Overview: Can a paper bag really help you when you are hyperventilating? It turns out that it can. In part 2 of our look at your respiratory system Hank explains how your blood cells exchange oxygen and CO2 to maintain homeostasis. We'll dive into partial pressure gradients, and how they, along with changes in blood temperature, acidity, and CO2 concentrations, change how hemoglobin binds to gases in your blood. (And yes, we'll explain the paper bag thing too!)