the pathway of air from the atmosphere to the lungs

step 1

Air is drawn in through the nose or mouth, then the air enters the trachea

step 2

• As the air moves down the trachea, dirt, bacteria, pollen or pathogens become trapped by sticky mucus produced by some of the cells that line the airway

• Other cells are covered with tiny hair-like structure called cilia. These sweep the mucus (with the trapped dirt, bacteria, pollen or pathogens) up to the back of the throat where it’s swallowed

step 3

the trachea branches into bronchi - one bronchus to each lung

step 4

each bronchus divides into many smaller tubes called bronchioles that take the air further into the lungs

step 5

each bronchiole ends in a structure called an alveolus

step 6

• the exchange of gases by diffusion takes place in the alveoli

• oxygen from inhaled air diffuses from the alveoli into the blood

• carbon dioxide diffuses from the blood to the alveoli