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What types of bone matter do you know. What are bones made of

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 walling up 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.

The skeleton is the basis of the musculoskeletal system, the main foundation of the body. It consists of bones that serve as a support for all soft tissues. What is in the bones themselves, because it is impossible to imagine them empty?

Where is one of the most important bone tissue located?

Bone is an organ, and like any other, it is made up of several types of tissue. One of the main ones is a compact bone substance, without which bone formation is impossible in principle. It is adjacent to an important spongy substance. Their opposition will be discussed below.

Human bones are of different types

Bones come in several types and differ from each other not only in size. Each of them has an individual purpose. In connection with the function assumed by the bone, it occupies the most suitable location in the skeleton. The same principle applies to bones.

Therefore, compact bone tissue, more precisely, its larger amount is located in the bones responsible for the mobility of the skeleton, as well as those that perform the function of support.

The following bones do not do without a compact substance:

Long. Responsible for the skeleton of the limbs. Their tubular middle part is completely filled with compact matter;
Flat. Their outer part is covered with a compact substance;
Short. Compact bone tissue also covers them from the outside, in a thin layer.

The structure of the compact substance of the bone

For a better understanding of the structure of compact bone tissue, you should first familiarize yourself with the structure of the bone as a whole.

On a cut of a bone, types of a plate

Taking a section of the bone and magnifying it with a microscope, you can see many bone plates centered around a special channel that contains nerves and blood vessels. These plates are a system called Osteon. It is the main structural unit of bone.

Such plates are ordered in accordance with the load that the bone takes on. The osteons then organize into larger bony elements called trabeculae. And only then the bone substance of two types is formed.

The whole process depends on the density of formation of these bone elements:

In the case when trabeculae lay down in a loose plane, special cells are formed that resemble a spongy surface. This is how spongy bone tissue is formed;
When trabeculae lie down in a dense layer, a compact bone substance is formed.

The difference between the two types of bone substance is that spongy tissue is responsible for lightness and elasticity, and therefore has a significantly reduced density. Compact bone tissue forms the entire cortical layer of bones. This is due to its high density and strength of the structure. Therefore, this substance is quite heavy and makes up the bulk of the bones of the skeleton.

Thus, the compact substance of the bone consists of the primary structural unit of the osteon, which is mainly responsible for its strength.

Learn about the structure of the skeleton from the proposed video.

Functions of compact bone tissue

In childhood, children often hear from their parents a call for active participation in sports or gymnastics. Unfortunately, not everyone follows the advice of their elders and only over time they understand how important parental phrases were.

Bone is of two types

Considering the reason for the above, one should pay attention to the following: the bone substance is divided into two types, each of which has a different composition. While the spongy substance is formed from organic chemical elements (ossein), the compact substance of the bone consists of inorganic substances. Their main composition is calcium salts, lime phosphate. They are responsible for the firmness of the fabric.

A small organism has a large amount of ossein, which determines the flexibility of growing bones. When the process of bone growth approaches the completion phase, some cartilage is replaced by bones, and the bones themselves acquire the necessary number of hardened protrusions and depressions on which ligaments and the muscle system are attached.

The more muscle mass the body accumulates during the period of growth, the greater the number of necessary irregularities that the bones have time to create. Then the compact bone tissue forms a dense cortical layer, and the structure of the skeleton is practically not subject to further changes.

As can be seen, the compact tissue comes into full action secondarily, after the spongy one. This is due to the main protective function of the bone.

Also, the compact substance of the bone stores all the chemical elements necessary for the bones. It is it that contains in its structure a large number of nutritional holes through which blood vessels carrying nutrition penetrate.

Due to the well-coordinated work of the compact substance, nerves and vessels of the bone, it has the ability to grow in thickness, which is necessary.

The compact substance of the bone, making up most of the bone structure, forms its bulk. Performing the main function of protecting the skeleton, and hence supporting the whole organism as a whole, a compact substance, with age, requires sufficient attention in the form of additional sources of mineral elements, namely vitamins A, D and, of course, calcium.

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Mar 18, 2016Violetta Lekar

vselekari.com

Types of bone tissue, the structure of the tubular bone

Bone tissue is reticulofibrous and lamellar.

Reticulofibrous (coarse fibrous) bone tissue

Reticulofibrous bone tissue (textus osseus reticulofibrosus) is found mainly in embryos. In adults, it can be found at the site of overgrown cranial sutures, at the points of attachment of tendons to bones. Randomly arranged collagen fibers form thick bundles in it, clearly visible microscopically even at low magnifications.

In the main substance of the reticulofibrous 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 periosteum.

lamellar bone tissue

Lamellar bone tissue (textus osseus lamellaris) is the most common type of bone tissue in the adult body. It consists of bone plates (lamellae ossea). The thickness and length of the latter ranges from several tens to hundreds of micrometers. They are not monolithic, but contain fibrils oriented in different planes.

In the central part of the plates, the fibrils have a predominantly longitudinal direction; along the periphery, the tangential and transverse directions are added. The plates can delaminate, and the fibrils of one plate can continue into the neighboring ones, creating a single fibrous bone base. In addition, the bone plates are permeated with individual fibrils and fibers oriented perpendicular to the bone plates, woven into the intermediate layers between them, thereby achieving greater strength of the lamellar bone tissue. Both compact and spongy matter are built from this tissue in most flat and tubular bones of the skeleton.

Histological structure of the tubular bone as an organ

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

Periosteum, or periosteum. There are two layers in the periosteum: outer (fibrous) and inner (cellular). The outer layer is formed mainly by fibrous connective tissue. The inner layer contains osteogenic cambial cells, preosteoblasts, and osteoblasts of varying degrees of differentiation. Spindle-shaped cambial cells have a small amount of cytoplasm and a moderately developed synthetic apparatus. Preosteoblasts are vigorously proliferating oval-shaped cells capable of synthesizing mucopolysaccharides. Osteoblasts are characterized by a highly developed protein-synthesizing (collagen) apparatus. Vessels and nerves supplying the bone pass through the periosteum.

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

The structure of the diaphysis

The compact substance that forms the diaphysis of the bone consists of bone plates, [the thickness of which varies from 4 to 12-15 microns]. Bone plates are arranged in a certain order, forming complex formations - osteons, or Haversian systems. There are three layers in the diaphysis:

outer layer of common lamellae,

middle, osteon layer, and

inner layer of common lamellae.

External common (general) plates do not form complete rings around the diaphysis of the bone, they overlap on the surface with the following layers of plates. The internal common plates are well developed only where the compact substance of the bone directly borders the medullary cavity. In the same places where the compact substance passes into the spongy one, its internal common plates continue into the plates of the crossbars of the spongy substance.

Perforating (Volkmann) channels lie in the outer common plates, through which vessels enter the bone from the periosteum into the bone. From the side of the periosteum, collagen fibers penetrate into the bone at different angles. These fibers are called perforating (Sharpey) fibers. Most often, they branch only in the outer layer of the common lamellae, but they can also penetrate into the middle osteon layer, but they never enter the osteon lamellae.

In the middle layer, bone plates are located in osteons. In the bone plates are collagen fibrils soldered into a calcified matrix. The fibrils have different directions, but they are predominantly oriented parallel to the long axis of the osteon.

Osteons (Haversian systems) are the structural units of the compact substance of the tubular bone. They are cylinders, consisting of bone plates, as if inserted into each other. In the bone plates and between them are the bodies of bone cells and their processes, immured in the bone intercellular substance. Each osteon is delimited from neighboring osteons by the so-called cleavage line formed by the main substance that cements them. In the central canal of the osteon, blood vessels pass with their accompanying connective tissue and osteogenic cells.

In the diaphysis of a long bone, osteons are located predominantly parallel to the long axis. The osteon channels anastomose with each other. , in places of anastomoses, the plates adjacent to them change their direction. Such channels are called perforating, or nourishing. The vessels located in the osteon channels communicate with each other and with the vessels of the bone marrow and periosteum.

Most of the diaphysis is the compact substance of tubular bones. On the inner surface of the diaphysis, bordering the medullary cavity, the lamellar bone tissue forms the bone crossbars of the cancellous bone. The cavity of the diaphysis of tubular bones is filled with bone marrow.

Endost (endosteum) - a membrane covering the bone from the side of the medullary cavity. In the endosteum of the formed bone surface, an osmiophilic line is distinguished on the outer edge of the mineralized bone substance; osteoid layer, consisting of an amorphous substance, collagen fibrils and osteoblasts, blood capillaries and nerve endings, a layer of squamous cells that indistinctly separate the endosteum from the elements of the bone marrow. The thickness of the endosteum exceeds 1-2 microns, but less than that of the periosteum.

In areas of active bone formation, the thickness of the endosteum increases by 10-20 times due to the osteoid layer due to an increase in the synthetic activity of osteoblasts and their precursors. During bone remodeling, osteoclasts are found in the endosteum. In the endosteum of aging bone, the population of osteoblasts and progenitor cells decreases, but the activity of osteoclasts increases, which leads to thinning of the compact layer and restructuring of the cancellous bone.

Between the endosteum and the periosteum, there is a certain microcirculation of fluid and minerals due to the lacunar-canal system of bone tissue.

Bone vascularization. Blood vessels form a dense network in the inner layer of the periosteum. From here, thin arterial branches originate, which, in addition to blood supply to osteons, penetrate into the bone marrow through nutrient holes and take part in the formation of a network of capillaries that feed it. Lymphatic vessels are located mainly in the outer layer of the periosteum.

Bone innervation. In the periosteum, myelinated and unmyelinated nerve fibers form a plexus. Part of the fibers accompanies the blood vessels and penetrates with them through the nutrient holes into the channels of the same name, and then into the osteon channels and then reaches the bone marrow. Another part of the fibers ends in the periosteum with free nerve ramifications, and also participates in the formation of encapsulated bodies.

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Human bones: structure, composition, their connection and arrangement of joints

General characteristics of human bones

Bone tissue 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 in shape are 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 unit of bone tissue is the 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.

The structure of the human bone

Bone tissue 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.

Bone structure: compact and spongy substance

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

Compact and spongy bone

Connection of human bones

All bone joints can be divided into two groups:

Continuous compounds, earlier in development in phylogeny, immobile or inactive in function;
discontinuous connections, later in development and more mobile in function.

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

The structure of the human joint

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

The 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 the name of the joints in shape: spherical (shoulder), elliptical (radio-carpal), cylindrical (radio-ulnar), etc.

Since the movements of the articulating links are performed around one, two or many axes, the joints are also usually divided according to the number of axes of rotation into multi-axial (spherical), biaxial (ellipsoidal, saddle-shaped) and uniaxial (cylindrical, block-shaped).

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 articulated.

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The structure and types of bone tissue. bone tissues

Bones perform four main functions:

They provide strength to limbs and body cavities containing vital organs. In diseases that weaken or disrupt the structure of the skeleton, it is impossible to maintain a straight posture, and disorders of the internal organs occur. An example is cardiopulmonary failure that develops in patients with severe kyphosis due to compression fractures of the vertebrae.
Bones are essential for movement because they form effective levers and attachment points for muscles. Deformation of the bones "spoils" these levers, which leads to severe gait disorders.
Bones serve as a large reservoir of ions, from where the body draws the calcium, phosphorus, magnesium and sodium necessary for life when it is impossible to obtain them from the external environment.
The bones contain the hematopoietic system. More and more evidence indicates trophic relationships between bone stromal cells and hematopoietic elements.

The structure of the bone

The structure of the bone provides an ideal balance of its hardness and elasticity. Bone is hard enough to withstand external forces, although poorly mineralized bone is brittle and prone to fracture. At the same time, the bone must be light enough to move when the muscles contract. Long bones are built primarily from a compact substance (densely packed layers of mineralized collagen) that gives the tissue its hardness. Trabecular bones appear spongy in cross section, giving them strength and elasticity. Spongy substance makes up the main part of the spine. Diseases accompanied by a violation of the structure or a decrease in the mass of the compact substance of the bone lead to fractures of long bones, and those in which the spongy substance suffers - to fractures of the vertebrae. Fractures of long bones are also possible in cases of defects in the spongy substance. Two-thirds of the weight of the bones is in minerals, and the rest is in water and type I collagen. Non-collagenous bone matrix proteins include proteoglycans, y-carboxyglutamate-containing proteins, osteonectin glycoprotein, osteopontin phosphoprotein, and growth factors. There is also a small amount of lipids in the bone tissue.

Bone Minerals Bone contains minerals in two forms. The main form is hydroxyapatite crystals of various maturity. The rest are amorphous calcium phosphate salts with a lower ratio of calcium to phosphate than in pure hydroxyapatite. These salts are localized in areas of active bone tissue formation and are present in greater amounts in young bone.

Bone Cells Bone is made up of three types of cells: osteoblasts, osteocytes, and osteoclasts.

Osteoblasts Osteoblasts are the main bone-forming cells. Their precursors are bone marrow mesenchymal cells, which in the process of differentiation begin to express PTH and vitamin D receptors, alkaline phosphatase (released into the extracellular environment), as well as bone matrix proteins (type I collagen, osteocalcin, osteopontin, etc.). Mature osteoblasts move to the surface of the bone, where they line the areas of bone tissue neoplasm, located under the bone matrix (osteoid) and causing its mineralization - the deposition of hydroxyapatite crystals on collagen layers. As a result, lamellar bone tissue is formed. Mineralization requires the presence of sufficient calcium and phosphate in the extracellular fluid, as well as alkaline phosphatase, which is secreted by active osteoblasts. Some "aging" osteoblasts flatten out, turning into inactive cells lining the surface of the trabeculae, others sink into the compact bone substance, turning into osteocytes, and still others undergo apoptosis.

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Osteocytes Osteoblasts remaining in the compact bone during bone renewal become osteocytes. Their ability to synthesize protein drops sharply, but many processes (tubules) appear in the cells, stretching beyond the resorption cavity (lacunae) and connecting with capillaries, processes of other osteocytes of this bone unit (osteon) and processes of superficial osteoblasts. It is believed that osteocytes form syncytium, which ensures the movement of minerals from the bone surface, and, in addition, play the role of mechanical load sensors that generate the main signal for the formation and renewal of bone tissue.

Osteoclasts Osteoclasts are giant multinucleated cells that specialize in bone resorption. They come from hematopoietic cells and no longer divide. Osteoclast formation is stimulated by osteoblasts, which interact with their surface molecule RANKL with the nuclear factor-kappa-B activating receptor (RANK) on the surface of precursors and mature osteoclasts. Osteoblasts also secrete macrophage colony-stimulating factor-1 (M-CSF-1), which enhances the effect of RANKL on osteoclastogenesis. In addition, osteoblasts and other cells produce a decoy osteoprotegerin (OPG) receptor that binds to RANKL and blocks its action. PTH and 1,25(OH) 2 D (as well as cytokines IL-1, IL-6 and IL-11) stimulate RANKL synthesis in osteoblasts. TNF potentiates the stimulating effect of RANKL on osteoclastogenesis, while IFNγ blocks this process by acting directly on osteoclasts.

Mobile osteoclasts surround the area of the bone surface with a dense ring, and their membrane adjacent to the bone folds into a special structure called a corrugated border. The corrugated border is a separate organelle but acts like a giant lysosome that dissolves and breaks down the bone matrix by secreting acid and proteases (primarily cathepsin K). Collagen peptides formed as a result of bone resorption contain pyridinoline structures, the level of which in urine can be used to judge the intensity of bone resorption. Thus, bone resorption depends on the rate of maturation of osteoclasts and the activity of their mature forms. Mature osteoclasts have receptors for calcitonin, but not for PTH or vitamin D.

Bone update

Bone renewal is a continuous process of destruction and formation of bone tissue that continues throughout life. In childhood and adolescence, bone renewal proceeds at a high rate, but the process of bone formation and an increase in bone mass quantitatively predominates. After the bone mass reaches its maximum, the processes that determine the dynamics of bone mass throughout the rest of life begin to dominate. Renewal occurs in separate areas of the bone surface throughout the skeleton. Normally, about 90% of the bone surface is at rest, being covered with a thin layer of cells. In response to physical or biochemical signals, bone marrow progenitor cells migrate to certain places on the bone surface, where they merge, forming multinucleated osteoclasts that “eat away” the cavity in the bone. Renewal of the compact bone substance begins from inside the conical cavity, continuing into the tunnel. Osteoblasts crawl into this tunnel, forming a cylinder of new bone and gradually narrowing the tunnel until a narrow Haversian canal remains, through which the cells remaining in the form of osteocytes feed. The bone formed in one conical cavity is called the osteon. During the resorption of the spongy substance, a jagged area of the bone surface is formed, called the gauship lacuna. After 2-3 months, the resorption phase ends, leaving behind a cavity about 60 µm deep, into the base of which osteoblast precursors grow from the bone marrow stroma. These cells acquire the osteoblast phenotype, that is, they begin to secrete bone proteins such as alkaline phosphatase, osteopontin, and osteocalcin, and gradually replace the resorbed bone with new bone matrix. When the newly formed osteoid reaches a thickness of about 20 µm, mineralization begins. The entire cycle of bone renewal normally lasts about 6 months. This process does not need hormonal influences, with the only exception that 1,25 (OH) 2 D supports the absorption of minerals in the intestine and thus provides the renewing bone with calcium and phosphorus. For example, with hypoparathyroidism, nothing happens to the bone tissue, except for a slowdown in its metabolism. However, systemic hormones use bones as a source of minerals to maintain a constant extracellular level of calcium. At the same time, bone mass is replenished. For example, when PTH activates bone resorption (to correct hypocalcemia), the processes of new bone tissue formation are also enhanced, aimed at replenishing its mass. The role of osteoblasts in the regulation of osteoclast activity has been studied in some detail, but the mechanism of “attraction” of osteoblasts to bone resorption foci remains unclear. One possibility is that during bone resorption, IGF-1 is released from the bone matrix, which stimulates the proliferation and differentiation of osteoblasts.

Resorbed bone is not completely replaced, and at the end of each renewal cycle, some bone mass deficit remains. Over the course of life, the deficit increases, which determines the well-known phenomenon of age-related decrease in bone mass. This process begins shortly after the cessation of body growth. Various influences (malnutrition, hormones and medicinal substances) affect bone metabolism in a common way - through a change in the rate of bone tissue renewal, but by different mechanisms. Changes in the hormonal environment (hyperthyroidism, hyperparathyroidism, hypervitaminosis D) usually increase the number of renewal foci. Other factors (high doses of glucocorticoids or ethanol) impair osteoblast activity. Estrogens or androgen deficiency increase osteoclast activity. At any given time, there is a transient shortage of bone mass called "renewal space", ie. still unfilled area of bone resorption. In response to any stimulus that changes the initial number of renewal sites ("renewal units"), the renewal space either increases or decreases until a new equilibrium is established. This is manifested by an increase or decrease in bone mass.

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

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

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

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

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

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

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

The structure and functions of lamellar bone tissue

Lamellar bone tissue is the most common type of bone tissue in the human body.

The functions of lamellar bone tissue are very important for the body. It protects the internal organs from damage (the lungs in the chest, the brain inside the skull, the pelvic organs, etc.), and also allows a person to move, bearing the weight of other tissues.

Bone tissue is resistant to deformation, can withstand a lot of weight, and is also able to regenerate and grow together in case of fractures.

Bone tissue consists of intercellular substance, as well as 3 types of bone cells:

osteoblasts. These are the youngest, often oval cells of bone tissue with a diameter of no more than 20 microns. It is these cells that synthesize the substance that fills the intercellular space of the bone tissue. This is the main function of cells. When a sufficient amount of this substance is formed, osteoblasts become overgrown with it and become osteocytes. Osteoblasts are able to divide, and also have an uneven surface with small processes, with which they are attached to neighboring cells. There are also inactive osteoblasts, they are often localized in the densest parts of the bone and have a small number of organelles.
Osteocytes. These are stem cells that can often be found inside the tissues of the periosteum (the upper, strong layer of the bone that protects it and allows it to heal quickly when damaged). When osteoblasts are overgrown with intercellular substance, they turn into osteocytes and are localized in the intercellular space. Their ability to synthesize is somewhat lower than that of osteoblasts.
Osteoclasts. The largest multinucleated bone tissue cells that are found only in vertebrates. Their main function is the regulation and destruction of old bone tissue. Osteoblasts create new bone cells, while osteoclasts break down old ones. Each such cell contains up to 20 nuclei.

You can find out the state of the bone tissue with the help of. Lamellar bone tissue plays an important role in the body, but it can be destroyed, worn out with a lack of calcium, and also due to infections.

Diseases of lamellar bone tissue:

Tumors. There is the concept of "bone cancer", but most often the tumor grows into the bone from other tissues, and does not originate in it. The tumor can originate from the cells of the bone marrow, but not the bone itself. Sarcoma (primary bone cancer) is quite rare. This disease is accompanied by severe pain in the bones, swelling of the soft tissues, limited mobility, swelling and deformity of the joints.
Osteoporosis. This is the most common bone disease, accompanied by a decrease in the amount of bone tissue, thinning of the bones. This is a complex disease that is asymptomatic for a long time. Spongy tissue begins to suffer first. The plates in it begin to empty, and the tissue itself is damaged from daily stress.
Osteonecrosis. Part of the bone dies due to impaired blood circulation. Osteocytes begin to die, which leads to necrosis. Most often, osteonecrosis affects the hip bones. Thrombosis and bacterial infections lead to this disease.
Paget's disease. This disease is more common in the elderly. Paget's disease is characterized by bone deformity and severe pain. The normal process of bone tissue repair is disrupted. The causes of this disease are unknown. In the affected areas, the bone thickens, deforms and becomes very brittle.

You can learn more about osteoporosis from the video.

Bone tissue is a type of connective tissue and consists of cells and intercellular substance, which contains a large amount of mineral salts, mainly calcium phosphate. Minerals make up 70% of bone tissue, organic - 30%.

Functions of bone tissue

mechanical;

protective;

participation in the mineral metabolism of the body - the depot of calcium and phosphorus.

Bone cells: osteoblasts, osteocytes, osteoclasts.

The main cells in the formed bone tissue are osteocytes.

osteoblasts

Osteoblasts are found only in developing bone tissue. They are absent in the formed bone tissue, but are usually contained in an inactive form in the periosteum. In developing bone tissue, they cover each bone plate along the periphery, tightly adhering to each other, forming a kind of epithelial layer. The shape of such actively functioning cells can be cubic, prismatic, angular.

Oteoclasts

There are no bone-destroying cells in the formed bone tissue. But they are contained in the periosteum and in places of destruction and restructuring of bone tissue. Since local processes of bone tissue restructuring are continuously carried out in ontogenesis, osteoclasts are necessarily present in these places. In the process of embryonic osteogenesis, these cells play an important role and are found in large numbers.

Intercellular substance of bone tissue

consists of the main substance and fibers, which contain calcium salts. The fibers consist of type I collagen and are folded into bundles that can be arranged in parallel (ordered) or disordered, on the basis of which the histological classification of bone tissues is built. The main substance of bone tissue, like other types of connective tissues, consists of glycosaminoglycans and proteoglycans, but the chemical composition of these substances is different. In particular, bone tissue contains less chondroitin sulfuric acids, but more citric and other acids that form complexes with calcium salts. In the process of development of bone tissue, an organic matrix, the main substance and collagen (ossein, type II collagen) fibers, are first formed, and then calcium salts (mainly phosphate) are deposited in them. Calcium salts form hydroxyapatite crystals, which are deposited both in the amorphous substance and in the fibers, but a small part of the salts is deposited amorphously. Providing bone strength, calcium phosphate salts are simultaneously a depot of calcium and phosphorus in the body. Therefore, bone tissue takes part in mineral metabolism.

Classification of bone tissue

There are two types of bone tissue:

reticulofibrous (coarse-fibrous);

lamellar (parallel fibrous).

In reticulofibrous bone tissue, bundles of collagen fibers are thick, tortuous, and disordered. In the mineralized intercellular substance, osteocytes are randomly located in the lacunae. Lamellar bone tissue consists of bone plates in which collagen fibers or their bundles are arranged parallel in each plate, but at right angles to the course of the fibers in adjacent plates. Between the plates in the gaps are osteocytes, while their processes pass through the tubules through the plates.

In the human body, bone tissue is represented almost exclusively by a lamellar form. Reticulofibrous bone tissue occurs only as a stage in the development of some bones (parietal, frontal). In adults, they are located in the area of attachment of the tendons to the bones, as well as in place of the ossified sutures of the skull (sagittal suture of the scales of the frontal bone).

When studying bone tissue, it is necessary to differentiate the concepts of bone tissue and bone.

Bone

Bone is an anatomical organ, the main structural component of which is bone tissue. Bone as an organ consists of the following elements:

bone;

periosteum;

bone marrow (red, yellow);

vessels and nerves.

Periosteum

(periosteum) surrounds the bone tissue along the periphery (with the exception of the articular surfaces) and has a structure similar to the perichondrium. In the periosteum, the outer fibrous and inner cellular or cambial layers are isolated. The inner layer contains osteoblasts and osteoclasts. A pronounced vascular network is localized in the periosteum, from which small vessels penetrate into the bone tissue through perforating channels. Red bone marrow is considered as an independent organ and belongs to the organs of hematopoiesis and immunogenesis.

The skeleton represents the framework that helps the body keep its shape, protect organs, move in space, and much more. In general, the structure of bone cells, like any tissue, is very specialized, due to which there is strength to mechanical stress, and with it plasticity, in parallel with this, regeneration processes occur. In addition, the cells are in a strictly defined mutual arrangement, due to which the bone, and not other tissue, is much stronger than the connective tissue. The main components of bone tissue are osteoblasts, osteoclasts, and osteocytes.

It is these cells that maintain the properties of the tissue, providing its histological structure. What is the secret of these three cells, which the bone has in its composition, determining many functions. After all, only the teeth, which contain the alveoli of the jaw, are stronger than the bones. Vessels and nerves pass through the bones, as in the skull, they contain the brain, which is the source of hematopoiesis, and protect the internal organs. Covered with a layer of cartilage on top, they provide normal movement.

What is an osteoblast

The structure of this cell is specific, it is an oval or cubic formation visible under a microscope. Laboratory equipment showed that inside the cytoplasm the nucleus of the osteoblast is large, light in color, located not centrally, but somewhat towards the periphery. There are a couple of nucleoli nearby, which indicates that the cell is capable of synthesizing many substances. It also has many ribosomes, organelles, due to which the synthesis of substances occurs. Also involved in this process is the granular endoplasmic reticulum, the Golgi complex, which brings the synthesis products out.

Numerous mitochondria are responsible for what energy supply will be. They have a lot of work to do, a lot of them are contained in muscle tissue. But in the cartilaginous, coarse fibrous connective tissue, in contrast to muscle, there are much fewer mitochondria.

Cell functions

The main job of the cell is to produce intercellular substance. They also provide mineralization of bone tissue, due to this it has a special strength. In addition, cells are involved in the synthesis of many important bone tissue enzymes, the main of which is alkaline phosphatase, collagen fibers of special strength, and much more. Enzymes, leaving the cell, provide bone mineralization.

Varieties of osteoblasts

In addition to the fact that the structure of cells is specific, they are functionally active to varying degrees. Active ones have a high synthetic ability, but inactive ones are located in the peripheral part of the bone. The latter are located near the bone canal, are part of the periosteum, the membrane that covers the bone. Their structure is reduced to a small number of organelles.

Osteocyte, its structure

This bone tissue cell is more differentiated than the previous one. The osteocyte has processes that are located in the tubules passing through the mineralized matrix of the bone, their direction is different. A flat body is located in a recess - lacunae, surrounded on all sides by a mineralized component. In the cytoplasm there is an oval-shaped nucleus, which occupies almost its entire volume.

Organelles are poorly developed, a small number of ribosomes, the channels of the endoplasmic reticulum are short, mitochondria, in contrast to muscle and cartilage tissue, are few. Through channels with gaps, cells can interact with each other. The microscopic space around the cell has a meager amount of tissue fluid. It contains calcium ions, residue, phosphorus, collagen fibers (mineralized or not).

Function

The task of the cell is to regulate the integrity of bone tissue, to participate in mineralization. Also, the function of the cell is to respond to the emerging load.

Recently, the fact that cells are involved in the processes of bone tissue metabolism, including the jaw, has become increasingly popular. There is an assumption that the work of the cell is additionally to regulate the ionic balance of the body.

In many ways, the functions of osteocytes depend on the stage of the life cycle, like cartilage, muscle tissue, as well as the effects of hormones on them.

Osteoclast, its secret

These cells are of considerable size, contain many nuclei, and, in essence, are derivatives of blood monocytes. On the periphery, the cell has a corrugated brush border. In the cytoplasm of the cell there are many ribosomes, mitochondria, tubules of the endoplasmic reticulum, as well as the Golgi complex. Also, the cell contains a large number of lysosomes, phagocytic organelles, all kinds of vacuoles, vesicles.

Tasks

This cell has its own tasks, it can create an acidic environment around itself as a result of biochemical reactions in bone tissue. As a result, mineral salts are dissolved, after which old or dead cells are dissolved and digested by enzymes and lysosomes.

Thus, the job of the cell is to gradually destroy the outdated tissue, but at the same time the structure of the bone tissue is updated. As a result, a new one appears in its place, due to which the bone structure is updated.

Other components

Despite its strength (as in the hip or lower jaw), the bone contains organic substances that are complemented by inorganic ones. The organic component is represented by 95% collagen proteins, the rest is occupied by non-collagen, as well as glycosminoglycans, proteoglycans.

The inorganic component of bone tissue is crystals of a substance called hydroxyapatite, which contains large amounts of calcium and phosphorus ions. Less in the lamellar structure of the bone contains salts of magnesium, potassium, fluorides, bicarbonates. There is a constant renewal of the lamellar structure, the intercellular substance around the cell.

Varieties

In total, bone tissue has two types, it all depends on its microscopic structure. The first is called reticulofibrous or coarse-fibered, the second is lamellar. Let's consider each separately.

In an embryo, a newborn

Reticulofibrous is widely represented in the embryo, the child after birth. An adult has a lot of connective tissue, and this variety is found only in the place where the tendon is attached to the bone, at the junction of the sutures on the skull, at the fracture line. Gradually, the reticulofibrous tissue is replaced by a lamellar one.

This bone tissue has a special structure, its cells are randomly located in the intercellular substance. Collagen fibers, which are a type of connective tissue, are powerful, poorly mineralized, and have a different direction. Reticulofibrous bone has a high density, but the cells are not oriented along the connective tissue of collagen fibers.

In an adult

As an infant grows, its bone contains mostly lamellar bone. This variety is interesting in that bone plates are formed by mineralized intercellular substance, having a thickness of 5 to 7 microns. Any plate consists of collagen fibers of the connective tissue, located in parallel, as close as possible, as well as impregnated with crystals of a special mineral - hydroxyapatite.

In neighboring plates, connective tissue fibers run at different angles, which provides strength, for example, in the thigh or jaw. Lacunas or alveoli between the plates in an orderly manner contain bone cells - osteocytes. Their processes through the tubules penetrate into adjacent plates, due to which intercellular contacts of neighboring cells are formed.

There are some record systems:

surrounding (external or located from the inside);
concentric (included in the structure of the osteon);
intercalary (residue of a collapsing osteon).

The structure of the cortical, spongy layer

At the heart of this layer are mineral salts, in the jaw it is here that implants are implanted through the alveoli. The basal layer is located the deepest, is the most durable, there are many partitions in the jaw, penetrated by capillaries, but there are few of them.

In the central section there is a spongy substance, there are some subtleties in its structure. It is built from partitions, capillaries. Due to the partitions, the bone has a density, and through the capillaries it receives blood. Their functions in the jaw are to nourish the teeth, oxygenate.

In the bones of the body, including the jaw, which contains alveoli, there is a compact, and then a spongy substance following it. Both of these components have a slightly different structure, but are formed by a lamellar-type tissue. The compact substance is located outside, muscle, cartilage or connective tissue is attached to it. Its function is to give bone density, as, for example, in the jaw, the alveoli of which bear the load from chewing food.

The spongy substance is located inside any bone, including the jaw, in the lower part it contains alveoli. Its functions are reduced to additional strengthening of the bone, in giving it plasticity, this part is the receptacle of the bone marrow, which produces blood cells.

Some facts

In total, a person contains from 208 to 214 bones, which consist of half of the inorganic component, a quarter is organic matter, and another quarter is water. All this is interconnected by connective tissue, collagen fibers and proteoglycans.

The composition of the bone has an organic component, as in muscle, connective or cartilage tissue, in total from 20 to 40%. The share of inorganic minerals is from 50 to 70%, cellular elements contain from 5 to 10%, and fats - 3%.

The weight of the human skeleton is on average 5 kg, much depends on age, gender, amount of connective tissue, body structure and growth rates. The amount of cortical bone is on average 4 kg, which is 80%. The spongy substance of tubular bones, jaws and others weighs about a kilogram, which is 20%. The volume of the skeleton is 1.4 liters.

The bone in the human skeleton is a separate organ that can have its own specific problems. It is in the bones that injuries often occur, which, depending on the type, have different healing times. If you look at the bone with the naked eye, it becomes clear that each of them differs in its shape. This is due to what functions it performs, what load it affects, how many muscles are attached.

Bones allow a person to move in space, they are protection for internal organs. And the more important the organ, the more it is surrounded by bones. With age, the ability to recover decreases and the fracture heals more slowly, cells lose the ability to rapidly divide. This is proved by microscopic studies, as well as the properties of bone tissue. The degree of mineralization of collagen fibers decreases, so injuries last longer.

It is the main supporting tissue and structural material for bones, i.e. for the skeleton. Fully differentiated bone is the strongest material in the body, with the exception of tooth enamel. It is highly resistant to compression and stretching and is exceptionally resistant to deformation. The surface of the bone (with the exception of the articulating surfaces) is covered with a membrane (periosteum) that provides bone healing after fractures.

Bone cells and intercellular substance

Bone cells (osteocytes) are interconnected by long processes and are surrounded on all sides by the main substance of the bone (extracellular matrix). The composition and structure of the basic substance of the bone is peculiar. The extracellular matrix is filled with collagen fibers located in the ground substance rich in inorganic salts (calcium salts, primarily phosphate and carbonate).

It contains 20-25% water, 25-30% organic matter and 50% various inorganic compounds. The minerals of the bone are in crystalline form, thus providing its high mechanical strength.

Due to a good blood supply, which favors increased metabolism, the bone has biological plasticity. Rigid and extremely durable bone material is a living tissue that can easily adapt to changes in static loads, including changes in their direction. There are no distinct boundaries between the organic and mineral components of the bone, and therefore their presence can only be established by microscopic examination. When burned, the bone retains only its mineral base and becomes brittle. If the bone is placed in acid, then only organic substances remain, and it becomes flexible, like rubber.

The structure of the tubular bone

The structure of the bone is especially clearly seen in the longitudinal cut of a long bone. There is a dense outer layer (substantia compacta, compacts, compact substance) and an inner (spongy) layer (substancia spongiosa, spongiosa). While a dense outer layer is characteristic of long bones and is especially noticeable on the body of the bone (diaphysis), the spongy layer is mainly found inside its ends (epiphyses).

This "lightweight design" provides bone strength with minimal material consumption. The bone adapts to the resulting loads through the orientation of the bony crossbars (trabeculae). Trabeculae are located along the lines of compression and tension that occur during loading. The space between the trabeculae in spongy bones is filled with red bone marrow, which provides hematopoiesis. White bone marrow (fatty marrow) is mainly located in the cavity of the diaphysis.

In long bones, the outer layer has a lamellar (lamellar) structure. Therefore, the bones are also called lamellar. The architecture of the lamellar network (osteon, or Haversian system) is clearly visible on the cuts. At the center of each osteon is a blood vessel that supplies nutrients from the blood to the bone.

Osteocytes and extracellular matrix are grouped around it. Osteocytes are always located between the plates, which contain spiralized collagen fibrils. Cells are connected to each other by means of processes passing through the smallest bone tubules (canalicules). Nutrients flow from the internal blood vessels through these tubules. As the osteon develops, the bone-forming cells (osteoblasts) begin to come in large numbers from the inside of the bone, forming the outer plate of the osteon. Collagen fibrils are superimposed on this plate, which spiralize. Crystals of inorganic salts are ordered between the fibrils.

Then the next plate is formed from the inside, in which the collagen fibrils are located perpendicular to the fibrils of the first plate. The process continues until there is only room in the center for the so-called Haversian canal, through which the blood vessel passes. Also in the channel is a small amount of connective tissue. Mature osteon reaches about 1 cm in length and consists of 10-20 cylindrical plates inserted one into the other. Bone cells are, as it were, walled up between the plates and are connected to neighboring cells through long thin processes. The osteons are connected to each other by canals (Volkmann canals), through which the branches of the vessels pass into the Haversian canals.

Spongy bones also have a lamellar structure, but in this case the plates are arranged in layers, as in a sheet of plywood. Since cancellous bone cells also have a high metabolic activity and need nutrients, the plates in this case are thin (about 0.5 mm). This is due to the fact that the exchange of nutrients between cells and bone marrow occurs solely due to diffusion.

Throughout the life of the organism, the osteons of the dense layer and the plates of spongy bones can adapt well to changes in static loads (for example, to fractures). At the same time, in a dense and spongy substance, the old lamellar structures are destroyed, and new ones arise. The plates are destroyed by special cells called osteoclasts, and the osteons that are in the process of renewal are called interstitial plates.

Bone development

At the first stage of human bone differentiation, lamellar tissue is not formed. Instead, reticulofibrous (coarse-fibrous) bone develops. This occurs in the embryonic period, as well as during the healing of fractures. In the coarse fibrous bone, the vessels and collagen fibers are arranged randomly, which makes it resemble a strong, fiber-rich connective tissue. Rough fibrous bone can be formed in two ways.

1. Membrane bone develops directly from the mesenchyme. This type of ossification is called intramembrane ossification or desmal ossification (direct route).

2. First, a cartilaginous rudiment is formed in the mesenchyme, which then turns into bone (endochondral bone). The process is called endochondral or indirect ossification.

Adapting to the needs of a growing organism, developing bones are constantly changing shape. Lamellar bones also change according to functional load, for example, as body weight increases.

Development of long bones

Most bones develop from the cartilaginous primordium along an indirect path. Only some bones (skulls and clavicles) are formed by intramembrane ossification. However, parts of long bones can form in a straight path even if the cartilage is already laid down, for example, in the form of a perichondral bony cuff, due to which the bone thickens (perichondral ossification).

Inside the bone, tissue is laid down along an indirect path, with cartilage cells being first removed by chondroclasts and then replaced by chondral ossification. On the border of the diaphysis and the epiphysis, the epiphyseal plate (cartilage) develops. In this place, the bone begins to grow in length due to the division of cartilage cells. Division continues until growth stops. Since the epiphyseal cartilage plate does not contain calcium, it is not visible on the x-ray. Bone growth within the epiphyses (ossification centers) begins only from the moment of birth. Many centers of ossification develop only in the first years of life. In places where muscles attach to bones (apophyses), special centers of ossification are formed.

Differences between bone and cartilage

Avascular bone cells form a dense substance that performs transport functions. Such a bone regenerates well and constantly adapts to changing static conditions. In avascular cartilage, cells are isolated from each other and from nutrient sources. Compared to bone, cartilage is less able to regenerate and has little adaptive capacity.

As the name implies, the science of biochemistry stands at the junction of two important disciplines. One is chemistry, the other is biology. And he studies biochemistry, respectively, the chemical composition of living cells and organisms. In addition, biological chemistry (or chemical biology) explores various chemical processes that underlie the vital activity of absolutely any living being. 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, the bones serve as a support base for the body. In the complex, it 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 fundamentally different from them. And not only in the physical plane. The bones of the horse skeleton also have a rather complex chemical composition.

Skeleton bones

Absolutely all bones in a horse are made up of various compounds. These compounds, in turn, are divided into organic and inorganic. The former can be safely attributed to 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, a bone is removed from the body of an adult, then 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 a fairly high hardness and strength. This largely depends on the high content of minerals and other necessary elements. Two more important properties are elasticity and resilience. Both are directly dependent on protein. In general, such a combination of hardness and elasticity is largely achieved due to the specific combination of organic and inorganic. And if we compare the bones of a horse with any material, then in terms of elasticity and strength it is the same as bronze or copper.

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

The location of the bones

Every bone in every horse is made up of bone tissue. The fabric itself is constantly and rather rapidly changing. In addition to all this, bone tissue is probably the only one in the whole body capable of complete regeneration. Interestingly, two diametrically opposite processes can occur in it at once - this is the process of restoration and the process of destruction. All these processes are strongly influenced by various mechanical forces that take place during the period of statics and / or dynamics of the animal.

By itself, the bone tissue of a horse consists of various cells and intercellular substance.

There are only a few types of bone cells:

osteoblasts.
Osteocytes.
Osteoclasts.

Osteoblasts are the youngest cells. They synthesize intercellular substance.

osteoblasts

When it accumulates, the osteoblasts in it are immured and become, subsequently, osteocytes. Another important function of them 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 "osteocytes" means "receptacle of the cell."

Osteocytes

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

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

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

osteoclasts

And the last thing that is part of the 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 the bone in the form of a system of two phases:

Crystalline hydroxyapatite.
Amorphous calcium phosphate.

The first phase contributes to the energy needed to transform the bones. Further, the bone becomes polar. The concave parts have a negative charge, the 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 (it is just the most - 50%). And the cellular composition here is quite complex: osteoblasts, osteocytes, osteoclasts and intercellular substance. It is clear that for a person who does not understand anything in chemistry, all this can be quite difficult.

But besides all this, two more main types of such fabric can be distinguished. These are: lamellar and coarse-fibered. Already by the names, one can imagine that the first type is more like a coarse fiber, and the second resembles plates.

Coarse fiber type

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 fibrous type of tissue is found only in those areas where the tendons are fastened to the bones. It can also be seen in the sutures of the skull, immediately after their direct overgrowth.

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

Here the main feature is that the protein and collagen fibers are arranged in a very strict order and form special cylindrical plates. They are inserted one into the other and "encircle" the vessels. Together with the vessels, these plates encircle the nerves, which are located in the Haversian canal.

plate type

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

Each such plate has a diameter of 3-4 mm. By themselves, the osteons are arranged in perfect order. And the functional load on the entire bone directly depends on this order. From the osteons, various crossbars of the bone substance are then formed. They are also called beams. The same beams form a kind of compact substance, if, of course, they lie "densely". 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 skeleton of an adult (mature) organism is built on the second type. However, elements of the first type are sometimes present in adults. And the elements of the second, in their infancy, in younger ones.

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

In our time, the main subjects of study of histology 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 most solid, durable, elastic and resilient.

Bone

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

cartilage tissue

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

Connective tissue also consists of three main types of cells (fibroplasts, 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.

Connective tissue

Myeloid tissue is responsible for red bone marrow and the development of cells that affect the horse.

Myeloid tissue

The liquid tissues of the internal environment include blood and, which are involved in the transport of oxygen, carbon dioxide, nutrients and all end products of metabolism. They perform three important functions at once: transport, trophic (regulation of the composition of the intercellular fluid) and protective. By the way, an interesting fact is connected 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.

Endothelium

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

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

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

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

Periosteum.
Compact and spongy substance.
Bone marrow cavity with endosteum.
Bone marrow.
Articular cartilage.

But the bone that grows, in addition to the five components described above, also has some others necessary for the formation of growth zones. Here you can immediately distinguish three subspecies 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.

Periosteum

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

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

Immediately below it, you can see another substance - spongy. It is built absolutely from the same tissue from which compact matter is built. That's just what distinguishes its bone crossbars, which are rather loose in their properties. They, in turn, form special cells.

Inside the bone itself, a cavity can be found. It is called bone marrow. The walls of this cavity (however, like 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 membrane is called the endosteum. It contains osteoblasts.

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

red bone marrow

In the bone marrow, the processes of blood formation take place. In the course, as well as in newborn individuals, all bones are involved in the process of blood formation. With age, this begins to gradually pass, and the red brain turns into yellow.

And finally, articular cartilage.

articular cartilage

It is built from hyaline tissue. It covers the surfaces of the joints in the bones. Cartilage thickness varies greatly. It is thinner in the proximal section. It has no 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 the structure of the bone. This has been 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 arcuate (these include ribs) and tubular. The latter act as a kind of levers of movement. They consist of a long part of the body (also called the diaphysis) and thickened ends (they are called the epiphysis). Between them is a metaphysis, which ensures the growth of the bone.

The shorter bones are composed mainly of spongy matter. Outside, they are covered with a thin layer of compact or articular cartilage. Located in places of greater mobility and greater load. They are sort of like springs.

Flat bones form the walls of the cavities and the girdle of the limbs (shoulder or pelvis). They can be represented as a fairly wide surface, which is designed for muscle attachment. On flat bones, you can clearly see the edges and corners. They usually consist of three layers of compacta. Between them is a little spongy substance. At the same time, they actively perform the function of protection. Examples of such bones are: skull roof bones, sternum, shoulder blades, and pelvic bones.

From the name it is very clear that "os pneumaticum" or air bones are associated with "carrying air". Inside their so-called body, these bones have a cavity of a certain size. These cavities can be safely attributed to the sinus and sinus. From the inside, both of them are lined with mucous membranes.

Shells include:

Maxillary.
wedge-shaped.
Frontal.

All of them are filled with air in one way 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 at once. They consist of those parts that have a 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".

Scheme of a variety of bones

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

The primary ones develop from the so-called mesenchyme, and there are only two stages of development: bone and connective tissue. Numerous integumentary bones of the skull can be attributed to the primary bones: maxillary, frontal, interparietal, nasal, incisal, parietal and scales of the temporal bone.

primary bones

They are especially endemic ossification. That is, ossification in the 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:

Connective tissue.
cartilaginous.
Bone.

Thus, the absolute majority of the bones of the skeleton develop.

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

Ossification process

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

Perichondral begins when osteoblasts on the inside of the perichondrium form fibrous tissue, and then lamellar. In the same place, the perichondrium is transformed into the periosteum and forms a bone cuff. It also disrupts the nutrition of the cartilage, and it gradually collapses.

Endochondral ossification begins approximately when the perichondral ossification ends. The centers of this type of ossification appear at different times in the epiphases of long bones. In the same centers, the cartilage is resorbed, after which the endochondral 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 the diaphysis are connected with the help of cartilaginous plates in the tubular bones.

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

Cartilaginous plates

These cartilages are located, just the same, 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 that, they are combined 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 regularity was first revealed by P.F. Lesgaft, the founder of modern functional anatomy.

Among these patterns, Lesgaft especially emphasized the principle of bone tissue formation. Further, 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 the bones, about the external form and its subsequent restructuring.

Now I would like to say in more detail about bone tissue. It "has a habit" to form precisely in those places where the greatest tension or compression occurs.

There is a certain pattern: in direct proportion to the development of the bone structure. That is, the better the muscles are developed, the better the bones will be developed.

Intensity of muscle activity

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

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

In itself, the external shape of the bones directly depends on the pressure exerted on them (the bones) by the surrounding tissues. In addition, the external shape may change somewhat with pressure on the bone of various organs. Here it is worth explaining: the bones form the so-called “bone receptacles” or pits for the organs. Accordingly, the slightest change in the bones will lead to a change in the 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 be well rebuilt. 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 very smoothed.

Smoothed bone relief

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

And all of the 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 proper assistance, then the animal will live a long and eventful life.

Influence of various factors on bone development

Speaking about the various factors that affect 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 secreted into the blood by endocrine cells. In addition to internal organs, the endocrine system has a rather significant influence on the development of all bones of the skeleton. And thus, all the main ossification points appear even before the start 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 the trophism of the bone. 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 the trophism weakens, the bone, accordingly, is discharged. And another unpleasant disease begins - osteoporosis.

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

Effect on the bones of the circulatory system

The process of ossification itself, starting from the moment the very first ossification point appears 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 proceed in a very close relationship and depend on the blood supply. This is due to the fact that the formation of bone plates is based around blood vessels.

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

It is thanks to them that the compact substance inside is radically rebuilt. In this case, an increase in the size and number of osteons can be observed. If the load is not dosed correctly, then serious complications can occur. If, on the contrary, it is correct, then this will significantly slow down all the aging processes in the bone.

At a young age, of course, the resorption rate is still quite low, and the bone matrix is formed quickly. In mature and senile 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. It is able to adapt to constantly changing environmental conditions.

From school lessons in chemistry, everyone knows that the human body contains almost all the elements from the periodic table of D. I. Mendeleev. The percentage content of some is very significant, while others are present only in trace amounts. But each of the chemical elements found in the body performs its important role. In the human body, minerals are found in organic matter as carbohydrates, proteins, and others. Deficiency or excess of any of them leads to disruption of normal life.

The chemical composition of bones includes a number of elements and their substances, to a greater extent these are calcium salts and collagen, as well as others, the percentage of which is much less, but their role is no less significant. The strength and health of the skeleton depends on the balance of the composition, which, in turn, is determined by many factors, ranging from a healthy diet to the ecological situation of the environment.

Compounds that form the skeleton

and inorganic origin. Exactly half of the mass is water, the remaining 50% is divided by ossein, fat and lime, phosphorus salts of calcium and magnesium, and the mineral part accounts for about 22%, and the organic part, represented by proteins, polysaccharides, citric acid and enzymes, fills approximately 28% . Bones contain 99% of the calcium found in the human body. Similar component composition have teeth, nails and hair.

Transformations in various media

In an anatomical laboratory, the following analysis can be performed to confirm the chemical composition of the bones. To determine the organic part, the tissue is exposed to a medium strength acid solution, for example, hydrochloric acid, with a concentration of about 15%. In the resulting medium, calcium salts dissolve, and the ossein "skeleton" remains intact. Such a bone acquires the maximum property of elasticity, it can literally be tied into a knot.

The inorganic component, which is part of the chemical composition of human bones, can be isolated by burning the organic part, it is easily oxidized to carbon dioxide and water. The mineral core is characterized by the former form, but is extremely fragile. The slightest mechanical impact - and it will simply crumble.

When bones enter the soil, bacteria process organic matter, and the mineral part is completely saturated with calcium and turns into stone. In places where there is no access to moisture and microorganisms, tissues eventually undergo natural mummification.

Through the microscope

Any textbook on anatomy will tell you about the chemical composition and structure of bones. At the cellular level, tissue is defined as a special type of connective tissue. At the base lie surrounded by plates composed of a crystalline substance - the calcium mineral - hydroxylapatite (basic phosphate). In parallel, there are star-like voids containing bone cells and blood vessels. Due to its unique microscopic structure, this fabric is surprisingly light.

The main functions of compounds of different nature

The normal functioning of the musculoskeletal system depends on the chemical composition of the bones, whether organic and mineral substances are contained in sufficient quantities. Lime and phosphorus calcium salts, which make up 95% of the inorganic part of the skeleton, and some other mineral compounds determine the hardness and strength of the bone. Thanks to them, the fabric is resistant to serious loads.

The collagen component and its normal content are responsible for such a function as elasticity, resistance to compression, stretching, bending and other mechanical influences. But only in a coordinated "union" organic matter and the mineral component provide the bone tissue with the unique properties that it possesses.

The composition of bones in childhood

The percentage of substances, which indicates the chemical composition of human bones, may vary in the same representative. Depending on age, lifestyle and other factors of influence, the amount of certain compounds may vary. In particular, in children it is only formed and consists to a greater extent of the organic component - collagen. Therefore, the skeleton of the child is more flexible and elastic.

For the proper formation of the tissues of the child, the intake of vitamins is extremely important. In particular, such as D 3 . Only in its presence the chemical composition of the bones is fully replenished with calcium. A deficiency of this vitamin can lead to the development of chronic diseases and excessive fragility of the skeleton due to the fact that the tissue was not filled with Ca 2+ salts in time.

The hardness of bones is compared with the strength of metal surfaces. Their microchemical composition is represented by the following components:

water - 50%
elements of protein origin (ossein) - 12.5%
inorganic inclusions with tricalcium phosphate - 21.8%
lipids - 15.7%

Table 1. Existing subspecies.

Cartilaginous tissues cover the articular surfaces, on top of them is the periosteum, inside is the bone marrow.

Analysis of the anatomy of the skeleton in the video:

The structure of the bones

To better understand the topic of our article, you should first familiarize yourself with the structure of the bone as a whole.

Taking a section of the studied material and magnifying it with a microscope, you can see a lot of bone plates centered around a special channel that contains nerves and blood vessels. These plates are a system called osteon. This is the main structural unit.

The osteon contains 5-20 bone scales arranged according to the principle of a cylinder, consisting of:

Osteoclasts are of great importance in the procedure of bone tissue morphogenesis - due to them, the body destroys calcified cartilage and corrects the shape of incompletely formed tissue.

Connection of bones

Clutches are divided into two main subgroups:

Continuous type - with sedentary or fixed functionality. It is formed from connective, cartilaginous and bone units.
Discontinuous - mobile, formed in a later period.

The second connection option is the joints, consisting of the articular cavity, bag and surfaces. Free sliding in them is provided by a special lubricant that is released from the inner layer of the articular bag.

Types of joints

There are a large number of articular apparatus, experts divide them according to their appearance. The classification is based on figures from geometry:

Secondary division occurs according to the number of axes of rotation:

triaxial include spherical
biaxial - saddle and elliptical
uniaxial - block-shaped and cylindrical

Articular apparatuses are simple (with the adhesion of two bones) and complex (with the connection of three or more).

Compact and spongy substance

When sawing, two substructures are clearly visible:

Compact component - in which the bone scales are ordered and compactly adjacent to each other.
Spongy - with loose placement of elements (located inside). To When the trabeculae lay down in a loose plane, special cells are formed that resemble a spongy surface.

Bone tissue changes throughout a person's life. With hard physical work, compact layers reach a greater development. All changes are load related.

What is a compact substance

It provides security, supporting functions, is a receptacle of substances. With the help of a compact component, the formation of the cortical layer occurs in most bones. It is highly durable, accounting for up to 80% of the total weight of the human skeleton.

Where is one of the most important bone structures located?

Bone is an organ, and like any other, it is made up of several types of tissue. One of the main ones is a compact bone substance, without which the formation of tissues is impossible in principle. It is adjacent to an important spongy substance. Their opposition will be discussed below.

In connection with the function assumed by the bone, it occupies the most suitable location in the skeleton. The same principle applies to bones.

Therefore, compact bone tissue, more precisely, its larger amount is located in the bones responsible for the mobility of the skeleton, as well as those that perform the function of support.

Table 2. Species that are not do not do without a compact component.

The structure of a compact substance

The mentioned component consists of the primary structural unit of the osteon, which is mainly responsible for its strength.

Learn about the structure of the skeleton from the proposed video.

Functions of compact bone tissue

Considering the reason for the above, one should pay attention to the following: the bone substance is divided into two types, each of which has a different composition. While the spongy substance is formed from organic chemical elements (ossein), the compact substance consists of inorganic substances. Their main composition is calcium salts, lime phosphate. They are responsible for the firmness of the fabric.

A small organism has a large amount of ossein, which determines the flexibility of growing tissues. When the growth process approaches the completion phase, some cartilage is replaced by bones, and the bones themselves acquire the necessary number of hardened protrusions and depressions on which the ligaments and the muscle system are attached.

As can be seen, the compact tissue comes into full action secondarily, after the spongy one. This is due to the main protective function of the bone.

Also, the compact component stores all the chemical elements needed by the bones. It is it that contains in its structure a large number of nutritional holes through which blood vessels carrying nutrition penetrate.

Due to the well-coordinated work of a compact substance, nerves and blood vessels, it has the ability to grow in thickness, which is necessary.

The compact component, making up the bulk of the bone structure, forms its bulk. Performing the main function of protecting the skeleton, and hence supporting the whole organism as a whole, a compact substance, with age, requires sufficient attention in the form of additional sources of mineral elements, namely vitamins A, D and, of course, calcium.

Mar 18, 2016 Violetta Doctor

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What types of bone matter do you know. What are bones made of

General characteristics of human bones

The structure of human bones

Bone structure: compact and spongy substance

Connection of human bones

Types of joints

Where is one of the most important bone tissue located?

The structure of the compact substance of the bone

Functions of compact bone tissue

Types of bone tissue, the structure of the tubular bone

Reticulofibrous (coarse fibrous) bone tissue

lamellar bone tissue

Histological structure of the tubular bone as an organ

The structure of the diaphysis

Human bones: structure, composition, their connection and arrangement of joints

General characteristics of human bones

The structure of human bones

Bone structure: compact and spongy substance

Connection of human bones

Types of joints

The structure and types of bone tissue. bone tissues

The structure of the bone

Bone update

The structure and functions of lamellar bone tissue

Functions of bone tissue

osteoblasts

Oteoclasts

Intercellular substance of bone tissue

Classification of bone tissue

reticulofibrous (coarse-fibrous);

lamellar (parallel fibrous).

Bone

Periosteum

What is an osteoblast

Cell functions

Varieties of osteoblasts

Osteocyte, its structure

Function

Osteoclast, its secret

Tasks

Other components

Varieties

In an embryo, a newborn

In an adult

The structure of the cortical, spongy layer

Some facts

Bone cells and intercellular substance

The structure of the tubular bone

Bone development

Development of long bones

Differences between bone and cartilage

Influence of various factors on bone development

Compounds that form the skeleton

Transformations in various media

Through the microscope

The main functions of compounds of different nature

The composition of bones in childhood

The structure of the bones

Connection of bones

Types of joints

Compact and spongy substance

What is a compact substance

Where is one of the most important bone structures located?

The structure of a compact substance

Functions of compact bone tissue

What else to read

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