Properties, composition, and structure of bones. Fabrics

First of all, our bones consist of bone substance, which contains calcium salts. In general, bone as an organ also consists of such soft tissues as articular cartilage and periosteum (in the language of specialists, periosteum), bone marrow inside the bones, as well as blood vessels and nerves that pass through the periosteum and ‎ .

Bone substance

Bone matter makes up the bulk of our bones. It is very strong, as it contains calcium (experts talk about calcium salts), its weight can reach up to 70% of the weight of the bones. Bone matter occurs in bones mainly in two forms: compact bone substance And cancellous bone substance.

Compact bone substance is a hard, dense, whitish mass. First of all, it seems to envelop (cover) with a thick layer the bone marrow cavities inside long tubular bones (for example, femurs or humeri). But cancellous bone substance consists of fairly thin plates/bars. It can be found in our short, flat bones, such as the vertebrae.

Bone substance consists of mature bone cells called osteocytes. Osteocytes have processes and with the help of these processes they connect with each other. Working together with young osteoblast cells, which are responsible for bone formation, new bone begins to grow. Bone tissue is destroyed by cells called osteoclasts.

Articular cartilage

Articular cartilage is found in almost all bones, with the exception of the skull bones. They cover the articular surfaces and are the last remaining part of the skeleton from embryonic development.

Periosteum

The periosteum (which experts call the periosteum) covers the outside of all our bones. Therefore, the bone substance itself is nowhere to be seen. It is covered by either periosteum or articular cartilage.

Bone marrow

Bone marrow is the soft mass that is found in cavities inside bones. Bone marrow is red and yellow. Red Bone marrow Responsible for hematopoiesis in the body. And yellow bone marrow is mostly adipose tissue.

Yellow bone marrow does not appear in a person immediately, but gradually during human development, red bone marrow is replaced by yellow one. Therefore, the older a person gets, the more yellow bone marrow he has. In adults, yellow bone marrow fills the central part of long tubular bones (this could be, for example, the humerus), which experts call the diaphysis. Red bone marrow is found primarily inside short, flat bones (such as inside the vertebrae).

Blood vessels and nerves

Blood vessels and nerves are found in the bone substance, in the periosteum, and in the bone marrow. They transmit information, nutrients and oxygen to bone cells. Through tiny holes on the surface of the bones, they enter the bone, and from the bone they exit into the circulatory system or, respectively, into the nerves that connect them to the nervous system.

A collection of cells and intercellular substance similar in origin, structure and functions is called cloth. In the human body they secrete 4 main groups of fabrics: epithelial, connective, muscular, nervous.

Epithelial tissue(epithelium) forms a layer of cells that make up the integument of the body and the mucous membranes of all internal organs and cavities of the body and some glands. Through epithelial tissue, metabolism occurs between the body and environment. In epithelial tissue, cells are very close to each other, there is little intercellular substance.

This creates an obstacle to the penetration of microbes and harmful substances and reliable protection of the tissues underlying the epithelium. Due to the fact that the epithelium is constantly exposed to various external influences, its cells die in large quantities and are replaced with new ones. Cell replacement occurs due to the ability of epithelial cells and rapid.

There are several types of epithelium - skin, intestinal, respiratory.

Derivatives of the skin epithelium include nails and hair. The intestinal epithelium is monosyllabic. It also forms glands. These are, for example, the pancreas, liver, salivary, sweat glands, etc. Enzymes secreted by the glands break down nutrients. Decomposition products nutrients are absorbed by the intestinal epithelium and enter the blood vessels. The respiratory tract is lined with ciliated epithelium. Its cells have outward-facing motile cilia. With their help, particulate matter trapped in the air is removed from the body.

Connective tissue. A feature of connective tissue is the strong development of intercellular substance.

The main functions of connective tissue are nutritional and supporting. Connective tissue includes blood, lymph, cartilage, bone, and adipose tissue. Blood and lymph consist of a liquid intercellular substance and blood cells floating in it. These tissues provide communication between organisms, carrying various gases and substances. Fibrous and connective tissue consists of cells connected to each other by an intercellular substance in the form of fibers. The fibers can lie tightly or loosely. Fibrous connective tissue is found in all organs. Adipose tissue also looks like loose tissue. It is rich in cells that are filled with fat.

IN cartilage tissue the cells are large, the intercellular substance is elastic, dense, contains elastic and other fibers. There is a lot of cartilage tissue in the joints, between the vertebral bodies.

Bone consists of bone plates, inside of which lie cells. The cells are connected to each other by numerous thin processes. Bone tissue is hard.

Muscle. This tissue is formed by muscles. Their cytoplasm contains thin filaments capable of contraction. Smooth and striated muscle tissue is distinguished.

The fabric is called cross-striped because its fibers have a transverse striation, which is an alternation of light and dark areas. Smooth muscle tissue is part of the walls of internal organs (stomach, intestines, bladder, blood vessels). Striated muscle tissue is divided into skeletal and cardiac. Skeletal muscle tissue consists of elongated fibers reaching a length of 10–12 cm. Cardiac muscle tissue, like skeletal muscle tissue, has transverse striations. However, unlike skeletal muscle, there are special areas where the muscle fibers close tightly together. Thanks to this structure, the contraction of one fiber is quickly transmitted to neighboring ones. This ensures simultaneous contraction of large areas of the heart muscle. Muscle contraction is of great importance. The contraction of skeletal muscles ensures the movement of the body in space and the movement of some parts in relation to others. Due to smooth muscles, internal organs contract and the diameter of blood vessels changes.

Nervous tissue. The structural unit of nervous tissue is a nerve cell - a neuron.

A neuron consists of a body and processes. The body of a neuron can be of various shapes - oval, stellate, polygonal. A neuron has one nucleus, usually located in the center of the cell. Most neurons have short, thick, strongly branching processes near the body and long (up to 1.5 m), thin, and branching processes only at the very end. Long processes of nerve cells form nerve fibers. The main properties of a neuron are the ability to be excited and the ability to conduct this excitation along nerve fibers. In nervous tissue these properties are especially well expressed, although they are also characteristic of muscles and glands. Excitation is transmitted along the neuron and can be transmitted to other neurons or muscles connected to it, causing it to contract. The importance of the nervous tissue that forms the nervous system is enormous. Nervous tissue not only forms part of the body as part of it, but also ensures the unification of the functions of all other parts of the body.

Bone tissue is distinguished by a number of very unique qualities that sharply distinguish it from all other tissues and systems of the human body and place it in a separate place. Main and main feature bone tissue is its richness in mineral salts.

If we take the body weight of an adult as an average of 70 kg, then the bone skeleton weighs 7 kg, and together with the bone marrow - 10 kg (muscles - “meat” - weigh 30 kg). The bones themselves, by weight, are 25% water, 30% organic matter and 45% minerals. The water content and therefore the relative content of other ingredients varies. The amount of water is comparatively very large in embryonic life, it decreases in childhood and gradually decreases with the growth and development of the child, adolescent and mature person, reaching in old age the smallest ratio to total weight. With age, bones literally dry out.

The organic composition of bones is formed mainly from proteins - proteins, mainly ossein, but the complex organic part of bone tissue also includes some albumins, mucoids and other substances of a very complex chemical structure.

What is the mineral composition of bone matter that interests us most? 85% of the salts are lime phosphate, 10.5% calcium carbonate, 1.5% magnesium phosphate, and the remaining 3% are sodium, potassium, chlorine and some elements rare for the human body. Calcium phosphate, therefore constituting 19/20 of the contents of the total salty bone matter, forms 58% of the total weight of the bones.

Phosphoric acid salts have a crystalline structure, and the crystals are located in the bone correctly and naturally. A very thorough study of the mineral skeleton of bone matter, carried out in the 30s using the most advanced methods, primarily through x-ray structural analysis, showed that inorganic human bone matter has the structure of phosphatite-apatite, namely hydroxyl-apatite. It is interesting that the apatite in human bones (and teeth) is close or even similar to the natural mineral apatite in dead nature. This identity of apatite of human bone and mining origin is also indicated by their comparative study in polarized light. Human bone apatite is also distinguished by the content of a small amount of chlorine or fluorine halogen. Some structural analysis specialists are of the opinion that in human bones apatite is still associated with other chemical compounds, i.e. that crystals of inorganic bone substance are a mixture of two inorganic chemicals, one of which is close to apatite. It is believed that the most correct physical and chemical structure of bone apatite was deciphered by the Hungarian scientist St. Naray-Szabo. The most probable formula for the structure of the inorganic composition of bone is: ZSA 3 (PO 4) 2. CaX 2, where X is either Cl, F, OH, V2O, 1/2 SO 4, 1/2 CO 3, etc. There are also indications that apatite consists of two molecules - CaF. Ca 4 (PO 4) 3 or CaC1. Ca 4 (PO 4) 3.

Extremely interesting are the indications of Reynolds et al. that during certain pathological processes bones lose their normal chemical apatite structure. This occurs, for example, in hyperparathyroid osteodystrophy (Recklinghausen's disease), while in Paget's disease the apatite crystal structure is completely preserved.

Bone tissue is, albeit very ancient in phylogeny, but at the same time highly developed and extremely finely and in detail differentiated, extremely complex in all its life manifestations mesenchymal connective tissue.

Changes in bones during various pathological processes are infinitely diverse; for each individual disease, in each individual bone, in each individual case, the pathoanatomical and pathophysiological, and therefore the x-ray picture, has its own characteristics. All this enormous variety of painful phenomena is reduced, however, in the end only to some not so numerous elementary qualitative and quantitative processes.

A disease, as is known, is not only a perverted arithmetic sum of individual normal phenomena; under pathological conditions, specific qualitative changes arise in the whole organism and in individual organs and tissues, for which there are no normal prototypes. Painfully altered bone also undergoes deep qualitative metamorphosis. The periosteum, for example, forming a callus at the site of a diaphyseal fracture, begins to perform a new function that is not normally characteristic of it, it produces cartilage tissue. A bone tumor is associated with the development, for example, of epithelial, myxomatous, giant cell and other formations that are as foreign to normal bone histologically as deposits of cholesterol in xanthomatosis or kerasin in Gaucher disease are chemically unusual for it. The bone apparatus during rickets or Paget's restructuring acquires completely new physical, chemical, biological and other qualities for which in normal bone we are not able to find quantitative criteria for comparison.

But these qualitative properties, specific to pathological processes in the bone substance, unfortunately, cannot themselves be directly determined radiographically; they appear on radiographs only in the form of indirect, secondary symptoms. The power of radiology does not lie in recognizing and studying them. Only when the qualitatively changed tissue in its quantitative definition has reached the level of possible detection does the x-ray method of research come into its own. Through impeccable experimental research, Pauline Mack has proven that from various components bone tissue absorbs x-rays by 95% due to mineral composition(80% of the rays are blocked by calcium and 15% by phosphorus), and only up to 5% of the shadow image of bones is due to the organic “soft” ingredient of bone tissue. Therefore, due to the very nature of X-ray examination, in the X-ray diagnosis of diseases of bones and joints, the assessment of quantitative changes in bone tissue comes to the fore. You cannot measure distance with scales. The radiologist, using his extremely valuable, but still one-sided method, is currently still forced to limit himself to the analysis of mainly two main quantitative processes of bone activity, namely the creation of bone and its destruction.

A person knows a lot about his body, for example, where the organs are located, what function they perform. Why not penetrate deep into the bone and find out its structure and composition? It's very interesting, because chemical composition bones are very diverse. It helps to understand why each bone element is very important and what function it has.

basic information

Living bone in adults has:

• 50% - water;
• 21.85% - substances of inorganic type;
• 15.75% - fat;
• 12.4% - collagen fibers.

Inorganic substances are different salts. Most of them are represented by lime phosphate (sixty percent). Calcium carbonate and magnesium sulfate are present in smaller quantities (5.9 and 1.4%, respectively). Interestingly, all earthly elements are represented in the bones. Mineral salts can be dissolved. To do this, you need a weak solution of nitric or hydrochloric acid. The process of dissolution in these substances has its own name - decalcification. After it, only organic matter remains, which retains its bone form.

Organic matter is porous and elastic. It can be compared to a sponge. What happens when this substance is removed through combustion? The shape of the bone remains the same, but now it becomes brittle.

It is clear that only the interaction of inorganic and organic substances makes the bone element strong and elastic. The bone becomes even stronger due to the composition of the spongy and compact substance.

Inorganic composition

About a century ago, it was suggested that human bone tissue, or rather its crystals, are similar in structure to apatites. Over time this has been proven. Bone crystals are hydroxylapatites, and their shape is similar to rods and plates. But the crystals are only a fraction of the mineral phase of the tissue, the other fraction is amorphous calcium phosphate. Its content depends on the age of the person. Young people, teenagers and children have a lot of it, more than crystals. Subsequently, the ratio changes, so at an older age there are more crystals.

Every day, the bones of the human skeleton lose and gain again about eight hundred milligrams of calcium

The adult human body has more than one kilogram of calcium. It is found mainly in dental and bone elements. When combined with phosphate, hydroxyapatite is formed, which does not dissolve. The peculiarity is that in the bones the main part of calcium is regularly renewed. Every day, the bones of the human skeleton lose and gain again about eight hundred milligrams of calcium.

The mineral lobe has many ions, but pure hydroxyapatite does not contain them. There are ions of chlorine, magnesium and other elements.

Organic composition

95% of the organic type matrix is ​​collagen. If we talk about its significance, then, together with mineral elements, it is the main factor on which the mechanical properties of bone depend. Bone tissue collagen has the following features:

• it contains more hydroxyproline compared to skin collagen;
• it contains many free ε-amino groups of oxylysine and lysine residues;
• it contains more phosphate, the main part of which is associated with serine residues.

Dry demineralized bone matrix contains almost twenty percent non-collagenous proteins. Among them there are parts of proteoglycans, but they are few. The organic matrix contains glycosaminoglycans. They are believed to be directly related to ossification. In addition, if they change, ossification occurs. The bone matrix contains lipids, a direct component of bone tissue. They are involved in mineralization. The bone matrix has another feature - it contains a lot of citrate. Almost ninety percent of it is the share of bone tissue. Citrate is believed to be important for the mineralization process.

Substances of bone

Most of the bones of an adult human contain lamellar bone tissue, from which two types of substance are formed: spongy and compact. Their distribution depends on the functional loads placed on the bone.

If we consider the structure of bones, then the compact substance plays an important role in the formation of the diaphysis of tubular bone elements. It, like a thin plate, covers the outside of their epiphyses, flat, spongy bones, which are built from spongy substance. The compact substance contains a lot of thin tubules, which consist of blood vessels and nerve fibers. Some canals are essentially parallel to the bony surface.

The walls of the channels located in the center are formed by plates whose thickness ranges from four to fifteen microns. They seem to be inserted into each other. One channel near itself can have twenty similar records. The composition of the bone includes an osteon, that is, the union of a canal located in the center with plates near it. Between the osteons there are spaces that are filled with intercalary plates.

In the structure of bone, spongy substance is no less important. Its name suggests that it is similar to a sponge. The way it is. It is built with beams, between which there are cells. Human bone is constantly under stress in the form of compression and tension. They determine the dimensions of the beams and their location.

The bone structure includes the periosteum, that is, the connective tissue membrane. It is firmly connected to the bone element with the help of fibers that extend into its depth. The bone has two layers:

1. External, fibrous. It is formed by collagen fibers, thanks to which the shell is durable. This layer contains nerves and blood vessels.
2. Internal, sprout. Its structure contains osteogenic cells, thanks to which the bone expands and recovers after injury.

It turns out that the periosteum performs three main functions: trophic, protective, bone-forming. Speaking about the structure of bone, we should also mention the endosteum. The bone is covered from the inside with it. It looks like a thin plate and has an osteogenic function.

A little more about bones

Due to their amazing structure and composition, bones have unique characteristics. They are very flexible. When a person performs physical activity and trains, the bones become flexible and adapt to changing circumstances. That is, depending on the load, the number of osteons increases or decreases, and the thickness of the plates of substances changes.

Every person can contribute to optimal bone development. To do this, you need to exercise regularly and moderately. If your life is dominated by sedentary activities, your bones will begin to weaken and become thinner. There are bone diseases that weaken them, for example, osteoporosis, osteomyelitis. Bone structure can be influenced by occupation. Of course, heredity plays an important role.

So, on to some features bone structure a person is unable to influence. Still, some factors depend on it. If, from childhood, parents ensure that the child eats properly and engages in moderate physical activity, his bones will be in excellent condition. This will significantly affect his future, because the child will grow up to be a strong, healthy, that is, successful person.

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.