It is obvious from morphological studies that osteocytes originate from osteoblasts. However, the origin of osteoblasts and osteoclasts have been subject to controversy. Until recently, original investigations by Young (1962) and Tonna (1965) had suggested that osteoblasts and osteoclasts both originate from mesenchyme or progenitor cells; these cells are independently stimulated by different hormones or different stresses and differentiate into osteoclasts and osteoblasts, which resorb and form bone, respectively. There is some evidence that osteoclasts may form from osteogenic cells (Tonna and Cronkite, 1968). However, the studies were carried out in young growing rats and may represent the rapid change from bone formation to bone resorption in bone that is in the process of rapid turnover. The same situation may exist for infants, but it is not likely to be true of the bone of juveniles or adults of the human species. Nevertheless, it represents a rapid cycling of nuclear material that occurs at a slower rate in all bone cells. The origin of osteoclasts from osteoblasts has been challenged by Young (1964).
KeywordsBone Formation Progenitor Cell Serum Calcium Level Osteoclastic Bone Resorption Tritiated Thymidine
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