What are the primary monosaccharides absorbed by the small intestine?

• A. Glucose, galactose, and fructose
• B. Fructose, ribose, and glucose
• C. Glucose, lactose, and starch
• D. Galactose, sucrose, and maltose

Answer: (A)

The key idea is how the small intestine takes up sugars after digestion. The three main monosaccharides absorbed are glucose, galactose, and fructose. Glucose and galactose enter enterocytes via the SGLT1 transporter, which uses the sodium gradient to drive active uptake, while fructose is absorbed by GLUT5 through facilitated diffusion. Once inside the cell, all three exit into the bloodstream via GLUT2 on the basolateral side. Other sugars listed aren’t absorbed as monosaccharides: ribose is a different sugar not typically a major dietary product, and lactose, sucrose, and maltose must be broken down by brush-border enzymes into glucose, galactose, and/or fructose before absorption.