Final answer:
Heartburn is caused by a weakening or malfunction of the esophagus, specifically the gastro-esophageal sphincter, which results in stomach acid entering the esophagus and causing a painful burning sensation. The correct option is 1.
Step-by-step explanation:
Heartburn tends to be a weakening or malfunction of the esophagus, specifically, a malfunction of the gastro-esophageal sphincter (or cardiac sphincter). This sphincter serves as a valve between the esophagus and the stomach, and its primary function is to prevent stomach contents, which are highly acidic, from flowing back into the esophagus.
When this sphincter is weak or fails to close properly, it results in the backflow of stomach acid into the esophagus, causing a burning sensation known as heartburn. Over time, frequent heartburn can lead to gastroesophageal reflux disease (GERD).
Individuals with heartburn may experience relief through dietary and lifestyle changes that decrease the amount and acidity of reflux. Effective management of heartburn can potentially prevent damage to the esophagus and increases the overall quality of life.