Intramembranous Ossification

Intramembranous ossification

When bone tissue  develop directly from mesenchyme (embryonic connective) tissue, process is called intramembranous ossification.

Intramembranous ossification begins at approximately 5th week of development with formation of mesenchymal membrane.

Ossification of membrane begin -- Approximately 8th weak of development and completed by approximately 2 year of age.

Site of intramembranous ossification

Such as; flat bones of skull, mandible, clavicle

Process of Intramembranous Ossification

Mesenchymal stem cells aggregated and form osteoblast by differentiation.

1. Development of ossification center 

These bone forming oesteoblast are going to come together and form ossification center. 

Oesteoblasts begin to secrete osteoid (substance, hardening bone, unmineralized bone)

Peripheral mesenchymal cell continue to differentiate.

2. Calcification

Osteoblasts secrete osteoid inward toward ossification center.

Oesteoblasts become trapped in osteoid, causing differentiation into osteocytes.

Osteoid calcifies and hardens after several days.

Osteoid continues to be deposited, assembles, in random manner around embryonic blood vessels.

3. Formation of Trabeculae

Finely waven trabeculae forms blood vessels grow into spaces between trabeculae.

Mesenchyme begins to differentiate in periosteum.

Lamellar (compact) bone replaces woven bone at outer edge 

Layered

Internal spongy bone remains

Vascular tissue within Trabeculae spaces forms red marrow.

Oesteoblasts remains on bone surface to remodel when needed development of periosteum (outer covering of bone).