Which statement best describes the primary sites of nutrient absorption in the small intestine?

• A. Iron and calcium absorbed mainly in the ileum; sugars in the duodenum
• B. Iron and calcium absorbed mainly in the jejunum; sugars and amino acids mostly in the ileum
• C. Iron and calcium absorbed mainly in the jejunum; sugars absorbed in the duodenum
• D. Iron and calcium absorbed mainly in the duodenum; sugars and amino acids mostly in the jejunum

Answer: (D)

Absorption along the small intestine is region-specific. Iron and calcium are absorbed primarily in the proximal part, especially the duodenum, where the necessary transporters and conditions are present. In contrast, the bulk of monosaccharide (sugars) and amino acid absorption occurs further along in the jejunum, which has a large surface area from villi and microvilli and a high density of relevant transporters. Because of this distribution, the statement that iron and calcium are absorbed mainly in the duodenum while sugars and amino acids are absorbed mostly in the jejunum best describes the primary sites of nutrient absorption.