The two requirements necessary in order for calcium at concentrations less than 5 mmol/L to be absorbed through the ileum are vitamin:
A)C and a receptor site on the surface of the ileum.
B)D₃ and a carrier protein.
C)K and pepsin.
D)B₁₂ and carboxypeptidase.

Question

Quizplus · Accepted Answer

When its concentration in the lumen is greater than 5 mmol/L, calcium is absorbed by passive diffusion. At concentrations less than 5 mmol/L, calcium is transported actively across cell membranes, bound to a carrier protein. The carrier formation requires the presence of the active form of vitamin D₃ (1,25-dihydroxyvitamin D).

The Two Requirements Necessary in Order for Calcium at Concentrations