The Pancreas and Vitamin B₁₂ Absorption

The intestinal absorption of physiologic amounts of vitamin B₁₂ — about 1 μg daily — depends on a complex sequence of events in the gastrointestinal tract. Major steps in this sequence are the secretion of intrinsic factor (IF) (a glycoprotein with a molecular weight of 60,000) by gastric parietal cells, the formation of intrinsic-factor-vitamin B₁₂ complex (IF-B₁₂) in the intestinal lumen, the binding of IF-B₁₂ by specific “receptors” on the microvilli of distal small-bowel epithelial cells, and the subsequent transfer of vitamin B₁₂ across the epithelium.1,2 Each step in this normal process may be.