<P> Endochondral ossification is responsible for the initial bone development from cartilage in utero and infants and the longitudinal growth of long bones in the epiphyseal plate . The plate's chondrocytes are under constant division by mitosis . These daughter cells stack facing the epiphysis while the older cells are pushed towards the diaphysis . As the older chondrocytes degenerate, osteoblasts ossify the remains to form new bone . In puberty increasing levels of estrogen, in both females and males, leads to increased apoptosis of chondrocytes in the epiphyseal plate . Depletion of chondrocytes due to apoptosis leads to less ossification and growth slows down and later stops when the entire cartilage have become replaced by bone, leaving only a thin epiphyseal scar which later disappears . </P> <P> The growth plate has a very specific morphology in having a zonal arrangement . </P> <Table> <Tr> <Th> Epiphyseal plate zone (from epiphysis to diaphysis </Th> <Th> Description </Th> </Tr> <Tr> <Td> Zone of reserve </Td> <Td> Quiescent chondrocytes are found at the epiphyseal end </Td> </Tr> <Tr> <Td> Zone of proliferation </Td> <Td> Chondrocytes undergo rapid mitosis under influence of growth hormone </Td> </Tr> <Tr> <Td> Zone of maturation and hypertrophy </Td> <Td> Chondrocytes stop mitosis, and begin to hypertrophy by accumulating glycogen, lipids, and alkaline phosphatase </Td> </Tr> <Tr> <Td> Zone of calcification </Td> <Td> Chondrocytes undergo apoptosis . Cartilagenous matrix begins to calcify . </Td> </Tr> <Tr> <Td> Zone of ossification </Td> <Td> Osteoclasts and osteoblasts from the diaphyseal side break down the calcified cartilage and replace with mineralized bone tissue . </Td> </Tr> </Table> <Tr> <Th> Epiphyseal plate zone (from epiphysis to diaphysis </Th> <Th> Description </Th> </Tr>

On the diaphyseal side of the epiphyseal plate is the