Sometimes an ulcer makes a hole in the wall of your stomach or duodenum. When this happens, bacteria and partly digested food can get in. This causes infection and redness or swelling (inflammation). Narrowing and blockage (obstruction). Ulcers that are found where the duodenum joins the stomach can cause swelling and scarring.

Duodenal ulcers develop due to a disruption in the equilibrium between aggressive factors (gastric acid) and protective factors (mucus and bicarbonate [HCO 3 -]) (StatPearls: Duodenal Ulcer [Accessed 1 September 2023]) Erosion of the mucosal barrier exposes submucosal layers to gastric acid and enzymes

A peptic ulcer is an erosion in a segment of the gastrointestinal mucosa, typically in the stomach (gastric ulcer) or the first few centimeters of the duodenum (duodenal ulcer), that penetrates through the muscularis mucosae. Nearly all ulcers are caused by Helicobacter pylori infection or nonsteroidal anti-inflammatory drug (NSAID) use.

peptic ulcer, lesion that occurs primarily in the mucous membrane of the stomach or duodenum (the upper segment of the small intestine); it is produced when external factors reduce the ability of the mucosal lining to resist the acidic effects of gastric juice (a mixture of digestive enzymes and hydrochloric acid).