MICROANATOMY

Detailed explanation-1: -PTH exerts direct effects on bone and kidney and indirect effects on the intestine through calcitriol. PTH increases synthesis of calcitriol by activating renal mitochondrial 1--hydroxylation of calcidiol derived from the circulation. Calcitriol, in turn, increases calcium absorption from the intestine.

Detailed explanation-2: -On a more chronic basis, PTH also stimulates the conversion of calcidiol (25-hydroxyvitamin D) to calcitriol in renal tubular cells, thereby stimulating intestinal calcium absorption as well as bone turnover.

Detailed explanation-3: -Calcitriol also stimulates release of calcium from bone by its action on the specific type of bone cells referred to as osteoblasts, causing them to release RANKL, which in turn activates osteoclasts. Calcitriol acts in concert with parathyroid hormone (PTH) in all three of these roles.

Detailed explanation-4: -Parathyroid hormone stimulates calcitriol production in the kidney by increasing the synthesis of 1- hydroxylase. Calcitriol has several important functions in the body.

Detailed explanation-5: -Parathyroid hormone (PTH) is a hormone that your parathyroid glands make and release to control the level of calcium in your blood, not your bones. Calcium is one of the most important and common minerals in your body.