الفهرس 
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Abstract
Calcium is a divalent cation involved in many critical cellular processes. Several biochemical and physiological studies have demonstrated the importance of calcium in regulating myocardial and vascular contraction, activating membrane receptors during signal transduction, releasing many hormones by exocytosis, controlling several transport processes and promoting thrombus formation. Serum [Ca2+] is determined by the interplay of intestinal absorption, renal excretion and bone remodeling (bone resorption and formation). Each component is hormonally regulated. To maintain Ca2+ balance, net intestinal absorption must be exactly balanced by urinary excretion. The primary endocrinopathies producing alterations in serum calcium metabolism are hyperparathyroidism and hypoparathyroidism. However, the finding of either hypercalcemia or hypocalcemia is not diagnostic for these two diseases as many other causes exist for these biochemical abnormalities. Hypocalcemia is a less frequently encountered clinical entity than hypercalcemia. However, it can be life threatenting when it is caused by hypoparathyroidism. The list of rule-outs for hypocalcemia is long but only a few are clinically important. Primary hypoparathyroidism is a naturally occuring disease in which theparathyroid glands decrease or cease secretion of PTH leading to clinically significant hypocalcemia. Symptomatic hypocalcaemia does not usually occur unless plasma calcium falls below 7 mg/dL (1.8mmol/L), and may not be present even at lower concentrations. Symptoms may depend on the rate at which hypocalcaemia has developed. If symptomatic hypocalcaemia is present, an intravenous infusion of calcium may be necessary. Vitamin D deficiency is best treated with vitamin D and not with any of the vitamin D metabolites. Hypercalcaemia is an elevated calcium level in the blood. (Normal range: 9–10.5 mg/dL or 2.2–2.6 mmol/L). It can be an asymptomatic laboratory finding, but because an elevated calcium level is often indicative of other diseases, a diagnosis should be undertaken if it persists. It can be due to excessive skeletal calcium release, increased intestinal calcium absorption, or decreased renal calcium excretion. There is a general mnemonic for remembering the effects of hypercalcaemia: ”groans (constipation), moans (psychic moans (e.g., fatigue, lethargy, depression)), bones (bone pain, especially if PTH is elevated), stones (kidney stones), and psychiatric overtones (including depression and confusion).” Abnormal heart rhythms can result, and ECG findings of a short QT interval and a widened T wave suggest hypercalcaemia. Finally, peptic ulcers may also occur.