Peptic ulcer disease (PUD) occurs most commonly in duodenal bulb (duodenal ulcer, DU) and stomach (gastric ulcer, GU). It may also occur in esophagus, pyloric channel, duodenal loop, jejunum, and Meckel's diverticulum. PUD results when “aggressive” factors (gastric acid, pepsin) overwhelm “defensive” factors involved in mucosal resistance (gastric mucus, bicarbonate, microcirculation, prostaglandins, mucosal “barrier”) and from effects of Helicobacter pylori.