the cause of gerd is complex. there probably are multiple causes and different causes may be operative in different individuals or even in the same individual at different times. a small number of patients with gerd produce abnormally large amounts of acid but this is uncommon and not a contributing factor in the vast majority of patients. the factors that contribute to gerd are the lower esophageal sphincter hiatal hernias esophageal contractions and emptying of the stomach. lower esophageal sphincter the action of the lower esophageal sphincter or les is perhaps the most important factor (mechanism) for preventing reflux. the esophagus is a muscular tube that extends from the lower throat to the stomach. the les is a specialized ring of muscle that surrounds the lower-most end of the esophagus where it joins the stomach. the muscle that makes up the les is active most of the time. this means that it is contracting and closing off the passage from the esophagus into the stomach. this closing of the passage prevents reflux. when food or saliva is swallowed the les relaxes for a few seconds to allow the food or saliva to pass from the esophagus into the stomach and then it closes again. several different abnormalities of the les have been found in patients with gerd. two of them involve the function of the les. the first is abnormally weak contraction of the les which reduces its ability to prevent reflux. the second is abnormal relaxations of the les called transient les relaxations. the most recently described abnormality in patients with gerd is laxity of the les. specifically similar distending pressures open the les more in patients with gerd than in individuals without gerd. hiatal hernia hiatal hernias contribute to reflux although the way in which they contribute is not clear. a majority of patients with gerd have hiatal hernias but many do not. therefore it is not necessary to have a hiatal hernia in order to have gerd. moreover many people have hiatal hernias but do not have gerd. it is not known for certain how or why hiatal hernias develop. esophageal contractions swallows are important in eliminating acid in the esophagus. swallowing causes a ring-like wave of contraction of the esophageal muscles which narrows the lumen (inner cavity) of the esophagus. the contraction referred to as peristalsis begins in the upper esophagus and travels to the lower esophagus. it pushes food saliva and whatever else is in the esophagus into the stomach. when the wave of contraction is defective refluxed acid is not pushed back into the stomach. in patients with gerd several abnormalities of contraction have been described. for example waves of contraction may not begin after each swallow or the waves of contraction may die out before they reach the stomach. also the pressure generated by the contractions may be too weak to push the acid back into the stomach. such abnormalities of contraction which reduce the clearance of acid from the esophagus are found frequently in patients with gerd. in fact they are found most frequently in those patients with the most severe gerd. the effects of abnormal esophageal contractions would be expected to be worse at night when gravity is not helping to return refluxed acid to the stomach. note that smoking also substantially reduces the clearance of acid from the esophagus. this effect continues for at least 6 hours after the last cigarette. emptying of the stomach most reflux during the day occurs after meals. this reflux probably is due to transient les relaxations that are caused by distention of the stomach with food. a minority of patients with gerd about 20% has been found to have stomachs that empty abnormally slowly after a meal. the slower emptying of the stomach prolongs the distention of the stomach with food after meals. therefore the slower emptying prolongs the period of time during which reflux is more likely to occur.
what causes acid reflux also known as gerd?