Which structure in the small intestine increases surface area for absorption?

• A. Alveoli
• B. Villi
• C. Stomach folds
• D. Teeth

Answer: (B)

Increasing surface area in the small intestine for absorption is achieved by specialized lining structures. The villi are the main feature here—tiny finger-like projections that line the intestinal wall. Each villus is covered with even smaller extensions called microvilli, forming a brush border that massively expands the contact area available for nutrients to pass into the cells. This combination of circular folds plus the villi and microvilli makes the intestine incredibly efficient at absorbing digested food. Alveoli belong to the lungs and handle gas exchange, not digestion. The stomach’s folds (rugae) help it stretch and mix contents, not maximize surface area for absorption in the small intestine. Teeth are for breaking down food in the mouth. So the structure responsible for increasing surface area is the villi.