Bone Tissue - Bone formation or ossification.
Bone formation, also known as ossification or osteogenesis, is the process by which new bone tissue is formed. There are two main types of ossification: intramembranous ossification and endochondral ossification.
Intramembranous Ossification
Intramembranous ossification is a direct process of bone formation where osteoblasts differentiate directly from mesenchymal stem cells and begin secreting osteoid. This process is responsible for the formation of most flat bones, including the skull bones, clavicle, and mandible.
The steps in intramembranous ossification are:
- 1. Mesenchymal cells aggregate and differentiate into osteoprogenitor cells, which further differentiate into osteoblasts.
These events occur in ossification centres within condensed mesenchyme.
- 2. Osteoblasts secrete osteoid, the organic component of the bone matrix. Osteoid is composed primarily of type I collagen, along with other proteins and proteoglycans.
- 3. Calcium salts are deposited within the osteoid in a process called calcification or mineralisation. This deposition of hydroxyapatite crystals hardens the matrix and forms woven bone.
- 4. As bone formation continues, trabeculae of woven bone fuse together, forming a network of interconnected bone tissue. This network eventually becomes remodelled into compact bone at the periphery and cancellous bone in the centre.