The stomach, intestines, and digestive glands secrete hydrochloric acid and various enzymes, including pepsin that break down and digest food. The stomach must also be protected from the same acid and enzymes, or it too can be attacked by the gastric juices. This causes heartburn. It commonly occurs after meals and is brought on by excess intra-abdominal pressure like lifting weights or straining. Ulcers also occur as a result of over secretion of acid.
Duodenal ulcers are three times more common than gastric ulcers.
Hydrochloric acid, secreted in the stomach, is one of the factors in the development of ulcers, but is not solely responsible. Acid production in patients with duodenal ulcers tends to be higher than normal, while in those with stomach or gastric ulcers, it is usually normal or lower. Excessively large amounts of acid secretion occur in certain situations, such as in a condition known as Zollinger-Ellison Syndrome, in which large amounts of secretion are stimulated by tumours located in the pancreas or duodenum. Pepsin is an enzyme that breaks down proteins. Pepsin and hydrochloric acid cause damage to the stomach or duodenum if the stomach's protective system is altered or damaged.