1. Synthesis and activation of vitamin D (cholecalciferol)
Synthesis and activation of vitamin D (cholecalciferol). Vitamin D is supplied from the diet and by synthesis from cholesterol-based precursors in the skin. Activation of vitamin D occurs in two stages: 25-hydroxylation in the liver (not regulated) and 1-hydroxylation in the kidney (stimulated by parathyroid hormone and hypophosphatemia).
Source: Endocrine Physiology, Medical Physiology: The Big Picture
Citation: Kibble JD, Halsey CR. Medical Physiology: The Big Picture; 2015 Available at: Accessed: December 28, 2017
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