Chapter 55 - Skeletal Development

formation of calcified osteoid matrix INSIDE of a cartilage framework flat bones, clavicles, and the skull

occurs at growth plates and within fracture callous and is characterized by osteoid production ONTO a cartilage anlage

• reserve zone - sparse distribution of cells in a vast matrix, chondrocytes are not participating in longitudinal growth, type II collgen is highest here • proliferative zone - longitudinal columns of flattened cells, uppermost cell is the progenitor cell and is responsible for longitudinal growth - maturation zone • hypertrophic zone - weakest layer, novel matrix protein synthesis occurs here, chondrocytes participate in matrix mineralization thru alkaline phosphatase synthesis, neutral protease synthesis, type X collagen synthesis

preferentially effects proliferative and upper hypertrophic zone chondrocytes - has a direct mitogenic effect on these chondrocytes - increases proteoglycan synthesis

the proliferative zone - no metabolites are found in the hypertrophic zone

zone of hypertrophy

Autosomal recessive defect in alkaline phosphatase normal levels of calcium nd phosphate inability to calcify matrix WIDENED hypertrophic zone zone of provisional calcification never forms

X-linked dominant low serum calcium low serum phosphorous alkaline phosphatase activity is high abnormal conversion of vitamin d to its metabolites

metaphyseal region

zone of proliferation

widened zone of hypertrophy metaphyseal flaring

vitamin C deficiency decreased chondroitin sulfate and collagen synthesis seen preferentially at the metaphysis where tI collagen is highest

frenkel lines - radiodense lines representing the zone of provisional calcification metaphyseal flaring metaphyseal osteopenia