The Eustachian Tube equalizes the air pressure in the Middle Ear Cavity.
The Eustachian Tube extends from the middle ear cavity to the back of the naso-pharyngeal port (where the adenoids are).
One of the problems with adenoids, if they become swollen, is that they can block the Eustachian tube and hinder the air equalization process.
The tubes are usually collapsed. But the muscles that close the soft palate during eating, also open the tubes as part of the same process.
That is why when you chew gum while taking off in an airplane,the tubes are open and the air is continually equalized in the middle ear cavity.
In the dark ages (60 years ago) it was a popular trick, in order to get attention at a party, to force cigarette smoke from the mouth up through the Eustachian Tubes and out the ears to make smoke rings. Today, that would be considered pathetic, I‰m happy to say.