Respiration requires oxygen as a substrate and produces carbon dioxide.
That means we need to get oxygen into the body and carbon dioxide out.
The main part of the human gas exchange system is the lungs, which moves
air in and of the body Air enters the lungs via the trachea (wind pipe), which
then divide into bronchus and further divide into bronchioles in the lungs.
At the end of the bronchioles are alveoli, which are small air sacs where the
gas exchange occurs.