main function of respiration system is to exchang gases , the transfer of oxygen from the inhaled air into the blood, and of carbon dioxide from the blood into the lungs; it is the primary function of the lungs. The respiratory gases such as oxygen and carbon dioxide move freely by the process of diffusion.
Exchange of Gases in Tissues :
The exchange of oxygen and carbon dioxide between tissue blood capillaries and tissue cells takes place which is also called internal respiration.
Exchange of Gases of Lungs :
In the lungs, exchange of gases takes place between alveoli and blood capillaries. This is also called external respiration.