Structure and composition of bones. Human bones: structure, composition, their connection and structure of joints Osteocyte, its structure

1. Describe the structure and composition of bones.

The composition of bones includes mineral and organic substances. Minerals (bones contain all the phosphorus and calcium of the body, 0.5% magnesium and sodium) give bones hardness and make up 70% of the bone mass. Bones are capable of releasing minerals into the blood. Organic substances give the bones elasticity and resilience and make up 30% of the bone mass. Bone consists of all types of tissues, but bone predominates. Bone tissue is connective tissue and consists of cells (osteocytes, osteoblasts, osteoclasts) and intercellular substance (collagen and osein fibers). The bone is covered with periosteum (connective tissue membrane). The outer layer consists of collagen fibers (give strength), nerves and blood vessels pass through here. The inner layer is bone tissue. It contains bone tissue cells, due to which development, growth in thickness and regeneration of bones after damage occurs.

Functions of the periosteum:

a) protective;

b) trophic;

c) bone-forming.

Bone growth in thickness occurs due to the division of cells on the inner surface of the periosteum, in length - due to the division of cells of cartilaginous plates located near the ends of the bones.

Bone growth is influenced by growth hormones, such as hormones secreted by the pituitary gland. Bone growth occurs until the age of 22-25. The replacement of old bone substance with new continues throughout a person’s life.

The greater the load on the skeleton, the more active the processes of bone renewal occur and the stronger the bone substance becomes.

2. What types of bones are there?

Depending on the shape, structure, function and development, 4 groups of bones are distinguished:

a) Tubular bones are located in parts of the skeleton where movements with large amplitude are performed (limbs). They are divided into long (shoulder, forearm, thigh, lower leg) and short (distal part of the phalanx of the fingers). Tubular bone consists of a diaphysis (bone body) and an epiphysis. Inside the diaphysis - a cavity filled with yellow bone marrow. In the pineal gland— red bone marrow is a hematopoietic organ.

Tubular bones are the basis of the skeleton of the limbs. They are very durable and can withstand heavy physical load. The cavity inside the bones, without reducing strength, significantly reduces their mass.

b) Spongy bones consist of spongy substance, covered with a thin layer of compact. Long (ribs, sternum) and short (vertebrae).

c) Flat bones are 2 plates of compact bone substance, between which there is spongy substance (sternum, roof of the skull). The main function is protective.

d) Mixed bones consist of several parts that have different functions and development (bones of the base of the skull).

3. What types of bone connections are distinguished in the human skeleton? Give a description of each of them. Give examples.

There are three types of bone connections in the human skeleton:

a) Fixed joints are formed by fusion of bones (coccyx vertebrae). The bones of the skull are connected thanks to the numerous protrusions of one bone that fit into depressions of the corresponding shape and size of the other. This connection is called a bone suture. It provides greater strength to the connection of the skull bones that protect the brain.

b) Semi-movable joints. Many bones are connected to each other by cartilage pads that have elasticity and elasticity. For example, cartilage pads between the vertebrae provide flexibility to the spine. Material from the site

c) Movable joints - joints. The most typical plan for the structure of a joint is as follows: on one of the articulating bones there is an articular cavity into which the head of the other bone fits. The glenoid cavity and the head correspond to each other in shape and size, and their surface is covered with a layer of smooth cartilage. The articular surfaces of the bones are in close contact with each other. This is ensured by the presence of intra-articular ligaments - strong strands of connective tissue. The articulating surfaces of the bones are surrounded by an articular capsule. It contains a small amount of mucous fluid that acts as a lubricant, which reduces friction and ensures the head of one bone slides into the glenoid cavity of another bone during movements in the joint. Examples: shoulder, hip joints.

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

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

Skeleton bones

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

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

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

Location of bone sections

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

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

There are only a few types of bone cells:

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

Osteoblasts are the youngest cells. They synthesize intercellular substance.

Osteoblasts

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

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

Osteocytes

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

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

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

Osteoclasts

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

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

• Crystalline hydroxyapatite.
• Amorphous calcium phosphate.

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

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

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

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-fiber type of tissue is found only in those areas where the tendons are attached to the bones. It can also be seen in the sutures of the skull, immediately after their immediate healing.

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

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

Plate type

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

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

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

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

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

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

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

Bone

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

Cartilage tissue

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

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

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

Connective tissue

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

Myeloid tissue

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

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

Endothelium

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

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

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

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

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

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

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

Periosteum

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

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

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

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

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

Red bone marrow

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

And finally, articular cartilage.

Articular cartilage

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

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

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

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

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

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

These include shells:

• Maxillary.
• Wedge-shaped.
• Frontal.

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

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

Diagram of bone varieties

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

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

Primary bones

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

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

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

Thus, the vast majority of skeletal bones develop.

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

Ossification process

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

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

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

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

Cartilaginous plates

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

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

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

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

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

Intensity of muscle activity

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

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

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

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

Smoothed bone relief

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

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

The influence of various factors on bone development

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

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

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

Effect on the bones of the circulatory system

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

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

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

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

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

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

Where is one of the most important bone tissues located?

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

Human bones come in different types

There are several types of bones and they differ from each other not only in size. Each of them has an individual purpose. Due to the function it assumes, the bone occupies the most suitable location in the skeleton. Bone tissue also operates according to this principle.

Therefore, compact bone tissue, or rather a larger amount of it, is found in the bones responsible for the mobility of the skeleton, as well as those that perform the function of support.

The following bones cannot do without compact substance:

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

The structure of compact bone

To better understand the structure of compact bone tissue, you should first become familiar with the structure of bone as a whole.

Types of plates on a bone section

By taking a section of bone and magnifying it with a microscope, you can see many bone plates concentrated around a special canal that contains nerves and blood vessels. These plates represent a system called Osteon. This is the main structural unit of bone.

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

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

• When the trabeculae lie in a loose plane, special cells are formed that resemble a spongy surface. This is how spongy bone tissue is formed;
• When the trabeculae lie 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 ensured by its high density and structural strength. Therefore, this substance is quite heavy and makes up the bulk of the bones of the skeleton.

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

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

Functions of compact bone tissue

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

There are two types of bone matter

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

The 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 required number of roughened projections and depressions on which ligaments and muscle systems are attached.

The more muscle mass the body accumulates during growth, the more necessary irregularities the bones manage 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 you can see, compact tissue comes into full action second, after spongy tissue. This determines the main protective function of bone.

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

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

Compact bone substance, making up the majority of the bone structure, forms its bulk. Performing the main function of protecting the skeleton, and therefore supporting the entire body as a whole, the 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, structure of 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 sites 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 reticulofibrous bone tissue there are elongated oval-shaped bone lacunae with long anastomosing tubules in which osteocytes with their processes lie. On 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 range 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, tangential and transverse directions are added. Laminae can delaminate, and the fibrils of one lamina can continue into adjacent ones, creating a single fibrous base of the bone. In addition, the bone plates are penetrated by 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 the compact and spongy substances in most flat and tubular bones of the skeleton are built from this tissue.

Histological structure of tubular bone as an organ

Tubular bone as an organ is mainly constructed from lamellar bone tissue, except for the tubercles. On the outside, the bone is covered with periosteum, with the exception of the articular surfaces of the epiphyses, which are covered with hyaline cartilage.

Periosteum, or periosteum. The periosteum has two layers: 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 volume 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. The vessels and nerves that supply the bone pass through the periosteum.

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

Diaphysis structure

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

outer layer of common plates,

middle, osteonic layer, and

inner layer of common laminae.

The external common (general) plates do not form complete rings around the bone diaphysis; they are overlapped on the surface by subsequent 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 substance, its internal common plates continue into the plates of the trabeculae of the spongy substance.

The outer common plates contain perforating (Volkmann) canals, through which vessels enter the bone from the periosteum. From 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 laminae, but they can also penetrate into the middle osteonic layer, but they never enter the osteon laminae.

In the middle layer, bone plates are located in osteons. The bone plates contain collagen fibrils embedded in 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 structural units of the compact substance of tubular bone. They are cylinders consisting of bone plates, as if inserted into each other. In the bone plates and between them are located 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 fusion line formed by the ground substance that cements them. The central canal of the osteon contains blood vessels with accompanying connective tissue and osteogenic cells.

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

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

Endosteum is 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 scale-like cells that vaguely separate the endosteum from the elements of the bone marrow. The thickness of the endosteum exceeds 1-2 microns, but is less than that of the periosteum.

In areas of active bone formation, the thickness of the endosteum increases 10-20 times due to the osteoid layer due to increased 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-canalicular system of bone tissue.

Vascularization of bone tissue. Blood vessels form a dense network in the inner layer of the periosteum. This is where thin arterial branches originate, which, in addition to supplying blood to osteons, penetrate into the bone marrow through nutrient openings and take part in the formation of the capillary network that feeds it. Lymphatic vessels are located mainly in the outer layer of the periosteum.

Innervation of bone tissue. In the periosteum, myelinated and unmyelinated nerve fibers form a plexus. Some of the fibers accompany the blood vessels and penetrate with them through the nutrient openings into the canals of the same name, and then into the osteon canals and then reach the bone marrow. Another part of the fibers ends in the periosteum with free nerve branches, and also participates in the formation of encapsulated bodies.

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

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 fatty tissue, blood and lymphatic vessels, and nerves.

Bone tissue has high mechanical properties; its strength can be compared to the strength of metal. The chemical composition of 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 are divided into:

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

The structure of human bones

The basic structural unit of bone tissue is the osteon, which is visible under a microscope at low magnification. Each osteon includes from 5 to 20 concentrically located 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 canal - the osteon canal; vessels pass through it. Intercalated bone plates are located between adjacent osteons.

Human bone structure

Bone tissue is formed by osteoblasts, secreting the intercellular substance and immuring itself in it, they turn into osteocytes - process-shaped cells, incapable of mitosis, with poorly defined 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 lymphatic endings. The periosteum ensures bone growth in thickness and nutrition of the bone.

Osteoclasts contain a large number of lysosomes and are capable of secreting enzymes, which may explain their dissolution of bone matter. These cells take part in the destruction of bone. In pathological conditions in 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

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

Compact and spongy bone

This bone structure fully complies with the basic principle of structural mechanics - to ensure maximum strength of the structure with the least amount of material and great lightness. 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 compressive, tensile and torsional forces.

Bone structure 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 changes 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 connections 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 one - from continuous to discontinuous or vice versa - half-joint.

The structure of the human joint

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

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

The articular capsule covers the articular surfaces of the bones, forming an airtight capsule. The joint capsule consists of two layers, the outer layer of which passes into the periosteum. The inner layer releases fluid into the joint cavity, which acts as a lubricant, ensuring free sliding of the articular surfaces.

Types of joints

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

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

Depending on the number of bones that articulate, 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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Structure and types of bone tissue. Bone tissue

Bones perform four main functions:

1. They provide strength to the limbs and body cavities containing vital organs. With 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, which develops in patients with severe kyphosis due to vertebral compression fractures.
2. Bones are essential for movement because they form effective levers and muscle attachments. Bone deformation “spoils” these levers, leading to severe gait disturbances.
3. 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.
4. The bones contain the hematopoietic system. Increasing evidence suggests trophic connections between bone stromal cells and hematopoietic elements.

Bone structure

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

Bone Minerals Bone contains minerals in two forms. The main form is hydroxyapatite crystals of varying maturity. The rest are amorphous salts of calcium phosphate with a lower calcium to phosphate ratio than in pure hydroxyapatite. These salts are localized in areas of active bone tissue formation and are present in greater quantities 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 mesenchymal cells of the bone marrow, which, during 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 areas of new bone tissue, 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 “senescent” osteoblasts flatten, 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.

(module direct4)

Osteocytes Osteoblasts that remain in the compact substance of the bone during its renewal turn into osteocytes. Their ability to synthesize protein drops sharply, but many processes (tubules) appear in the cells, extending beyond the resorption cavity (lacuna) and connecting with capillaries, processes of other osteocytes of a given bone unit (osteon) and processes of superficial osteoblasts. It is believed that osteocytes form a syncytium that ensures the movement of minerals from the bone surface, and, in addition, play the role of mechanical load sensors, generating the main signal for the formation and renewal of bone tissue.

Osteoclasts Osteoclasts are giant multinucleated cells specialized in bone resorption. They come from hematopoietic cells and no longer divide. Osteoclast formation is stimulated by osteoblasts, which, through their surface molecule RANKL, interact with the receptor activator of nuclear factor kappa B (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 the decoy receptor osteoprotegerin (OPG), which binds to RANKL and blocks its action. PTH and 1,25(OH) 2 D (as well as the cytokines IL-1, IL-6 and IL-11) stimulate the synthesis of RANKL in osteoblasts. TNF potentiates the stimulating effect of RANKL on osteoclastogenesis, and IFNγ blocks this process by acting directly on osteoclasts.

Mobile osteoclasts surround 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 as a giant lysosome that dissolves and breaks down the bone matrix, secreting acid and proteases (mainly 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 osteoclast maturation and the activity of their mature forms. Mature osteoclasts have calcitonin receptors, but not 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 turnover occurs at a high rate, but quantitatively the process of bone formation and increase in bone mass predominates. Once bone mass reaches its maximum, the processes that determine bone mass dynamics throughout the rest of life begin to predominate. Renewal occurs in individual areas of the bone surface throughout the skeleton. Normally, about 90% of the bone surface is at rest, covered with a thin layer of cells. In response to physical or biochemical signals, bone marrow progenitor cells migrate to specific locations on the bone surface, where they fuse to form multinucleated osteoclasts, which “eat away” a cavity in the bone. Renewal of the compact bone substance begins from within a conical cavity that extends into a 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 are fed. The bone formed in one conical cavity is called an osteon. When the spongy substance is resorption, a jagged section of the bone surface is formed, called a gauchip lacuna. After 2-3 months, the resorption phase ends, leaving behind a cavity about 60 microns deep, into the base of which osteoblast precursors grow from the bone marrow stroma. These cells acquire an 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 approximately 20 µm, mineralization begins. The entire cycle of bone renewal normally lasts about 6 months. This process does not require hormonal influences, with the only exception that 1,25(OH) 2 D supports the absorption of minerals in the intestine and thereby provides the renewed bone with calcium and phosphorus. For example, with hypoparathyroidism, nothing happens to bone tissue except a slowdown in its turnover. However, systemic hormones use bone as a source of minerals to maintain constant extracellular calcium levels. At the same time, bone mass is replenished. For example, when PTH activates bone resorption (to correct hypocalcemia), the processes of new bone formation aimed at replenishing its mass are also enhanced. The role of osteoblasts in the regulation of osteoclast activity has been studied in some detail, but the mechanism of “attraction” of osteoblasts to sites of bone resorption remains unclear. One possibility is that bone resorption releases IGF-1 from the bone matrix, which stimulates osteoblast proliferation and differentiation.

Resorbed bone is not completely replaced, and at the end of each turnover cycle, some bone loss 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 soon after the body stops growing. Various influences (dietary disorders, hormones and drugs) affect bone turnover in a common way - through changing the rate of bone tissue turnover, 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) interfere with osteoblast activity. Estrogens or androgen deficiency increase osteoclast activity. At any given time, there is a transient deficit in bone mass, called the "renewal space", i.e. still unfilled area of ​​bone resorption. In response to any stimulus that changes the initial number of update sites ("update units"), the update 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 protecting internal organs, movement, and participates in metabolism. Bone tissue also includes dental tissue. Bone is a hard and at the same time plastic 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 plastic and resistant to deformation, durable.

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

1. Coarse fibrous. This is denser but less elastic bone tissue. There is very little of it in the adult body. It is mainly found at the junction of bone and cartilage, at the junction of cranial sutures, and also at the healing sites of fractures. Coarse fibrous bone tissue is found in large quantities during human embryonic development. It acts as the rudiment of the skeleton, and then gradually degenerates into a lamellar one. The peculiarity of this type of tissue is that its cells are arranged randomly, which makes it denser.
2. Lamellar. Lamellar bone tissue is the main one in the human skeleton. It is part of all the bones of the human body. A feature of this tissue is the arrangement of cells. They form fibers, which in turn form plates. The fibers that make up the plates can be positioned 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 spongy tissue that contains bone marrow, which is 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 on the outside of the bone, covering and protecting it from damage, cracks, and fractures. Compact bone tissue makes up the majority of the skeleton (about 80%).

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 internal organs from damage (lungs in the chest, brain inside the skull, pelvic organs, etc.), and also allows a person to move while supporting the weight of other tissues.

Bone tissue is resistant to deformation, can withstand heavy weight, and is also capable of regenerating and healing during fractures.

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

1. Osteoblasts. These are the youngest, most 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 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 capable of dividing and also have an uneven surface with small processes with which they attach 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.
2. Osteocytes. These are stem cells that can often be found inside the tissues of the periosteum (the upper, strong layer of bone that protects it and allows it to heal quickly when damaged). When osteoblasts become 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.
3. Osteoclasts. The largest multinucleated cells of bone tissue, which are found only in vertebrates. Their main function is the regulation and destruction of old bone tissue. Osteoblasts create new bone cells, and osteoclasts destroy old ones. Each such cell contains up to 20 nuclei.

You can find out the condition of bone tissue using. Lamellar bone tissue plays an important role in the body, but it can be subject to destruction and wear due to a lack of calcium, as well as due to infections.

Diseases of lamellar bone tissue:

• Tumors. There is a concept of “bone cancer,” but most often the tumor grows into the bone from other tissues, rather than originating in it. A tumor can originate from bone marrow cells, but not from the bone itself. Sarcoma (primary bone cancer) is quite rare. This disease is accompanied by severe bone pain, soft tissue swelling, limited mobility, swelling and deformation of the joints.
• Osteoporosis. This is the most common bone disease, accompanied by a decrease in the amount of bone tissue and thinning of the bones. This is a complex disease that remains asymptomatic for a long time. The spongy tissue begins to suffer first. The plates in it begin to become 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. The hip bones most often suffer from osteonecrosis. This disease is caused by thrombosis and bacterial infections.
• Paget's disease. This disease is more common in old age. Paget's disease is characterized by bone deformation and severe pain. The normal process of bone tissue restoration is disrupted. The causes of this disease are unknown. In the affected areas, the bone thickens, deforms and becomes very fragile.

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 substances - 30%.

Functions of bone tissue

mechanical;

protective;

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

Bone cells: osteoblasts, osteocytes, osteoclasts.

The main cells in formed bone tissue are osteocytes.

Osteoblasts

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

Oteoclasts

Bone-destructive cells are absent in 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 during ontogenesis, osteoclasts are necessarily present in these places. During the process of embryonic osteohistogenesis, these cells play an important role and are found in large numbers.

Intercellular substance of bone tissue

consists of a main substance and fibers that contain calcium salts. The fibers consist of type I collagen and are folded into bundles, which can be arranged in parallel (ordered) or disordered, on the basis of which the histological classification of bone tissue is based. The main substance of bone tissue, like other types of connective tissues, consists of glycosaminoglycans and proteoglycans, but the chemical composition of these substances differs. In particular, bone tissue contains less chondroitinsulfuric acids, but more citric and other acids that form complexes with calcium salts. In the process of bone tissue development, an organic matrix substance and collagen (ossein, type II collagen) fibers are first formed, and then calcium salts (mainly phosphates) are deposited in them. Calcium salts form hydroxyapatite crystals, 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 also 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, the bundles of collagen fibers are thick, tortuous, and arranged in a disorderly manner. 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 located parallel in each plate, but at right angles to the course of the fibers in adjacent plates. Osteocytes are located between the plates in the lacunae, while their processes pass through the plates in the tubules.

In the human body, bone tissue is presented almost exclusively in the 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 tendons to bones, as well as at the site of ossified sutures of the skull (sagittal suture of the squama of the frontal bone).

When studying bone tissue, the concepts of bone tissue and bone should be differentiated.

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 periphery of bone tissue (with the exception of articular surfaces) and has a structure similar to the perichondrium. The periosteum is divided into outer fibrous and inner cellular or cambial layers. 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 provides the framework that helps the body maintain its shape, protect organs, move through 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 along with it plasticity, in parallel with this, regeneration processes occur. In addition, the cells are in a strictly defined relative position, due to which bone, and not other tissue, is much stronger than connective tissue. The main components of bone tissue are osteoblasts, osteoclasts, and osteocytes.

It is these cells that maintain the properties of the tissue, ensuring its histological structure. What is the secret of these three cells that bone contains, determining many functions. After all, the only stronger bones are the teeth, which contain the alveoli of the jaw. 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 cartilaginous layer on top, they ensure normal movement.

Osteoblast, what is it?

The structure of this cell is specific; it is an oval or cubic formation visible under a microscope. Laboratory techniques showed that inside the cytoplasm, the nucleus of the osteoblast is large, light in color, and located not centrally, but somewhat towards the periphery. There are a couple of nucleoli nearby, this 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 removes the products of synthesis to the outside.

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

Cell functions

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

Types of osteoblasts

In addition to the fact that the structure of the 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 and are part of the periosteum, the membrane covering 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 bone matrix, their direction is different. The flat body is located in a recess - lacunae, surrounded on all sides by a mineralized component. The cytoplasm has an oval-shaped nucleus, occupying almost its entire volume.

The organelles are poorly developed, there are a small number of ribosomes, the channels of the endoplasmic reticulum are short, and mitochondria, unlike muscle and cartilage tissue, are few in number. Through channels that have lacunae, 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 cell's task is to regulate the integrity of bone tissue and participate in mineralization. Also, the functions of the cell are to respond to the resulting load.

Recently, the fact that cells participate in the metabolic processes of bone tissue, including the jaw, has become increasingly popular. There is an assumption that the cell's job 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, such as cartilage and muscle tissue, as well as the effects of hormones on them.

Osteoclast, its secret

These cells are large in size, contain many nuclei, and are essentially derivatives of blood monocytes. Along 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 are developed. The cell also contains a large number of lysosomes, phagocytic organelles, various vacuoles, and 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 dissolve, after which old or dead cells are dissolved and digested by enzymes and lysosomes.

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

Other components

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

The inorganic component of bone tissue is crystals of a substance called hydroxyapatite, which contains large amounts of calcium and phosphorus ions. The lamellar structure of the bone contains less magnesium salts, potassium salts, fluorides, and bicarbonates. The lamellar structure, the intercellular substance around the cell, is constantly being renewed.

Varieties

In total, bone tissue has two types, everything depends on its microscopic structure. The first is called reticulofibrous or coarse fibrous, the second is lamellar. Let's look at each one separately.

In an embryo, newborn

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

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

In an adult

When a baby grows up, its bone contains mostly lamellar bone tissue. This variety is interesting in that the mineralized intercellular substance forms bone plates with a thickness of 5 to 7 microns. Any plate consists of collagen fibers of connective tissue, located in parallel, as close as possible, and also impregnated with crystals of a special mineral - hydroxyapatite.

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

There are some plate systems:

• surrounding (external or located inside);
• concentric (part of the osteon structure);
• intercalary (remnant of a collapsing osteon).

The structure of the cortical, spongy layer

This layer is based on mineral salts; it is here that implants are implanted in the jaw 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 not many of them.

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

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

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, giving it plasticity; this part is the receptacle for 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 of organic substances, and another quarter of water. All this is connected by connective tissue, collagen fibers and proteoglycans.

Bone contains an organic component, like muscle, connective or cartilage tissue, only 20 to 40%. The share of inorganic minerals ranges 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 averages 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 may 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 is placed on it, and 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 quickly divide. This is proven 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 very resistant to compression and tension and is extremely resistant to deformation. The surface of the bone (except for the articulated surfaces) is covered with a membrane (periosteum), which allows bone to heal after fractures.

Bone cells and intercellular substance

Bone cells (osteocytes) are connected to each other by long processes and are surrounded on all sides by the main substance of the bone (extracellular matrix). The basic substance of bone is unique in composition and structure. 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. Bone minerals are in crystalline form, thus providing it with high mechanical strength.

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

The structure of the tubular bone

The structure of the bone is especially clearly visible 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 the 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” ensures bone strength with minimal material consumption. The bone adapts to the resulting loads through the orientation of the bone bars (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 (fat marrow) is mainly found in the diaphyseal cavity.

In long bones, the outer layer has a lamellar (plate-like) structure. Therefore, bones are also called lamellar. The architecture of the lamellar network (osteon, or Haversian system) is clearly visible in the saw cuts. At the center of each osteon there is a blood vessel through which nutrients are supplied to the bone from the blood.

Osteocytes and extracellular matrix are grouped around it. Osteocytes are always located between the plates, which contain spiralized collagen fibrils. The cells are connected to each other by processes passing through the smallest bone tubules (canaliculi). Nutrients are supplied through these tubules from the internal blood vessels. As osteon develops, bone-forming cells (osteoblasts) begin to emerge in large numbers from the interior of the bone, forming the outer lamina of the osteon. Collagen fibrils are superimposed on this plate and spiralized. Crystals of inorganic salts are arranged in an orderly manner between the fibrils.

Then, on the inside, the next plate is formed, in which 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. There is also a small amount of connective tissue in the canal. A 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, immured between the plates and are connected to neighboring cells through long, thin processes. The osteons are connected to each other by canals (Volkmann's 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, like in a sheet of plywood. Since trabecular bone cells also have high metabolic activity and require 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 exclusively through diffusion.

Throughout the life of the organism, osteons of the dense layer and plates of cancellous bones can adapt well to changes in static loads (for example, to fractures). At the same time, in dense and spongy matter, old lamellar structures are destroyed and new ones appear. The plates are destroyed by special cells called osteoclasts, and 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 (roughly fibrous) bone occurs. This occurs in the embryonic period, as well as during the healing of fractures. In coarse-fibered bone, vessels and collagen fibers are arranged in a disorderly manner, which makes it resemble strong, fiber-rich connective tissue. Rough fibrous bone can form in two ways.

1. Membranous bone develops directly from the mesenchyme. This type of ossification is called intramembranous ossification or desmal ossification (direct path).

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 constantly change shape. Lamellar bones also change in accordance with functional load, for example, as body weight increases.

Development of long bones

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

Within bone, tissue is laid down in an indirect manner, with cartilage cells first being removed by chondroclasts and then replaced by chondral ossification. At the border of the diaphysis and epiphysis, the epiphyseal plate (cartilage) develops. At this point, the bone begins to grow in length due to the division of cartilage cells. Division continues until growth stops. Because the epiphyseal cartilage plate does not contain calcium, it is not visible on x-rays. Bone growth within the epiphyses (ossification centers) begins only from the moment of birth. Many ossification centers develop only in the first years of life. At the points of attachment of muscles to bones (apophyses), special ossification centers are formed.

Differences between bone and cartilage

Avascular bone cells form a dense substance that performs transport functions. Such 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 capable of regeneration and has little adaptive capacity.

From school chemistry lessons, everyone knows that the human body contains almost all the elements from D.I. Mendeleev’s periodic table. The percentages of some are quite significant, while others are present only in trace amounts. But each of the chemical elements found in the body plays its own important role. In the human body, minerals are contained in organic forms such as carbohydrates, proteins and others. A 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, mostly calcium salts and collagen, as well as others, the percentage of which is much smaller, 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 calcareous, phosphorus salts of calcium and magnesium, as well as 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. Teeth, nails and hair have a similar component composition.

Transformations in different environments

The following tests can be performed in an anatomy laboratory 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 environment, calcium salts dissolve, and the ossein “skeleton” remains intact. Such a bone acquires maximum 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 skeleton is characterized by the same shape, but extreme fragility. 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 undergo natural mummification over time.

Through a microscope

Any anatomy textbook 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. The base is surrounded by plates composed of a crystalline substance - the calcium mineral - hydroxyapatite (basic phosphate). In parallel, there are star-like voids containing bone cells and blood vessels. Thanks to its unique microscopic structure, this fabric is amazingly light.

The main functions of compounds of different natures

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

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

Composition of bones in childhood

The percentage of substances indicating the chemical composition of human bones may vary within the same representative. Depending on age, lifestyle and other influencing factors, the amount of certain compounds may vary. In particular, in children it is just being formed and consists largely of an organic component - collagen. Therefore, the child’s skeleton is more flexible and elastic.

For the proper formation of a child’s tissues, the consumption of vitamins is extremely important. In particular, such as D 3. Only in its presence is the chemical composition of bones 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 is not filled with Ca 2+ salts in time.