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Esophagus

Esophagus

The esophagus is a hollow muscular tube that forms the upper part of the digestive system. It’s approximately 25 cm in length and 2 cm in diameter, and lies immediately anterior to the vertebral column. The esophagus descends through the neck and mediastinum to pass through the esophageal hiatus in the right crus of the diaphragm. It then terminates at the level of the seventh costal cartilage and eleventh thoracic vertebra (T11) by entering the cardiac orifice of the stomach. The main function of the esophagus is to convey food from the pharynx to the stomach.

Divisions

The esophagus can be divided into three portions according to its region (cervical, thoracic, and abdominal). The cervical esophagus lies posterior to the trachea, and is attached to it by loose connective tissue. It deviates to the left at the lower neck. The thoracic esophagus is positioned to the left in the superior mediastinum, between the trachea and the vertebral column. At the level of the tenth thoracic vertebra (T10), it enters the abdomen  via the esophageal hiatus of the diaphragm to become the abdominal esophagus. The abdominal esophagus is located left of the midline and  terminates at the cardiac orifice of the stomach, where it is slightly broader.

Muscles

The esophagus is composed of two layers of muscles: the internal circular muscle and the external longitudinal muscle. The external layer contracts to shorten the esophagus, while the internal layer carries out the squeezing motion. The upper third of the external layer is comprised of voluntary, striated muscle, the lower third is comprised of involuntary, smooth muscle, and the middle third is comprised of both striated and smooth muscle. Because of the peristaltic action of these muscles, the food passes through the esophagus rapidly. Below the junction of the throat and the esophagus, a muscular band called the upper esophageal sphincter is present. The lower esophageal sphincter lies above the junction of the esophagus and stomach. When the esophagus is not actively in use, these sphincters contract to prevent the reflux of food and stomach acid from the stomach to the mouth, unlike during swallowing, where they relax. Both the esophageal muscles and sphincters weaken with age.

Neurovasculature

The arterial supply of the cervical esophagus is provided by the inferior thyroid artery, while the thoracic portion is supplied by the bronchial and esophageal branches of the thoracic aorta. Esophageal branches arise from the aorta and descend towards the esophagus to form a vascular chain that anastomoses with the esophageal branches of the inferior thyroid arteries from above, and with the ascending branches from the left phrenic and gastric arteries from below. The abdominal esophagus is supplied by the esophageal branches of the left gastric artery, the upper short gastric arteries, the terminal branches of the esophageal branches of the thoracic aorta, and occasionally an ascending branch of the posterior gastric artery. 

The cervical esophageal veins drain into the inferior thyroid veins, while the thoracic portion predominantly drains into the azygos veins. Veins of the abdominal esophagus return blood through plexuses to the left gastric and upper short gastric veins. The left gastric vein joins the lower esophageal veins to drain into the portal vein. 

In terms of innervation, the esophagus is supplied by the esophageal plexus formed by the vagal trunks and the thoracic sympathetic trunks.

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