ACID REFLUX / HEARTBURN

Gastroesophageal reflux disease, often known as GERD or chronic acid reflux, is a condition in the digestive system when a weak GI (gastrointestinal) tract with low muscle tone can allow the liquid content of the stomach to regurgitate (reverse or reflux) into the esophagus. The liquid can inflame and damage the delicate lining of the esophagus although visible signs of inflammation are infrequent.
Gravity, swallowing, and saliva are important protective mechanisms for the esophagus, but they are effective only when individuals are in the upright position and have good pharyngeal, gastro-intestinal and abdominal muscle tone. Muscles, including the smooth muscle of the GI tract, contract in response to nerve stimulation.
Greater stimulation means more contraction. Less stimulation means less contraction.