Which organ functions primarily in nutrient absorption in digestion?

• A. Esophagus
• B. Stomach
• C. Liver
• D. Small intestine

Answer: (D)

The main concept is that nutrient absorption happens mostly in the small intestine because its lining is highly folded with villi and microvilli, which greatly increases surface area for uptake. Digestive products are absorbed across the intestinal wall: simple sugars and amino acids enter the bloodstream through capillaries in the villi, while fatty acids and monoglycerides are packaged into chylomicrons and absorbed into the lymphatic system via the lacteals. The duodenum and jejunum are the primary sites of absorption, with the ileum also taking up bile acids and vitamin B12. The esophagus and stomach are more about moving and breaking down food, while the liver processes absorbed nutrients rather than serving as the initial site of absorption. The large intestine handles water and electrolyte absorption.