A substance produced in the stomach that is responsible for heartburn is:

• A. Enzyme
• B. Mucus
• C. Bile
• D. Acid

Answer: (D)

Heartburn is caused by the stomach’s acid irritating the esophagus. The digestive juice responsible is gastric acid, mainly hydrochloric acid, which is produced by the stomach lining to aid digestion. When this acid moves back up into the esophagus, it irritates the lining and creates the burning sensation behind the chest.

Enzymes like pepsin can be present in the stomach, and mucus helps protect the stomach lining, but heartburn itself is driven by acid, not these other substances. Bile isn’t produced in the stomach (it comes from the liver and is involved later in digestion), so it isn’t the cause of heartburn.