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
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.