In this article, we review the anatomy, physiology and pathophysiology of the UOS along with the current opinions on investigation and treatment of UOS dysfunction. The result has been that pathological change is inconsistently characterized and management is instigated without a satisfactory evidence base. Many physiological characteristics have been attributed to UOS function following videofluoroscopic swallow examinations, manometry and electromyography but a range of normal values remains controversial and their utility uncertain. Relaxation of the UOS occurs during swallowing as well as in sleep while UOS pressure rises with stress, slow oesophageal distension, intra-oesophageal acid infusion and pharyngeal stimulation with air or water. The thyropharyngeus muscle is superior to the cricopharyngeus muscle, and during normal swallowing, the thyropharyngeus contracts while the cricopharyngeus relaxes to propel the food into the esophagus. Basal tone within the UOS is contributed to by all three muscles with asymmetry in the axial plane. The inferior pharyngeal constrictor muscle subdivides into the thyropharyngeus and cricopharyngeus muscle. Cricopharyngeus is the most important muscle with contributions from inferior pharyngeal constrictor and cervical oesophagus. However, it must also allow the reflux of material during belching or vomiting. Its primary function is to allow food into the oesophagus and prevent air ingestion. The pharynx extends from the base of the skull down to the inferior border of the cricoid. It is therefore divisible into nasal, oral, and laryngeal parts: the (1) nasopharynx, (2) oropharynx, and (3) laryngopharynx. The upper oesophageal sphincter (UOS) is a high-pressure zone comprising functional activity of three adjacent muscles together with cartilage and connective tissue. The pharynx is the part of the digestive system situated posterior to the nasal and oral cavities and posterior to the larynx.
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