Figure 12.1: Human alimentary tract.   

b.Esophagus: It is also known as food pipe or gullet, is about 25 cm long. It presents behind the trachea and heart. Its primary function is to conduct food from pharynx to the stomach. Food in esophagus is pushed is pushed downward by involuntary muscle contraction of circular muscle, this movement is called as peristalsis. Due to contraction of the longitudinal muscles lower part of esophagus become short which pushes its wall outward so that it can receive the bolus. The circular muscles of esophagus then relax. The contractions are repeated in a wave that moves downward to the stomach as shown in Figure 12.2. The cardiac sphincter lies between esophagus and stomach allows the conduction of bolus into stomach. The sphincter closes again. Medulla oblongata controls the peristalsis.