The Esophagus is an organ which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels to the stomach via peristalsis — a radially symmetrical contraction and relaxation of muscles that propagate in a wave downward.
The word esophagus is derived from the Greek word oisophagos, meaning “entrance for eating.” In humans the esophagus is continuous with the laryngeal part of the pharynx at the level of the cervical C6 vertebrae. The esophagus passes through posterior mediastinum in thorax and enters abdomen through a hole in the diaphragm at the level of the thoracic T10 vertebrae.
Depending on individual height, the esophagus ranges in length from 4 to 20 inches. It is divided into cervical, thoracic and abdominal parts. The entry to the esophagus only opens when swallowing, belching or vomiting.
There are four layers of the esophagus: the mucosa, submucosa, muscularis externa, and adventitia.
The esophagus has three anatomic constrictions at the following levels: the esophageal inlet where the pharynx joins the esophagus, behind the cricoid cartilage; where the anterior surface is crossed by the aortic arch and the left bronchus; and where it pierces the diaphragm.
The junction between the esophagus and the stomach (the gastroesophageal junction or GE junction) is not actually considered a valve as it actually better resembles a structure. In much of the gastrointestinal tract smooth muscles contract in sequence to produce a peristaltic wave which forces a ball of food while in the esophagus.
Image Caption: Head and Neck Overview. Credit: Arcadian/Wikipedia