The sensation of<unk>  is caused by  exposure of the lower esophagus to the acidic contents of the stomach. Normally, the lower esophageal sphincter (LES) separating the stomach from the esophagus is supposed to contract to prevent this situation. If the sphincter relaxes for any reason (as normally occurs during swallowing), stomach contents, mixed with gastric acid, can return into the esophagus. This return is also known as reflux, and may progress to gastroesophageal reflux disease (GERD) if it occurs frequently. If this is the case, the gastric acid and pepsin now located in the esophagus can injure the tight junction proteins in the esophageal epithelium. This results  in increased paracellular permeability and dilated intercellular space and edema in the submucosa, which is amplified by an immunological mechanism mediated by inflammatory cytokines.
Heartburn pathophysiology
Palpitation pathophysiology
Boerhaave syndrome pathophysiology
Anaphylaxis pathophysiology
Dyspepsia pathophysiology
Mallory-Weiss syndrome epidemiology and demographics
Sick sinus syndrome pathophysiology
Abdominal angina pathophysiology