Final answer:
The epiglottis is the flexible cartilaginous structure that closes over the larynx during swallowing, preventing food from entering the respiratory tract and directing it towards the esophagus.
Step-by-step explanation:
When successful swallowing occurs, the epiglottis closes over the opening to the larynx to prevent materials from entering the larynx. During this process, the larynx is lifted superiorly and the epiglottis, a piece of flexible cartilage, folds downwards covering the glottis (the opening to the larynx). This action blocks access to the trachea and bronchi, preventing aspiration of food into the respiratory tract. If food does accidentally enter the trachea, this triggers a strong cough reflex which typically expels the food back into the pharynx. The esophagus, which is the muscular tube connecting the pharynx to the stomach, remains closed at both ends by sphincters, except when swallowing occurs.