The esophagus is the muscular tube that transports food and liquid from your throat (pharynx) to your stomach. Although a simple structure, it is a critical part of the digestive system. Several health conditions can affect the esophagus, including acid reflux (heartburn), achalasia, and esophageal cancer. Understanding the anatomy and physiology of this important body part can help you identify these disorders and seek appropriate care.
Your esophagus is about 8 inches (20 centimeters) long and is made of muscle. It has an inner and outer layer of smooth muscle and a central area of skeletal muscle. The muscles of the esophagus contract to move foods and liquid down the tube in a process called peristalsis. The esophagus also has taste buds and secreting cells of the pharyngeal gland.
The pharyngeal gland secretes thick fluids called saliva, which is a mixture of water, salt, and enzymes. These fluids moisten the walls of the esophagus and aid in digestion by coating your food as it moves down the tube. The esophagus also contains a circular bundle of muscle known as the upper esophageal sphincter, or UES, and a non-anatomical sphincter of the esophagus, the lower esophageal sphincter, that normally remains closed in a contracted position until you swallow food. Swallowing opens the UES and LS, and a bolus of food and liquid is then propelled through the esophagus by primary and secondary peristalsis.
While the esophagus is a straight tube, it curves slightly at its base in rodents. It extends from the larynx, through the trachea and bronchi, through the diaphragm and into the stomach. It enters the stomach at a site just left of center in the thoracic cavity and passes behind the heart through the pericardial sac (see slide 125).
The esophagus is innervated by the thoracic esophageal nerve plexus, which includes both parasympathetic and sympathetic fibers. The parasympathetic fibers are derived from the vagus nerve and the spinal nerves running along the neck. The sympathetic fibers originate in the thoracic sympathetic trunk, which runs down from the fifth to twelfth thoracic vertebrae. Through a tightly regulated interplay between the two branches, the tone of the UES and LS is maintained, muscle and glandular contractions are generated, peristalsis is stimulated, and fluids and solids are propelled through the esophagus to the stomach. The esophagus receives sensation from the thoracic esophageal plexus and from the thoracic sympathetic chain, with the vagus nerve more specifically detecting pressure that can translate to pain and the thoracic spinal nerves more directly sensing pain.
