American Board of Surgery Qualifying Exam (ABS QE) Practice Test

What mechanism is involved in the absorption of fructose?

1. Facilitated absorption using a carrier with energy expended

2. Simple diffusion across cell membranes

3. Facilitated absorption using a carrier, no energy expended

4. Active transport requiring ATP

The correct answer is: Facilitated absorption using a carrier, no energy expended

Fructose absorption in the intestine primarily occurs through facilitated diffusion involving a specific transporter known as GLUT5. This transporter allows fructose to cross the intestinal epithelial cell membrane without the direct expenditure of energy in the form of ATP. It operates by utilizing the concentration gradient of fructose—meaning that fructose moves from an area of higher concentration in the intestinal lumen to an area of lower concentration within the epithelial cells, which is characteristic of facilitated diffusion. This mechanism is distinct from active transport, which requires energy to move substances against their concentration gradient and typically involves different types of transporters, such as those utilizing ATP. The key aspect of fructose absorption is that while it does rely on a carrier, it does not necessitate energy expenditure, placing it squarely within the realm of facilitated diffusion. Understanding the absorption mechanisms of different sugars can illuminate the nuances of nutrient transport and metabolism in the human body, highlighting the role of specific transporters and energy dynamics.