A patient with chronic pancreatitis has malabsorption of fat-soluble vitamins. Which vitamin absorption is uniquely impaired even in the ABSENCE of pancreatic insufficiency or bile salt deficiency, because it requires a specific gastric secretion?

• A Vitamin A — requires retinol esterase secreted by the stomach
• B Vitamin D — requires acidification by gastric HCl for solubilization
• C Vitamin K — requires gastric lipase for initial emulsification before micellar solubilization
• D Vitamin B12 (cobalamin) — requires intrinsic factor secreted by gastric parietal cells for terminal ileum absorption ✓

Explanation

Vitamin B12 absorption is uniquely dependent on intrinsic factor (IF), a glycoprotein secreted by gastric parietal cells. Dietary B12 is released from proteins by pepsin/HCl, initially binds R-proteins (haptocorrins) in the stomach, and then in the duodenum pancreatic proteases degrade R-proteins allowing B12 to bind IF. The IF-B12 complex is resistant to digestion and binds specific receptors (cubam: cubilin + amnionless) in the terminal ileum for endocytosis. Gastrectomy, atrophic gastritis (autoimmune destruction of parietal cells), and IF antibodies cause B12 deficiency regardless of pancreatic function.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.