Pathway of air into the lungs

Air is inhaled through the nose or mouth. It then enters the trachea

As air moves down the trachea, cilia sweep mucus up to the back of the throat where it's swallowed.

The trachea branches into the bronchi

Each bronchus is divided into bronchioles that take air further down into the lungs

The bronchiole ends up in the alveolus

Gas exhanchange then take place in the alveoli by diffusion. Oxygen is diffused into the blood and carbon dioxide diffuses from the blood to the alveoli