How does respiratory system maintains homeostasis?!

The respiratory system excretes CO2 and utilizes Oxygen to continue life's processes. These gases are exchanged by diffusion from the blood, through the membranous tissue of the alveoli, and out through the trachea. Through this process, the acid-base balance of the blood (pH) is maintained to avoid the death of cells through respiratory acidosis or respiratory alkalosis.

There's a ton more information on this topic, as this is a big question. Check here: http://en.wikipedia.org/wiki/Human_homeostasis

You should probably ask two questions for the second part in relation to the exercise. Good luck.