Final answer:
Calcitriol is the active form of vitamin D synthesized in the kidney. Sunlight initiates its synthesis in the skin, converting cholesterol derivatives to vitamin D3, which is then activated in the liver and kidneys. This vitamin D synthesis is essential for calcium and phosphate homeostasis and bone health.
Step-by-step explanation:
Calcitriol is the primary active form of vitamin D. It can be synthesized with the help of sunlight and subsequent enzymatic actions in the liver and kidney. It acts as a hormone to regulate calcium absorption in the digestive tract, its reabsorption in the kidneys, and is essential for maintaining healthy bones.
The synthesis of vitamin D starts in the skin when UV radiation from sunlight converts 7-dehydrocholesterol to cholecalciferol (vitamin D3). The liver then metabolizes cholecalciferol to calcidiol (25(OH)D), which is carried to the kidney. In the kidney, with the help of the enzyme 25(OH)D3-1-hydroxylase, calcidiol is transformed into calcitriol, the bioactive form of vitamin D.
This vitamin D synthesis is crucial for several functions, including maintaining optimal blood levels of calcium and phosphate, which are necessary for bone formation, growth, and repair, as well as muscle function and immune system regulation.