The average adult human body contains about 3.3 lb. (1.5 kg) of calcium, almost 99% of which is stored in bones, 0.1% is in the extra cellular fluid, and approximately 1% is in the cells. The usual plasma concentration of calcium is kept rather constant due to the regulatory action of the parathyroid gland. When the dietary calcium absorption by the intestine is not enough to keep the plasma concentration at normal levels, the parathyroid triggers calcium reabsorbtion from the bones to avoid a significant depletion. Such fine control is important because calcium takes part in several physiological functions, such as the contraction of cardiac, skeletal, and smooth muscles, synaptic signal transmission (i.e., communication between neural cells), blood coagulation, regulation of intra cellular metabolism, and bone formation. Even a slight shortage of calcium (hypocalcemia) for instance, may trigger progressive neural excitement. When calcium levels fall below...