Functions of parathyroid hormone

When serum calcium levels are low it stimulates the production and release of parathyroid hormone from parathyroid glands which are 4 in number. the parathyroid hormone acts on bones and Kidneys. when it acts on bone the parathyroid hormone increases the bone resorption. bone resorption means that bone is broken down to release calcium. the effects of parathormone on kidney are such that it increases the formation of Vitamin D. it increases calcium reabsorption and it increases phosphate excretion. the vitamin D production is stimulated by induced if effects on 1 Alpha hydroxylase .so we can conclude that the conditions in which parathyroid hormone is in excess there will be too much excretion of phosphate from body and hence hypophosphatemia.