A Peptic Ulcer is a distinct breach in the mucosal lining of the stomach (gastric ulcer) or the first part of the small intestine (duodenal ulcer), a result of caustic effects of acid and pepsin in the lumen. Histologically, peptic ulcer is identified as necrosis of the mucosa which produces lesions equal to or greater than 0.5 cm (1/5″). It is the most common ulcer of an area of the gastrointestinal tract that is usually acidic and thus extremely painful. Helicobacter pylori is one of the most common causes of peptic ulcer. Ulcers can also be caused or worsened by drugs such as aspirin, ibuprofen, and other NSAIDs.
Four times as many peptic ulcers arise in the duodenum—the first part of the small intestine, just beyond the stomach—as in the stomach itself. About 4% of gastric ulcers are caused by a malignant tumor, so multiple biopsies are needed to exclude cancer. Duodenal ulcers are generally benign.
The appearance of an ulcer can be either the classic erosive, concave, crater-like ulcer (the image held by most patients) or convex, perhaps resembling a colonic polyp. As a generalization, the erosive concave type tend to be located in the stomach proper while the convex type tend to be found in the pylorus/duodenum.
Source: http://en.wikipedia.org/wiki/Stomach_ulcers
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