Hormonal control of calcium homeostasis.

Calcium homeostasis in the extracellular fluid is tightly controlled and defended physiologically. Hypercalcemia always represents considerable underlying pathology and occurs when the hormonal control of calcium homeostasis is overwhelmed. The major hormones that are responsible for normal calcium homeostasis are parathyroid hormone and 1,25-dihydroxyvitamin D; these hormones control extracellular fluid calcium on a chronic basis. Over- or underproduction of these hormones or the tumor peptide, parathyroid hormone-related peptide, are the major causes of aberrant extracellular fluid calcium concentrations. These hormonal defense mechanisms are reviewed here.