Regulation of Osteoblast Activity and the Osteoblast-Osteocyte Transformation
According to currently held concepts of bone formation (Table 1), osteoblasts develop from mitotically competent marrow stromal cells by a process of non-mitotic differentiation (modulation) (1,2). Osteoblasts are attracted to the bone surfaces, and are activated to elaborate lamellae of collagen-rich organic matrix (osteoid) which is subsequently mineralized. Inactive osteoblasts, having completed a cycle of bone formation, remain attached to bone, where they appear as flattened, biosynthetically dormant cells. A small proportion of osteoblasts are trapped in the newly secreted osteoid and are buried in successively formed layers of bone. These internalized cells, termed osteocytes, remain connected to each other and to surface osteoblasts by slender processes that traverse the microcanalicular system of bone (3), yielding an apparent syncytium that provides an enormous surface area for mineral exchange and a mechanism for conducting ions from bone to vascular channels. Indeed, the osteocyte network may mediate, at least in part, the role of the skeleton in maintaining mineral and acid-base homeostasis (Table 1).
KeywordsBone Cell Osteoblast Activity Chicken Embryo Fibroblast Autologous Growth Factor Chondrocyte Growth
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