Alright, everybody. We now want to spend some time really diving into some of those details of respiration. But before we get into all the nitty gritty, I want to sort of step back, kind of reset the table here, and give an overview of this whole thing. So when we get into those, you know, fine details, we remember how all these puzzle pieces fit together. Alright. So remember that respiration is the exchange of oxygen and carbon dioxide with the blood. And we said that respiration relies on pressure gradients. And remember, that's why we spent so much time talking about Dalton's law of partial pressure, because oxygen and carbon dioxide are always going to be moving from areas of high pressure to areas of low pressure. But importantly, when we're talking about that, we're always talking about those gases' individual partial pressures that they're moving in response to. Alright. When we talked about respiration, we broke it up into sort of 2 steps. We have external respiration and internal respiration. External respiration happens in the alveoli, and that's going to be exchanging these gases between the air and the blood. And just knowing that, and you probably already know the basic direction that these gases move in, we should be able to figure out generally what these pressure gradients are. So for oxygen, well, oxygen, there's going to be a net movement from the air into the blood in the alveoli. So knowing that, we now know that the partial pressure of oxygen in the air must be greater than the partial pressure of oxygen in the blood because that oxygen is going to move down its pressure gradient into the blood. Well, in contrast, that carbon dioxide well, the partial pressure of carbon dioxide in the air, well, it must be less than the partial pressure of carbon dioxide in the blood. Because in the alveoli, carbon dioxide moves down its pressure gradient from the blood and into the air so we can breathe it out of our body. Alright. Now we can look at internal respiration. Well, internal respiration, after those gases have exchanged with the blood in the alveoli, that blood travels to the tissues of the body. So this happens in the tissues. And again, just knowing which way these gases move, we can figure out just generally what these pressure gradients are going to be. Well, in the tissues, there's going to be a net movement of this oxygen from the blood into the tissues where it's used as part of cellular respiration. So that means that the partial pressure of oxygen in the blood must be greater than the partial pressure of oxygen in the tissues because it's going to move down its pressure gradient. Now in contrast, well, the partial pressure of carbon dioxide in the blood must be less than the partial pressure of carbon dioxide in the tissues. Because carbon dioxide is made in the tissues as a waste product of cellular respiration, it's going to be there's going to be a lot of it there. It's going to move down its pressure gradient into the blood, and then it's carried by the blood back to the alveoli where it moves down its pressure gradient again, so it connects to the body. Alright. Quick note here, we've been talking about partial pressures, but here we've been talking about partial pressures of these gases, both in a gas in the alveoli and in liquids either dissolved in the blood or dissolved in the cytoplasm of cells in the tissues. Well, that's because remember Henry's law. Henry's law allows us to convert from that partial pressure in a gas into how much of that molecule is going to dissolve into a liquid. So we're going to say here, Henry's law allows us to use the same unit. We can use that unit of partial pressure for both gases and gases dissolved in a liquid. So from here on out, we're always going to be using that unit, partial pressure. Alright. As I said, we're going to get into a lot more details coming up. I'm looking forward to it, and I will see you there.