A peptic ulcer is an open sore or raw area that tends to develop in one of two places:

• The lining of the stomach (gastric ulcer)
• The upper part of the small intestine -- the duodenum (duodenal ulcer)

In the U.S., duodenal ulcers are 3 times more common than gastric ulcers.

Ulcers average between one-quarter and one-half inch in diameter. They develop when digestive juices produced in the stomach, intestines, and digestive glands damage the lining of the stomach or duodenum.

The two important digestive juices components are hydrochloric acid and the enzyme pepsin. Both substances are critical in the breakdown and digestion of starches, fats, and proteins in food. They play different roles in ulcers:

• Hydrochloric acid. A common misbelief is that excess hydrochloric acid, which is secreted in the stomach, is solely responsible for producing ulcers. Patients with duodenal ulcers do tend to have higher-than-normal levels of hydrochloric acid, but most patients with gastric ulcers have normal or lower-than-normal acid levels. Some stomach acid is important for protecting against H. pylori, the bacteria that causes most peptic ulcers. [Note: An exception is ulcers that occur in Zollinger-Ellison syndrome. This is a rare genetic condition in which very high levels of gastrin, a hormone that stimulates secretions of hydrochloric acid, are secreted by tumors in the pancreas or duodenum.
• Pepsin. Pepsin is an enzyme that breaks down proteins in food. Since the stomach and duodenum are also composed of protein, they are also susceptible to the actions of pepsin. Pepsin is, therefore, also an important factor in the formation of ulcers.

Fortunately, the body has a defense system to protect the stomach and intestine against these two powerful substances:

• The mucous layer, which coats the stomach and duodenum, forms the first line of defense.
• Bicarbonate, which the mucous layer secretes, neutralizes the digestive acids.
• Hormone-like substances called prostaglandins help dilate the blood vessels in the stomach, to ensure good blood flow and protect against injury. Prostaglandins are also believed to stimulate bicarbonate and mucus production.