Calcium homeostasis

The regulation of plasma calcium concentration and bone homeostasis is briefly described. The components of plasma calcium and the method for deriving these components are presented. The factors which regulate plasma calcium concentration are discussed with particular reference to the role of the kidney. The mechanisms responsible for the maintenance of the skeleton are described and the failure of these mechanisms in the pathogenesis of osteoporosis is outlined. In postmenopausal women there is increased excretion of calcium and recent works suggest that this is due to an increase in the complexed fraction of calcium as a result of an increase in plasma bicarbonate and anion gap. The significance of the increase in urine calcium excretion in postmenopausal women and its impact on dietary calcium requirement are discussed.