THE FINE STRUCTURE OF OSTEOBLASTS IN THE METAPHYSIS OF THE TIBIA OF THE YOUNG RAT D. A. CAMERON, M.D.S. From the Department of Pathology, University of Sydney, New South Wales, Australia
THE ROLE OF OSTEOBLASTS IN MINERALIZATION Osteoblasts are present on surfaces of bone where ac-tivebone formation is occurring. Inactive surfaces are also believed to be covered with cells, specifically quiescent osteoblasts and bone lining cells.
The number of osteoblasts in the BMU is a function of the available supply of new osteoblasts from local progenitors and the life span of the mature cell.
The active osteoblasts increase in number, but the active osteoclasts develop, after transients, to a practically identical equilibrium( Fig. 2A , bottomgraphic).
363 Extensive bone metabolism studies have shown that the rate at which osteoclasts resorb bone and osteoblasts replace the lost bone with new bone are tightly coupled, creating a scenario in which osteoclasts and osteoblasts communicate to maintain a balance of bone resorption and formation.
We have studied the survival requirements of osteoblasts to test the hypothesis that osteoblasts undergo pro grammed cell death (PCD) or apoptosis unless they are
osteoblasts through to mature osteoblasts, to bone-lining cells and osteocytes (Fig. 1). All these stages are likely to occur in normal bone turnover and during fracture heal
Osteoblast Isolation •Wong G, Cohn DV. Separation of parathyroid hormone and calcitonin-sensitive cells from non-responsive bone cells. Nature 1974 252:713-715.
Osteoblasts were treated with 10 m of the inhibitor for 4 d in differentiation medium. The expression of ALP was mea sured histochemically by staining (Fig. 1A, upper panel).
The next region is the mineralizedfibrocartilage zone, with hypertrophicchondrocytes surrounded by a mineralized matrix containing collagen type X. 6,15 Thelastregionis thesubchondral bone, within which osteoblasts, osteocytes, and osteoclasts are embedded inamineralized collage type I matrix.