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Thermoregulation mechanisms

Why do we shiver when it's cold? How do our muscles make sure we don't freeze or have a heat stroke? Learn how the skin, brain, blood vessels, and muscles work together to maintain our core body temperature.  By Raja Narayan. Created by Raja Narayan.

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  • mr pants teal style avatar for user Gio
    6-fingered hand...?? I'm confused. And what happens to the skeletal muscle when the external temperature is high? relax?
    (20 votes)
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  • blobby green style avatar for user aravind
    Is radiation(heat loss) in hot environment is only due to energy produced from reactions taking(clashing of components) within blood ?
    (3 votes)
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    • leaf red style avatar for user Ijoni Lisha
      Actually radiation has nothing to do with the clashing of components within blood. Radiation is the loss of energy due to eletromagnetic waves produced from all bodies in normal condition. In hot temperature radiation plays little role in the cooling process, as does convection(air gasped in and out) and conduction(due to thermal movement of particles). What plays the major role is sweat release. For evaporation of sweat it is required a giant amount of energy(water has high specific heat), energy that is taken from our body, thus leaving it cooler in the process.
      (6 votes)
  • leaf green style avatar for user surianojulio
    How would temperature affect cardiac output as a result of vaso-constriction or vaso-dilation in an athlete such as an American Football player (i.e. wide receiver)? Most professional athletes have high stroke volume so even at a low heart rate a large amount of blood is sent to the body, but I'm wondering if temperature is significant or when does it become significant enough to see performance effects?
    (7 votes)
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  • mr pink red style avatar for user Sydney
    he didn't mention skeletal muscle when it's hot? Does it also vasodilate like smooth muscle?
    (2 votes)
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  • starky ultimate style avatar for user Dhrutisundar Sahoo
    Well, I understood very well about why we do shiver in cold environments. My question is, when we do physical exercises in cold environments, there is vasodilation, more of heat is produced, blood circulation increases and as a result we sweat. But when we have fever, our internal body temperature rises due to increased blood circulation(vaso-dilation) so as to kill the pathogens. But in this case we shiver and do not sweat! Why does this happen?
    (2 votes)
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    • duskpin ultimate style avatar for user Alberto
      I'm no doctor, so take my response with a grain of salt. This is how I interpret things:
      If our body raises its internal temperature via vasodilation in order to attack a pathogen, then it follows that if it wants to keep raising that temperature it will shiver and prevent sweating because it wants to raise its internal temperature even more.
      (5 votes)
  • mr pants teal style avatar for user Wrath Of Academy
    What's the common name for vasodilation in response to heat?
    (2 votes)
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    • leaf blue style avatar for user eira
      Well, I think in our day-to-day lives most of us do not think about the vasodilation that occurs when it is hot around us. Instead we pay attention to the sweating. Even if the purpose of sweating is the same, to get rid of excess body heat, it is a separate process from the vasodilation. Still I think we might commonly be talking about sweating at times where vasodilation is involved, because both the vasodialtion and the sweating is happening at the same time.

      Just a thought on my part :)
      (2 votes)
  • female robot amelia style avatar for user Irma Vazquez
    What accounts for the variance in how individuals respond to hot or cold temps? Why are our tolerance levels of either hot or cold in climate so variable?
    (3 votes)
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  • starky tree style avatar for user Elijah
    is there a reason the guy has six fingers
    (1 vote)
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  • old spice man green style avatar for user Jeet Kaur
    Does vasodilation or vasoconstriction apply to only arterioles/arteries? What about venules/veins? Just curious. The overall definition of vasoconstriction and vasodilation applies to blood vessels. But perhaps arterioles/arteries contributes MORE to controlling heat temperature? Any one?
    (1 vote)
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    • aqualine ultimate style avatar for user Anastasia
      The process of vasodilation of arterioles in more important in losing heat than of say, venules, because arterioles control capillaries. When arterioles vasoliate, they increase blood flow to capillaries in the skin close to the surface, and this is the main site of heat escaping the body. There was a video in the Circulatory system section of this site that explained that capillaries work like windows of the house letting the heat out, while skin is a kind of the thermal insulation of the house. This is the link to the video:

      Thus, because arterioles control the blood flow in the capillary beds, their vasoconstriction or vasodilation of plays major role in theormoregulation. Moreover, veins and venules don't have such a big and strong layer of smooth muscle in their tunica media to be able change their lumen size as significantly as arteries and arterioles.
      (4 votes)
  • purple pi pink style avatar for user wildwind7
    Haha, it's funny that the hand accidentally got drawn with six fingers.
    (2 votes)
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Video transcript

Why do we shiver when it's cold? What do the five fingers say to the face? In this video, we'll talk about how our body uses our muscles to maintain a core body temperature. That process is called thermal regulation, the regulation of body temperature. So in order to do that, I'll first give you guys an overview of how thermal regulation works. Next, we'll talk about how our bodies respond to hot temperatures, before finally talking about how our bodies respond to cold temperatures. So first, if we have this gentleman right here, who doesn't look very impressed. And he's holding his hand up one day and notices it's really hot outside. That looks really hot. So the skin on his hand and his arm, the rest of his body, will perceive that it's really warm. And in doing so, this will create a neuronal signal, a signal that's sent across neurons, up into the brain. And the part of the brain that perceives that it's really warm outside has a specific name. It's called the hypothalamus. And in fact, we split up the hypothalamus into two different parts to respond to two different types of temperature. There's the anterior hypothalamus, which just means the front of the hypothalamus. And then there's also the posterior hypothalamus. And that's just the back of the hypothalamus. But which one responds to what kind of temperature? Well, the way I remember it is that if it's hot outside, we like to use the front of our hypothalamus or the anterior part of our hypothalamus to respond to temperatures that make it feel like we're on fire. So if we're on fire, we're going to use the front of our hypothalamus to respond. Well, what if it's cold? In those situations, we'll use the posterior part, or the back of our hypothalamus, to respond to climates that make us say, brr. We say brr because it's really cold outside. So we use the back of our hypothalamus. OK. So that all sounds good. But what happens after our brain knows that it's really hot outside? Well, then it sends back a signal to our bodies telling it to respond, to maintain our core body temperature. And of all things to take point from here and act, it's going to be muscles in our body that will do something to make sure we can maintain our core body temperature. That'll involve smooth muscle. And when it's cold, we also use skeletal muscle to respond to changing temperature. So how does that work? Let's take a look. When we're in a hot or a cold environment, how do muscle help us respond here? Well, the way to talk about this is to go through the two main types of muscle that will act here. First, there's smooth muscle. Specifically, it's smooth muscle that lines our arterioles. Now, arterioles are just smaller versions of our arteries, arterioles. The other type of muscle that functions here is called skeletal muscle. And that's the type of muscle that works in your biceps, your triceps, all right. Now, let's answer this question here. Why do you think arterioles have anything to do with temperature? I mean how does that change whether we have a lot of heat in our body or not? Well, the way that works is that if you take a look at a blood vessel-- and I'll just draw a small one right here-- it's got a bunch of red blood cells, and white blood cells, and proteins, and whatnot. All of this is just kind of running around through the bloodstream. And the way it does that is just kind of in a random sort of motion or manner. It's never directly forward. But it's just kind of bumps around like that and moves this way. So overall, you've got a general movement in the forward direction. But you kind of are bumping around to do this. And the interesting thing is this movement here, this momentum that your red blood cells, white blood cells, or whatever you have in your bloodstream make, that's energy. So we have a ton of energy in our bloodstream. And energy is just another form of heat. So if we are in a hot environment, we want to get rid of this heat. So we're going to put more heat to our most superficial or the most external parts of our body, our skin. So the more blood flow we get to our skin, the more heat we can have leave our bodies. And that's how we get to regulate our temperature. So let's talk about it here. When it's hot, our smooth muscle then is going to relax. And in doing so, the arterioles then are going to become wider or larger. And this process is called vasodilation. Your arterioles are dilating. They're becoming wider. And so the way you could see that happen is that this blood vessel that was about yay big, is now going to become that big in the skin. And so that means that you're going to have a lot more blood flow going in here to the skin. You're going to have tons of red and white blood vessels and protein just kind of merrily tumbling about, going like this. That means you're going to have a ton more heat or energy that's present here, that can then dissipate and leave. And so that helps you cool off. You're losing all of this energy or this heat that you have by diverting blood flow to your skin. Now, what does skeletal muscle do here? They don't do anything when it's hot. They'll respond in a second-- and we'll talk about that-- when it gets cold. What do smooth muscle do when we're in the cold? Well, you can imagine that if we relaxed when it was hot, it's fair to think that we're going to contract when it's cold. And so this process then in the arterioles is going to be called vasoconstriction, which just means the narrowing of our arterioles. And so if I were to draw that on a diagram right here, you would see that this blood vessel, that looked like this in our normal state, is now going to turn into something more like that, kind of a pipsqueak, really tiny. So you're going to have red blood cells, white blood cells, and protein just kind of shifting through here like this. But there's not a lot of opportunity to kind of tumble around and be naughty. They just got to go forward. They can only go in one direction because there's not a lot of space here for blood flow. And so in the skin, you're going to have less energy or less heat that's present at this very external or superficial part of your body. The more blood that you have that gets away from the skin, the more that's going to go towards your core. Your core will then have more energy or more heat to help you stay warm when it's cold outside. So that's what your smooth muscle does. What do skeletal muscle do? Well, skeletal muscle will also contract when it's cold. But there's a very different purpose for why that happens. When skeletal muscle contracts, it's going to take ATP, or adenosine tri-- or three-- phosphate and break that to make adenosine diphosphate, ADP. So that's two phosphates. And we just snapped off a little phosphate group. I'll write an "I" here to show that it just snapped off. But these aren't the only two things that are made. You actually will produce energy as well. And we call this reaction an exothermic reaction, "exo" meaning exiting or the leaving of. "Thermo" or "thermic" meaning heat or energy. And so we're actually producing energy here by contracting our skeletal muscle. This happens in our core muscle groups that cause more of the heat that's being produced from this reaction to be stored there, to help us respond to these cold environments. Now, this isn't such an unusual process that's so foreign to us. The contraction of our core skeletal muscle groups is actually just called shivering. This is the whole reason why we shiver when it's cold. Because we need to produce some energy by breaking off some phosphate from this ATP. And that shivering then will help us warm up when we're in the cold. And that's how our muscles help us respond to temperature change.