The function of the small intestine in nutrient absorption is to break down food and absorb essential nutrients and minerals. After food passes through the stomach, it enters the small intestine, where enzymes and bile facilitate digestion. The walls of the small intestine contain villi and microvilli, which increase the surface area for absorption. Through these structures, nutrients like amino acids, fatty acids, and simple sugars are transported into the bloodstream, contributing to overall health and energy.