The esophagus is a 25-cm long muscular tube that connects the pharynx to the stomach. [1] The length of the esophagus at birth varies between 8 and 10 cm and measures about 19 cm at age 15 years. [2]
The esophagus extends from the lower border of the cricoid cartilage (at the level of the sixth cervical vertebra) to the cardiac orifice of the stomach at the side of the body of the 11th thoracic vertebra. The upper limit in the newborn infant is found at the level of the fourth or fifth cervical vertebra, and it ends higher, at the level of the ninth thoracic vertebra. [2, 3]
In its vertical course, the esophagus has 2 gentle curves in the coronal plane. The first curve begins a little below the commencement of the esophagus and inclines to the left as far as the root of the neck and returns to the midline at the level of fifth thoracic vertebra. The second curve to the left is formed as the esophagus bends to cross the descending thoracic aorta, before it pierces the diaphragm. The esophagus also has anteroposterior curvatures that correspond to the curvatures of the cervical and thoracic part of the vertebral column. [1, 2]
The video below depicts the esophagus as viewed through an esophagoscope in a 3-year-old child.
Nerve supply
Recurrent laryngeal branches of the vagus nerve supply the striated muscle in the upper third of the esophagus, and cell bodies for these fibers are situated in the rostral part of the nucleus ambiguus. Motor supply to the nonstriated muscle is parasympathetic, and cell bodies for these fibers are situated in the dorsal nucleus of vagus. These fibers reach the esophagus through the vagus and its recurrent laryngeal branches. They synapse in the esophagus wall in the ganglia of submucosal plexus (Meissner) and myenteric plexus (Auerbach). The myenteric is situated between the outer longitudinal and inner circular muscle fibers. From these plexuses, short, postganglionic fibers emerge to innervate the mucous glands and smooth muscle fibers within the walls of the esophagus
The image below depicts the esophageal musculature.
Musculature of the esophagus.
Histologically, the esophagus has the following 4 concentric layers (see the image below) [3] :
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Mucosal layer
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Submucosal layer
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Muscular layer
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Adventitial layer
The proximal one-third of the esophagus consists primarily of striated muscle. Smooth muscle predominates in the distal portion. [3]
The fourth and the outermost fibrous layer is formed by external adventitia of irregular, dense connective tissue containing many elastic fibers.
The most common congenital anomalies of the esophagus are esophageal atresia and tracheoesophageal fistula. The cause of esophageal atresia is thought to be a failure of the esophageal endoderm to proliferate rapidly during the fifth week to keep up with the elongation of the embryo. The cause for tracheoesophageal fistula and why the 2 defects are usually found together is related to the fact that the respiratory diverticulum buds anteriorly from the cranial foregut and is therefore intimately related to esophageal development. [4]
Congenital esophageal mucosal webs or muscular hypertrophy can cause symptomatic narrowing of the esophagus. Esophageal duplication can take many forms and may manifest as a neck mass or dysphagia. Dysphagia lusoria is induced by vascular anomalies involving the aortic root.