According to Freud, which part of the personality is considered a mediator?

Ego

The ego is the mediator or regulator of the personality because it works out realistic ways of satisfying the id's demands, while also seeking to satisfy the superego by considering realities, norms, and etiquette and avoiding negative societal consequences.

Air goes past the epiglottis and into the trachea when you breathe in. from there, it goes to your vocal cords in the larynx until it reaches the bronchi. from the bronchi, air passes into each lung.