Histology
During endochondral ossification, five distinct zones can be seen at the light-microscope level.
| Name | Definition |
|---|---|
| Zone of resting cartilage | This zone contains normal, resting hyaline cartilage. |
| Zone of proliferation / cell columns | In this zone, chondrocytes undergo rapid mitosis, forming distinctive looking stacks. |
| Zone of maturation / hypertrophy | It is during this zone that the chondrocytes undergo hypertrophy (become enlarged). Chondrocytes contain large amounts of glycogen and begin to secrete alkaline phosphatase. |
| Zone of calcification | In this zone, chondrocytes are either dying or dead, leaving cavities that will later become invaded by bone-forming cells. Chondrocytes here die when they can no longer receive nutrients or eliminate wastes via diffusion. This is because the calcified matrix is much less hydrated than hyaline cartilage. |
| Zone of ossification | Osteoprogenitor cells invade the area and differentiate into osteoblasts, which elaborate matrix that becomes calcified on the surface of calcified cartilage. This is followed by resorption of the calcified cartilage/calcified bone complex. |
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