What anatomical structures maximize surface area for nutrient absorption in the small intestine?

• A. Villi and microvilli (brush border)
• B. Plicae circulares
• C. Lacteals
• D. Goblet cells

Answer: (A)

The small intestine boosts nutrient absorption by dramatically increasing its surface area with specialized structures. Villi are fingerlike projections that raise the mucosal surface, and their surface is covered with microvilli on the absorptive cells, forming the brush border. Together, these features expand the available contact area for nutrients far beyond a flat surface, with microvilli on the cell surface providing a substantial additional increase. The brush border also hosts digestive enzymes that finish the breakdown of nutrients right at the site of absorption.

Plicae circulares add some extra surface area by folding the mucosa and submucosa, but their contribution is smaller than that of villi and microvilli. Lacteals are lymphatic vessels inside the villi that transport absorbed fats, not structures that increase surface area. Goblet cells secrete mucus to protect and lubricate the lining, not to enhance absorptive area.