Physiology, Esophagus

The esophagus is a muscular channel that carries food from the pharynx to the stomach. It starts with the upper esophageal sphincter, formed in part by the cricopharyngeus muscle, and ends with the lower esophageal sphincter, surrounded by the crural diaphragm. When food enters the mouth, it mixes with saliva. The actions of salivary enzymes convert food into a mass called a food bolus. Once the food bolus reaches the pharynx, swallowing starts, and relaxation of the upper esophageal sphincter ensues to allow passage of the food bolus into the esophagus. The bolus then travels down the esophageal body aided by peristaltic contractions of the esophageal muscles. When it finally reaches the distal end of the esophageal body, it triggers relaxation of the lower esophageal sphincter, which in turn permits entry of the food bolus into the stomach.