MH 029b Bone

Endochondral Bone Formation

Endochondral bone formation occurs at the epiphyseal plate of long bones. It can be identified by the layer of basophilic hyaline cartilage.

• Resting Zone - thin layer of non-dividing chondrocytes.
• Proliferative Zone - rapidly dividing chondrocytes (basophilic) that organize into distinct columns ("stacks of coins").
• Zone of Hypertrophy - chondrocytes (basophilic) cease dividing and grow in size. The cartilage matrix forms (lightly basophilic) linear bands between the columns of hypertrophied cells.
• Zone of Calcification - the cartilage matrix becomes calcified inhibiting the diffusion of nutrients. The dying chondrocytes are removed leaving longitudinal spicules of calcified cartilage (intensely basophilic).
• Zone of Ossification - osteoprogenitor cells migrate into the cavities with the new blood vessels. New bone (eosinophilic) forms on the scaffold of calcified cartilage (basophilic).
  • Osteoblasts - condense on the spicules of calcified cartilage and produce new bone (osteoid).
  • Osteoclasts (#1,#2,#3) - large, multinucleated cells that remove bone tissue (both mineralized matrix and type I collagen).