The esophagus (latin: oesophagus) is a fixed fibromuscular tube forming part of the gastrointestinal tract, which passes food and liquid aided by peristaltic contractions from the pharynx to the stomach.
The esophagus generally starts around the level of the sixth cervical vertebra (C6) and travels behind the trachea and the heart, passes through the diaphragm and enters in the cardia of the stomach at the level of the eleventh thoracic vertebra (T11). The overall length of the esophagus is about 25 cm.
The wall of the esophagus is formed by four layers: the mucosal membrane lining the inside of the esophagus; the submucosa below the mucous membrane housing the esophageal glands, the muscular layer consisting of an inner circular and an outer longitudinal layer, and the adventitia, which is 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.
The muscular layer of the esophageal wall in the upper one-third of the organ is striated, in the middle third is composed of striated and smooth muscle, but in the distal third consist only of smooth muscle bundles. That is why the muscles of the esophagus are innervated by both somatic and autonomic nervous systems. The striated musculature and the upper esophageal sphincter are innervated by somatic neurons via the vagus nerve (CN X) from the nucleus ambiguus, while the visceral motor neurons from the dorsal motor nucleus act through connection with the esophageal myenteric nervous system and innervate the smooth musculature and the lower esophageal sphincter. The parasympathetic fibers also stimulate glandular secretion of the mucosal glands of the esophagus and initiates peristalsis.
The esophageal glands are small tubuloacinar mucous glands located in the submucosa of the esophageal wall. In the region close to the pharynx the glands are simpler in form, but glands of the abdominal esophagus closely resemble the cardiac glands of the stomach, and are therefore called esophageal cardiac glands. The glandular secretion of these glands is regulated by the sympathetic and parasympathetic nervous systems. The parasympathetic nerve supply comes from the dorsal nucleus of the vagus nerve (CN X) via the esophageal branches of the recurrent laryngeal nerve. The sympathetic nerve supply comes from the cervical and thoracic parts of the sympathetic chain.