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

The structure in the small intestine that enhances the surface area for absorption is indeed a combination of villi and microvilli. Villi are small, finger-like projections that extend into the lumen of the small intestine and significantly increase the surface area available for nutrient absorption. Each villus is covered with even smaller projections called microvilli, which form a brush border that further amplifies the absorptive surface area.

The presence of both villi and microvilli is crucial for the efficiency of nutrient absorption. Villi provide a larger area for absorption than the flat surface of the intestinal lining alone, while microvilli increase this surface area even more at the cellular level by creating a dense, effective brush-border that facilitates the absorption process. Together, they ensure that the intestine effectively absorbs vitamins, minerals, and nutrients from digested food.