The upper esophageal sphincter: anatomy and physiology

The upper esophageal sphincter (UES), also known as the pharyngoesophageal segment (PES), is a 4-cm segment of the digestive tract that separates the esophagus from the pharynx and larynx. This narrative review represents an overview of the anatomy and physiology of this critical component of the airway protective mechanism. The structure is bounded anteriorly by the larynx, posterolaterally by the pharyngoesophageal muscles, superiorly by the pharynx and inferiorly by the esophagus. Guarding the entrance of the esophagus, the UES controls inflow and outflow through the region, preventing aerophagia in the anterograde direction as well as regurgitation in the retrograde. Although the cricopharyngeus muscle (CPM) is often considered synonymous with the UES, in reality it is but one component of the complicated anatomy. In fact, relaxation of the CPM is not the primary contributor to UES opening. During the act of swallow, the relaxation of the CPM, elevation of the larynx and propulsion of the food bolus by the pharynx coordinate to open the UES and facilitate deglutition. An understanding of the anatomy of the region in addition to the phases of UES opening facilitates more refined therapeutic interventions for patients with pharyngoesophageal swallow impairment and dysphagia.