At the physis, chondrocytes proliferate, ma- ture, and secrete extracellular matrix, which eventually ossifies. The physis is polar: mov- ing away from the epiphysis and joint sur- face toward the metaphysis, there is increas- ing maturation of the cells. Just below the epiphysis is a zone of immature resting cells; just above the metaphysis, calcification takes place in the setting of programmed cell death (apoptosis) of the hypertrophic chondro- cytes. New bone formation thus occurs at the point farthest from the articular surface, at the junction between the physis and the metaphysis. This region is named the zone of provisional calcification.

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