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is a relatively short segment between the laryngopharynx and the cricopha-ryngeus muscle, the lowest part of the inferior pharyngeal constrictor that defines the upper esophageal sphincter (UES). The cervical esophagus begins when the fibers of the cricopharyngeus muscle form the outer longitudinal and inner circular layers of the muscularis, and it extends down to the level of the first thoracic vertebra. The cervical esophagus is about 5 cm long and tends to run more on the left side of the trachea, making it easier to surgically access this structure through a left neck incision. The thoracic segment starts once it is in the posterior mediastinum, and it deviates slightly to the left as it passes behind the great vessels and the aortic arch. After coursing behind the left mainstem bronchus, it then curves to the right in the subcari-nal region; this is the reason that surgical exposure of the midesophagus is best approached through a right chest incision. Just before going through the diaphragmatic hiatus near the level of T11, the esophagus returns to a slightly left-sided position. The abdominal esophagus, which varies from one to several centimeters in normal individuals, constitutes the segment between the esophageal hiatus at the level of the diaphragm and the esoph-agogastric junction. The lower thoracic esophagus and the abdominal esophagus are most approachable through a left-sided chest incision or an upper midline abdominal incision.

Normal Anatomic Constrictions

The esophagus has three points of naturally occurring constrictions (Fig. 8-1). The cricopharyngeus sphincter makes up the cervical or cricopharyngeal constriction, which is considered the narrowest point of the entire gastrointestinal tract. The next area of constriction is the bronchoaortic or aortic constriction, where the left mainstem bronchus and the aortic arch cross the esophagus. As the name implies, the diaphragmatic or hiatal constriction is located at a point where the esophagus passes the diaphragmatic hiatus, and it therefore defines the transition point between the thoracic esophagus and the abdominal esophagus.

Vascular Supply

The arterial blood supply to the esophagus is provided by a number of sources, with abundant collateral communications within each segment. The superior thyroid arteries and the inferior thyroid arteries both supply the cervical esophagus. In the thoracic esophagus, direct branches from the aorta, as well as the inferior thyroid arteries, intercostals, bronchial arteries, inferior phrenic arteries, and left gastric artery, all contribute to forming a network of capillaries before penetrating the muscularis layer. The distal portion of the esophagus, including the abdominal segment, has its arterial supply based mainly on the left gastric artery. The network of venous return generally follows the arterial system and drains into the inferior thyroid vein in the cervical segment; the bronchial, azygous, and hemiazygos veins in the thoracic segment; and the coronary vein in the abdominal segment.

25 cm

Cervical constriction

Broncho-aortic constriction

Pharynx

Cervical constriction

Broncho-aortic constriction

25 cm

Stomach

Diaphragmatic constriction

Stomach

Figure 8-1 Three points of naturally occurring constrictions of the esophagus. Because of various normal anatomic factors, the esophageal lumen is narrowed in three distinct areas: cervical (or cricopharyngeal) constriction, bron-choaortic (or aortic) constriction, and diaphragmatic (or hiatal) constriction. The cervical constriction is typically the narrowest point of the entire gastrointestinal tract, and the diaphragmatic constriction defines the transition point between the thoracic esophagus and the abdominal esophagus. (Source: Illustration by William Parker, PhD.)

Lymphatic Drainage

Learning the anatomy of the lymphatic system is important to understand some of the principles of esophageal oncology. The lymphatic drainage of the esophagus occurs in the submucosal plexus in a longitudinal fashion, such that lymph can travel along the esophagus over a long distance along the submucosal layer before going through the muscularis and entering a set of regional lymph nodes. The direction of the lymph flow typically is cephalad in the upper two-thirds of the esophagus and caudad in the lower one-third. Groups of regional lymph nodes draining the esophagus include the cervical, paratracheal, hilar, sub-carinal, paraesophageal, and paraaortic nodes in the upper two-thirds, and paraesophageal, paraaortic, left gastric, and celiac nodes in the lower third.

Autonomic Innervations

The autonomic innervation provides the esophagus with various motor, sensory, and secretory functions. The parasympathetic innervation comes predominantly from the vagus nerve, which is present on the right and the left side of the esophagus throughout the majority of its length but coalesces to form anterior and posterior trunks distally. The superior laryngeal nerve that arises from the vagus nerve in the cervical segment divides into the external laryngeal branch, which innervates the motor function of the cricothy-roid muscle and inferior pharyngeal constrictor, and internal laryngeal branch, which provides the sensory nerves to the pharyngeal surface and the base of the tongue. The recurrent laryngeal nerve emanating from the vagus nerve also provides parasympathetic innervation to the cervical esophagus and the UES; injury to this structure might lead not only to hoarseness but also to secondary tracheobronchial aspiration during swallowing. Within the eso-phageal wall, Meissner's plexus provides the intrinsic autonomic innervation in the submucosal layer and Auerbach's plexus in between the longitudinal and circular muscle layers.

Upper and Lower Esophageal Sphincters

The UES is a true anatomic structure created by the function of cricopharyn-geus muscle. The basal resting pressure ranges widely from about 20 to 120 mmHg, with a mean pressure of approximately 40 mmHg. The lower esophageal sphincter (LES), on the other hand, is only a functional sphincter, in that a high-pressure zone (HPZ) in a 3- to 5-cm segment of the distal esophagus has been demonstrated manometrically but no true anatomic sphincter is known to exist; it is therefore, often referred to as the LES mechanism or the distal esophageal HPZ. The resting pressure of this HPZ typically ranges from 10 to 20 mmHg. Although the absolute value of the HPZ resting pressure does not define competence or incompetence of the LES mechanism, mean resting pressures of less than 6 mmHg or overall LES mechanism length of less than 2 cm are more apt to be associated with gastroesophageal (GE) reflux. Furthermore, the resting pressure of HPZ may be affected by a wide variety of factors such as hormones (increased by gastrin, motilin, prostaglandin F2a, and bombesin; decreased by secretin, cholecystokinin, glucagons, progesterone, estrogen, and prostaglandins Ej,E2, A1),drugs (increased by caffeine, norepinephrine, phenylephrine, edrophonium, bethanechol, methacholine, and metoclopramide; decreased by phentolamine, atropine, theophylline, isoproterenol, ethanol, epinephrine, nicotine, and nitroglycerin), foods (increased by protein; decreased by fat and chocolate), and environmental conditions (increased by gastric alkalinization and gastric distention; decreased by gastric acidification, gastrectomy, hypo-glycemia, hypothyroidism, amyloidosis, pernicious anemia, and epidermolysis bullosa).

Contractions of the Esophageal Body

The motor function of the esophagus is physiologically driven by three different types of contractions or waveforms. Primary waves describe the cranial-to-caudal, sequential contractions (peristalsis) that send the food bolus down to the stomach with swallowing. Secondary waves then clear the esophagus of any residual debris by providing another set of sequential, peristaltic contractions, but only after the original food bolus has passed into the stomach. Tertiary waves, on the other hand, are nonsequential, monophasic, or multiphasic contractions that often occur in older individuals and have no known true functions.

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