The esophagus is a muscular tube that extends from the level of the sixth cervical vertebra to the 11th thoracic vertebra, spanning three anatomic regions. The cervical esophagus lies left of the midline and posterior to the larynx and trachea. This portion receives its blood supply from branches of the inferior thyroid arteries and drains into the inferior thyroid veins. The upper portion of the thoracic esophagus passes behind the tracheal bifurcation and the left mainstem bronchus. The lower portion of the thoracic esophagus passes behind the left atrium and then enters the abdomen through the esophageal hiatus of the diaphragm.
The thoracic esophagus is supplied by the bronchial arteries (upper portion) and the branches of the thoracic aorta (midportion) and drains into the hemiazygos and azygos veins. The abdominal esophagus ends at the level of the junction with the stomach. The lowermost thoracic esophagus and the abdominal esophagus are nourished by the branches of the left gastric and inferior phrenic arteries and drain into the left gastric veins. Abundant lymphatics form a dense submucosal plexus. Lymph from the upper esophagus drains mostly in the cervical and paratracheal lymph nodes, whereas the lower thoracic and abdominal esophagus drains preferentially into the retrocardiac and celiac nodes.
The architecture of the esophageal wall consists of three layers. The mucosa is made of squamous epithelium overlying a lamina propria and a muscularis mucosa. The submucosa is made of elastic and fibrous tissue and is the strongest layer of the esophageal wall. The esophageal muscle is composed of an inner circular and outer longitudinal layer. The upper third of the esophageal musculature consists of skeletal muscle and the lower two thirds consist of smooth muscle. The upper esophageal sphincter (UES) is formed by the cricopharyngeus muscle along with the inferior constrictors of the pharynx and fibers of the esophageal wall. The lower esophageal sphincter (LES) is not a distinct anatomic structure. Unlike the remainder of the gastrointestinal tract, the esophagus does not have a serosal layer.
The coordinated activity of the UES, the esophageal body, and the LES is responsible for the motor function of the esophagus.
Upper Esophageal Sphincter
The UES receives motor innervation directly from the brain (ie, the nucleus ambiguus). Contributions from the inferior pharyngeal constrictor, cricopharyngeus, and cervical esophageal form this muscular sphincter, with the primary contributor being the cricopharyngeus. The sphincter is continuously in a state of tonic contraction, with a resting pressure of approximately 60–100 mm Hg. The sphincter prevents both the passage of air from the pharynx into the esophagus and the reflux of esophageal contents into the pharynx. During swallowing, a food bolus is moved by the tongue into the pharynx, which contracts while the UES relaxes. Supra- and infrahyoid musculature contribute to pulling the laryngotracheal apparatus away from the spinal column and further dilating the UES. After the food bolus has reached the esophagus, the ...