Abnormalities of calcium, phosphorus, and magnesium homeostasis are common and collectively are called ''disorders of mineral metabolism.'' Normal homeostatic regulation maintains serum levels, intracellular levels, and optimal mineral content in bone. This regulation occurs at three major target organs, the intestine, kidney, and bone, principally via the complex integration of two hormones, parathyroid hormone (PTH) and vitamin D. To diagnose accurately and treat disorders of mineral metabolism, an understanding of normal physiology is necessary. Therefore normal physiology is reviewed briefly before the differential diagnosis and treatment of specific disorders are discussed.
Normal physiology
Parathyroid hormone
A decrease in ionized calcium stimulates a release of PTH, which maintains calcium homeostasis by (1) increasing bone mineral dissolution, thus releasing calcium and phosphorus; (2) increasing renal reabsorption of calcium and excretion of phosphorus; and (3) enhancing the gastrointestinal absorption of both calcium and phosphorus indirectly through its effects on the synthesis of 1,25(OH) 2 D (calcitriol). In healthy subjects, this increase in serum PTH level in response to hypocalcemia effectively restores serum calcium levels and maintains normal serum phosphorus levels. PTH also