MH 046 Bone Development

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Intramembranous Bone Formation

Different stages of intramembranous bone formation are seen in the (calvarium) when moving from the center to the right.

- mesenchymal cells migrate and aggregate into areas where bone will form (a bone blastema).
- the condensation of mesenchymal cells initiates the differentiation of osteoprogenitor cells.
- the synthesis of components of the bone matrix indicates the further differentiation of osteoprogenitor cells into osteoblasts. Their basophilic cytoplasm is from the synthesis of proteins in osteoid (mostly type I collagen).
- unmineralized, organic portion (type I collagen and ground substance) of bone matrix. Narrow, light-pink region between osteoblasts and the bone spicule.
- osteoblasts trapped inside lacunae of the bone.
- composed of women immature (or primary) bone with mineralized osteoid that is more basophilic than unmineralized osteoid.
- form from bone spicules that fuse with each other to provide the general shape of a developing bone.
Haversian System - developing osteons (,,) can be recognized by blood vessels at the center of an area surrounded by osteoblasts.