The eustachian tube (pharyngotympanic tube) connects the middle ear cavity with the nasopharynx. It aerates the middle ear system and clears mucus from the middle ear into the nasopharynx. Opening and closing functions of the eustachian tube are physiologically and pathologically important.

This air-containing space is maintained by the Eustachian tube, which opens intermittently to equalize the intratympanic air pressure with the pressure in the external auditory canal. It also removes secretion and epithelial debris from the middle ear by ciliary motion and gravity.