eso-, es-, eis-

(Greek: inward, into; within)

gastroesophageal
Flow of the stomach's contents back up into the esophagus.

This happens when the muscle between the esophagus and the stomach (the lower esophageal sphincter) is weak or relaxes when it shouldn't which may cause esophagitis.

Also called esophageal reflux or reflux esophagitis.