Commonly called the “food pipe”, it is a narrow muscular tube, about nine and a half inches long, that begins below the tongue and ends at the stomach. It consists of an outer layer of fibrous tissue, a middle layer containing smoother muscle, and an inner membrane, which contains numerous tiny glands. It has muscular sphincters at both its upper and lower ends. The upper sphincter relaxes to allow passage of swallowed food that is then propelled down the esophagus into the stomach by the wave-like peristaltic contractions of the esophageal muscles. There is no protective mucosal layer, so problems can arise when digestive acids reflux into the esophagus from the stomach.