How does the presence of glucose in the lumen of the small intestine impact sodium absorption?

• A. It inhibits sodium absorption
• B. It has no effect on absorption
• C. It facilitates sodium and water uptake via co-transport
• D. It displaces sodium from transporters

Answer: (C)

Glucose in the lumen drives sodium absorption through a sodium-glucose co-transport system in the enterocyte (SGLT1). This is secondary active transport: Na+ moves into the cell together with glucose, powered by the sodium gradient across the apical membrane that is maintained by the Na+/K+ ATPase on the basolateral side. As sodium is brought in with glucose, water follows osmotically, increasing overall absorption of both sodium and water. That’s why the presence of luminal glucose facilitates sodium and water uptake via co-transport.