 The whole point of the entire thing, all those crazy tubes in, out, pressure, volume, what? The whole point was gas exchange. There is external respiration. And external respiration is when you have gas exchange between the alveoli to the capillaries. This gas is exchanged between the alveoli and the capillaries, and I'm actually following oxygen here. Oxygen goes from the alveoli into capillaries. What do capillaries do with their freshly oxygenated blood? They take it to your body cells. And while external respiration is the form of gas exchange that we were just talking about that relates to the lungs, you have to also have internal respiration. And internal respiration happens when the capillary exchanges with the cells, so the oxygen actually travels into the cell. That's oxygen. That's internal. Oh, look, I wrote it down already. And the final one, the final one that hopefully you all like, oh, there's one more respiration. Write cellular respiration. What is cellular respiration? That's just using glucose. Okay, I got to write the whole thing down and I'm writing it in a new color because cellular respiration might be one of my favorite things ever. C6H12O6 glucose plus oxygen in your what? So all this is happening in your mitochondria in your cells. So internal respiration had to happen to get you some oxygen so that you could use it with your glucose. And you needed your digestive system to get you the sugar. And then magic happens. Magic that we actually understand, which is so cool, happens inside the mitochondria. And we end up with carbon dioxide and water. And what else? ATP. What is ATP? Dudes of all dudes. It's energy. That's basically money in your cells to do work. And I'm functioning right now because I have a whole lot of ATP, a shocking amount of ATP really because for a change I haven't gotten much sleep. All right, what? Is it true story? We just did the respiratory system. And now you are going to take an exam unless you're a YouTube student in which case you don't have to take my exam. And that might make you happy. All right, bye-bye. Quit smoking.