What is the esophagus?

Structure and Function

The esophagus lies between the spine and the trachea and is part of the digestive system. The esophagus, however, does not produce or secrete any digestive enzymes, and absorption of nutrients in this part of the digestive system is almost nil. The esophagus pierces the diaphragm as it moves through the thoracic cavity and into the abdominopelvic cavity, where it joins with the stomach.

All parts of the digestive system have four tunics (tissues): from superficial to deep, tunica serosa, tunica muscularis, tunica submucosa, and tunica mucosa. Tunica serosa anchors the esophagus in the mesentery. Tunica muscularis is composed of smooth muscle fibers arranged in circular and longitudinal fibers. These two layers of muscles are important as they are able to squeeze the food bolus (chewed mass of food) and move it down toward the stomach. The muscles are involuntary and perform peristaltic contractions behind the bolus, pushing it downward, as if a tennis ball were being pushed through a leg of panty hose. Tunica submucosa is a layer of loose connective tissue; blood vessels and nerves, including the important submucosa plexus, are found in this layer. The innermost layer, tunica mucosa, is comprised of epithelial cells and is the layer in contact with the bolus. Of all the tunics, tunica mucosa is the most variable along the length of the digestive system. The epithelium here is stratified squamous
epithelial tissue to protect the esophagus from sharp or dangerous food items, such as bones, hot pizza, or insufficiently chewed carrots.

The esophagus has an upper and a lower sphincter. When one swallows, the upper sphincter relaxes. In a coordinated effort, the larynx pulls forward and the epiglottis clamps down to cover this opening into the respiratory system (lungs). Glands produce mucus to lubricate food as it passes along the lumen. The lower sphincter closes once the bolus has passed into the stomach. Failure to do so would allow stomach acids to leak up into the esophagus, causing what is commonly called heartburn or acid indigestion, more properly known as gastroesophageal reflux disease.

Disorders and Diseases

The most common medical problem with the esophagus is gastroesophageal reflux disease (GERD), which is caused when the lower sphincter fails to close properly. Stomach contents, which are acidic, then leak into the esophagus and irritate it. Left untreated, GERD can damage the esophagus.

Barrett’s esophagus is a disease often is found in patients with GERD. In Barrett’s esophagus, the tissue that lines the esophagus, tunica mucosa, is replaced by tissue that is more similar to tissue lining the intestines. The process is called intestinal metaplasia. Barrett’s esophagus may lead to the development of esophageal cancer,
but this is a rare event. It should be emphasized that not all patients with GERD develop Barrett’s esophagus and that very few people with Barrett’s esophagus develop cancer. The cause of Barrett’s esophagus is unknown, as is the cause of esophageal cancer.

Bibliography

"Digestive System." MedlinePlus, January 14, 2013.

"Esophagus Disorders." MedlinePlus, June 12, 2013.

Johnson, Leonard R., ed. Gastrointestinal Physiology. 7th ed. Philadelphia: Mosby/Elsevier, 2007.

Mayo Clinic. Mayo Clinic on Digestive Health: Enjoy Better Digestion with Answers to More than Twelve Common Conditions. 2d ed. Rochester, Minn.: Author, 2004.

Scanlon, Valerie, and Tina Sanders. Essentials of Anatomy and Physiology. 6th ed. Philadelphia: F. A. Davis, 2012.

Wood, Debra, Daus Mahnke, and Brian Randall. "Heartburn—Overview." Health Library, March 18, 2013.