Skeletal System, Bone

The supporting frame of the body, representing a collection of articulating bones; determines the appearance and shape of the body of humans and vertebrates. Bone is a complex formation consisting of bone tissue (the main mass of bone), bone marrow, articular cartilage, nerves and blood vessels.

The outside of the bones, with the exception of the articular surfaces, are covered with periosteum. The periosteum is a thin, strong connective tissue film, rich in blood vessels and nerves. Based on their shape and structure, there are four main types of bones: tubular, spongy, flat or wide, and mixed.

Tubular bone consists of a diaphysis (compact bone), which contains bone marrow, and two epiphyses, which have an articular surface covered with cartilage (bones of the lower and upper extremities). Spongy bones consist primarily of spongy substance covered with a thin layer of compact substance - ribs, vertebrae, small bones of the foot and hand.

Flat, or wide, bones form cavities for internal organs (bones of the skull, pelvis). Mixed bones include bones consisting of several parts, such as the bones of the base of the skull.

The bones of the skeleton are connected to each other using joints, ligaments, membranes, cartilage and sutures. The organic part of the bone consists of 95% collagen protein, 5% is non-collagenous proteins, carbohydrates and fats. The elasticity of bone depends on organic substances, and its hardness on mineral substances.

The combination of these components in bone gives it significant strength and elasticity. The skeletal system performs a number of mechanical and biological functions in the body. The mechanical functions of the skeleton provide support and movement, as well as protection of internal organs. Support and movement are possible due to the structure of bones like long and short levers connected by movable joints, easily set in motion by muscles attached to the bones.

In addition, bones form channels and cavities, etc. protect internal organs. Thus, the bony canal of the spine protects the spinal cord, the bones of the skull - the brain, the chest - the heart, lungs, etc.

The biological functions of the skeletal system are determined by its participation in the processes of hematopoiesis and metabolism. For example, bone marrow, located inside the bone, carries out the process of formation of blood cells. Bone is directly involved in the metabolism of mineral substances, being a mobile depot of mineral components. The skeleton contains about 99% of tissue calcium, 87% of phosphorus and 50% of magnesium.

Bone cells are in constant contact with the surrounding tissue fluid, and due to the small size of hydroxyapatite crystals (the main mineral component of bone) and the peculiarities of its structure, rapid exchange of ions occurs. Over the course of a person's life, bone undergoes various changes.

In the prenatal period, bone consists of cartilage tissue. Ossification points begin to appear at 7-8 weeks of intrauterine life. By the time of birth, all diaphyses have ossified, after which the ossification process continues in the area of ​​the epiphyses. For different bones, the timing of the appearance of ossification points and the completion of the mineralization process is different. However, for each bone they are quite constant, which makes it possible to judge the development and maturation of the skeletal system.

Age-related changes in bones are so characteristic that anthropologists, based on studying the general appearance, the diameter of long tubular bones and the medullary canal, the thickness of the walls of the diaphysis of short tubular bones, and x-ray data, establish a person’s age.

Bone chemistry also changes significantly with age. Young children have more organic matter in their bones, so their bones are more flexible and rarely break. On the contrary, in old age, when the specific gravity of organic components decreases, bones become less elastic and more fragile, as a result of which the