Lower esophageal sphincter

The action of the lower esophageal sphincter (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. They are abnormal in that they do not accompany swallows and they last for a long time, up to several minutes. These prolonged relaxations allow reflux to occur more easily. The transient LES relaxations occur in patients with GERD most commonly after meals when the stomach is distended with food. Transient LES relaxations also occur in individuals without GERD, but they are infrequent.

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. At least theoretically, this would allow easier opening of the LES and/or greater backward flow of acid into the esophagus when the LES is open.