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

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.