The main functions of the esophagus are to transport food and fluids from the pharynx to the stomach, prevent the passive diffusion of substances from the food into the blood and to prevent the reflux of gastric contents into the esophagus.  Food is transported from the pharynx to the stomach by a coordinated peristaltic contraction initiated in the upper esophagus, which temporally follows a descending wave of inhibition.  The control of the LES is critical to esophageal function.  Maintenance of sphincter tone is necessary to prevent the reflux of gastric contents, which are under positive pressure relative to the esophagus due to their location in the peritoneal cavity.