Diagram of Human Mouth and Throat (Cut View)

Esophageal Muscle

Just above the point where the esophagus joins the stomach, some of the circular muscle fibers in its wall are thickened. These fibers are usually contracted, and function to close the entrance to the stomach. In this way, they help prevent regurgitation of the stomach contents into the esophagus. When peristaltic waves reach the stomach, the muscle fibers that guard its entrance relax and allow the food to enter.