Bones are particularly hard organs, with shape, density and size varying according to the functions performed. Together, they participate in the formation of the skeletal system, an apparently inert structure, but alive and endowed with numerous, very important, functions.
How many bones in the human body
There are approximately 212 bones in the human body, distributed as follows:
Lower limbs: 60 bones;
Upper limbs: 60 bones;
Spinal column: 33 bones;
Coasts: 24 bones;
Skull: 22 bones;
Ear: 6 bones;
Scapular track: 4 bones;
Sternum: 3 bones;
Pelvic track: 2 bones connected to the spine;
Hyoid bone: 1 bone.
From this list are excluded sesamoid and wormian bones because they vary in number and in some cases even absent. The former improve muscle efficiency, as in the case of the patella, while the wormianas are small supernumerary bones included in the sutures of the skull. The number of bones varies according to the age of the individual. In the children, in particular, they are more numerous, because at the birth some of them, especially the skulls, have cartilaginous segments which ossify and join with the growth. This is, obviously, a very important characteristic; the membranous spaces separating the bones of the skull of the newborns, called small fountains, may move, avoiding that the brain suffers an excessive pressure during the delivery or its development.
In adults, this type of cartilage (called hyaline) is maintained only where a high degree of flexibility is required, as in the nose, around the articular surfaces and in the front part of the ribs (a necessary characteristic to allow the enlargements, the constrictions and the modifications of the thoracic cage during the breath). Small variations in the number of bones in the body are also found in individuals of the same age. Together with the cartilage tissue, the bones form the human skeleton, which alone represents less than 20% of body weight (a lower percentage than the muscles, which together account for 35 to 40% of body mass). Bones, therefore, have four important characteristics, exceptional because they are difficult to combine: lightness, strength, hardness and elasticity.
The skeleton is divided didactically into:
axile: as the name implies, it constitutes the main axis of the human body and includes the head (skull) and the trunk (vertebral column, ribs and sternum); appendicular: as the name implies, it includes the skeleton of the appendages, i.e. the limbs, together with the scapular and pelvic belts.
The primary function of the skeleton is to provide a scaffold to support and protect the soft tissues of the body, helping to maintain its characteristic shape.
Functions of the bones and skeleton
The particular structure of the tissue that composes them, gives the bones a certain degree of hardness and strength, making them suitable to cover functions of support and protection. In fact, they form the skeleton, protect the internal organs and represent a support for the attack of muscles and tendons. To these functions must be added an important hematopoietic and metabolic role. The human skeleton is given by the set of anatomical structures having the function of support and protection of soft tissues. The bones that compose it, thanks to the connection with the muscular system, also function as levers to allow movement.
The bones of the human body differ in shape and size, covering equally diverse functions. According to these characteristics, they are divided into: long bones, when length prevails over other dimensions; flat or wide bones, when width or length prevails over thickness; short bones, when the three dimensions are almost equal.
they are formed by a central part, called diaphysis, and by two extremities, or heads, bigger, called epiphysis. The epiphysis contracts relationships with the near bones and they are provided with articular surface. The central mass (diaphysis) is made up of compact tissue and, further inside, a cavity in which the bone marrow is generally contained. Typical long bones are those of the limbs (femur, tibia, fibula, humerus, radius, ulna).
Sometimes, we distinguish a third, small, cartilaginous area, called metaphysis and placed between epiphysis and diaphysis. It is present in the child and in the young adolescent, while it disappears in the adult; it is essential for the growth in length of the long bones.
characterized by length and diameter of similar size; they consist of spongy tissue completely wrapped in a sheet of compact tissue. Examples of short bones of the human body are those of the wrist, heel and vertebrae.
Similar to long bones, they have a, albeit reduced, central part of spongy tissue (called diploe) where the bone marrow is located. The whole is covered by two layers (one on each side) of compact tissue (called planks). Typical flat bones are those of the skull, pelvis and sternum.
Special anatomical terms are used to describe the macroscopic characteristics of bones. Let’s see the main ones.
In long bones, they can be recognized:
epiphysis: these are the two ends of the long bones, slightly swollen and joined by the central diaphysis; diaphysis: it represents the central part of the long bones. The epiphyses have particular forms that allow them to draw articular relationships with neighboring bones, matching them. When this correspondence is missing, the relationship between the two articular surfaces is established through the interposition of fibro-cartilaginous structures, as in the case of the knee menisci.
The two epiphyses are distinguished from each other by the distal and proximal terms. Inside, they contain spongy bone tissue, among the meshes of which there is hematopoietic red marrow. On the other hand, throughout the diaphysis, it is possible to recognize a central channel, called the diaphyseal channel, which contains the yellow marrow. The coasts and the clavicles, even if long bones, do not have the diaphyseal channel and do not contain yellow marrow. The bony surface may have protrusions; the terms crests, lines, apophysis, spines, processes, tuberosity and drafts define their characteristics.
Head: roundish bony portion, which rests on a narrower part, called the neck. The surface of the bones of the human body may also have indentations or depressions (ditches, channels, cavities):
Cavities: small gaps present inside the bones that can be of articular nature and not, depending on whether or not they participate in a joint.
Hollows are connections between adjacent, non-joint bones when they are a point of attachment for ligaments or tendons, or when they accept organs or make the bone lighter without diminishing its resistance. There may also be holes and channels to allow vessels and nerve fibres to pass through.