The esophagus begins below the pharynx and extends through the chest into the abdomen where it joins the stomach. It functions to move food and liquid from the mouth to the stomach. There are valves, or sphincters, located at the upper and lower end of the esophagus. Failure of the upper esophageal sphincter to open properly leads to difficulty with swallowing or aspiration. Dysfunction of the lower esophageal sphincter can lead to dysphagia (difficulty swallowing) if it is not opening properly, or gastroesophageal reflux if it doesn't close securely. Infections, injury, loss of motility, diverticula, and tumors can also affect the esophagus.