 Hey everybody, Dr. O here. Let's talk about thermal regulation. So first, as you can see, this is an example of a negative feedback because our body has a set point that it wants to maintain. It says here 36.5 to 37.5 degrees Celsius. That'd be in the neighborhood of 97.7 to 99.5 degrees Fahrenheit. So if there's a change, our body wants to restore homeostasis to bring us back to normal and that's why it's an example of negative feedback. And a note before we jump in is that remember that 60% of the energy produced by your metabolism is heat. So we have a lot of heat that we have to deal with. But at the same time, we as a species can maintain a core body temperature, whether we're at 20 degrees below zero or 110 degrees above zero. So we have these thermal regulation processes that allow that. Let's go ahead and look at the two examples here. What happens when our body temperature goes down or up? So on the top, it shows snowflakes, it's cold, your body temperature goes down. The thermostat and your hypothalamus that maintains homeostasis doesn't like that. So it's going to kick in the mechanisms that are going to bring your body temperature up. So the first one it shows here is your blood vessels. Superficial arteries of the skin are going to be constricted. So your skin's going to look pale because you don't want, remember, your blood is warmer than the rest of your body. It's 100.4 degrees. We don't want your warm blood going to the surface to lose heat through radiation. So you're going to decrease the blood flow to the skin. You're also going to decrease the blood flow to the digestive system because there's a huge surface area in there as well. So you don't want to be losing heat into your gut or out into the environment. So that's why you're going to see the constriction of these superficial blood vessels. You want your warm blood staying at your core, keeping your liver and the rest of your core temperature normal or elevated. Then you see shivering. So shivering is going to be muscle contraction, which is going to require energy. So shivering is going to increase the amount of your metabolism that's going to generate heat as a byproduct. And then the last one there, you see the thyroid gland is going to release more thyroid hormones to increase metabolic heat production. All those things should bring your body temperature back up and you should be fine. Now, if you can't get out of the, obviously getting out of the cold is the best thing to do. If you can't do that, then certainly this system can fail at some point and you can develop hypothermia. On the flip side, point number five there, if it's hot out and your body temperature gets high, the hypothalamus will not like that either. And it's going to do it again to bring your temperature down. It's going to dilate superficial arteries. You want more blood flowing, more blood flowing to your skin and your gut because those two huge surface areas are a great way to lose heat, but the skin being most important. That warm blood rushes to your skin and radiates off heat. And on top of that, the second point there, sweating is going to be initiated. So now, not only are you going to be radiating heat or maybe if you find a nice breeze or use a fan, you'll be getting rid of heat from convection. But you also will be getting rid of heat now from sweat of aberration. And remember that sweat of aberration is dependent on humidity. If it's very humid out, sweat of aberration is not going to work very much. It doesn't mean you won't sweat. You're going to sweat a ton, but it won't be very effective or productive sweat. And third, the thyroid's going to do the opposite. The thyroid's going to turn itself down to try to decrease metabolic heat production. And in the end, that's to bring your temperature back to normal. If you're in a situation where you can't get out of the heat and you stay real hot, that can certainly lead to heat-based illness. And if you've sweat so much and you're so dehydrated that you can't sweat anymore so your skin gets real hot and dry, that can certainly lead to heat stroke. And remember, humidity is a key player there. So dress warmly if you're going to go outside when it's cold. Stay hydrated if you're going to go outside when it's hot. And keep yourself safe. One last thing to note here is there is something called cold thermogenesis. I think you can guess that as you get cold. You see two reasons why your metabolism goes up between the shivering and the metabolic changes. This is why some people do like cold plunges or they sit in ice baths. They're actually trying to stimulate their metabolism by making themselves cold. It's usually called non-shivering thermogenesis because they're not trying to get so cold they shiver because that can lead to dangerous hypothermia. But there are people that do that. Now, if that works, and I think it probably does, but I don't know if it's worth the time and effort. But if it does, it would probably lead to an increase in brown fat being used. So remember, you have two types of fat. Your white adipose tissue is stored energy. You can store somewhere in the ballpark of 3,500 calories and a pound of it. Brown fat's different. It has these uncoupling proteins in it, which means it's basically just burned for heat. The analogy I use with brown fat is lights. 99% of the energy released by a light is in the form of heat. Only 1% of it is doing the job we needed to, which is to light up the room. So brown fat is like that. It can kind of waste energy and it will also increase your heat. So if you have more brown fat and you're getting cold, you should be able to burn energy and release it as heat to bring your temperature back up. So it's kind of interesting there. All right, I hope this helps. Have a wonderful day. Be blessed.