Longitudinal bone growth
The epiphyseal plate is responsible for longitudinal bone growth. This illustration shows the zones bordering the epiphyseal plate of the epiphysis. The topmost layer of the epiphysis is the reserve zone. The second zone, the proliferative zone, is where chondrocytes are continually undergoing mitosis. The next zone is the zone of maturation and hypertrophy where lipids, glycogen, and alkaline phosphatase accumulate, causing the cartilaginous matrix to calcify. The following zone is the calcified matrix where the chondrocytes have hardened and die as the matrix around them has calcified. The bottom-most row is the zone of ossification which is part of the metaphysis. The newly-deposited bone tissue at the top of the zone of ossification is called the primary spongiosa, while the older bone is labeled the secondary spongiosa.
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