Which organ is the primary site of nutrient absorption?

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

Answer: (C)

Nutrients cross into the body most efficiently through the small intestine because its lining is highly specialized for absorption. The inner surface is folded into fingerlike villi and even smaller microvilli, giving a huge area for contact with digested food. This setup houses enterocytes equipped with transporters and enzymes that move carbohydrates, proteins, and fats from the intestinal lumen into the body's fluids. Carbohydrates are broken down to simple sugars and absorbed into the bloodstream, proteins to amino acids, and fats to fatty acids and monoglycerides. Fats have a distinct path: they’re reassembled into triglycerides inside enterocytes and packaged into chylomicrons that enter the lymphatic system before reaching the bloodstream. Once absorbed, nutrients travel via the portal vein to the liver for processing and storage.

The stomach mainly digests and absorbs only small amounts of water, alcohol, and some other substances. The large intestine primarily absorbs water and electrolytes, with limited nutrient absorption. The liver processes nutrients after absorption rather than serving as the primary site of nutrient uptake.