<prompt> Most important pathophysiological cause of GERD is:Hiatus herniatransient LES relaxationLES hypotensionInadequate esophageal clearance  <response>: Ans is b i.e. transient LES relaxation Transient LES relaxations account for at least 90 of reflux in normal subjects or GERD patients without hiatus hernia HarrisonTransient lower esophageal sphincter relaxations account for essentially all reflux events in individuals with a normal LES pressure at the time of reflux Pathogenesis of gastroesophageal reflux disease GERDThe primary event in the pathogenesis of gastroesophageal reflux disease GERD is movement of gastric juice from the stomach into the esophagus.The three dominant pathophysiologic mechanisms causing gastroesophageal junction incompetence are:Transient lower esophageal sphincter relaxations tLESRsA hypotensive lower esophageal sphincter LESAnatomic disruption of the gastroesophageal junction, often associated with a hiatal herniaThe latest concept is that the dominant mechanism varies as a function of disease severity with tLESRs predominating with mild disease and mechanisms associated with a hiatus hernia andor a weak sphincter predominating with more severe disease Transient LES relaxations are different from swallow-induced LES relaxation: tLESRs occur without an associated pharyngeal contraction, are unaccompanied by esophageal peristalsis, and persist for longer periods 10 sec than do swallow-induced LES relaxations. tLESRs are the physiological mechanism of belching. 