Esophageal terminology can be classified by function, anatomy, or surgical divisions. Anatomically, the esophagus is divided into cervical, thoracic, and abdominal portions. Surgeons further classify esophageal anatomy based on therapeutic approach and adjacent structures as cervical, proximal, middle, distal thoracic, and abdominal.
The esophagus ranges from 21 to 34 cm in length from the cricopharyngeus to the lower esophageal sphincter (LES), with an average length of 23 cm in females and 28 cm in males. The cervical esophagus ranges from 3 to 5 cm in length, the thoracic portion 18 to 22 cm, and the abdominal portion 3 to 5 cm. The distance from the incisors to the cricoid cartilage is 13 cm.3
Nonkeratinizing, stratified squamous epithelium lines most of the esophageal lumen. This mucosa contains only alveolar serous glands, which are small, tubular mucus glands originating from the submucosa. In the terminal esophagus, cardiac glands, much like those found in the stomach, project through the epithelium to form papillae. Endoscopically, the transition between the esophageal squamous mucosa and the columnar gastric mucosa starts as four-to-six pink tongues projecting up through the paler distal esophagus at what is known as the “Z-line” just proximal to the esophagogastric junction. Replacement of the distal esophageal squamous mucosa by columnar epithelium is diagnostic of Barrett esophagus, a premalignant condition.3 For further information on Barrett esophagus, see Chapter 41.
The lamina propria mucosa lies deep to the mucosa and consists of an areolar, elastic, and collagenous network of fibers that contains small blood vessels, follicles, and mucus glands. The muscularis mucosa is a thin layer of smooth muscular bundles. The submucosa consists of loose areolar connective tissue and elastic and collagen fibers with numerous blood vessels, lymphatics, nerves (including Meissner plexus), and deep mucus glands (Fig. 28-3).
The esophagus is lined with stratified squamous epithelium. The mucosa of the esophagus is comprised of epithelium, lamina propria, and muscularis mucosa. The submucosa is deep to this, then the inner circular muscular layer and the outer longitudinal muscular layer.
The pharyngeal and esophageal muscles coordinate to form coordinated contractions to make swallowing and speech possible. Pharyngeal muscle is striated, whereas the esophagus transitions to more smooth muscle as it descends past the level of the carina and the lower two-thirds of the esophagus. The tunica muscularis is composed of oblique muscle fibers in a single layer in the pharynx, but two layers throughout the esophagus: a longitudinal outer layer and circular inner layer. The circular layer is an extension of the cricopharyngeus muscle.3
The upper esophageal sphincter (UES) acts as the gatekeeper for entry of a food bolus from the pharynx to the esophagus during swallowing. The posterior cricoid cartilage forms the anterior wall of the UES, and a muscular sling of the lower inferior pharyngeal constrictor forms the posterior UES. This sphincter functions to prevent esophageal distension during respiration and to prevent reflux, as it remains in a tonic state of contraction with 30 to 142 mm Hg of pressure between episodes of swallowing.
The LES does not have anatomy as discrete as the UES. The LES is composed in part from a thickening of the circular esophageal fibers that superimpose on each other approximately 3 cm from the gastroesophageal junction. It is not macroscopically or grossly detectable. The LES, in conjunction with the diaphragmatic crura, angle of His, and intra-abdominal length of esophagus, provides a tonic pressure of 14.5 to 34 mm Hg to prevent reflux.3 Liebermann-Meffert4 described short transverse clasp fibers and oblique sling fibers in cadavers that curve around the greater curve that aid in the sphincter effect and help account for the asymmetric anatomy of the LES. For more information regarding the pathophysiology of the esophageal sphincters, see Chapter 33.
Only loose adventitia adheres the esophagus to its surrounding mediastinum, as it has no serosa or mesentery. These loose attachments allow for considerable cephalocaudal movement during respiration.
The esophagus receives arterial blood from multiple sources as it courses through the neck, chest, and abdomen.
The superior thyroid artery gives off smaller arteries that supply the UES and pharynx. The inferior thyroid arteries supply the cervical esophagus. They give off 2 to 3 cm branches called tracheoesophageal arteries that travel inferiorly and medially on each side. The tracheoesophageal arteries subdivide into tracheal and esophageal branches, which in turn subdivide several more times before they eventually enter the esophageal wall.3
The thoracic esophagus derives its blood supply from the superior and inferior thyroid arteries superiorly and the aorta inferiorly. Both the tracheobronchial arteries and the bronchoesophageal artery originate from the aortic arch and further subdivide to provide branches to the trachea. The proper aortic esophageal arteries are unpaired and arise from the descending aorta.3
The abdominal esophagus is supplied by the left gastric artery, ascending branches from the left phrenic artery, and the splenic artery. The splenic artery delivers arterial blood to the posterior and left lateral distal esophagus. Branches from both extend beyond the diaphragmatic hiatus. The repetitive branching of the arterial supply eventually forms a rich submucosal arterial plexus that allows for ligation of extramural vessels without compromising the underlying esophagus (Fig. 28-4).
Arterial blood supply to the esophagus. The cervical esophagus is supplied by the inferior thyroid arteries. The thoracic esophagus is mainly supplied by direct branches off the aorta, and the abdominal esophagus is supplied by the left gastric and inferior phrenic arteries.
A submucosal venous plexus drains blood from the subepithelial venous network. This plexus then empties into communicating veins that traverse the muscular wall along with the perforating arteries. The superior esophagus drains into the internal jugular veins or the azygos or hemiazygos veins. The inferior veins drain into the left gastric and splenic veins. There are no valves in the esophageal venous system.3
The lymphatic system of the esophagus is poorly described. Lymph from the thoracic esophagus likely drains to paratracheal, tracheobronchial bifurcation, juxtaesophageal, and intra-aorticoesophageal nodes. The abdominal esophagus likely drains to superior gastric, pericardiac, and inferior diaphragmatic nodes. All areas of the esophageal lymph system eventually empty into the thoracic duct. Lymphatic channels are more abundant as longitudinal submucosal channels than in the muscular layers.3
The visceral autonomic nervous system innervates the esophagus, pharynx, and larynx. The sympathetic efferent pathways cause vasoconstriction, sphincter contraction, and relaxation of the muscular wall via the cervical and thoracic sympathetic chains. The parasympathetic nervous system increases glandular and peristaltic activity via the vagus (cranial nerve X). The vagus also carries somatic and visceral sensory and skeletal motor fibers to the esophagus. The superior laryngeal nerve mainly has a secretory and sensory function, but it also supplies motor branches to the larynx and cricopharyngeus muscle, which controls the timbre of the voice.3