The pharyngoesophageal segment: Normal structure and function

In conclusion, the striated musculature of the PES, along with the cricoid and thyroid cartilages, the hyoid bone, their ligaments, and the supra- and infrahyoid musculature form a functional unit which selectively controls the opening and closing of the esophageal inlet. At rest, upper esophageal tone acts as a barrier against both entry of air into the esophagus and regurgitation of materials coming from the proximal esophagus. However, reflexive responses of the sphincter offer no substantial protection against regurgitation of stomach contents that cause substantial esophageal distension. Although esophageal distension can experimentally induce sphincter contraction, this potential protective reflex against esophagopharyngeal reflux has not been observed during spontaneous gastroesophageal reflux episodes. Furthermore, regurgitation may be more likely when acid and gaseous gastroesophageal reflux occur altogether. The physiologic correlate to sphincter contraction induced by esophageal distension may be the sustained elevation of sphincter pressure terminating the pharyngeal phase of swallowing. Modulation of the timing and the extent of sphincter opening during swallowing is intimately correlated with the volume and physical properties of the bolus, along with co-ordinated activity of the tongue, pharyngeal constrictors and hyoid musculature, which suggest continuous sensory feedback throughout the pharyngeal swallow.