Bones of the human body

The human skeleton is given by the "set of anatomical structures which have the function of supporting and protecting the soft tissues. The bones that compose it, thanks to the connection with the muscular system, also function as levers to allow movement. The additional functions of the skeleton are reported in this article.

Bones: classification

The bones of the human body differ from each other in shape and size, covering equally diverse functions. On the basis of these characteristics, they are divided into: long bones, when length prevails over other dimensions; flat or broad bones, when width or length prevails over thickness; short bones, when the three dimensions are nearly equal.

LONG BONES: they are formed by a central part, called diaphysis, and by two ends, or heads, larger, called epiphyses.

The epifiysis they contract with neighboring bones and are provided with an articular surface.
The central mass (diaphysis) is made up of compact tissue and, more internally, of 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, a third, small, cartilage area is distinguished, called the metaphysis and located between the 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 long bones.

SHORT OR SHORT BONES: characterized by similar length and diameter; they consist of spongy fabric completely wrapped in a compact fabric sheet. Examples of short bones in the human body are those of the wrist, heel and vertebrae.

FLAT BONES: similar to long bones, they have a central part of spongy tissue (called diploe), albeit reduced, where the bone marrow is located. All covered by two layers (one on each side) of compact fabric (called boards). Typical flat bones are those of the skull, pelvis and sternum.

IRREGULAR BONES: they are characterized by an irregular shape (sphenoid and ethmoid of the skull).

PNEUMATIC BONES: they have small cavities (sinuses) filled with air that communicate with the nasal cavities (maxillary, frontal, sphenoid and ethmoid).

SESAMOID BONES: at the tendon level, they favor the mechanics of movement (the patella, for example, is a sesamoid bone which, in addition to protecting the knee, facilitates the action of the quadriceps muscle during leg extension).

WORMIANE BONES: small supernumerary flat bones located, but only in some individuals, between the cranial bones, along the course of the sutures.

Bones: macroscopic characteristics

Special anatomical terms are used to describe the macroscopic characteristics of the bones. Let's see the main ones.

In the long bones we recognize:

epiphysis: these are the two ends of the long bones, slightly swollen and joined by the central diaphysis;

diaphysis: represents the central part of the long bones.

The epiphyses have particular shapes that allow them to draw joint relationships with the neighboring bones, matching them. When there is no such correspondence, the relationship between the two articular surfaces is established through the interposition of fibro-cartilaginous structures, as in the case of the menisci of the knee.

The two epiphyses are distinguished from each other by the distal and proximal term. Inside, they contain spongy bone tissue, between the meshes of which there is a hematopoietic red marrow.

In the whole of the diaphysis, on the other hand, it is possible to recognize a central canal, called the diaphyseal canal, which contains yellow medulla. The ribs and the clavicles, although they are long bones, have no diaphyseal canal and do not contain yellow medulla.

The bony surface may have protrusions; the terms crests, lines, apophysis, spines, processes, tuberosity and drafts define its characteristics.

Process or apophysis: particularly voluminous and marked prominence

Condyle: round / oval shaped process

Tubercle: small roundish process

Tuberosity: conspicuous rounded process

Trochanter: conspicuous process, of various shapes

Crest: thin bony relief

Spine: thin and pointed process

Head: rounded bony portion, which rests on a narrower part, called the neck

Coracoid process of the scapula Xiphoid apophysis Femoral condyles

The two trochanters of the femur Iliac crest Spine of the scapula

The surface of the bones of the human body can also have indentations or depressions (pits, canals, cavities):

cavity: small gaps present inside the bones that can be of an articular or non-articular nature, depending on whether they participate in a joint or not.

Cavities form connections between contiguous non-articular bones when they form an attachment point for ligaments or tendons, or when they accommodate organs or make bone lighter without decreasing its strength.

There may also be holes and channels to allow for the passage of vessels and nerve fibers.