Which statement best describes the transporters responsible for intestinal monosaccharide absorption on the enterocyte apical and basolateral membranes, and their modes of transport?

Which statement best describes the transporters responsible for intestinal monosaccharide absorption on the enterocyte apical and basolateral membranes, and their modes of transport?

• A. GLUT5 on the apical membrane and GLUT2 on the basolateral side, with glucose uptake passive.
• B. GLUT2 on the apical membrane and SGLT1 on the basolateral side, with all monosaccharides absorbed passively.
• C. SGLT1 on the basolateral membrane and GLUT5 on the apical membrane, with glucose and galactose absorbed passively.
• D. SGLT1 on the apical membrane and GLUT2/GLUT5 on the basolateral side; glucose and galactose uptake is active, fructose via GLUT5 is passive.

Answer: (D)

Absorption of intestinal monosaccharides uses distinct transporters at different enterocyte surfaces, with one transporter driving uptake into the cell and others governing exit into the bloodstream. Glucose and galactose are brought from the lumen into the cell by SGLT1, a sodium-driven transporter on the apical membrane, which makes their entry an active process powered by the Na+ gradient. Fructose enters the cell through a facilitator, GLUT5, moving down its concentration gradient in a passive manner. Once inside, all three sugars exit into the blood via GLUT2 on the basolateral membrane by facilitated diffusion. This combination—apical SGLT1 for active uptake of glucose and galactose, fructose handled by a facilitated transporter, and basolateral GLUT2 for export—encapsulates the correct directional flow and modes of transport. Note that GLUT5 is the fructose transporter and is primarily responsible for fructose entry, while GLUT2 handles the final exit on the basolateral side.

Absorption of intestinal monosaccharides uses distinct transporters at different enterocyte surfaces, with one transporter driving uptake into the cell and others governing exit into the bloodstream. Glucose and galactose are brought from the lumen into the cell by SGLT1, a sodium-driven transporter on the apical membrane, which makes their entry an active process powered by the Na+ gradient. Fructose enters the cell through a facilitator, GLUT5, moving down its concentration gradient in a passive manner. Once inside, all three sugars exit into the blood via GLUT2 on the basolateral membrane by facilitated diffusion. This combination—apical SGLT1 for active uptake of glucose and galactose, fructose handled by a facilitated transporter, and basolateral GLUT2 for export—encapsulates the correct directional flow and modes of transport. Note that GLUT5 is the fructose transporter and is primarily responsible for fructose entry, while GLUT2 handles the final exit on the basolateral side.