How does high luminal sodium concentration affect glucose absorption?

How does high luminal sodium concentration affect glucose absorption?

• A. Decreases glucose transport
• B. Increases glucose transport
• C. No effect on glucose transport
• D. Increases then decreases

Answer: (B)

Glucose absorption in the small intestine is driven by a sodium-dependent transporter on the apical membrane that co-transports Na+ and glucose into the enterocyte. This transporter relies on the Na+ gradient across the brush border, which is kept favorable by the Na+/K+ ATPase pumping Na+ out of the cell. When luminal sodium concentration is higher, the gradient that favors Na+ entry into the cell becomes stronger, providing greater driving force for Na+-glucose cotransport and thus increasing glucose uptake from the lumen. Once inside, glucose moves to the bloodstream via basolateral transporters. So higher luminal Na+ boosts glucose transport rather than inhibiting it, and the effect is not biphasic.

Glucose absorption in the small intestine is driven by a sodium-dependent transporter on the apical membrane that co-transports Na+ and glucose into the enterocyte. This transporter relies on the Na+ gradient across the brush border, which is kept favorable by the Na+/K+ ATPase pumping Na+ out of the cell. When luminal sodium concentration is higher, the gradient that favors Na+ entry into the cell becomes stronger, providing greater driving force for Na+-glucose cotransport and thus increasing glucose uptake from the lumen. Once inside, glucose moves to the bloodstream via basolateral transporters. So higher luminal Na+ boosts glucose transport rather than inhibiting it, and the effect is not biphasic.