when you swallow food it travels through a tube called the esophagus the esophagus leads into the stomach through a hole in a sheet of muscle called the diaphragm there's a round muscle at the bottom of the esophagus that works like a valve the muscle relaxes when you swallow allowing food to pass into the stomach certain cells in your stomach called proton pumps release acid to help digest the food the lining of your stomach protects it from the acid the esophagus has a different type of lining which looks like it's made of smooth tiles the valve is designed to close tightly after you swallow so nothing comes back into the esophagus your diaphragm is also meant to pinch securely around the esophagus closing off the opening to your stomach it's normal for a small amount of acid to occasionally Splash into the esophagus this is called reflux that word means flowing back a small amount of reflux doesn't usually cause any harm but if acid splashes up into the esophagus over and over again for years the esophagus can be damaged there are several reasons this might happen it's not uncommon for the valve to become weaker so it doesn't close tightly that allows acid and partially digested food to come up into the esophagus sometimes the diaphragm weakens around the esophagus allowing the hole to become larger this hole is called the Hiatus when it becomes larger part of the stomach May bulge through it this is called a hiatal hernia the hernia may cause the esophagus and the valve to move up in that case the diaphragm is no longer reinforcing the valve that makes it more likely that acid will get into the esophagus when acident Foods Splash up into the esophagus repeatedly it's called gastro esophageal reflux disease or gird gastro for the stomach or gastric system esophageal for the esophagus Mayo Clinic's division of gastroenterology and hepatology is recognized as number one by US News and World Report go to mayoclinic.org to find out how to request an appointment with a Mayo Clinic physician