Intramembranous and Endochondral Ossification

Locate regions of intramembranous bone development in this section of fetal rodent head . Identify the mesenchymal cells, vasculature, growing bone trabeculae, osteoblasts, osteocytes, and osteoclasts.

Locate the cartilaginous region on this slide of endochondral ossification. Carefully study all areas of the epiphyseal growth plate, moving from the cartilage to the diaphysis of the bone. Concentrate on the chondrocytes and matrix, noting the changes in these structures as you move through the various functional zones.

• Zone of reserve cartilage (R)
• Zone of proliferation (P)
• Zone of hypertrophy (H)
• Zone of calcified cartilage (C)
• Zone of ossification (O)
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Now for joints.

Clinical note:  Achondroplasia is an inherited disorder in which there is reduced proliferation of the chondrocytes in the epiphyseal plate of long bones. The result is a form of dwarfism in which the trunk is of normal length, but the extremities are short.