There are four parathyroid glands are found in the back side of the thyroid. When blood calcium levels becomes low, the parathyroid gland secrets parathyroid hormone or parathormone(PTH). This hormone helps to raise blood calcium levels by stimulating osteoclasts thatcauses the desorption of bones and releases calcium into the blood. PTH also signals the kidneys to maintain calcium by reducing the amount excreted in urine. PTH increases the formation of active vitamin D, which increases intestinal calcium and phosphorus absorption.