- Discussion:
- calcium homeostasis is the summation of regulatory feedback systems involved in the
control of plasma Ca concentrations;
- despite the small quantity of ionized calcium (as compared to the amount of calcium in
bone), calcium is maintained in blood at a closely regulated concentration;
- rate of passive Ca fluxes lies in cellular processes that influence and regulate calcium efflux from bone;
- two main hormonal regulators of calcium homeostasis are
1,25 Vit D and
parathyroid hormone;
- calcium homeostasis allows rapid but controlled changes in calcium efflux, thru a negative feedback
system between plasma calcium ion levels and parathyroid hormone secretion;
- as a part of the feedback system active
osteoblasts are capable of
controlling extracellular environment needed for
mineralization, while
also participating in control of plasma Ca concentrations;
- if adequate dietary calcium is not available, calcium is first released from bone surfaces;
- if dietary calcium deficiency continues, parathyroid hormone secretion rises,
& rates of bone
resorption are increased thru production & activity of
osteoclasts;
- these cells digest all components of bone w/ the effect of adding calcium to extracellular fluid;
Calcium flux and endogenous calcium content in isolated mammalian
growth-plate chondrocytes, hyaline-cartilage chondrocytes, and hepatocytes.
