Factors influencing plasma level of Calcium-

1) Parathroid hormone- It increase calcium absorption from ileum in the presence of vitamin D.
2) Vitamin D- It enhances absorption of calcium from the intestine and thus maintains the normal plasma calcium concentration
3) Plasma proteins- As mentioned above nearly half of the blood calcium is bound to plasma protein will be accompanied by the decrease in the total calcium level.
4) Plasma phosphate- Calcium and phosphate ions in plasma have a reciprocal relationship.
5) Calcitonin- An increase in the ionized calcium level in the plasma is the stimulus for the production of calcitonin which then causes a deposition of calcium in bones.