What structure in the airway prevents food and liquids from entering the airway?

Larynx (voice box): During the act of swallowing, the larynx rises and the epiglottis falls back and down as the oral tongue pushes the food or liquid back down the throat. The false cords and true vocal cords also close together like a valve to prevent aspiration.

Vocal cords: Although most people are taught that it is the epiglottis that prevents aspiration, that is not completely correct. The true vocal cords are more important for this function. If the epiglottis is surgically removed, most people won't aspirate, but if one or both vocal cords don't work, most people will aspirate.