1- internal respiration = cellular respiration (metabolism)
2 - external respiration = body respiration (breathing)
CO2 triggers breathing. High CO2 levels will lower pH (making it more acidic), which can quickly cause problems. Exhaling is the main drive for respiration.
The other factor is Oxygen. But what is the main purpose of oxygen that we need? It ties in to metabolism. Oxygen is simply needed as the "final electron acceptor".
|Slide from Dr. Ashworth's Power Point|