ANATOMY

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: -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-3: -Parathyroid hormone stimulates calcitriol production in the kidney by increasing the synthesis of 1- hydroxylase. Calcitriol has several important functions in the body. It maintains serum calcium levels by increasing calcium absorption in the gastrointestinal tract.

Detailed explanation-4: -PTH also helps control the levels of phosphorus (a mineral) and vitamin D (a hormone) in your blood and bones.

Detailed explanation-5: -Calcitriol is used to treat and prevent low levels of calcium and bone disease in patients whose kidneys or parathyroid glands (glands in the neck that release natural substances to control the amount of calcium in the blood) are not working normally.