text: When we eat and swallow our chewed food, that food moves down our esophagus through rhythmic contractions of muscle tissue. The esophageal sphincter is a ring-structured muscle that effectively acts as a door to food going from theesophagus into the stomach. It normally stays closed but opens only when letting food into the stomach from the esophagus. Some people have a condition called GERD in which the contents of the stomach- which are very acidic- reflux (flow back into) the esophagus, irritating it, This condition is believed to be caused by a malfunctioning esophageal sphincter that sometimes stays open by accident.