Here my answer but I don't know if its logical, if I'm completely off explain it to me better.
Before air enters the lungs, the hair and the mucous lining of the nose remove dust and dirt. While the air enters the lungs, It is here that oxygen diffuses into the blood vessel and carbon dioxide is diffuse out, where it is exhale out. Mean while the red blood cells carries the oxygen rich blood head straight to the lower chamber of the heart and into the arteries. The arteries carry blood from the heart to the entire body.