ABSTRACT

Adequate concentrations of extracellular calcium help to sustain a number of normal physiological processes as diverse as bone formation and turnover, neuronal cell excitability, muscle contractility, and blood clotting. Significant shifts in extracellular fluid calcium concentration can have adverse effects on these physiological functions. The extracellular concentration of calcium is normally affected by intermittent changes in calcium absorption in the gut, continuous mineral turnover in bone, and calcium losses in the urine. Extracellular calcium levels are set within a very narrow range by the concerted action of regulatory ‘‘calciotropic’’ hormones on calcium handling by the gastrointestinal tract, bone, and kidney. In children and adolescents, maintenance of adequate calcium balance is particularly important because bone accretion and growth are closely linked to calcium availability. Children require an adequate supply of calcium to sustain bone mineralization and achieve an adequate peak bone mass without disrupting the tight regulation of extracellular calcium. Abnormalities in the organs that express calciotropic hormones, the abnormal function of these hormones or the failure of the gastrointestinal tract, bone or kidney to handle calcium properly can cause either hypo or hypercalcemia. This chapter will describe the physiology of calcium homeostasis, the clinical disorders linked to alterations of calcium concentration in the extracellular compartment, their evaluation and treatment.