The small intestine digests and absorbs nutrients from food. It is divided into three parts - the duodenum, jejunum, and ileum. Digestive enzymes break down proteins into amino acids, fats into fatty acids and glycerol, and some carbohydrates into simple sugars. The digested nutrients are then absorbed through the intestinal wall into the bloodstream and transported to the rest of the body. It typically takes 3-6 hours for a meal to pass through the small intestine.