The human skeleton is given by the set of anatomical structures with the function of supporting and protecting soft tissues. The bones that compose it, thanks to the connection with the muscular system, also work as levers to allow movement. Further features of the skeleton are given in this article.
Bones: classification
The bones of the human body differ in shape and size, covering equally diverse functions. Based on these characteristics, they are divided into: long bones, when the length prevails over the other dimensions; flat or broad bones, when width or length prevail over thickness; short bones, when the three dimensions are almost the same.
LONG BONES : they are formed by a central part, called diaphysis, and by two ends, or heads, larger, called epiphyses .
The epiphysis has relationships with neighboring bones and has an articular surface.
The central mass (diaphysis) consists of compact tissue and, more inland, 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, there is a third, small, cartilaginous area, called the metaphysis and located between epiphyses and diaphysis. It is present in the child and in the young adolescent, while it disappears in the adult; it is essential for long bone length growth.
SHORT OR SHORT BONE : characterized by length and diameter of similar size; they are made of spongy fabric completely wrapped in a sheet of compact fabric. Examples of short bones of the human body are those of the wrist, calcaneus and vertebrae.
FLAT BONES : similar to the long bones, they have a, although reduced, central part of spongy tissue (called diploe) where the bone marrow is located. All covered with two layers (one on each side) of compact fabric (called boarding). 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) full of air that communicate with the nasal cavities (maxillary, frontal, sphenoid and ethmoid).
BONE SESAMOIDS : 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).
WORMIAN BONES : small supernumerary flat bones located, but only in some individuals, between the cranial bones, along the course of the sutures.
Bones: macroscopic features
Specific anatomical terms are used to describe the macroscopic characteristics of the bones. Let's see the main ones.
In long bones we can recognize:
epiphyses: 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 articular relationships with the neighboring bones, matching them. When this correspondence is missing, the relationship between the two articular surfaces is established by 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 terms. Inside, they contain spongy bone tissue, among whose meshes there is red hematopoietic marrow.
Inside the diaphyses, on the other hand, it is possible to recognize a central channel, called the diaphyseal channel, which contains yellow marrow. The ribs and the clavicles, despite being long bones, are devoid of the diaphyseal channel and do not contain yellow marrow.
The bone surface may have protrusions; the terms ridges, lines, apophyses, thorns, processes, tuberosity and drafts define its characteristics.
Process or apophysis: particularly voluminous and marked prominence
Condilo: round / oval shape process
Tubercle: small roundish process
Tuberosity: conspicuous roundish process
Trochanter: conspicuous process, of varied form
Crest: thin bone relief
Plug: thin and pointed process
Head: roundish bony portion, resting on a narrower part, called neck
| Coracoid process of the scapula | Xyphoid apophysis | Femoral condyles |
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| The two trochanters of the femur | Iliac crest | Spine of the scapula |
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The surface of the bones of the human body can also present indentations or depressions (pits, canals, cavities):
cavity: small gaps present inside the bone that can be articular or not, depending on whether or not they participate in a joint.
The cavities constitute connections between contiguous non-articular bones when they constitute an attachment point for ligaments or tendons, or when they receive organs or make the bone lighter without diminishing its resistance.
There may also be holes and channels to allow the passage of vessels and nerve fibers.
