The esophagus is a fixed fibromuscular tube forming part of the digestive tract. Aided by peristaltic contractions from the pharynx, it passes food and liquid to the stomach. Therefore the esophagus connects the pharynx with the stomach.

The esophagus generally starts around the level of the sixth cervical vertebra (C6). It travels behind the trachea and the heart, passes through the diaphragm via esophageal hiatus, and enters the cardia of the stomach at the level of the eleventh thoracic vertebra (T11).

The overall length of the esophagus is about 25-30 cm.

The esophagus has three anatomical parts:

Cervical part - extends from the esophageal opening at the level of the superior border of the cricoid cartilage of the larynx to the thoracic inlet; it goes behind the trachea;
Thoracic parts - extends from the thoracic inlet to the esophageal hiatus of the diaphragm; this part is located in the superior and posterior mediastinum; it contains curves and constrictions;
Abdominal part - goes from the esophageal hiatus of the diaphragm to the cardiac orifice of the stomach.

The esophagus has four anatomical constrictions:

Pharyngoesophageal constriction - it is located at the esophageal opening;
Aortic constriction - at the level where the esophagus crosses the aortic arch (Th4);
Bronchial constriction - at the site where the esophagus crosses the left main bronchus (Th5);
Diaphragmatic or phrenic constriction - at the Th10 level, where the esophagus goes through the diaphragm.

Above mentioned constrictions are present in live and dead people, but there are also physiological constrictions present only in live people.

The first one is located below the bronchial constriction, and the second one is located at the Th8 level, where the esophagus crosses the aorta.

The esophagus has two sphincters on both ends, preventing the backflow of the stomach acid in the esophagus and air passage to the stomach when digestion is not happening.

The upper sphincter is located between the pharynx and the esophagus, it is made by striated skeletal muscle fibers. This sphincter is an anatomical sphincter.

The second or the lower sphincter is more a physiological sphincter. It is located between the stomach and esophagus. It is made of smooth muscle fibers.

The wall of the esophagus is formed by four layers:

Mucous membrane - lines the inside of the esophagus;
Submucosa - below the mucous membrane, houses the esophageal glands;
Muscular layer - consists of an inner circular and an outer longitudinal layer; the upper one-third of the esophagus contains striated skeletal muscles, the middle third has a combination of striated skeletal and smooth muscle cells, but the lower third contains only smooth muscle fibers;
Adventitia - formed by fibrous tissue covering the cervical and thoracic parts of the esophagus, while in the abdominal part the outside of the esophagus is covered by the peritoneum instead of adventitia.

Neurovascular supply of the esophagus

The arterial blood supply of the esophagus is provided by vessels called the esophageal arteries.

These arteries arise from three different origins that also correspond to the part of the esophagus they supply:

The veins collecting the deoxygenated blood from the esophagus are called the esophageal veins.

They follow a similar course to their corresponding arteries and drain into different vessels according to the parts of the esophagus they drain.

Veins that collect venous blood from the cervical part of the esophagus drain into the inferior thyroid veins (next to brachiocephalic and superior vena cava).
Veins from the thoracic part drain into the azygos and hemiazygos venous systems, which carry blood next to the superior vena cava. Also, the intercostal and bronchial veins and inferior thyroid veins help to drain the middle part of the esophagus.
The abdominal part of the esophagus is drained by veins that flow into the left and short gastric veins and next to the system of the portal vein.

The esophagus is innervated by nerves of the autonomic nervous system via parasympathetic and sympathetic nerve fibers carried by different nerves.

The cervical part receives parasympathetic innervation via the recurrent laryngeal nerve, a branch of the vagus nerve (CN X). The sympathetic fibers innervating this part arise from the cervical part of the sympathetic trunk.
The thoracic part is mainly innervated by branches arising from the esophageal nerve plexus - a nerve network surrounding the esophagus. The parasympathetic fibers of this plexus arise from the vagus nerve, while the sympathetic component originates from the cervical and thoracic sympathetic trunk.
The parasympathetic innervation of the abdominal part of the esophagus comes from the esophageal and superior gastric nerve plexuses from the vagus nerve, while the sympathetic fibers are provided by the fifth to twelfth thoracic spinal nerves (T5 - T12).

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Esophagus