bone plates fit tightly to each other, then a dense (compact) bone substance is obtained. If the bone crossbars are loosely located, then spongy bone substance is formed, which contains red bone marrow.

The outside of the bone is covered with periosteum. It contains blood vessels and nerves.

Due to the periosteum, the bone grows in thickness. Due to the epiphyses, the bone grows in length.

Inside the bone there is a cavity filled with yellow bone marrow.

Internal structure of bone

Classification of bones according to form:

1. Tubular bones- have a general structural plan, they distinguish between a body (diaphysis) and two ends (epiphyses); cylindrical or triangular shape; length prevails over width; On the outside, the tubular bone is covered with a connective tissue layer (periosteum):

• long (femoral, shoulder);
• short (phalanxes of fingers).

• long (sternum);
• short (vertebrae, sacrum)
• sesamoid bones - located in the thickness of the tendons and usually lie on the surface of other bones (patella).

• skull bones (roof of the skull);
• flat (pelvic bone, shoulder blades, bones of the girdles of the upper and lower extremities).

Bones are built from bone tissue and are covered on top with periosteum (Fig. 5). Bone is divided into compact bone substance and spongy bone substance. The compact substance has a lamellar structure. There are common outer plates; Haversian plate systems, or osteons; insertion plates located between the osteons and under the periosteum, where they form the outer layer of the compact substance.

Osteons are structural and functional units of bones and are formed by tube-shaped plates inserted into each other. Depending on the type of animal, age and position of the bone, the number of these plates is from two to twenty. These tubes are placed around the vascular (Haversian) canals, in which blood vessels and nerves pass. The plates consist of an intercellular substance, in which a basic structureless substance and a fibrous part are distinguished. The fibrous part is collagen fibers. Bone cells are located between the plates. The structureless substance consists of organic compounds that have come into close contact with mineral inclusions, which gives the bone special strength.

Spongy bone substance is found under the compact substance in the thickened ends of long bones, in all short bones, and inside long curved bones. Spongy bone substance has a porous structure due to crossbars located along the force lines of compression and tension. These crossbars are formed during the growth process from the remains of osteons, intercalary and other plates. Thanks to the spongy structure, strength and elasticity increase, the surface of the bones increases with a minimum of their mass. Between the trabeculae of the spongy bone there is red bone marrow and numerous blood vessels.

Each bone is surrounded on the outside by periosteum, which contains many blood vessels that penetrate through special tubules into the Haversian canal system, providing nutrition to the bone. The periosteum consists of two layers of dense connective tissue. The outer layer contains thick bundles of collagen fibers, the inner layer contains thinner bundles, and there are also elastic fibers. The superficial layer of the periosteum is especially thick at the sites of attachment of tendons and ligaments, as bundles of collagen fibers penetrate into the thickness of the bone.

The deep layer is abundantly supplied with cells - osteoblasts. As bone grows, they multiply vigorously, produce intercellular substance of bone tissue and, one after another, turn into real bone cells of newly formed bone layers. This is how the bone grows thicker on the outside. In a mature body, osteoblasts are preserved in the periosteum not in a continuous layer, but in patches and participate in the restoration of damaged areas of the bone.

According to their shape and function, bones are divided into long tubular, long curved, short symmetrical, short asymmetrical, and lamellar.

Long tubular bones act as levers of movement and support and make up the skeleton of the limbs. In a long tubular bone, a body is distinguished - a diaphysis with a medullary region and two thickened ends: proximal (upper) and distal (lower) - epiphyses. On some bones there are bony processes - apophyses.

Long curved bones - ribs - form the side walls of the chest, giving it shape, and protect the organs of the chest cavity. The ribs act as levers of movement for the muscles of the chest walls, ensuring the process of inhalation and exhalation.

Short symmetrical bones - vertebrae - provide mobility of the spinal column,

Short asymmetrical bones - the right and left bones of the wrist, tarsus, kneecaps - have a spring function.

Lamellar bones - the bones of the skull, scapula, pelvic bones - provide support for the organs located in them and increase the surface for muscle attachment.

Pneumatic bones in the frontal, jaw and other bones have bony cavities filled with air. These bones lighten the weight of the body.

The properties of bones depend on their structure, chemical composition and location in the skeleton. Fresh bones contain on average water up to 50%, fat up to 15, organic matter (ossein) up to 13, minerals up to 22%: including lime phosphate up to 85%, lime carbonate up to 9, lime fluoride up to 3, iron up to 0.6 , chlorine up to 0.2%. Bones have great compressive strength, tensile strength and fracture strength. The compressive strength of 1 cm3 of bone is 1400 kg, tensile strength is 1055 kg and depends on the species, sex, age of the animal, topography of the bone in the skeleton, conditions of keeping and feeding.

Bone (os) is an organ that is a component of the system of organs of support and movement, having a typical shape and structure, characteristic architecture of blood vessels and nerves, built primarily from bone tissue, covered on the outside with periosteum (periosteum) and containing bone marrow (medulla osseum) inside.

Each bone has a specific shape, size and position in the human body. The formation of bones is significantly influenced by the conditions in which bones develop and the functional loads that bones experience during the life of the body. Each bone is characterized by a certain number of sources of blood supply (arteries), the presence of certain places of their localization and the characteristic intraorgan architecture of blood vessels. These features also apply to the nerves innervating this bone.
Each bone consists of several tissues that are in certain proportions, but, of course, the main one is lamellar bone tissue. Let us consider its structure using the example of the diaphysis of a long tubular bone.
The main part of the diaphysis of the tubular bone, located between the outer and inner surrounding plates, consists of osteons and intercalated plates (residual osteons). The osteon, or Haversian system, is a structural and functional unit of bone. Osteons can be viewed in thin sections or histological preparations (Fig. 1.1).
The osteon is represented by concentrically located bone plates (Haversian), which in the form of cylinders of different diameters, nested within each other, surround the Haversian canal. The latter contains blood vessels and nerves. Osteons are mostly located parallel to the length of the bone, repeatedly anastomosing with each other. The number of osteons is individual for each bone; in the femur it is 1.8 per 1 mm[*]. In this case, the Haversian canal accounts for 0.2-0.3 mm2. Between the osteons there are intercalary, or intermediate, plates that run in all directions. Intercalated plates are the remaining parts of old osteons that have undergone destruction. The processes of new formation and destruction of osteons constantly occur in bones.
Outside, the bone is surrounded by several layers of general, or common, plates, which are located directly under the periosteum (periosteum). Perforating channels (Volkmann's) pass through them, which contain blood vessels of the same name. At the border with the medullary cavity in the tubular bones there is a layer of internal surrounding plates. They are penetrated by numerous channels expanding into cells. The medullary cavity is lined with endosteum, which is a thin connective tissue layer containing flattened inactive osteogenic cells.

In bone plates shaped like cylinders, ossein fibrils are closely and parallel to each other. Osteocytes are located between the concentrically lying bone plates of osteons. The processes of bone cells, spreading along the tubules, pass towards the processes of neighboring osteocytes, enter into intercellular connections, forming a spatially oriented lacunar-tubular system involved in metabolic processes.
The osteon contains up to 20 or more concentric bone plates. The osteon canal contains 1-2 microvasculature vessels, unmyelinated nerve fibers, lymphatic capillaries, accompanied by layers of loose connective tissue containing osteogenic elements, including perivascular cells and osteoblasts. The osteon channels are connected to each other, to the periosteum and the medullary cavity due to perforating channels, which contributes to the anastomosis of the bone vessels as a whole.
The outside of the bone is covered with periosteum, formed by fibrous connective tissue. It distinguishes between the outer (fibrous) layer and the inner (cellular). Cambial precursor cells (preosteoblasts) are localized in the latter. The main functions of the periosteum are protective, trophic (due to the blood vessels passing here) and participation in regeneration (due to the presence of cambial cells).
The periosteum covers the outside of the bone (Fig. 1.2), with the exception of those places where articular cartilage is located and muscle tendons or ligaments are attached (on the articular surfaces, tuberosities and tuberosities). The periosteum delimits the bone from surrounding tissues. It is a thin, durable film consisting of dense connective tissue in which blood and lymphatic vessels and nerves are located. The latter penetrate from the periosteum into the substance of the bone.
The periosteum plays a large role in the development (growth in thickness) and nutrition of the bone. Its inner osteogenic layer is the site of bone tissue formation. The periosteum is richly innervated and therefore highly sensitive. A bone deprived of periosteum becomes nonviable and dies. During surgical interventions on bones for fractures, the periosteum must be preserved.
Almost all bones (with the exception of most

1. skull bones) have articular surfaces for articulation with other bones. The articular surfaces are covered not by periosteum, but by articular cartilage (cartilago articularis). Articular cartilage is more often hyaline in structure and less often fibrous.

1. The spongy substance or the bone marrow cavity (cavitas medullaris) contains bone marrow. It comes in red and yellow. In fetuses and newborns, the bones contain only red (blood-forming) bone marrow. He is

Rice. 1.3. Human skeleton (front view):
1 skull; 2 - sternum; 3 clavicle: 4 - ribs; 5 - humerus; 6 - ulna; 7 radius; 8 hand bones; 9 pelvic bone; 10 femur; 11 patella; 12 fibula; 13 - tibia; 14 foot bones
a homogeneous mass of red color, rich in blood vessels, blood cells and reticular tissue. Red bone marrow also contains bone cells and osteocytes. The total amount of red bone marrow is about 1500 cm[†].
In an adult, the bone marrow is partially replaced by yellow marrow, which is mainly represented by fat cells. Only bone marrow located within the medullary cavity can be replaced. It should be noted that the inside of the bone marrow cavity is lined with a special membrane called endosteum.
The study of bones is called osteology. It is impossible to indicate the exact number of bones, since their number changes with age. During life, more than 800 individual bone elements are formed, of which 270 appear in the prenatal period, the rest after birth. At the same time, most of the individual bone elements in childhood and adolescence grow together. The adult human skeleton contains only 206 bones (Fig. 1.3, 1.4). In addition to permanent bones, in adulthood there may be unstable (sesamoid) bones, the appearance of which is determined by the individual characteristics of the structure and functions of the body.
Bones together with their connections in the human body make up the skeleton. The skeleton is understood as a complex of dense anatomical formations that perform primarily mechanical functions in the life of the body. We can distinguish a hard skeleton, represented by bones, and a soft skeleton, represented by ligaments, membranes and cartilaginous joints.
Individual bones and the human skeleton as a whole perform various functions in the body. The bones of the trunk and lower extremities perform a supporting function for soft tissues (muscles, ligaments, fascia, internal organs). Most bones are levers. Muscles that are attached to them
provide locomotor function (moving the body in space). Both of these functions allow us to call the skeleton a passive part of the musculoskeletal system.
The human skeleton is an anti-gravity structure that counteracts the force of gravity. Under the influence of the latter, the human body is pressed to the ground, while the skeleton prevents the body from changing its shape.
The bones of the skull, torso and pelvic bones serve as protection against possible damage to vital organs, large vessels and nerve trunks. Thus, the skull is a container for the brain, the organ of vision, the organ of hearing and balance. The spinal cord is located in the spinal canal. The chest protects the heart, lungs, large vessels and nerve trunks. The pelvic bones protect the rectum, bladder and internal genital organs from damage.
Most bones contain red bone marrow, which is a hematopoietic organ and also an organ of the body's immune system. At the same time, the bones protect the red bone marrow from damage and create favorable conditions for its trophism and the maturation of blood cells.
Bones take part in mineral metabolism. Numerous chemical elements are deposited in them, mainly calcium and phosphorus salts. Thus, when radioactive calcium is introduced into the body, within a day more than half of this substance accumulates in the bones.

As the name suggests, the science of biochemistry stands at the intersection of two important disciplines. One of them is chemistry, the other is biology. And biochemistry studies, respectively, the chemical composition of living cells and organisms. In addition, biological chemistry (or chemical biology) studies various chemical processes that underlie the life activity of absolutely any living creature. But, in this case, the most interesting will be the structure of the horse’s bone from the point of view of biochemistry.

Like any vertebrate animal, bones provide support for the body. In the complex, this is the backbone or, which participates in the movements of the animal’s body and also protects the internal organs. On the one hand, the skeleton of horses is very similar to the skeleton of the same big cats or, for example, wolves (all these types of animals are known to move on four limbs). But, on the other hand, horses are radically different from them. And not just physically. The bones of the horse skeleton also have a rather complex chemical composition.

Skeleton bones

Absolutely all bones in a horse consist of various compounds. These compounds, in turn, are divided into organic and inorganic. The first can safely include protein (scientifically - ossein), as well as lipids (this is yellow bone marrow). The latter most often include water and various mineral salts. Among them: calcium, potassium, sodium, magnesium, phosphorus and other chemical elements. And if, for example, you remove a bone from the body of an adult, you can see that half of it consists of water, 22% of minerals, 12% of protein and 16% of lipids.

According to their properties, the bones of horses have quite high hardness and strength. This largely depends on the high content of minerals and other essential elements. Two more important properties are elasticity and resilience. Both of them are directly dependent on protein. In general, this combination of hardness and elasticity is largely achieved due to a specific combination of organics and inorganics. And if you compare horse bones with any material, then in terms of elasticity and strength it is the same as bronze or copper.

But horses’ bones will not always be so hard and elastic. The ratio of many components in the bone composition depends, first of all, on the age of the horse, and only then on nutrition and time of year. For example, a young animal has a 1:1 ratio of protein to minerals. In an adult animal – 1:2. And the old one has 1:7.

Every bone in every horse is made up of bone tissue. The fabric itself is constantly and quite quickly modified. In addition to all this, bone tissue is probably the only one in the entire body capable of complete regeneration. What’s interesting is that two processes that are diametrically opposed to each other can occur in it at once - the process of restoration and the process of destruction. All these processes are strongly influenced by various mechanical forces that occur during the period of statics and/or dynamics of the animal.

The horse's bone tissue itself consists of various cells and intercellular substance.

There are only a few types of bone cells:

1. Osteoblasts.
2. Osteocytes.
3. Osteoclasts.

Osteoblasts are the youngest cells. They synthesize intercellular substance.

When it accumulates, the osteoblasts become immured in it and subsequently become osteocytes. Another important function is their direct participation in the processes of calcium deposition in the same intercellular matrix. This process is called calcification.

Translated from Greek, the word “osteocyte” means “cell container”.

These cells are found in mature individuals. As mentioned above, they are formed from osteoblasts. Their bodies are located in the cavities of the ground substance, and their processes are located in the tubules extending from the cavities. According to many scientists, they take an active part in the formation of protein and dissolve intercellular non-mineralized substance. It is they who are given the ability to ensure the unification of the bone, as well as its structural integration.

Osteoclasts are huge cells with many nuclei (15-20 closely located).

Their diameter is approximately 40 microns. They are able to appear in places where the bone structure is resorbed. These cells remove bone tissue by breaking down collagen as well as dissolving minerals. Thus, their main function is the removal of decay products in the bones, and, of course, the dissolution of mineral structures.

And the last thing that makes up bone tissue is the intercellular substance. It is also called bone matrix. It is represented mainly by collagen fibers, as well as one amorphous component.

Thanks to collagen, minerals are deposited in bones in a system of two phases:

• Crystalline hydroxyapatite.
• Amorphous calcium phosphate.

The first phase contributes to the appearance of energy necessary for the transformation of bones. Next, the bone becomes polar. Concave parts have a negative charge, convex parts have a positive charge.

As you know, bone tissue is quite complex in its chemical structure. It contains proteins (ossein), various minerals, and, of course, water (the most of it - 50%). And the cellular composition here is quite complex: osteoblasts, osteocytes, osteoclasts and intercellular substance. It’s clear that for a person who doesn’t understand anything about chemistry, all this can be quite complicated.

But besides all this, we can distinguish two more main types of such fabric. These are: lamellar and coarse fiber. Just by the names you can imagine that the first type is more like a coarse fiber, while the second resembles plates.

The coarse fibrous type of horse bone tissue is more consistent with the chaotic arrangement of collagen in the intercellular matrix.

It is from this type of bone tissue that the main skeleton of the fetus is built, as well as the skeleton of a newborn animal. In adults, the coarse-fiber type of tissue is found only in those areas where the tendons are attached to the bones. It can also be seen in the sutures of the skull, immediately after their immediate healing.

But the plate type is a completely different story, so to speak.

The main feature here is that the protein and collagen fibers are arranged in a very strict order and form special cylindrical plates. They are inserted into one another and “encircle” the vessels. Together with the vessels, these plates also surround the nerves, which are located in the Haversian canal.

In general, all these formations received one single name: “osteon”. That is, the structural unit of lamellar tissue is precisely the osteon. Each osteon, in turn, consists of several cylindrical plates (usually from 5 to 20).

Each such plate has a diameter of 3-4 mm. The osteons themselves are arranged in perfect order. And the functional load on the entire bone directly depends on this order. The osteons then form the various struts of bone substance. They are also called beams. These same beams form a kind of compact substance, if, of course, they lie “tightly”. Otherwise, if the crossbars lie “loosely,” then the beams form a spongy substance.

If the first type of bone tissue is more characteristic of a young organism, then the second type is used to build the skeleton of an adult (mature) organism. However, elements of the first type are sometimes present in adult individuals. And elements of the second, in their infancy, are found in younger people.

The body of any vertebrate animal, including humans, contains a large number of different tissues. And all these tissues are studied by such a science as histology. It is clear that histology itself is divided into even more highly specialized disciplines. The name of histology is translated from Greek as “knowledge of tissues.” A person involved in this exact science is called a histologist.

Nowadays, the main subjects of histology study are the following types of tissues:

• Bone.
• Cartilaginous.
• Connective.
• Myeloid.
• Liquid tissues of the internal environment.
• Endothelium.
• Nervous tissue.

The bones of the skeleton are formed from bone tissue. It is the hardest, most durable, elastic and resilient.

Cartilages are formed from cartilaginous tissue. It consists of chondroblasts, chondrocytes, chondroclasts and intercellular substance.

Also, there are three types of cartilage tissue in horses: hyaline (joints, ribs), fibrous (intervertebral discs) and elastic (ears).

Connective tissue also consists of three main types of cells (fibroblasts, fibrocytes and fibroclasts) and intercellular substance.

Among other things, it contains fibers and amorphous substances (neutral and acidic glycosaminoglycans). There are also two types of connective tissue in horses. These are: loose (accompanies blood vessels and nerves) and dense (forms the fibrous layer of the periosteum). Its main function becomes extremely clear from the name.

Myeloid tissue is responsible for red bone marrow and cell development that affects the horse.

Liquid tissues of the internal environment include blood and, which are involved in the transport of oxygen, carbon dioxide, nutrients and all final metabolic products. They perform three important functions at once: transport, trophic (regulation of the composition of intercellular fluid) and protective. By the way, an interesting fact is associated with liquid tissues - about 50% of all venous blood is contained in the bones.

Endothelium is a special type of epithelial tissue that forms the inner wall of blood vessels.

Another important thing that is important for a histologist is nervous tissue. It consists of nerves and nerve endings.

And if any type of tissue is damaged or in poor condition, then there is a very high chance that the animal may become seriously ill and die. And to prevent this from happening, you need proper care, proper nutrition, and, of course, care.

In general, a science such as anatomy is “not intended,” so to speak, for the study of bones. Anatomy is aimed, rather, at studying the body as a whole, as well as at studying the internal shape and structure of organs. But, since everything in the body of any living creature is interconnected, the skeleton can be studied in an anatomical manner. This is what an anatomist does. And from the point of view of this same anatomist, bone (translated from Latin, by the way, means “axis”) is a completely independent organ.

And it has a certain size, structure and shape. Thus, in the bone of an adult individual several specific layers can be distinguished:

1. Periosteum.
2. Compact and spongy substance.
3. Bone marrow cavity with endosteum.
4. Bone marrow.
5. Articular cartilage.

But a bone that grows, in addition to the five components described above, also has some others necessary for the formation of growth zones. Here we can immediately distinguish three subtypes of bone tissue and, of course, metaphyseal cartilage.

The periosteum is located inside the bone on its very surface. It usually consists of two layers: an inner layer and an outer layer.

The first is dense connective tissue. And, as usual, it performs protection functions. The second is that the tissue is the most loose, and due to it, regeneration occurs along with growth. The periosteum itself is responsible for three very important functions at once: bone-forming, trophic and protective.

The compact (or dense, as it is also called) substance is located behind the periosteum itself. It consists of lamellar fabric. A distinctive feature of this substance is its strength and density.

Immediately below it you can see another substance - spongy. It is constructed from absolutely the same fabric from which the compact substance is constructed. The only thing that distinguishes it is its bone crossbars, which are quite loose in their properties. They, in turn, form special cells.

A cavity can be found inside the bone itself. It is called bone marrow. The walls of this cavity (as well as the walls of the bone beams) are covered with a very thin membrane consisting of fibers. But the walls of this shell are lined with connective tissue. This shell is called endostome. It consists of osteoblasts.

And the red bone marrow itself can be found inside the cells of the spongy substance or even in the bone marrow cavity.

The processes of blood formation take place in the bone marrow. During the course, as well as in newborns, all bones participate in the process of blood formation. With age, this gradually begins to subside, and the red brain turns into yellow.

And finally, articular cartilage.

It is constructed from hyaline tissue. It covers the surfaces of the joints in the bones. The thickness of cartilage varies greatly. It is thinner in the proximal section. It does not have perichondrium as such, and is almost not subject to ossification. A decent load can contribute to its thinning.

The skeleton of an adult horse (and any other higher vertebrate animal) consists of several specific types of bones. Based on this, several main classifications can be distinguished. The first of these is bone structure. This was discussed in previous articles. The second is the shape of the bone. For example, the rib bones and lower leg bones are very different. The third classification of bones in a horse is by development (the bones of a young and old animal are different) And, finally, the fourth is by function.

The long bones of a horse are divided into arched (these include ribs) and tubular. The latter act as unique levers of movement. They consist of a long part of the body (also called the diaphysis) and thickened ends (they are called the pineal gland). Between them is the metaphysis, which ensures bone growth.

Shorter bones are composed mainly of spongy substance. On the outside, they are covered with a thin layer of compact substance or articular cartilage. Located in places of greater mobility and greater load. They seem to be a kind of springs.

Flat bones form the walls of cavities and the girdle of the limbs (shoulder or pelvic). They can be imagined as a fairly wide surface, which is intended for attaching muscles. On flat bones you can clearly see the edges and corners. Compacts usually consist of three layers. Between them there is a little spongy substance. At the same time, they actively perform a protection function. Examples of such bones include: bones of the skull roof, sternum, scapula, and pelvic bones.

From the name it is very clear that “os pneumaticum” or pneumatic bones are associated with “carrying air”. Inside their so-called body, these bones have a cavity of a certain size. These cavities can easily include the sinus and sinus. From the inside, both are lined with mucous membranes.

These include shells:

• Maxillary.
• Wedge-shaped.
• Frontal.

All of them are filled with air to one degree or another. In addition, they can communicate well with the nasal cavity.

The last of the subspecies are bones of the mixed type, which have a rather complicated shape. Most often, this type combines several features of several specific options. They consist of those parts that have completely different structure and shape. They may also be different in origin. These include, for example, bones or vertebrae located at the very base of the skull. By the way, a very large number of veins can pass through some cranial bones. And such bones are called “diplosis”.

If we analyze the classification of bones by origin, we can distinguish two main types. These are primary bones and secondary bones.

Primary ones develop from the so-called mesenchyme, and there are only two stages of development: bone and connective tissue. The primary bones include numerous integumentary bones of the skull: maxillary, frontal, interparietal, nasal, incisive, parietal and squama of the temporal bone.

They are particularly characterized by endesemal ossification. That is, ossification into connective tissue.

Secondary bones develop from the rudiment of the formation of bone and cartilage tissues of the body (mesoderm sclerotome). Unlike primary bones, secondary bones go through three main stages of development at once:

1. Connective tissue.
2. Cartilaginous.
3. Bone.

Thus, the vast majority of skeletal bones develop.

The process of ossification or ossification of secondary bones is much more difficult. Three points of ossification are involved here at once, two of which are epiphase, one is diaphase.

The bones themselves are formed on the basis of the rudiments of cartilage. Cartilage tissue is then replaced by bone tissue and includes two types of ossification: perichondral ossification and enchondral ossification.

Perichondral begins when osteoblasts on the inner side of the perichondrium form fibrous tissue, and then lamellar tissue. In the same place, the perichondrium transforms into the periosteum and forms the bony cuff. It disrupts the nutrition of the cartilage, and it gradually collapses.

Enchondral ossification begins approximately when perichondral ossification ends. The centers of this type of ossification appear at different times in the epiphases of long bones. In these same centers, cartilage is resorbed, after which enchondral bone is formed. After it, the perichondral bone appears. Additional points of ossification - apophyses - appear towards the end of the fetal period. The ossified epiphases and diaphysis are connected by cartilaginous plates in the tubular bones.

Cartilaginous plates are otherwise called metaphyseal cartilages (number 5 in the figure).

These cartilages are located precisely in the zone of direct growth. And the bone grows precisely due to them. Growth stops followed by ossification. Simply put, all the main points and additional ones merge together. After which they unite into one continuous mass, and further synostosis occurs.

The bones of any vertebrate animal are formed not just like that, but according to a certain pattern. This pattern was first identified by P.F. Lesgaft, founder of modern functional anatomy.

Among these laws, Lesgaft especially emphasized the principle of bone tissue formation. Next, he spoke about the degrees of bone development, since development also occurs according to a certain pattern. Lesgaft also did not forget about the strength and lightness of bones, about the external form and its subsequent restructuring.

Now I would like to talk in more detail about bone tissue. It “has the habit” of forming precisely in those places where the greatest tension or compression occurs.

There is a certain pattern: it is directly proportional to the development of the bone structure. That is, the better the muscles are developed, the better the bones will be developed.

Their external shape (bones) can change under pressure or stretching. Relief and shape also depend on the muscles. Thus, if a muscle is connected to a bone by a tendon, a tubercle is formed. If the muscle is woven into the periosteum, then there is a depression.

With optimal use of bone material, the arched and tubular structure of the bones provides greater strength and lightness.

The external shape of the bones itself directly depends on the pressure that the surrounding tissues exert on them (the bones). In addition, the external shape may change somewhat due to pressure on the bone of various organs. It’s worth clarifying here: bones form so-called “bone receptacles” or pits for organs. Accordingly, the slightest change in bones will lead to changes in organs and vice versa. Where the vessels pass, there are certain grooves on the bones. In addition, the shape of the bones can change with an increase or decrease in pressure.

In addition, the shape of the bone can change quite well. This happens under the influence of various external forces. Time also has a strong influence on restructuring. For example, if you observe young and old animals, it turns out that in young animals the bone relief is greatly smoothed out.

But in old animals, on the contrary, it is very, very pronounced.

And everything described above once again confirms how everything in the body is interconnected. For example, if an animal (or even a person) has damaged bones, this will also affect the internal tissues and organs. And if you provide timely and correct assistance, the animal will live a long and rich life.

The influence of various factors on bone development

Speaking about various factors that influence the bones of the skeleton, one cannot fail to mention the endocrine system. With the help of certain hormones (female or male), the same system regulates the activity of all internal organs. The hormones themselves are released into the blood by endocrine cells. In addition to internal organs, the endocrine system has a fairly significant influence on the development of all skeletal bones. And thus, all the main points of ossification appear even before the onset of maturation.

In addition, the dependence of the structure of the skeleton on the condition of the horse was revealed. The central nervous system carries out all bone trophism. When trophism increases, the amount of bone tissue in it increases significantly. It becomes much denser and more compact. If it becomes too dense and too compact, then there is a risk of developing osteosclerosis. When trophism weakens, the bone, accordingly, is discharged. And another unpleasant disease begins - osteoporosis.

In addition to the endocrine and nervous systems, the condition of the bone also depends on the circulatory system.

The process of ossification itself, starting from the appearance of the very first point of ossification and ending with synostosis, takes place with the participation of blood vessels. Penetrating into the cartilage, the vessels destroy it even more. The cartilage itself will be replaced by bone tissue. After birth, ossification and bone growth also occur in a very close relationship and depend on the blood supply. This occurs due to the fact that the formation of bone plates is based around blood vessels.

All changes that occur in the bone, as mentioned above, depend on physical activity.

It is thanks to them that the compact substance inside is radically reconstructed. In this case, an increase in the size and number of osteons may be observed. If the load is incorrectly dosed, serious complications can occur. If, on the contrary, it is correct, then this will significantly slow down all aging processes in the bone.

At a young age, of course, the rate of resorption is still quite low, and the bone matrix is ​​formed quickly. In mature and old age, all changes in the skeleton are associated with a significantly increased rate of resorption and low processes of bone formation.

One way or another, the bone of absolutely any living organism is a dynamic structure. She is able to adapt to constantly changing environmental conditions.

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Bone(os) is an organ that is a component of the system of organs of support and movement, having a typical shape and structure, characteristic architecture of blood vessels and nerves, built primarily from bone tissue, covered externally with periosteum (periosteum) and containing bone marrow (medulla osseum) inside.

Each bone has a specific shape, size and position in the human body. The formation of bones is significantly influenced by the conditions in which bones develop and the functional loads that bones experience during the life of the body. Each bone is characterized by a certain number of sources of blood supply (arteries), the presence of certain places of their localization and the characteristic intraorgan architecture of blood vessels. These features also apply to the nerves innervating this bone.

Each bone consists of several tissues that are in certain proportions, but, of course, the main one is lamellar bone tissue. Let us consider its structure using the example of the diaphysis of a long tubular bone.

The main part of the diaphysis of the tubular bone, located between the outer and inner surrounding plates, consists of osteons and intercalated plates (residual osteons). The osteon, or Haversian system, is a structural and functional unit of bone. Osteons can be viewed in thin sections or histological preparations.

Internal bone structure: 1 - bone tissue; 2 - osteon (reconstruction); 3 - longitudinal section of osteon

External structure of the humerus: 1 - proximal (upper) epiphysis; 2 - diaphysis (body); 3 - distal (lower) epiphysis; 4 - periosteum

Human skeleton (front view): 1 - skull; 2 - sternum; 3 - collarbone; 4 - ribs; 5 - humerus; 6 - ulna; 7 - radius; 8 - hand bones; 9 - pelvic bone; 10 - femur; 11 - patella; 12 - fibula; 13 - tibia; 14 - foot bones	Human skeleton (back view): 1 - parietal bone; 2 - occipital bone; 3 - blade; 4 - humerus; 5 - ribs; 6 - vertebrae; 7 - bones of the forearm; 8 - carpal bones; 9 - metacarpus bones; 10 - phalanges of fingers; 11 - femur; 12 - tibia; 13 - fibula; 14 - tarsal bones; 15 - metatarsal bones; 16 - phalanges of fingers

Bones together with their compounds in the human body make up the skeleton. The skeleton is understood as a complex of dense anatomical formations that perform primarily mechanical functions in the life of the body. We can distinguish a hard skeleton, represented by bones, and a soft skeleton, represented by ligaments, membranes and cartilaginous joints.

Individual bones and the human skeleton as a whole perform various functions in the body. The bones of the trunk and lower extremities perform a supporting function for soft tissues (muscles, ligaments, fascia, internal organs). Most bones are levers. Muscles that provide locomotor function (moving the body in space) are attached to them. Both of these functions allow us to call the skeleton a passive part of the musculoskeletal system.

The human skeleton is an anti-gravity structure that counteracts the force of gravity. Under the influence of the latter, the human body is pressed to the ground, while the skeleton prevents the body from changing its shape.

The bones of the skull, torso and pelvic bones serve as protection against possible damage to vital organs, large vessels and nerve trunks. Thus, the skull is a container for the brain, the organ of vision, the organ of hearing and balance. The spinal cord is located in the spinal canal. The chest protects the heart, lungs, large vessels and nerve trunks. The pelvic bones protect the rectum, bladder and internal genital organs from damage.

Most bones contain red bone marrow, which is a hematopoietic organ and also an organ of the body's immune system. At the same time, the bones protect the red bone marrow from damage and create favorable conditions for its trophism and the maturation of blood cells.

Bones take part in mineral metabolism. Numerous chemical elements are deposited in them, mainly calcium and phosphorus salts. Thus, when radioactive calcium is introduced into the body, within a day more than half of this substance accumulates in the bones.

Joint diseases