Hi. In this video, we'll be talking about gas exchange and respiratory physiology. Now, gas exchange allows animals to get the oxygen that they need for cellular respiration, as it's the final electron acceptor in the electron transport chain. Animals can perform gas exchange across their body surfaces due to their high surface area to volume ratio. And you'll see this in organisms like Platyhelminths, you know, flatworms, that sort of thing. Now, for larger animals, we're going to need respiratory organs that are specialized to allow us to perform gas exchange. The lungs are going to be the example we'll be looking at. Essentially, these organs provide the surface area necessary for gas exchange. And here, you can see mammalian, specifically human respiratory anatomy. We have air that will enter through, well, I guess the mouth or the nose, really. Either way, it's going to go down the trachea, and split into the bronchi which will diverge into bronchioles all through the lungs, and of course, those will end in alveoli. In the alveoli, that's where the magic happens. That's where gas exchange occurs. Oxygen that is inhaled is going to move into the bloodstream in those capillaries that surround the alveoli. And carbon dioxide is going to move from the bloodstream into the alveoli to, of course, be exhaled. Now, where these molecules are going to and from is cells, and specifically, mitochondria in cells. So, the oxygen is going to be transported through the blood and delivered to tissues, where it will make its way to the mitochondria to act as the final electron acceptor in the electron transport chain. And of course, CO₂ from the mitochondria is going to be transported into the blood, and out into the alveoli to be exhaled. And that CO₂ is coming as a byproduct of metabolism. You know, specifically like the citric acid cycle, where those carbon compounds are broken down, and the carbons are oxidized and given off as CO₂. So, respiratory organs provide that surface area for gas exchange, but we need a way of getting air in and out of the lungs; the diaphragm comes into play. The diaphragm is what we use, of course, not everyone does it like humans or mammals do, and we actually will see that there are different types of ventilation, and we're going to look at positive pressure and negative pressure ventilation real quick. So, essentially positive pressure, not just ventilation, but in general, positive pressure is like a form of pushing. It's like a squeezing pushing force. Negative pressure is more like a pulling force. You know, think about, for example, taking some container and sucking the air out of it. Like, I don't know if you've ever done this, but like you take a glass and you stick it up to your mouth and just suck all the air out of it, and it just stays stuck to your face. That's because of that pulling force, that negative pressure that is pulling it onto you. So with positive pressure ventilation, we have air pushed into the lungs. This is like what frogs do; that's why they inflate that big pouch in their mouth and then they actually squeeze that air through positive pressure down into their lungs. We, on the other hand, we use our diaphragms, and what we do is basically, we let me jump out of the way here. Here's our diaphragm, that muscle, we pull it down and at the same time we draw out our ribs, and by doing this, we create negative pressure in this area known as the thoracic cavity. So basically by expanding the volume of that cavity, we create negative pressure, and then all you really have to do is just open your mouth and the air is going to come shooting into your lungs. Right? It's going to get pulled in. And when we exhale, we just relax that diaphragm, relax our ribs, and they move down and that, you know, changes the volume of this cavity and causes the air to be exhaled. So, we breathe using that system. It's called negative pressure ventilation. It involves a negative pressure, sort of pulling force, and we rely on our diaphragm and the movement of our ribs to generate that negative pressure. Now with that, let's flip the page.