What is the primary site of absorption for most nutrients (carbohydrates, amino acids, lipids) in the GI tract?

• A. Duodenum
• B. Jejunum
• C. Ileum
• D. Stomach

Answer: (B)

The key idea is where the small intestine does most of the nutrient uptake. The jejunum has the largest absorptive surface and the highest density of transporters for sugars, amino acids, and the products of fat digestion. Monosaccharides and amino acids are moved from the intestinal lumen into enterocytes across the apical membrane and then into the blood; lipids follow a slightly different path, being emulsified and digested to fatty acids and monoglycerides that are absorbed into enterocytes, reassembled into triglycerides, and packed into chylomicrons for lymphatic transport. Because of this specialization and surface area, the jejunum is the primary site for the absorption of most nutrients. The duodenum mainly handles digestion and initiates absorption, the ileum takes up bile acids and certain vitamins (like B12), and the stomach has limited nutrient absorption.