What is the esophagus?

The esophagus is the portion of the alimentary canal that connects the pharynx to the stomach. Chewed food is partially digested by enzymes in saliva and then directed through this tube, from the mouth to the stomach. The bolus passage is facilitated by the contraction of muscle in the wall of the esophagus.

From a structural point of view, the esophagus (traveling from the outermost layer to the innermost layer) consists of: an outer skin of connective tissue and two types of muscles. The upper third of the esophagus consists of striated muscle and the lower third contain smooth muscle, while the middle third contains a mixture of both. 

The esophagus is approximately 25 cm in length, with a diameter of about 2.5 cm.  It starts at the neck, at the sixth cervical vertebra, enters the chest and ends at the lower end of the stomach, at the eleventh thoracic vertebra. Given its length, it is possible to differentiate the esophagus through its portions. The cervical portion is about 4-5 cm long, between the sixth cervical vertebra and the second thoracic vertebra); the thoracic portion is about 15 centimeters long and happens to be in contact with the first portion and with the dorsal wall of the trachea as well as the bronchus and left heart atrium; the diaphragm portion is about 1-2 centimeters long; and the abdominal portion measures up to 3 centimeters, situated between the esophageal opening of the diaphragm and its outlet in the stomach. 

The esophagus is then characterized by four constrictions that, counting from the top are distinguished as: the cricoid constriction, the aortic constriction, the bronchial constriction and the diaphragmatic constriction. At the narrowing, the cricoid constriction is where the pharynx joins the esophagus; the aortic constriction and bronchial constriction is where the aortic arch and left bronchus cross each other; and finally the diaphragmic constriction is where the orifice of the diaphragm is located. The esophagus is also surrounded at the top and bottom by two muscular rings: the upper esophageal sphincter and the lower esophageal sphincter.

As being a long bodily structure, the esophagus is presented in relation to various structures within the human body. The cervical portion of the esophagus is partly connected to the trachea by means of bundles of connective tissue and through the tracheoesophagea muscle, as well as and partly covered by the left lobe of the thyroid . The chest region can be divided into two sections: one above and one below the intersection of the esophagus with the left bronchus. A muscle similar to that of the tracheoesophageal muscle brings together the left bronchus with the esophagus at the point where the two conduits intersect. This is known as the bronchoesophageal muscle. The diaphragmatic portion corresponds with the portion of the digestive tract that creeps the esophageal opening of the diaphragm. Finally, the lap portion of the esophagus is related to the anterior and posterior surfaces of the liver with the abdominal aorta.

There are various diseases that can be associated with the esophagus. One of the most common conditions is known as the gastroesophageal reflux, which occurs due to an insufficiency of the lower sphincter that causes stomach acid coming up from the stomach into the esophagus, in turn causing a burning sensation.


What function does the esophagus serve?

The main function of the esophagus is to allow food bolus to pass from the mouth to the stomach . When the bolus is swallowed, it reaches the bottom of the groove, where it passes into the esophagus through its mouth (which is a sphincter that opens specially and represents the beginning of the esophagus). The bolus then continues on its way to the stomach through the esophagus. Its passageway throughout the stomach greatly depends on the opening of the lower sphincter (cardia), which connects the esophagus with the stomach and represents the final portion of the esophagus.