Parathyroid hormone secreted by the parathyroid gland and calcitonin secreted by the thyroid gland maintain serum calcium levels at a range of between 8.5 to 10.5, whereby calcium is mobilized from bone reserves, and intestinal absorption of calcium is increased as needed. The parathormone can also affect renal functions to retain more calcium. When blood calcium goes up from too much parathyroid activity, calcitonin reduces availability of calcium from bone... Full Text