OSTEOGENESIS (English version)

OSTEOGENESIS

            Osteogenesis is the name given to the development of bone tissue. The bone growth begin from the change of another tissue before, The mesenchyme tissue of embryo will be changed become to be bone tissue or cartilage tissue that will be changed again become to be bone tissue.

            Osteogenesis of embryo divided into two kinds:

1.      Desmalis osteogenesis that form desmal bone

2.      Enchondralis osteogenesis that will form cartilage bone

A.    Desmalis Osteogenesis

Desmalis osteogenesis is also called intramembranous osteogenesis, because it occur in the tissue membrane. The bone that is formed called desmal bone. This osteogenesis occur during the embryonic development of many flat bones like bone of skull, mandible and clavicle.

Desmalis osteogenesis occurs in the following steps.

1.   Condensation of mesenchymal cells in well-vascularized primitive connective tissue.

First, mesenchyme tissue condensate become to primitive connective tissue that contain of a lot of blood vessel. Then they are connected each others by their protrusion. The intercellular substance formed smooth collagen fibers that hidden in the compact ground substance.

2.    Appearance of dense eosinophilic osteoid matrix and simultaneous transformation of mesenchymal cells to larger, more basophilic osteoblasts.

In this step, the first indication could be see that indicate the bone forming is the matrix that have eosinophilic color between 2 closed blood vessels. The matrix that is formed looked as plait because the place that will be the skull has blood vessel plait. The place of the beginning change called Primary Ossification Centre. The mesenchyme cells change become larger. At the same time the cells of the connective tissue arranged line up along the matrix surface and the form change to be cuboids. Whereas the cytoplasm become to be basophyl then called osteoblast.

3.    Initial production of bone spicules (trabeculae) with random collagen organization (woven bone).

Osteoblast undergo synthesize and secretion. Because of it, the bone matrix called osteoid increase steadily so the form become flat called trabecule that is thick. At the same time, it also occurs the tropocollagen molecules secretion that will form collagen, and also glycoprotein synthesize.

After the secretion by osteoblast, then it happen the calcium phosphate sedimentation in a part of the matrix so that it is left as a thin layer of osteoid matrix around the osteoblast.

The thicker trabecule makes the osteoblast hidden in the calcify matrix, named osteocyte. The protrusion of the cells still connected and also hidden in the canaliculi. The position of osteoblast, that have transform become to osteocyte, will be changed by the cells of the connective tissue around it.

4.     Compaction of trabeculae to form cortical bone.

The osteoblasts continue to transform become to osteocytes, and it makes the trabecule become thicker so the separated connective tissue become thin. The cavity among the trabecule is very narrow in the part that will transform to be compact bone. And the part that will transform to be cavity bone, the connective tissue that still exist will change to be bone marrow that will produce blood cells.

B.    Encondralis Osteogenesis

Enchondralis osteogenesis occur with a cartilage base. The bone that is formed called  cartilage bone because the forming by the formation of hyalin cartilage tissue. It occurs at the long bone and vertebrae. The primary enchondralis osteogenesis occurs in the diaphysis of the long bone, and the secondary occurs in the epiphysis.

Enchondralis osteogenesis, primary and secondary, occurs in the following steps. The first will happen primary osteogenesis, then continued with secondary osteogenesis.

1.      Hypertrophy (swelling) of chondrocytes (cartilage cells) in central portion of cartilage model.

The chondrocyte cells in the central portion of cartilage model undergo hypertrophy. Hypertrophy is the condition that the cells enlarge with swollen cytoplasm. Because of it, the cartilage matrix pressed become to be thin septum. In the cytoplasm of the chondrocytes there are glycogen accumulation. The perichondrium around the cartilage (ossification centre) have osteogenic potential so formed bone under it. The bone that is formed is a pipe surround the ossification centre that still have cavity. The bone called periosteum.

2.      Formation of bone collar between the periosteum and the shaft of the cartilage model.

After the periosteum formed, it also formed collar between the periosteum and the shaft of the cartilage model.

3.     Cartilage matrix calcification.

At the same time with the first step, the matrix of the cartilage ready to accept calcium sedimentation. It causes the cartilage cells die because they loose their nutrition. So it will formed cavity (marrow cavity) that connected each other as lacuna residue.

4.      Blood vessel invasion.

After the periosteal pipe formed, the blood vessels enter to the cartilage model by a periosteal bud, and then it penetrates in the primary marrow cavity through the bone collar. The blood bring cells then they are put on the matrix wall. The cells have osteogenic and hemopoietik potential. The cells will play role as osteoblast that secret osteoid matrix. The it formed bone marrow.

5.      Bone matrix layed down on scaffolding of calcified cartilage.

The cartilage calcified by cells that play roles as osteoblast. Trabecula also formed by the calcified cartilage and layered by the osteoid will undergo calcification. It makes the osteoid tissue transform to be bone tissue that still contain of calcified cartilage matrix in the middle of the bone.

After the primary osteogenesis finish, it continued by secondary osteogenesis that occurs in the epiphysis. Between epiphysis and diaphysis, there are a plate called discus epiphyseal. The structure show the growth area of the bone:

1.      Zone of reserve cartilage. This is typical hyaline cartilage and is a large zone in this preparation.

2.      Zone of cell proliferation (ZP). The cartilage cells are small and tend to be arranged in columns, which run parallel to the long axis of the cartilage.  This arrangement is indicative of their intense mitotic activity.

3.      Zone of cell and lacunar maturation and hypertrophy enlargement (ZH). Chondrocytes and lacunae are larger than in the previous zone.  The chondrocytes increase in size and resorb some their lacunar walls, enlarging them to such an extent that some of the lacunae become confluent.

4.      Zone of calcification (ZC). This is a small zone having a slightly darker appearance than the preceding zone due to the basophilic staining of the calcified cartilage.  The chondrocytes die in this zone.

5.   Zone of cartilage removal and bone deposition. Osseous elements are present among the pieces of calcified cartilage.