Mucosal defences and gastroduodenal disease.

Peptic ulcer disease occurs when there is an imbalance between aggressive factors and mucosal resistance. Mucus plays a key role in mucosal resistance. The mucus layer is relatively resistant to peptic digestion, it provides a layer through which there is a movement of hydrogen ions from the parietal cell to the lumen but a resistance to back-diffusion of hydrogen ions in the opposite direction. It maintains a pH gradient by 'sequestering' secreted bicarbonate and by its resistance to H+ back-diffusion. Colloidal bismuth subcitrate (De-Nol) binds to mucus to stabilize the mucous layer and increase the resistance to back-diffusion of hydrogen ions without significantly modifying the ion-exchange properties of mucus.