Q2. Correct answer: C
Vitamin B12 absorption requires intrinsic factor to bind B12 to facilitate absorption in the terminal ileum. Any interruption of terminal ileal absorptive capacity can thus lead to vitamin B12 deficiency (e.g. Crohn's disease, ileal resection). Intrinsic factor is produced by parietal cells, so any condition that leads to decreased parietal cell mass or function can lead to vitamin B12 deficiency (e.g. atrophic gastritis). In order for intrinsic factor to bind vitamin B12, B12 must first be released from binding with the R-protein, which occurs via pancreatic protease breakdown of the R-protein. Patients with chronic pancreatitis are not able to break down the R-protein as efficiently, and thus can develop vitamin B12 deficiency.
1. Green R. Vitamin B12 deficiency from the perspective of a practicing hematologist. Blood. 2017;129(19):2603-11.
2. Gueant GL, at al. Malabsorption of vitamin B12 in pancreatic insufficiency of the adult and of the child. Pancreas 1990 Sep;5(5):559-67.