Final answer:
Peristalsis consists of sequential muscle contractions that transport a bolus from the mouth through the pharynx and esophagus and into the stomach, with the process being controlled by the medulla oblongata and involving relaxation of sphincters to allow passage.
Step-by-step explanation:
The process known as peristalsis is essential for transporting a bolus of food from the mouth to the stomach. Initially, contractions of the pharyngeal constrictor muscles move the bolus through the oropharynx and laryngopharynx. Following this, the upper esophageal sphincter relaxes to allow the bolus to enter the esophagus.
Once in the esophagus, the esophageal phase begins, which is controlled by the medulla oblongata. Here, peristalsis involves sequential contractions of the circular muscle layer of the muscularis, constricting the esophagus and pushing the bolus forwards, while the longitudinal muscle layer contracts to shorten and expand the area to receive the bolus. This series of muscle contractions and relaxations propels the food toward the stomach efficiently. When the bolus is about to enter the stomach, the esophagus widens, triggering a reflex that relaxes the lower esophageal sphincter, allowing the bolus to pass into the stomach.