Step 1 Study Topics: Calcium Regulation


This page is dedicated to compiling Step 1 study notes for the topic of calcium regulation. This page is likely disorganized as it was made in haste.


Process overview:

  1. Conversion of 7-dehydrocholesterol to vitamin D3 (cholecalciferol): this is done by UV light in the skin
  2. Cholecalciferol is converted to 25-hydroxyvitmain D: this is done by 25-hydroxylase in the liver which does this first hydroxylation. 
  3. 25-hydroxyvitmain D is converted to 1,25-dihydroxyvitmain D: this is done by 1-alpha-hydroxylase in the kidneys. This second hydroxylation is responsible for putting vitamin D in it’s active form! 
    1. During times of increased serum calcium, 25-hydroxyvitmain D is converted to 4,25-dihydroxyvitmain D: this is the INACTIVE form of vitamin D. 


The kidney converts 25-Hydroxycholecalciferol to its active form 1,25-dihydroxycholecalciferol



Page Updated: 04.18.2017