[BLANK_AUDIO] Welcome to week four of Vital Signs. This week we're going to be thinking about body temperature. How body temperature is regulated? How we assess body temperature? And what happens when your body temperature falls outside of the normal range? We're building on a foundation that was established last week when we thought about metabolism. And how your body's metabolic rate rises and falls with the level of physical activity which you're performing. Metabolic rate, as you know, is actually a measure of all of the chemical reactions that are going on in your body at any given time. And when we think about the body's metabolism, one of the factors that we know, is that there are certain organs that have a higher continuous rate of metabolism, than do others. Specifically, the organs that are continuously metabolizing at a fairly constant and relatively high rate. Our organs that are present in what we think of as the body core. Which organs do you think of when you think of when I talk about the body core? >> Your heart? >> Your heart is in the core, for sure. What else Warren? >> Your stomach? >> Your stomach. Not so much, because of course you're going to have more activity in your stomach when you are digesting food than, than when you are waiting for the next meal. So what also might be in this area. Lydia. >> Your brain. >> Your brain is definitely one. So brain, heart. >> Lungs. >> Lungs kind of. When I think of though, the next, the next organs, brain, heart. Liver and kidneys are always metabolizing at a fairly constant background level, helping to create a sustained resting metabolic rate. So even if you're resting, or doing anything your liver, your heart, your brain, your kidneys are all still doing their work and creating metabolic heat. So, when you are resting, generally your skeletal muscles are not contributing much to your metabolic rate. And your skeletal muscles actually make up that at least half. Typically, at least half of your body mass. And so they can, if they become active, they can contribute significantly to your metabolic rate. And so what did we see, when Stephanie was doing the step test in the metabolic assessment last week? We saw her MET level go up, right? And her MET level going up reflected the fact that more heat production was occurring in her body. If our cells were one hundred percent efficient they would capture all of the energy that's released during fuel oxidation, and they would package all of that energy as ATP energy. However, the cells are not 100% efficient and so some of the energy that's wrapped up in our macromolecules, it's released as heat. And, that's a good thing. Because, it helps us maintain our body's temperature. So often, when people talk about the core temperature, they refer to it as being 37 degrees c. That's a normal core temperature. But, in reality, the core temperature has a normal range there's no single temperature that's normal. And the range can vary somewhere between 35.8 and 38.2 degrees C. Now, having said that I'll also say that whats a normal core temperature for me may not be a normal core temperature for Lydia, or Laura, or Ryan. Core temperatures can vary, within that normal range and its not very remarkable. Within each individual, core temperature fluctuates on a, on a regular and predictable basis over a 24 hour period. We expect that your core temperature will be lowest early in the morning, just about the time you're waking up. And then it will be at its highest in the 24 hour period in the late afternoon or early evening. So there are variations that are perfectly normal and acceptable. And, we have physiologic mechanisms that allow us to maintain our temperature within that normal range and that's really useful. Now, why do we have to maintain that normal range of body temperatures? What's the benefit to us? Any, ideas about why it's important? Lauren? >> Don't like enzymes in our body only function at like a certain temperature? >> Exactly. There are optimal temperatures for enzyme activity. And that normal range of body temperature is optimal for the enzymes in our body. So if we have a lower than normal body temperature, or a higher than normal body temperature, and sustain it, especially sustain it, for too long of a period, then those enzymes can be deactivated. And even their molecular structure can be changed so much that they can't function at all. And so we maintain our body temperature, so that our metabolism can continue to work optimally. Okay? So, we talk about the body core, and we maintain a fairly constant temperature there. All of the more surface tissues in the body constitute what we call the shell of the body. The shell of the body can fluctuate more temperature wise. You may have touched somebody's skin, maybe you shook their hand and you notice wow, they have cold hands, you know. Or wow, their hands are really warm. The shell can fluctuate in temperature and it does fluctuate in temperature based on atmosphere, the environment that's surrounding us, and based on our own body's metabolic rate. So the shell is kind of the intermediary between the core and the environment, and so fluctuations are going to reflect what the body is doing to help us maintain our normal core temperature, okay? So it's the blood that's the mechanism for heat transfer in the body. And if you can imagine what happens as blood flows through organs and the body core. They're metabolizing at a fairly high and constant rate, blood's going to pick up heat. And then when that blood circulates out to places that are away from the body core, closer to the body surface, or maybe in your upper and lower extremities. The blood is going to carry heat into those areas that aren't very metabolically active, right? Okay. So, what's going to happen then? We are always going to be exchanging heat with the outside environment, and that exchange will happen across the shell. And I think if you look at the picture that we have open in front of us, you'll be able to start using this picture to think about the avenues for that exchange between the environment and the body. When we think about how does heat get transferred from one, from either the body to the environment or from the environment to the body. [BLANK_AUDIO] So looking at the picture, what can you hypothesize? [BLANK_AUDIO] Lydia. >> They're sitting in a hot tub, so their body's are probably gaining heat from the hot water. >> Exactly. So we see someone sitting in a hot tub. This could happen if you were, like hiking in the wilderness and come on a hot spring too and you jump in to like, kind of soak your sore feet, right? So you're sitting in a body of water that's hotter than you are, right? The water is transferring heat to the body, correct? Okay. That kind of transfer; what do you think we call that kind of transfer? [BLANK_AUDIO] Because we're talking about the water transferring it right to the body directly, Lauren? >> conduction. >> Yes, now that is conduction. And when we think about conduction, what we have to keep in mind is that heat will transfer from the hotter to the cooler object. Right? So the water is hotter, body is cooler. And the objects have to be in direct contact. Okay? So the part of the body that's submerged in the water is going to be taking on heat through conduction. What about the part of the body that's exposed and out of the water? Is it picking up any heat? [BLANK_AUDIO] Lauren. >> well, if the body's, like, hotter than the outside air, wouldn't it be losing heat? >> It really depends, right? Exactly. So, maybe the water is so hot that it's warmed the air around the part of the body that's exposed to the air. And in that case, transfer of energy would always be from the hotter air to the exposed body surface, right? But what if the air is cooler? Then like Lauren said the transfer of heat will go from the exposed skin to the air. Right? Now that kind of heat transfer when were just thinking about transfer from the exposed part of the body to the surrounding air, what do we call that? [BLANK_AUDIO] Yeah? >> Is it radiation. >> It's radiation, right. And, you know, based on this picture it's really hard to tell which way the heat transfer is happening in this situation. Right? Okay, so how else could heat be being transferred? [BLANK_AUDIO] I don't know if you've ever heard this, but people say that if you fall into a body of very cold water. It's better if you make your body surface as small as possible. So you tuck in and you try not to move around a lot. Because if you move around a lot and create little currents of water movement around your body, you will lose more heat to the cold water. Right? And that's because the water that's directly in touch with your surface of your skin, that water is going to be heated by your body. And then when you move, you're going to move more water in by the body surface, which has to be heated. Right? And so if you thrash around in this cold water, you'll be losing more heat than if you try to keep your body surface small and move, the least amount possible. I hope you have a life vest on, if you fall into the very cold water. So in this situation, with that body that's submerged underwater. We can expect that even if the water is moving, she's not going to be losing heat because it's hot water, right? But when a moving fluid moves past the body surface, if that fluid, either air or water, is colder than the body surface, we lose heat by convection. Okay? Have you ever experienced this yourself. You're outside, it's a cold, blistery windy day. Lydia, what happens? >> If a big breeze blows you all of a sudden, you feel a lot colder. >> Yes. Exactly and in fact, weather forecasters in our area will report the temperature as recorded on a thermometer, but they will also report the windchill, meaning how cold does it feel, based on how strong that cold wind is blowing, right? So that's heat gain or heat loss through convection. And again heat is going to transfer from the warmer to the colder fluid and we really are most concerned about it when our body loses heat to the surrounding fluids through convection. And what other type of heat transfer could be happening in this situation where we have someone soaking in the hot tub. [BLANK_AUDIO] Lydie Steph, I'm sorry. >> Maybe if they, had their hand in the water and they took it out and a breeze came, it would make them feel like colder. >> Yeah, so it, again, that yes [CROSSTALK], oh, and so what's, what do we call that? >> Mechanism. >> Evaporation. >> Evaporation. So, when there's some kind of liquid on the body's surface, and that liquid vaporizes becomes water vapor. That process is evaporation. And, it actually requires heat to vaporize water. Right? So, when she brought her hand out of the water and she had water droplets on her skin and the wind evaporated them, there was a loss of heat from the body associated with that. It's important I think for you to remember that when we usually think of sweating as a mechanism through which we can lose heat from the body. Sweating itself doesn't cause heat loss. It's the evaporation of the sweat that causes the heat loss, right? So, again, if the humidity in the outside air is really high and we can't evaporate our sweat. We can sweat a lot, but still not feel much cooler, right? And so that phenomenon gave rise to another concept that we hear about, which is the heat index. The temperature as recorded by a thermometer, I can say one thing, but of the humidity in the atmosphere is too high and we can't evaporate our sweat properly. We may feel much hotter than the temperature on, on the thermometer would indicate. Sweating is part of a heat loss mechanism, we call sensible heat loss. Do you have any idea, Brian, why we would call it sensible heat loss? >> Is it because we can sense that it is happening? We, we know that it is happening when we're sweating. We're aware that we're sweating, we're aware that there's some sort of evaporation. >> Exactly, you can feel the sweat on your body, so you can sense it and we refer to it as sensible heat loss. There's also another kind of evaporation that occurs. And it results in insensible heat loss. Now what goes on in insensible heat loss? Lydia. >> Maybe you're losing heat, but you're just aren't aware of it. >> Exactly. Exactly. So the place where this can happen is in your airways as you inhale and exhale. And air is moving in and out of your airways. The air that's coming in often has less water vapor in it than the air that's deep in your lungs. And so as the air moves in, your airways give off heat and vaporize water, so that the air that reaches the lungs has a significant water content. And we're not aware of that heat loss happening, we can sometimes experience a little bit of a sensation if we're outside in really, really cold temperatures. And we breathe through our mouth, we can sometimes say that feels really cold. But normally we are not aware of heat transfer that occurs across the the surface of the airways, but we do lose a teeny tiny bit of heat through that mechanism. [BLANK_AUDIO]
