Which transporter primarily mediates glucose uptake across the apical membrane of enterocytes?

• A. GLUT2
• B. GLUT4
• C. GLUT1
• D. SGLT1

Answer: (D)

Glucose entry from the intestinal lumen into enterocytes at the apical surface is driven by SGLT1, a sodium-glucose co-transporter. It uses the inward Na+ gradient maintained by the Na+/K+ ATPase on the basolateral side to pull glucose into the cell, allowing uptake even when luminal glucose is scarce. Inside the cell, glucose then exits across the basolateral membrane into the bloodstream via GLUT2. Other transporters like GLUT1 or GLUT4 aren’t the primary routes for apical glucose uptake in enterocytes; they serve mainly other tissues or roles and aren’t located on the apical membrane under normal conditions. (Note: in some high-glucose conditions, GLUT2 can be recruited to the apical surface, but the standard, primary mechanism is SGLT1.)