Esophagus

Structure/Morphology

The esophagus is a musculomembranous tube, about 25 cm long, that extends from the pharynx superiorly to the stomach inferiorly. It can be divided into three parts, depending on which region it’s passing through. These include the cervical, thoracic, and abdominal parts. The esophagus is composed of internal circular and external longitudinal layers of muscle. The upper one third of the esophagus has striated muscle in its external layer, while the lower one third is composed of smooth muscle. The middle one third is a mixture of both muscle types.

Anatomical Relations

The esophagus begins as the cervical part of the esophagus at the lower border of the cricoid cartilage and sixth cervical vertebra. It largely lies in the midline, anterior to the vertebral bodies of the cervical vertebrae, but tends to deviate towards the left. As it passes through thoracic inlet, it is pushed back to the median plane by the aortic arch. It descends in the superior mediastinum to the level of the fourth thoracic vertebra. As it enters the posterior mediastinum, at the level of the sternal angle (T4/T5), it travels to the right of the descending thoracic aorta and posterior to the base of the heart. The esophagus deviates again to the left and passes through the esophageal hiatus of the respiratory diaphragm at the level of the tenth thoracic vertebra, anterior to the aorta. Inferior to the esophageal hiatus it becomes the abdominal part of the esophagus.

Along its course, the esophagus has three constrictions. The first is the cervical constriction found at the beginning of the esophagus and is caused by the cricopharyngeus muscle. The second constriction, the bronchoaortic (or thoracic) constriction, is formed where the aortic arch and left main bronchus crosses anterior to the esophagus. The final constriction is the diaphragmatic constriction formed when the esophagus passes through the esophageal hiatus.

Function

The esophagus is responsible for propelling the food bolus from the mouth to the stomach via peristaltic contractions of the muscles in the esophageal wall.

Arterial Supply

Since there are three parts to the esophagus, the cervical, thoracic, and abdominal, it receives three separate arterial sources. In the cervical region, the esophagus is supplied by the inferior thyroid artery. In the thorax, it receives arterial supply from esophageal branches of the descending thoracic aorta and from the right bronchial artery. The abdominal part of the esophagus is supplied by branches of the left inferior phrenic and left gastric arteries. The entire arterial supply of the esophagus forms an anastomosis between the different regions, ensuring constant arterial supply.

Venous Drainage

Initially, venous drainage of the esophagus emerges from a submucosal plexus, which drains into a periesophageal venous plexus. In the cervical region, the plexus is drained via the inferior thyroid veins. The thoracic part of the esophagus is drained mainly by the azygos vein, but also receives tributaries from the hemiazygos and posterior intercostal veins. The venous drainage of the abdominal esophagus occurs via the left gastric vein. This vein forms a union with the lower esophageal veins of the thoracic region, thus forming a portovenous anastomosis.

Innervation

Parasympathetic innervation of the upper one third of the esophagus is derived from the recurrent laryngeal nerve, which originated from the vagus nerve (CN X). The vagus nerve forms an esophageal plexus around the lower two thirds of the esophagus and supplies the smooth muscle of that region. The vagus nerve also has secretomotor fibers that supply the mucous glands of the esophageal mucosa.

Sympathetic fibers, which innervate the lower two thirds of the esophagus, arise from the greater splanchnic nerve that join the esophageal plexus. Afferent visceral pain fibers travel to the upper thoracic spinal cord, which also receives cardiac afferents. Therefore, distinguishing symptoms of esophageal and cardiac pain can be difficult.

Lymphatic Drainage

Lymphatic drainage of the cervical, thoracic, and abdominal parts of the esophagus is through the deep cervical, juxtaesophageal (part of the posterior mediastinal nodes), and left gastric lymph nodes, respectively.

List of Clinical Correlates

- Esophageal varices