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Bones
Last reviewed: 04.07.2025
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Some of the most important functions of the human body are holding the body and its parts in a certain position and moving in space. These static and dynamic functions are performed by the musculoskeletal system, which has a passive and active part. The passive part includes bones, which serve as a support for muscles and various organs (hard, rigid skeleton), and bone joints. The active part of the musculoskeletal system is the muscles, which, when contracted, act on the bone levers, setting them in motion. The human body also has a soft skeleton (framework), which is involved in holding organs near the bones. The soft skeleton includes fascia, ligaments, organ capsules and other connective tissue structures.
The bones of the skeleton are formed by bone and cartilage tissues, which are connective tissues. Bones consist of cells and dense intercellular substance.
The bones form a solid skeleton, which includes the spinal column (backbone), sternum and ribs (torso bones), skull, and bones of the upper and lower extremities. The skeleton performs the functions of support, movement, spring, protection, and is also a depot of various salts.
The supporting function of the skeleton is to form a rigid bone-cartilaginous framework of the body; muscles, fascia and many organs are attached to the bones of the skeleton. The function of movement is carried out due to the presence of movable joints between the bones, set in motion by the muscles. The spring function is determined by the presence of special anatomical formations that reduce and soften the shaking during movements (the arched structure of the foot, cartilaginous layers between the bones, etc.). The protective function is due to the participation of bones in the formation of bone receptacles for the brain and sensory organs (cranial cavity), for the spinal cord (spinal canal). Inside the bones is bone marrow, which is the source of the formation of blood cells and the immune system. Bones serve as a depot of mineral salts. In small quantities (up to 0.001%), bones contain more than 30 different chemical elements. Living bone contains vitamins A, B, C, etc.
The skeleton consists of 206 bones on average, of which 33-34 are unpaired bones, the rest are paired. In an adult, 23 bones form the skull, 26 bones form the spinal column, 25 bones form the ribs and sternum, 64 bones form the skeleton of the upper limbs and 62 bones form the skeleton of the lower limbs.
The vertebral column, skull, and rib cage make up the axial skeleton. The bones of the upper and lower limbs are called the accessory skeleton. The mass of the "living" skeleton is approximately 11% of the body mass in newborns, and from 9 to 18% in children of other age groups. In adults, the ratio of skeletal to body mass remains at about 20% for most of their lives. In elderly and old people, the mass of the skeleton decreases somewhat.
For educational purposes, specially processed (macerated) bones (sequentially degreased, bleached, dried) are used, which are aids for studying anatomy. Such a "dry" skeleton has a mass of 5-6 kg. This is approximately 8-10% of the mass of the entire body.
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Classification of bones
The classification of bones is based on the following principles: shape (bone structure), their development and function. The following groups of bones are distinguished: long (tubular), short (spongy), flat (wide), mixed (abnormal) and pneumatic.
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Structure and chemical composition of bones
Bones occupy a strictly defined place in the human body. Like any organ, bones are represented by different types of tissue, the main place among which is occupied by bone tissue, which is a type of connective tissue.
Bone (os) has a complex structure and chemical composition. In a living organism, the bone of an adult contains up to 50% water, 28.15% organic and 21.85% inorganic substances. Inorganic substances are represented by compounds of calcium, phosphorus, magnesium and other elements. Macerated bone consists of 1/3 organic substances, called "ossein", and 2/3 inorganic substances.
Structure and chemical composition of bones
X-ray anatomy of bones
The bones of a living person's skeleton can be studied using X-rays. The presence of calcium salts in bones makes them less "transparent" to X-rays than the soft tissues surrounding them. Due to the uneven structure of bones, the presence of a more or less thick layer of compact cortex, and spongy substance inside it, bones and their parts can be seen and distinguished on X-rays.
Bone development and growth
The fetal skeleton goes through connective tissue (membranous) and cartilaginous stages in its development. Two groups of bones can be distinguished, differing in origin. Some bones are formed directly on the basis of connective tissue, bypassing the cartilaginous stage. Bones formed in this way (membranous osteogenesis) are the bones of the cranial vault.