Upper Esophageal Sphincter

The upper esophageal sphincter (UES) is the high-pressure zone at the junction of the pharynx and esophagus, formed mainly by the cricopharyngeus muscle together with adjacent striated muscle. It stays tonically contracted at rest to keep the upper esophagus closed, then relaxes and is pulled open during swallowing to let the bolus pass. By closing between swallows it helps prevent air from entering the esophagus and reflux material from reaching the pharynx and airway.

Definition

The upper esophageal sphincter is the tonically contracted, predominantly striated-muscle high-pressure zone between the pharynx and the cervical esophagus, chiefly the cricopharyngeus, that relaxes and opens to admit a bolus during swallowing and closes between swallows.

Scope

This topic covers the normal physiology of the upper esophageal sphincter: its muscular components, its resting tone, and the coordinated relaxation and opening that occur during the pharyngeal phase of swallowing, together with its barrier role between swallows. It does not address disorders of UES function or their management.

Core questions

• Which muscles form the upper esophageal sphincter and generate its resting tone?
• How does the sphincter relax and open during a swallow?
• How is UES opening coordinated with the pharyngeal phase of swallowing?
• What barrier functions does the sphincter serve between swallows?

Key concepts

• Cricopharyngeus muscle
• Resting tonic contraction
• Deglutitive relaxation
• Laryngeal elevation and sphincter opening
• Striated-muscle sphincter
• Barrier against air entry and pharyngeal reflux

Mechanisms

At rest the upper esophageal sphincter is held closed by tonic contraction of the cricopharyngeus and adjacent striated muscle, sustained by continuous excitatory motor input. During the pharyngeal phase of swallowing this excitatory drive is briefly switched off so the muscle relaxes, and at the same time the larynx and hyoid are pulled upward and forward, which mechanically distracts and opens the sphincter so the bolus can pass; the passing bolus itself further distends the opening. After the bolus enters the cervical esophagus the muscle re-contracts above it, restoring the high-pressure barrier. This precise sequence is organized by the brainstem swallowing network, which times sphincter relaxation and opening with pharyngeal propulsion and airway protection, so that the sphincter opens only as the bolus arrives and closes promptly afterward.

Clinical relevance

Because the upper esophageal sphincter must open in tight coordination with the rest of the swallow, its normal physiology is central to understanding how the bolus passes from pharynx to esophagus and how the upper esophagus is protected between swallows. This entry describes that normal function and is reference material, not guidance for evaluating or treating sphincter dysfunction in any individual.

Evidence & guidelines

The account here draws on reviews of the physiology of the upper esophageal sphincter and of swallowing neurophysiology, which integrate manometric, electromyographic, and imaging studies of sphincter pressure, relaxation, and opening during deglutition.

Seminal works

• lang-shaker-1994
• ertekin-aydogdu-2003

Frequently asked questions

Which muscle mainly forms the upper esophageal sphincter?

The cricopharyngeus muscle is the principal component, acting together with adjacent striated muscle of the inferior pharyngeal constrictor and proximal cervical esophagus to form the high-pressure zone.

How does the upper esophageal sphincter open during swallowing?

The sphincter muscle first relaxes as its excitatory drive is switched off, and at the same time upward and forward movement of the larynx and hyoid pulls it open, allowing the bolus, which further distends it, to pass into the esophagus.