The second functional unit of swallowing consists of the musclar pump of the esophagus, the lower esophageal sphincter and the stomach as a resevoir.
A coordinated muscular contraction starts in the upper esophagus behind the bolus. 2 This contraction propagates down the esophagus behind the bolus. As the contraction moves down the esophagus the strength of contraction first drops slightly (? at the transition between skeletal and smooth muscle) and therafter increases. At the lower end of the esophagus the lower esophageal sphincter relaxes prior to arrival of the bolus. The bolus passes through the sphincter and into the stomach.
Disorders in this unit present as dysphagia. In the main these disorders may be classified as mechanical and functional.