 There are three gas laws that you are going to need to be comfortable with. And the good news is that I'm starting with the easiest one first. The first gas law is that gases only has one s. And gases move from high pressure areas to low pressure areas. Let's throw an exclamation point on that thing. So I'm talking about. Dude, that's easy. That blood flows from high pressure areas to low pressure areas. The end is the movement of air from a high pressure area to a low pressure area. There's nothing bizarre about this, and it's totally intuitive. Pressure. Pressure is a concept that we are definitely messing with here. And that's our next law, Old Boy Dalton. Dalton's law says the pressure of a gas is equal to the partial pressure of all the parts of that gas. Dude, did anybody understand what I just said? I'm giving you an example. This isn't actually what Dalton's law said. You could throw any gases in here. But I'm just saying we've got some oxygen gas, we've got some carbon dioxide gas, and we got a little bit of nitrogen gas. And we've got a ball, a blob, a box of gas. And it's got some oxygen in there, it's got some carbon dioxide, and it's got a bunch of nitrogen. Gotta get the color right if we're going for some nitrogen. Okay, what is pressure? Pressure, pressure. Let's define pressure while we're here. Pressure, remember, is nothing more than force divided by surface area. And so gases have pressure because they literally bang into stuff. So here's my friend, the gas molecule, and it really wants out of here. And so they literally bang into the walls. Ouch! And the more they bang into the walls, the higher the pressure. There are so many things that we can think about and figure out, we don't even have to memorize this stuff. Imagine that there are a whole bunch of gas molecules in here and they're really, really hot, so they're moving really fast. They're going to be bouncing into the walls like crazy and the pressure inside there is going to be really high. If all of a sudden we're like, dude, let's increase the area or the volume of the space that they can hang out in, they're going to have more space to run around and they're going to run into the walls left less. They'll probably run into the walls left and right. They'll run into them quite as often if the volume of the container is bigger. When we look at the pressure of the whole thing, let's just say, I'm going to make up some number. The pressure of the whole thing is going to be 100 millimeters of mercury. And again, we've seen these units for pressure before. Then the partial pressure of oxygen is, let's say, I don't know, 30 millimeters of mercury. And the partial pressure of carbon dioxide is what, it looked like there were maybe 40 of those guys. I don't know, I'm just making this stuff up. And then the partial pressure of my boy's nitrogen over there are going to be, we have to add up to 100, which means it's going to have to be another 30 millimeters of mercury. So the partial pressure of nitrogen is 30. The partial pressure of carbon dioxide is 40. The partial pressure of oxygen was 30. Now, the interesting, and why, who cares? Well, this is going to be extremely relevant when we start talking about gas exchange because gases move down, gases move down, partial pressure gradients. Molecules of salt move down concentration gradients. Molecules of gas move down partial pressure gradients. Same concepts apply for all our intents and purposes. You might as well think of concentration and partial pressure as the same thing, but partial pressure applies to a gas. Concentration applies to something else. We can calculate the concentration of a gas in the air or in a fluid, and we could spend our time trying to conceptualize that and we're not going to. So we're okay just being comfortable with knowing that we can break up our gases. The pressures of our gases based on the kind of gas we're dealing with and knowing that they move down their own partial pressure gradients. The third gas law, this one, Old Boy Dalton. Dalton's law is going to help us with gas exchange. Today, Old Boy Boyle is going to help us out. Boyle's law, again, I think super intuitive. Boyle's law says that volume and pressure of a gas are inversely related, which means this makes perfect sense. If you increase the volume, remember when I said, oh dude, let's make the room bigger. They're going to run into the walls less. I said I did it twice. They're not going to run into it left. They're going to run into it less. We just increase the volume of the space so the pressure decreases. If we increase the pressure, the only way to do that is to decrease the volume. Does that work for you? Just imagine people in boxes running into walls and then imagine how much, if you have to move the same pace. So I say you have to run two miles an hour in this room. No matter what happens, you cannot stop running two miles an hour. You will run into each other more and you will run into the walls more if I decrease the size of the room. That's going to be how often you run into the walls. That's pressure. Okay, are you good? Because Boyle's law is what we need to understand the process of pulmonary ventilation, which is, wasn't that the point of the entire lecture? We're about to get there.