The esophagus is a long, muscular tube that connects an animal’s stomach to its mouth. Distinct from the windpipe, which transports air into and out of the lungs, the esophagus usually carries food and water from the mouth to the stomach. However, during vomiting, the esophagus carries stomach acids and undigested food from the stomach back out through the mouth. The esophagus is about 1 inch in diameter, and approximately 10 to 14 inches in length.
The esophagus has two muscular control points, called sphincters. Similar to sphincters in other portions of the body, when the muscles in the sphincter contract, they prevent liquids from passing through. The esophagus features two sphincters, one at each end. The upper esophageal sphincter is involved in swallowing and breathing and is usually under an animal’s conscious control. By contrast, the lower esophageal sphincter, which prevents stomach acids or food from travelling back up the esophagus, is not usually under direct, voluntary control.
If the lower esophageal sphincter does not close completely or sufficiently, a condition called acid-reflux may occur, in which stomach acid travels back up into the esophagus. This can cause destruction to the esophagus, and if left untreated, can cause esophageal cancer.