Gastroesophageal reflux is a backward flow or reflux of stomach contents into the esophagus. Everybody has some reflux. Abnormal amounts of gastroesophageal reflux can cause gastroesophageal reflux disease (GERD). This occurs when the valve of smooth muscle between the esophagus and the stomach does not function properly. This muscle band is called the lower esophageal sphincter.

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