The esophagus is the muscular tube in humans and most other vertebrate organisms that carries food from the pharynx, or throat, down to the stomach. It is lined with a thick, moist pink tissue called mucosa.
In adult humans, the esophagus is approximately 8 inches long and terminates in sphincters, or bundles of muscle tissue, at either end. The upper esophageal sphincter, which is under voluntary muscle control, is responsible for preventing food from entering the trachea, or windpipe. It also moderates belching and vomiting. The lower esophageal sphincter is an involuntary muscle that controls the movement of food into the stomach as well as preventing the upward movement of partially digested food and acids from the stomach into the esophagus.