The longitudinal growth of long bones results from events that happen in their epiphyseal discs.
Five bands of cells (actually five discs) called zones can be distinguished in a longitudinal section of the disc. They zones depict a sequence of transformations that the cartilage cells undergo and that at the end of the disc are replaced by bone cells.
As the chondrocytes undergo subtle transitions from each zone to the nexttThe boundaries between the zones are not precise .
Zones of the epiphyseal disk:
Zone of resting cartilage
Zone of proliferation
Zone of hypertrophic cartilage
Zone of calcified cartilage
Zone of ossification
The first four zones are made of cartilaginous tissue and the last zone of newly produced bone tissue.
Zones of the Epiphyseal disc seen in a longitudinal section of the bone. Staining: HE. Magnification: small.
