Which organ is the main site of nutrient absorption?

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

Answer: (A)

Think about where nutrients must pass from the digestive tract into the body. The small intestine is built specifically for absorption: its lining has a huge surface area thanks to folds, villi, and microvilli, and the enterocytes on that surface actively transport sugars, amino acids, fats, vitamins, and minerals into the bloodstream or the lymphatic system. Enzymes from the pancreas and bile from the liver aid digestion here, making nutrients easier to take up. Most nutrients are absorbed in this section, including fats that are emulsified and packaged for transport via the lymphatic system.

The stomach mainly digests and only absorbs small amounts of water, some drugs, and alcohol. The lungs are for exchanging gases, not nutrients. The liver processes and stores absorbed nutrients after they reach the bloodstream, but the actual absorption happens mostly in the small intestine.