Where does most absorption occur in the small intestine?

• A. First 1-2 meters of the small intestine, proximal jejunum
• B. Distal ileum
• C. Duodenum
• D. Large intestine

Answer: (A)

The main idea is where the bulk of nutrient uptake happens along the small intestine. Most absorption occurs in the proximal part of the small intestine, especially the jejunum, which lies in the first portion after the duodenum. This region has the greatest absorptive surface area due to numerous villi and microvilli and contains abundant transporters for sugars, amino acids, fats, vitamins, and minerals. Because contact time and surface area are highest here, the majority of nutrient absorption takes place in the early small intestine. The duodenum does some absorption and initial digestion, the ileum handles bile acids and vitamin B12, and the large intestine mainly reabsorbs water and electrolytes, so they contribute far less to overall nutrient absorption than the proximal jejunum.