Hormone
Hormone
Hormone
Vitamin D3
(cholecalciferol)
(cholecalciferol)
- Originates from:
- Dietary intake
- Synthesis in the skin through effects of UV light on 7-dehydrocholesterol
- Modified by liver and kidney to form active 1-25-hydroxycholecalciferol - under the influence of parathyroid hormone
- Levels also increase in response to low phosphate levels
- Acts to increase serum calcium levels
- GI Tract: Increases GI absorption by upregulating number and activity of transport proteins
- Kidneys: Weak effect to increase calcium and phosphate reabsorption
- Plays a minimal role in calcium homeostasis, secreted only when levels rise above normal limits