Calcium levels are regulated by two systems: parathyroid hormone (PTH) released by the parathyroid gland (green arrows and white text) and vitamin D (white arrows and yellow text). Low calcium levels stimulate the four parathyroid glands to secrete PTH. PTH acts on bones, intestines and kidneys. In bone, PTH induces calcium release by stimulation of bone resorption. It also stimulates the uptake of calcium and vitamin D from the intestine. Furthermore, it promotes reabsorption of calcium from the glomerular filtrate in the kidneys. Vitamin D is absorbed from the intestine, converted into 25-OH vitamin D3 in the liver and into 1,25(OH)2vitamin D3 in the kidney. The 1,25(OH)2vitamin
See the Farmacotherapeutisch Kompas for more information on drugs in regulation of calcium metabolism.
I. Plasma 25-OH vitamin D3 levels are a reflection of dietary vitamin D intake. II. Too much sunlight causes hypercalcemia.
Extra info: Vitamin D from the diet is converted into 25-OH vitamin D3 in the liver. Sunlight on the skin stimulates previtamin D production. This prehormone is spontaneously converted into vitamin D after 3 days. However, continuous sunlight causes also photodegradation of previtamin D and thus controls vitamin D production.