 Okay, now I've drawn some context for you. We're talking about the factors that are going to complicate basically how many oxygens are attached to hemoglobins. And you would think that let's just fill up all our seats and when we get somewhere that we want to drop them off, let's just let them off and call it good. But it's not quite that clear. The fact is that hemoglobin forms different kinds of bonds with the oxygen depending on the partial pressure of oxygen in its surrounding zone. Okay, so look, if the PO2 of the plasma is 100 millimeters of mercury, I'm going to tell you right now that I know, I'm that smart. You knew that, didn't you? I know that 97.5% of my hemoglobins are saturated. 97.5% of all of my seats are full of oxygen. But if my partial pressure of oxygen was 40 millimeters of mercury, I know, because I'm that brilliant, just had to say that again, 75% of my hemoglobin seats are going to be full of oxygen molecules. Seriously? Who cares? I do. Look, there's a chart that it's called the hemoglobin saturation curve, and this thing is incredible. What wouldn't you expect that, I mean, I don't even know what you'd expect, but I would not expect some crazy, bizarre curve going on here where literally, think about this for a second, here's partial pressure of oxygen. So at what we call our arterial partial pressure, we have 97.5% saturation. If we go down to a partial pressure of 80, that's significantly less oxygen in our plasma. We drop to a whopping 95.8 of our seats are filled. Seriously? If we drop down to, let's say, 40, look at that. At 40, I'm about 75% of my hemoglobins are still attached to oxygen. Who cares? The significance of this is at a partial pressure that you see in the alveoli, all of the seats for oxygen are going to be filled, most of them, 97%. In fact, you don't even get up to 100% unless you go all the way up to like 600 millimeters of mercury of oxygen, which none of us are ever going to be exposed to. So we will never have all of our hemoglobin molecules full of oxygen, but you're 97.5% full. Like, that's awesome. That's a great load. But remember, in your cells, the capillaries are exposed to a partial pressure of oxygen from the cells of 40, which means now this is crazy. Now, just because the partial pressure is at 40, whatever the difference is between 75 and 97, just about a little bit, let's go 23. 23, okay, 22.5%. 22.5% less. I don't even know how to explain that to you. The difference here, we're going to get empty seats. We're now only going to have 75% of our seats full. Where did those other oxygen molecules go? They fell off. When I think about this, I go, okay, at high concentrations of high partial pressures of oxygen, hemoglobin is stickier for oxygen. Oxygen is more likely to stick to that hemoglobin. And as soon as you're exposed to a lower partial pressure of oxygen, like what you would see in a cell, then some of that oxygen will fall off. Not because the hemoglobin molecule says, oh, special delivery. I brought some oxygen for you little hungry cells. Literally because the environment changes the shape of the hemoglobin molecule and oxygen doesn't stick as well. Look at what happens. If you drop down to just 27%, why? Why would you ever drop down to a partial pressure of oxygen of 27% if you're working out and you're exercising a lot and using up a lot of oxygen because you need a lot of energy? Brilliant. You are now going to dump off half of the hemoglobin molecules that are sitting on your red blood cells. If you drop lower than that, look, I didn't have to drop that much lower and I got down to 25% of my hemoglobin. I'm going to suck all the oxygen off of the hemoglobin molecules that I get down to a low enough partial pressure of oxygen. This is fantastic because the more your cells need oxygen, the more willing hemoglobin is to let go of it. Okay, willing. The more the bus seats aren't even going to fit the oxygen molecules, the shape is going to change and the oxygen is going to get kicked off. If you have a lot of oxygen in your plasma, you're going to keep that oxygen. Why do you need oxygen? Why do you need to let go of it? You don't. And so, functionally, it works out fantastically. If you need oxygen because you have such a low oxygen content in your plasma, you don't have a problem. Hemoglobin changes its shape and the oxygen literally falls off. It's no longer sticky. I think of it as brand new Velcro seats up here and old school Velcro that has gone through the wash like 82 times and picked up every piece of lint under the bed that's possible. That Velcro isn't going to be nearly as sticky. And then, I'm not sure how we can connect our analogy to the environment, but I'll let you think about that and make that analogy for yourselves. We can shift the curve. I bet you didn't even think we could be shifting curves. Oh, yeah. So let's talk about different ways that we can move this curve.