Peptic Ulcer Disease
An ulcer forms wherever acid and pepsin overwhelm the mucosa's protective defences, so the site, the trigger and the danger of bleeding all fall out of that single imbalance.
First principles
Peptic ulcers are a mismatch between aggressive and protective forces in the mucosa
The gastroduodenal mucosa is normally protected from acid and pepsin by a mucus-bicarbonate barrier, adequate mucosal blood flow and prostaglandin-driven epithelial repair. An ulcer (a breach through the muscularis mucosae) forms when this defence is overwhelmed, either because acid/pepsin load is unusually high or, far more commonly, because the protective barrier itself has been weakened. The two dominant causes act on exactly this defence: Helicobacter pylori infection provokes chronic gastritis and impairs mucus and bicarbonate secretion, while NSAIDs directly inhibit cyclo-oxygenase and so deplete the protective prostaglandins. Understanding the cause as 'defence down' rather than 'acid up' explains why treatment targets the cause, not just the acid.
Educational content pending clinical review. Not medical advice.