The esophagus is a long muscle lined tube that connects the mouth to the stomach. Its role is simple:\ move liquid and solid food to the stomach for further digestion. The esophagus accomplishes this using gravity and an intricate muscular motion called peristalsis. Peristalsis involves contraction of alternating muscular segments in the esophagus which results in movement of food down to the stomach. To ensure that food does not come back into the mouth, the esophagus has a "pinch-cock" mechanism at its upper end. To protect the esophagus from food travel, a layer of squamous ephithelial cells (similar to skin cells) lines the lumen - making up the Mucosa. When not in use, the esophagus is collapsed. The connection between the stomach and the esophagus is called the cardia orifice and is surrounded by the important gastroesophageal sphincter. This sphincter acts as a true valve and is present to prevent stomach contents from leaking back into the esophagus. If stomach acid were to reach the esophagus, intense pain would result due to the reletivly sensitive nature of the esophageal mucosa compared to the stomach mucosa.