So these responses, although they're effective immediately, they're not actually very safe and they're not very effective. And so a much more safer and a much more effective and efficient way, a much more long term response is to actually increase the concentration of a molecule we call 23 BPG. And we'll see why that is in just a moment. And ultimately, what our body wants to do at a high altitude is it wants to increase the number of hemoglobin molecules inside our blood and also increase the number of red blood cells found in our cardiovascular system. Now, the question that I want to answer in this lecture is why does our body actually want to increase the number of two three BPG molecules? Well, recall that two three BPG, two three biphosphoglycerate are allosteric effectors of hemoglobin.