The |esophagus| is the long, flexible tube which leads from the |pharynx| in the upper throat to the |stomach|. The average |esophagus| is about ten inches long, and its walls are made of |muscle fibers| which contract in waves (called peristalsis) to push the ~bolus~ (globule) of chewed food and saliva down to the |stomach|. The common ailment of heartburn occurs when |stomach| acid washes back up into the |esophagus|. Since the |esophagus| has no protective mucosal layer, as does the |stomach|, this acid causes pain which generates just behind the |sternum| (breastbone) and seems to come from the |heart|, hence the term "heartburn" is often used.
