1.   Dr. Timothy Wang, gastroenterologist at Massachusetts General Hospital, explains that the lower esophageal sphincter works like tightening a rubber band around a straw.

2.   The food is propelled into the esophagus, where contractions usher it down to the lower esophageal sphincter, which allows entry into the stomach.

3.   The ring, called the lower esophageal sphincter, then closes immediately to prevent the acid contents of the stomach from backing up into the esophagus.

4.   The problem lies in the muscle that plugs the stomach, called the lower esophageal sphincter.