Calcium is an extremely important ion in the function of virtually all cells and organs.
1. Extracellular calcium is important in the mineralization and integrity of bone, in normal blood clotting, and maintenance of normal cell membrane function.
2. Intracellular calcium is important in muscle function, cellular secretion, neural function, and many other cellular functions.
Therefore, the control of calcium balance is highly regulated primarily by circulating parathyroid hormone and 1,25(OH)2vitamin D (the active form of vitamin D).