- Bacterial infection by Helicobacter pylori breaks down the gastroduodenal mucosal barrier.
- The bacteria burrows through the barrier and releases bacterial digestive enzymes that liquefy the barrier.
- Stomach acid then penetrates into the epithelium of the gastric wall and breaks it down.
- Most peptic ulcers occur in the stomach and proximal duodenum.  They arise as a result of an imbalance between acid secretion and mucosal defences.  Heliobacter pylori infection is a significant aetiological factor and the eradication of this organism, as well as the attenuation of acid secretion, form the cornerstones of medical treatment.  In a minority of cases the symptoms are not controlled by medical treatment alone and surgery is required.  'Very highly selective vagotomy' is a technique where only the afferent vagal fibres to the acid-secreting body are denervated thus not compromising the motor supply to the stomach and hence bypassing the need for a drainage procedure (e.g., gastrojejunostomy).

Reference:
1. Anatomy at a Glance. Omar Faiz and David Moffat.  Blackwell Science. 2002.