Biological Systems MCAT Practice Exam

Villi play a crucial role in the small intestine primarily through their function in nutrient absorption. These tiny, finger-like projections greatly increase the surface area of the intestinal lining, allowing for more efficient absorption of nutrients from the digested food that passes through the intestine. Each villus is also equipped with microvilli, further enhancing the surface area and creating what is often referred to as the "brush border." This structural adaptation facilitates the active transport and diffusion of nutrients, such as amino acids, simple sugars, and fatty acids, into the bloodstream. The other choices do not accurately describe the function of villi. While digestive enzymes are secreted by the pancreas and the lining of the intestine, the villi themselves do not produce these enzymes. Villi do not play a role in regulating bile flow, which is managed by the liver and gallbladder, nor do they contribute to the production of stomach acid, which occurs in the stomach lining. Overall, the primary function of villi in the small intestine is to maximize nutrient absorption, making them vital to the digestive process.