The esophagus, also referred to as the ?gullet? is a muscular tube that connects the throat or pharynx to the stomach. The length of the esophagus is approximately 8 inches. It is lined on the internal side by a moist membrane referred to as the mucus membrane. The esophagus is situated behind the windpipe or trachea and the heart. The esophagus enters the diaphragm just before it is connected to the stomach. At the top or upper part of the esophagus is situated the upper esophageal sphincter, which is a bundle of muscles that are under voluntary control. This upper esophageal sphincter is used while a person eats, breathes, belches and vomits. It is also responsible for preventing the passage of food and other secretion down the windpipe. At the lower end of the esophagus is situated the lower esophageal sphincter, which is also a bundle of muscles that are not controlled voluntarily. It prevents the passage of acid and other contents of the stomach from going back from the stomach into the esophagus.