On the surface of the thyroid gland there are 2 pairs of very small oval parathyroid glands. It contains two types of cells. Principal cells and oxyphil cells. Its weight is 140 mg. Parathyroid hormone or parathormone parathyrin is released from this gland. It increases calcium levels and decreases phosphate levels in the body. It activates vitamin-D. Vitamin-D deficiency causes rickets in children and osteomalacia in adults.