Match the nutrient to its primary absorption site correctly.

Match the nutrient to its primary absorption site correctly.

• A. Iron and Calcium — Duodenum
• B. Iron — Jejunum
• C. Vitamin B12 — Duodenum
• D. Folic acid — Ileum

Answer: (A)

Absorption sites in the gut depend on the nutrient’s transport needs, so certain nutrients have their primary uptake in specific sections of the small intestine. Iron and calcium are best absorbed in the proximal small intestine, especially the duodenum, because this region houses the key transport mechanisms and regulatory systems for these minerals. Iron is taken into enterocytes mainly as ferrous iron through the DMT1 transporter after gastric acid helps convert iron to a usable form, and then it exits into the bloodstream via ferroportin. This process is most efficient in the duodenum and relies on factors like vitamin C and overall iron status to influence absorption. Calcium absorption is highly active in the duodenum, using TRPV6 channels to move Ca2+ into cells, calbindin to shuttle it across the cytoplasm, and basal transporters to release it into the blood; vitamin D enhances this active transport by upregulating the involved proteins. Vitamin B12 requires intrinsic factor and is absorbed later in the gastrointestinal tract, specifically in the terminal ileum, so it is not primarily absorbed in the duodenum. Folic acid is absorbed primarily in the proximal small intestine (duodenum and jejunum), not predominantly in the ileum. That makes the pairing of iron and calcium with the duodenum the best match.

Absorption sites in the gut depend on the nutrient’s transport needs, so certain nutrients have their primary uptake in specific sections of the small intestine. Iron and calcium are best absorbed in the proximal small intestine, especially the duodenum, because this region houses the key transport mechanisms and regulatory systems for these minerals. Iron is taken into enterocytes mainly as ferrous iron through the DMT1 transporter after gastric acid helps convert iron to a usable form, and then it exits into the bloodstream via ferroportin. This process is most efficient in the duodenum and relies on factors like vitamin C and overall iron status to influence absorption. Calcium absorption is highly active in the duodenum, using TRPV6 channels to move Ca2+ into cells, calbindin to shuttle it across the cytoplasm, and basal transporters to release it into the blood; vitamin D enhances this active transport by upregulating the involved proteins.

Vitamin B12 requires intrinsic factor and is absorbed later in the gastrointestinal tract, specifically in the terminal ileum, so it is not primarily absorbed in the duodenum. Folic acid is absorbed primarily in the proximal small intestine (duodenum and jejunum), not predominantly in the ileum. That makes the pairing of iron and calcium with the duodenum the best match.