Achalasia

Achalasia, more fully esophageal achalasia, is a failure of smooth muscle fibers to relax, which can cause the lower esophageal sphincter, the muscle between the esophagus and stomach that normally opens to let food in and closes to keep stomach acid from returning up, to remain closed. Without a modifier the term usually refers to achalasia of the esophagus, though the condition can occur at other points along the gastrointestinal tract, such as achalasia of the rectum in Hirschsprung's disease. Its fully understood cause is unknown, and although a genetically transmissible form has been suggested, this is neither fully understood nor agreed upon.