Osteoclasts bone metabolism control

The second level involves two kinds of cellular participation resorption of existing bone by osteoclasts and deposition of new bone by osteoblasts. Over short periods these two processes, acting at different sites, approximately balance each other. Acting in conjunction, they not only continuously remodel the surface contour of the bone but also play a major part in the control of calcium and phosphorus metabolism for the whole organism. Coordination at this second level is achieved through hormonal mediation of calcium and phosphate homoeostasis which ensures that the concentrations of these ions in the plasma and tissue fluid remain constant (Chapter 30). 

Regulation of Calcium Level. Parathormone controls the metabolism of Ca++. It activates the osteoclasts and thereby causes a demineralization of bone and a rise of the Ca++ level in blood. It is not yet clear how these minerals are dissolved. Citrate probably plays a key role at least, it occurs in relatively high concentrations in bony tissue. Bone tissue contains the enzyme system for forming citrate, but little aconitase and isocitrate dehydrogenase. 

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