Formation of calcitriol:
The steroid-like hormone calcitriol arises from the precursor 7-dehydrocholesterol, which in turn is formed from cholesterol. In the course of its synthesis, the hormone passes through several stations: first the skin under the action of UV light, then the liver and finally the kidneys. Calciol (cholecalciferol), which is vitamin D3, is produced in the skin.
The hormone reached the liver via the bloodstream, bound to the transport protein vitamin D binding protein. Once in the liver, the conversion to calcidiol takes place and, in the kidneys, the conversion to the active hormone calcitriol.
The hormone is broken down by an enzyme (24-hydroxylase). The appropriate receptor for the hormone is intracellular.
Regulation of calcitriol:
The level of this hormone in the kidneys is influenced by the calcium and phosphate concentration in the blood, by parathyroid hormone, by prolactin and by calcitriol itself. A low calcium level and thus an increased amount of parathyroid hormone, a low phosphate concentration and prolactin increase the formation of calcitriol. The production of the hormone is reduced by calcitriol itself and by larger amounts of calcium and phosphate.
The hormone Calcitriol shows influence on the intestines, bone, Kidney, Plaster cake (Placenta), mammary glands and hair on. Overall, it promotes calcium absorption through the intestines and the mineralization of the bones.