Intramembranous ossification
- A DIRECT form of ossification mesenchymal cells directly differentiate to osteoblasts (no cartilaginous model is first formed), such as occurs with flat bones (the skull bones).
Intramembranous Ossification
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Steps of Intramembranous Ossification
- Embryologically, skeletal tissues typically derive from mesoderm: the midline (axial) skeleton derives from the somites and the appendicular (the limb) skeleton derives from the lateral plate.
- Mesenchymal cells migrate to vascularized gelatinous extracellular collagen fiber matrix (a primary spongiosa).
- They differentiate directly into osteoblasts.
- Osteoblasts form bone in a loosely arranged (disorganized), immature initial form of bone, called woven bone.
- Osteoblasts become trapped within their own bony matrix and become osteocytes; these bony matrices are referred to as trabeculae (aka fused spicules).
- Woven bone later matures to form lamellar bone, a much tougher form of bone that constitutes both compact bone and spongy bone.