How are glucose and galactose transported into the enterocyte?

• A. Passive diffusion
• B. Facilitated diffusion via GLUT-2
• C. SGLT-1 active transport
• D. Endocytosis

Answer: (C)

The main idea is that glucose and galactose enter the intestinal epithelial cell through a sodium-dependent co-transport mechanism on the apical surface. This transporter, SGLT-1, grabs Na+ from the lumen along with glucose or galactose and moves them into the cell against their own concentration gradients. The energy for this comes from the sodium gradient maintained by the Na+/K+-ATPase on the basolateral membrane. Once inside the enterocyte, these sugars exit into the bloodstream through a facilitated-diffusion transporter, primarily GLUT-2, on the basolateral side.

Passive diffusion wouldn’t work here because glucose and galactose are polar and not readily permeable across the lipid membrane. Facilitated diffusion via GLUT-2 isn’t used for apical uptake into the enterocyte; it handles transport across membranes down their concentration gradient, typically on the basolateral side for glucose after SGLT-1 brings it in. Endocytosis is not the mechanism for monosaccharide uptake.