How do our bodies maintain homeostasis regarding pH and gas exchange during exercise?

Answer 1

To put it simply, when you exercise, your cells make more waste product of CO2 (carbon dioxide = acid = low pH). You breathe faster and deeper and your heart pumps faster. This helps move CO2 from your tissue and blood to your lungs, where you breathe out the CO2 building up. Less CO2 means less acid in your body which helps to bring the pH back to its normal level.

Mind you, this is just regarding gas exchange and does not take into account kidney/metabolic buffering that also occurs.