Question

Explain how this system maximizes glucose absorption from the intestinal lumen into the epithelial cells and from the epithelial cells into the blood.

Answer 1

Transport of glucose from the intestinal lumen into the blood. Activity of the Na+/K+ ATPase (green) in the basolateral surface membrane generates Na+ and K+ concentration gradients, and the K+ gradient generates an inside-negative membrane potential.

Explanation:

The Na+K+ ATPase uses the energy of ATP hydrolysis to move Na+ out of the epithelial cells lining the intestine and into the blood. The reduced concentration of Na+ inside the cell coupled with high Na+ inside the lumen of the intestine results in a driving force for the movement of Na+ into the cell.

The cotransporters in the membrane of the epithelial cell facing the intestine allow Na+ to enter only when accompanied by either glucose or one of the amino acids (each have their own set of co-transporters).

Glucose then moves into the blood through the permease in the membrane between the cell and the blood. Thus, ATP is used as an energy source to drive Na+ out of the cell, resulting in glucose transport from the intestine to the blood.