Final answer:
Swallowing is a complex process that involves three stages: the voluntary phase, the pharyngeal phase, and the esophageal phase. The risk of food entering the respiratory pathways occurs during the pharyngeal phase and is blocked by the closure of the nasopharynx and the constriction of the laryngeal muscles.
Step-by-step explanation:
Swallowing, also known as deglutition, is a complex process that involves the nervous system to coordinate the actions of the upper respiratory and digestive systems. There are three stages of swallowing: the voluntary phase, the pharyngeal phase, and the esophageal phase. The risk of food entering the respiratory pathways occurs during the pharyngeal phase, but it is blocked by the closure of the nasopharynx and the constriction of the laryngeal muscles to prevent aspiration of food into the trachea.