The primary function of the small intestine in the human digestive system is to facilitate the absorption of nutrients from digested food. This organ consists of three segments: the duodenum, jejunum, and ileum. It plays a crucial role in breaking down food with the help of digestive enzymes and bile, allowing essential nutrients like amino acids, fatty acids, and carbohydrates to enter the bloodstream. The small intestine has a highly folded surface area, enhancing its absorption capabilities.