Acid reflux disease, also known as gastro-esophageal reflux disease, or GERD, occurs due to the coexistence of two medical conditions. The first acid reflux disease contributing condition is a retrograde flow of stomach contents into the esophagus. However, the reflux itself does not necessarily lead to gastro-esophageal reflux disease symptoms or histologic changes, and can occur among healthy individuals as well. In this case, the process is referred to as "physiologic gastroesophageal reflux".
The second acid reflux disease predisposing condition is a lower esophageal sphincter (LES) malfunction. The LES is a 3-cm to 4-cm ring of muscle, which is two to three times thicker than the proximal esophagus and acts as a valve between the esophagus and the stomach. In the case of acid reflux disease, the LES does not close perfectly and stomach contents splashes up into the esophagus. When pathologic symptoms follow this process, the whole condition is called acid reflux disease.
