Absorption mechanisms · Physiology

Calcium absorption is regulated by 1,25-dihydroxyvitamin D3. What is the role of calbindin in this process?

  1. It acts as a calcium-sensing receptor on the apical membrane
  2. It shuttles calcium across the cytosol to the basolateral membrane
  3. It pumps calcium into the lumen against its concentration gradient
  4. It binds calcium in the lumen to form an absorbable complex
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Correct answer: It shuttles calcium across the cytosol to the basolateral membrane

Calbindin is an intracellular binding protein that prevents free calcium levels from rising too high inside the enterocyte while facilitating its movement to the basolateral side. Its synthesis is directly stimulated by active Vitamin D.

Difficulty: Medium Question 29 of 40

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