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Chapter 12

### Key Concepts

• Physiology

• The basic function of the esophagus is to propagate a bolus from the oropharynx to the stomach.

• The coordination of esophageal muscle contractions, vagal innervation, and sphincter relaxation allows this event to occur.

• Function tests

• Primary esophageal motility disorders can be diagnosed using conventional- or high-resolution manometry.

• Various systems are available for reflux testing including 24-hour catheter-based pH monitoring, wireless capsule pH testing, and combined pH impedance.

• Endoscopic techniques

• High-resolution endoscopy, chromoendoscopy, narrow band imaging, and confocal endomicroscopy are techniques that enhance the esophageal mucosa, improving diagnostic yield in Barrett’s esophagus (BE) and early esophageal cancer.

• Endoscopic ultrasound adds imaging from adjacent structures, and is useful for staging and fine-needle aspiration.

• Multiple ablative techniques are now available for BE and early esophageal cancer, and include endoscopic mucosal resection, photodynamic therapy, radiofrequency ablation, cryotherapy, and endoscopic mucosal dissection.

### Physiology

Although the basic function of the esophagus is to simply propagate a bolus of food from the oropharynx to the stomach, the execution of this function remains complex. Ultimately, the swallow mechanism is a dynamic process between the muscles of the esophagus and its neural innervation, and involves the interplay between the upper esophageal sphincters (UESs) and lower esophageal sphincters (LESs).

The esophagus is a hollow tube, usually between 17 and 30 cm but averaging 23 cm.1 At the proximal end is the UES, which is approximately 1 cm in length. The UES is composed of striated cervical esophageal muscle, the cricopharyngeus, and the inferior pharyngeal constrictor muscles. The superior and inferior hyoid muscles and superior pharyngeal muscles also help facilitate UES opening. Innervation of the UES arises from branches of the vagus nerve stemming from the nucleus ambiguus. Tonic closure of the UES functions to prevent insufflation of air during inspiration and esophagopharyngeal reflux. Intermittent relaxation of the UES allows bolus transit and venting (belching).

The esophageal body is composed of two different types of myocytes. Although somewhat variable, in general, the proximal third of the esophagus is striated muscle and the distal two-thirds composed of smooth muscle. The transition is not abrupt, and thus there is a short segment in which the muscles fibers are mixed. The arrangement is such that there is an outer longitudinal muscle layer and an inner circular muscle layer. This arrangement facilitates peristalsis, which will be discussed below.

Between the longitudinal and circular muscle layers lies the myenteric or Auerbach’s plexus. This network of neurons contains ganglia arising from the vagus nerve, although the concentration of ganglia affecting the smooth muscle portion is higher than the striated muscle portion. Ganglia innervating striated muscle stem from the nucleus ambiguus while ganglia innervating smooth muscle stem from the dorsal motor nucleus of the vagus. The neurotransmitter acetylcholine plays a role in activation of both striated and smooth muscles in the esophagus. Acetylcholine released by nerve endings activates the esophageal striated ...

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