A 45-year-old man who underwent total gastrectomy for carcinoma develops progressive pallor and paraesthesiae two years later. Peripheral smear shows macro-ovalocytes and hypersegmented neutrophils. Which structure normally absorbs the nutrient whose deficiency explains his findings?

• A Duodenum via DMT1 transporter
• B Terminal ileum via cubam receptors ✓
• C Proximal jejunum via passive diffusion alone
• D Colon via bacterial synthesis followed by absorption

Explanation

Total gastrectomy removes parietal cells that secrete intrinsic factor, causing vitamin B12 deficiency. B12 bound to intrinsic factor is absorbed at specific cubam (cubilin-amnionless) receptors in the terminal ileum, so both gastrectomy and ileal resection cause deficiency. Iron is absorbed in the duodenum, and colonic bacterial B12 is not bioavailable to humans, which eliminates the other options.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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