Final answer:
The pharynx, part of both the digestive and respiratory systems, is a tube extending from the oral and nasal cavities to the esophagus and larynx, facilitating the passage of food and air and involving complex muscle movements during swallowing.
Step-by-step explanation:
The pharynx is a critical component shared by both the digestive and respiratory systems. As a tube of skeletal muscle lined with a mucous membrane, it extends from the posterior oral and nasal cavities to the openings of the esophagus and larynx. The pharynx serves as a pathway for the movement of food and air. It is divided into three parts: the nasopharynx, the oropharynx, and the laryngopharynx. The nasopharynx, located superiorly, is involved only in breathing and speech. The oropharynx and the laryngopharynx, however, have dual functions in both breathing and digestion.
Deglutition, or swallowing, involves the soft palate rising to close off the nasopharynx, elevation of the larynx, and folding of the epiglottis over the glottis to prevent food from entering the larynx. This intricate series of events prioritizes the passage of swallowed substances over inhaled air. During this process, the elevator skeletal muscles of the pharynx contract, raising and widening the space to accommodate the food bolus. After receiving food, these muscles relax and the constrictor muscles contract, propelling the bolus into the esophagus to initiate peristalsis.