 There are four factors, four factors that affect gas exchange in the body, and we are going to list all of those out. They will help us when analyzing various clinical scenarios. The first factor that affects gas exchange in the body is the most obvious, and it's obvious because, dude, it's what we've been talking about like this whole time. Partial pressure differences affect gas exchange. If you do not have a partial pressure difference, or if you have like a tiny partial pressure difference, you're not going to get very efficient gas exchange. So that's one factor that's going to affect the rate and the efficiency at which gas exchange takes place. And we're talking about both external respiration and internal respiration. The other factor, no, another factor that affects this whole thing is the distance between alveoli and the capillary. That would be this distance right here. Now, in conditions such as pulmonary lung, adema swelling, and you should be able to process, because of our lecture on capillary exchange, you should be able to process like what are some factors that might lead to pulmonary adema. We might end up with extra fluid in this space between the alveoli and the capillary. The larger the space, if for example, you know, the alveoli was up here and the capillary was down here, that's the larger space, that's more distance that the gases are going to have to diffuse across, and that is going to affect the efficiency of gas exchange. That's super intuitive. Related to that, or relevant because of that, another factor that affects gas exchange is the solubility of the gas. And this is relevant, and I think we already talked about this. Actually, I don't know if I did talk about this or not. Carbon dioxide is way more soluble in water than oxygen. And that's kind of, you know, you look at all of our concerns about carbon dioxide in the air, carbon dioxide diffusing into the oceans and making the oceans more acidic. That's all horrible and a very real concern, because carbon dioxide is super soluble in water. If you have carbon dioxide, if you left a cup of water out in the air, that water is eventually going to become acidic because the carbon dioxide is going to dissolve into the water and become carbonic acid in the system. Oxygen, on the other hand, is much less soluble in water. So what happens is sometimes when you have a situation like pulmonary edema, you might end up with normal carbon dioxide levels in your blood because carbon dioxide can get out no matter what the distance is because it's so soluble, whereas oxygen might have abnormal or low levels of oxygen in the blood because there wasn't enough time for oxygen to diffuse effectively across that really big distance. So that's something to consider when evaluating blood numbers, data. What's that called when you get blood data from your patient? Somebody out there knows the answer and I'm sure you will tell me. The last condition that is going to affect gas exchange is surface area of the alveoli. And I'm telling you this right now because I want you to stop smoking yesterday. And it's because your alveoli, they're surrounded not only by type 1 alveolar cells and type 2 alveolar cells. You also have alveolar macrophages that go around and eat up all the crud and try to keep your lungs clean. And when your alveolar macrophages have to work like super triple quadruple overtime and you are breathing in so much crap and poison into your lungs that they're having to like cleaning your lungs out constantly, one of the byproducts that they produce is an enzyme called elastase. Any elastase breaks down your alveoli. Number one, it breaks down the elastic fibers surrounding the alveoli, which makes it hard to exhale. Number two, it can literally break apart the walls of the alveoli. So where you might have used to have, you might have had 30 little alveoli in a bundle. If you break down the walls between all of them, you might end up with one big bubble with just an outer edge. Does that make sense? And the surface area of one big bubble is going to be much lower than the surface area of a whole bunch of bubbles. This is what happens to you if you get emphysema from smoking. So stop smoking because emphysema leads to decreased surface area of your alveoli, so you take a deep breath and you don't have enough surface area to effectively carry out gas exchange. So number one, you feel exhausted and you can't get enough oxygen to meet your energy needs, but then your little macrophages have been busting a move, trying to get rid of all the poison you put in there and breaking down your elastic fibers in the process so you can't exhale. Seriously, so people who have emphysema, they take a deep breath in and they take a deep, desperate breath in because they can't get enough oxygen into their blood, so they take a deep breath and then they're stuck and they have to provide some serious oomph in order to exhale because their lungs won't naturally just, what, elastically recoil and push the air out. They actually have to do the pushing of the air out using their muscles and their thoracic cavity. Dude, just stop smoking, seriously, it's time. Just stop smoking and I will stop eating as much ice cream. Okay, is it a deal? I mean, if you're in, all right, let's talk about oxygen. Specifically, you stopped smoking, thank you very much, so now your alveoli are going to be stoked and now that they're happy, you'll figure out how oxygen gets carried through the body. Thanks for stopping smoking.