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Calcium is an essential body electrolyte. It is involved in the maintenance of normal muscle and nerve function, is essential for normal cardiac function and blood clotting. Calcium is the fifth most abundant element in the body, and the major fraction is in the bone structure. Calcium plays an important role for the functional integrity of the nerves and muscular systems, where it has a major influence on the excitability of these tissues. It is necessary for normal cardiac function and one of the factors involved in the coagulation of the blood.
In general, the major absorption takes place in the more proximal section of the small intestine. Glucocorticoids and low concentrations of calcitonin depress calcium transport across the small intestine. The factors like vitamin D3 and parathyroid hormone clearly augment calcium absorption. The metabolites of vitamin D3 is required for the active transport of calcium in the small intestine. Parathyroid hormone also causes increased intestinal absorption of calcium. Calcium is secreted in the gastrointestinal tract, in saliva, bile and pancreatic juice. This endogenous calcium and the unabsorbed dietary calcium constitute the sources of the cations excreted in the faeces.
The urinary excretion of calcium is the net result of the quantity filtered and the amount reabsorbed.
