Chemical	Function
Alkaline phosphatase	Exact function unknown; isoenzyme is elevated in conditions such as rickets that are associated with high bone turnover
Calcitonin	Bone: inhibits resorption
	Intestine: inhibits calcium and phosphorus absorption
	Kidney: increases calcium excretion, inhibits production of calcitriol
Calcitriol	Bone: indirectly stimulates bone synthesis via increased calcium absorption in intestinal lumen
	Intestine: increases calcium, phosphorus, and magnesium absorption
	Kidney: autoregulation of calcitriol production by the kidney
	Parathyroid gland: negative feedback to decrease secretion of parathyroid hormone
Parathyroid hormone	Bone: mobilizes calcium and phosphorus
	Intestine: indirectly increases calcium and phosphorus absorption by increasing calcitriol
	Kidney: increases calcitriol, increases calcium reabsorption, decreases phosphorus reabsorption