Primary function of the small intestine

• A. Mechanical digestion and water absorption
• B. Chemical digestion and nutrient absorption
• C. Storage of feces
• D. Neutralization of gastric acid

Answer: (B)

Chemical digestion and nutrient absorption are the main duties of the small intestine. The duodenum mixes chyme with bile and pancreatic enzymes to break down carbohydrates, proteins, and fats, while the majority of nutrient absorption happens in the jejunum and ileum. The lining has a huge surface area due to circular folds, villi, and microvilli, which lets digested nutrients pass into enterocytes and then into the bloodstream or lymphatic system. While some water absorption occurs here and the intestinal muscles help mix and move contents, the defining role is enzymatic digestion and uptake of nutrients. Storage of feces happens in the colon, and neutralizing gastric acid is primarily a function of pancreatic bicarbonate entering the duodenum as part of digestion, not the small intestine’s main purpose.