alleryStart learning →Which step of vitamin D activation does the kidney carry out?
AIt converts cholecalciferol into calcidiol
BIt stores vitamin D until calcium runs low
CIt converts calcitriol back into calcidiol
DIt converts calcidiol into active calcitriol
Answer & Solution
Correct answer: D. It converts calcidiol into active calcitriol
1. Vitamin D reaches the kidney as calcidiol, which is not yet active.
2. The kidney performs a hydroxylation that converts calcidiol into calcitriol.
3. Calcitriol is the active form of vitamin D and the step is stimulated by parathyroid hormone.
4. Calcitriol then drives calcium absorption from the diet and its reabsorption in the kidney.
5. The conversion runs one way, so turning calcitriol back into calcidiol is not a renal function.
_Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 25 "The Urinary System", section 25.9 Regulation of Fluid Volume and Composition_
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