Osteogenesis

The osteogenesis is the process by which is worked out the bone tissue.

The bone is formed to leave:
- of an organic matrix (35%) primarily made up of Collagenous of the type I (90%), but also of others Protein S like the ostéonectine or the ostéocalcine, protein synthesized by the Osteoblast S (synthesis dependant vitamin K) from where it is secreted in the bone and a little in circulation but is not salted out during the osseous resorption (by the Ostéoclaste S),
- of a mineral matrix (60%) very rich in Calcium (in the form of calcium hydroxyapatite $Ca_ {10} (PO_4) _6 (OH) _2$ ) and in Phosphorus,
- of specific osseous cells (5%) (osteoblasts and osteoclasts) and of water.

Osteogenesis can be of three types:

a membranous or periostic ossification
an ossification enchondrale (endochondrale) or cartilagineuse
an ossification in conjunctive medium, more rare.

Membranous or periostic ossification

It represents that of the flat bones, of and the bone dome of the skull of the face.
The bone is preceded by a membranous conjunctive cartilagineuse model, without passing by a stage of cartilage, worked out by called cells of conjunctive fabric fibroblasts. It is thus about a bone of membrane.
Ossification is done starting from the periphery: the osseous spans of young people push back towards the depth of the bone the older spans.

Ossification in conjunctive medium

It is the ossification of the Mandibule, which is formed around a cartilagineux axis called cartilage of Meckel pertaining to the first arc branchial.

Ossification endochondrale or cartilagineuse

It is the ossification of all the long bones, of the Vertèbres and most of the base of the Crâne.
The bone is preceded by a cartilagineuse model. The ossification in-depth fact initially, starting from different points of ossification. In general, there exists a primitive point of ossification secondary diaphysaire and two points épiphysaires, associated with one or more complementary points.

Ossification diaphysaire

It is the first with apparaître.
The cartilagineuses cells gradually increase sizes and vessels coming from the Périchondre penetrate in the cellular zone of multiplication. Around these vessels the first osseous Travées appear, forming the primitive point of ossification which pushes back towards the épiphyses the remainder of the primitive cartilage of the diaphyse.
A zone of less resistance appears between the tablecloth of hypertrophied cartilagineuses cells and the tablecloth Ostéoïde in formation; in the child, this zone is at the origin of the " separations épiphysaires" who can disturb the growth of the member.

Ossification épiphysaire

It is delayed compared to ossification diaphysaire and the process is identique.
It is done in all the directions with part of the point épiphysaire. It leaves in periphery two to three mm of hyaline Cartilage, at the origin of the articular Cartilage, vestige in the adult of the cartilagineuse outline primitive.
The cartilage métaphysaire or Cartilage of conjugation allows the growth of the bone and the individual himself. At the end of the growth, this primitive cartilagineuse zone disappeared by welding from the zone from ossification diaphysaire and épiphysiare. The most active cartilages are located close to the knee and far from the elbow. The knowledge of the topography of the zones of ossification, the chronology of their appearance, but also of fusions between centers of ossifications have an importance in private clinic, or legal medicine and in anthropology. Thus, " the age osseux" can be given by studying the centers of ossification of the skeleton. Fusion épiphyse-diaphyse occurs in general one to two years earlier in the girls than among boys.

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