ABSTRACT
Esophageal Function The upper esophageal sphincter (or cricopharyngeal muscle) and the muscle of the proximal one-third of the esophagus are striated muscle under voluntary control. A transition from skeletal to smooth muscle occurs in the midesophagus. In the distal one-third of the esophagus, the muscle is smooth muscle that is under involuntary control. The lower esophageal sphincter is a zone of circular muscle located in the distal 2 to 3 cm of the esophagus. To transport food from the mouth through the negative pressure of the chest into the positive pressure of the abdomen, the esophagus must transport food against a pressure gradient. To prevent reflux of gastric contents, the lower esophagus has a sphincter for unidirectional flow. Normal esophageal motility accomplishes both transport of food and prevention of reflux.
