 Fever is a non-specific response that is what initiated by cytokines except a specific kind of cytokine. Can you follow that? You have all different kinds of cytokines, but the specific one that causes fever is called a pyrogen. So if you are getting a fever, because you've had some sort of immune reaction and your body has produced a chemical that acts as a pyrogen. So the cytokine is a pyrogen and that's going to cause a fever. So the question is, first of all, why? Why would you do this? Well, interestingly, some of your white blood cells function better at a little bit higher temperature. You know that your normal body temperature, homeostatic body temperature is about 98.6 degrees Fahrenheit. And that's, like, totally about. Like, there's a big homeostatic range to 99 and that's all in homeostatic range. But if that is actually maintained by the hypothalamus, hypothalamus, hypothalamus, a ton, the hypothalamus, remember, was in your brain. So essentially, the hypothalamus sends that if the temperature drops below, if your body temperature, if your core body temperature drops below 98.6-ish, then the hypothalamus is going to send out a message, dude, we need to increase body temperature. How are we going to do that? Well, you can start shivering with some clothes on. That's awesome. There will be strategies to increase your body temperature. And until it gets back to its homeostatic range and then the hypothalamus is... Body temperature goes higher than the homeostatic range. Then the hypothalamus is going to say, hey, let's initiate vasodilation in the skin. Let's cool off the blood by having vasodilation take place. Let's sweat. Let's sweat because sweating can sweating. Sweating cools you down. The water evaporates and pulls the heat away from your skin, takes the heat with it in order to evaporate so that you end up cooling down. The hypothalamus says, okay, cool, we're back to normal again. So some white blood cells, sometimes your white blood cells function better at a higher temperature. So there actually are advantages of fever. Disadvantages, obviously you feel like crap. When you have a fever, but what's happening? Cytokines pyrogens reset the thermostat. They reset what is normal. So what felt like normal at 98.6, your body said, okay, we're going to maintain it here. The normal range. And now normal is like what, 102. Oops, not 120. That'd be all bad. 102 is just an example. So now the hypothalamus says, if the body temperature is not 102, we're cold. That's why you get the shivery shakes. What is that called when you get the shivery shakes when you have a fever? I can't remember, it has a name. But you can call it the shivery shakes if you want. The shivery shakes are, I mean, that's just shivering. And so you're just increasing muscle activity, which is producing heat as a byproduct. It's going to happen until you get up to 102. If you go higher than 102, your body's going to be like, oh, it's too hot, man, whoa, we need to cool it down. You're going to get flushed, you're going to start sweating. Chills, that's what it's called when you have, when your body temperature, but your body temperature is actually high, but you feel cold. You get yourself all covered up in all your blankets and you're all cuddly and sad because the Deng pyrogens have reset your thermostat for a higher set point. All right, dude, what? Oh, look at this, another advantage of the fever is that sometimes the higher temperature is inhibitory to bacterial invaders. So they don't do quite as well in that hot, hot-er temperature, which makes it advantageous to make ourselves into a little furnace zone so we can blast out the bad guys. Next up is the acquired immune response, which holy Facebook platform. So relax, study this all up and then have fun in the acquired immune system.