To better understand indigestion, it helps to understand the anatomy of the esophagus and stomach.
The esophagus is a muscular tube that propels food from the mouth, to the stomach. It begins in the pharynx, just below the base of the tongue, and passes through the chest, next to the spine. It then passes through the diaphragm before emptying into the stomach.
The bottom of the esophagus opens (esophageal sphincter) during swallowing, and then closes after the food has entered the stomach. This prevents food from leaking back into the esophagus.