View Full Version : Body Heat....How does it work?

Salmo Trutta
09-29-2003, 02:13 AM
I feel like this question should have, and probably has been addressed, but I didn't find it. Either way I'll ask.

Where does body heat come from? Is is a molecular or cellular function? I would imagine it has to be a chemical reaction of some kind, but what chemicals? Probably from food sources, but what if I do not consume those chemicals? By necessity I would imagine the chemical reaction would use convert common elements (carbon, oxygen, etc) in a simple way to generate ambiant heat. (Anything to be learned about cheap non-polluting energy production?)

I know that it is possible to over stimulate that heating function (Like when you get a fever). But what regulates the 98 degree general temperature? A thermometer type mechanism.

Overall the whole heat thing baffles me.

Any insight?

09-29-2003, 02:27 AM
Almost all the body's systems produce some heat. The major source of heat, though is muscular movement. In warm-blooded animals, that source is used constantly, and other systems, such as sweat, and respiration, are balanced with it, to maintain a constant temperature, generally somewhat higher than the environment.

Shivering is the best example for you to consider. You shiver when you are cold. Shivering is simply the result of having the body's heat engine turned up to "high." Even when you are hot, and in an environment warmer than your body, the same engine is working, although at a much lower amplitude. The engine runs on a special neural signal, which tenses the muscles of the body slightly, and then stops. It does so very rapidly, and usually very gently.

It is also this same neural signal which maintains "muscle tone." In some people, the neural signal is generated much too strongly, and this results in spasticity. In extreme cases, this causes the body to be held rigid all the time and spastic paralysis results. It can be a disabling and sometimes fatal condition. The opposite, although rare, is also disabling in its extreme, causing weakness of the entire body, and a general lack of muscle tone which exercise can only mitigate.

For normal people, the only time they are aware of this constant movement of muscles is when they have shivers, or occasional twitches.


Salmo Trutta
09-29-2003, 02:40 AM
Thank you for your reply, but I'm not sure it quite answers my question.

Yes tensing ones muscles will cause heat. (I get hot when I run, I sweat to cool down.) But how. Your reply makes it sound perhaps like a product of friction. Muscles tensing causes some sort of friction and subsequently heat.

So do cold-blooded animals not have this constant nueral signal? (that would make sense as to why many reptiles can go for weeks or months without eating. (a more efficient use of fuel)

Am I right in assuming this is a product of friction, or does this neural signal cause an electro-chemical reaction that heats?

09-29-2003, 02:52 AM
The movement of muscles requires chemical energy, and the conversion of that energy into tension in the muscle produces heat as a by product. Glucose is used and oxidized within the cells. That produces heat.

How much heat? Take a soda cracker, and light it on fire in a well ventilated container, such as a tin can with lots of holes punched in it. (outdoors) You will find that the calories in a soda cracker represent rather a large amount of heat.


09-29-2003, 04:13 AM
From this thread (http://boards.academicpursuits.us/sdmb/showthread.php?s=&threadid=117206):A person using 2500 Calories (Kcal) a day puts out 2500/24 = 104 Kcal/hour
104Kcal/hour X 3.98 Btu/Kcal = 414.5 Btu/hour That's about the same heat output as a candle. The primary energy releasing reaction in a cell is ATP hydrolysis, i.e. ATP-> ADP + Pi + energy. In many mammals there are distinct fat deposits which are reponsible for most of the heat output. Called brown fat, because it is brown, these tissues contain large numbers of mitochondria whose job it is to generate heat. Humans do not have brown fat. Body heat generation in humans is thought to take place throughout the body, through the action of the cell membrane associated sodium potassium ATPase. Last I checked on this literature, it was still rather tentative. Perhaps someone has recently worked out a more detailed mechanism for human non-shivering thermogenesis ?

09-29-2003, 08:13 AM
glucose + oxygen ---> cabon dioxide + water
through a fairly complex series of reaction and produces ~36 new ATP molecules for every glucose molecule oxidised.

About half the energy from the glucose is trapped in this electrochemical process. The rest is lost to heat energy (leading to increased temperature) and entropy (incresed mixed upness of stuff).

The free energy content of a mole of glucose is ~ 686 kcal. The energy obtained froim the hydrolysis of ATP->ADP is about 7.3 kcal. So if you get 36 moles of ATP from one mole of glucose then (36x7.3)/686=~40% efficiency. The rest is lost as heat.

It is like the waste heat from an internal combustion engine. This has to be removed with a heat exchanger (radiator). Animal have to develop clever ways to use or get rid of this heat.

Chicago Faucet
09-29-2003, 09:35 AM

I was just coming to this board to post this very same question. I always thought that body heat came from billions of friction points in our bodies: blood cells against the walls of the arteries, tendons cells against bone cells, muscle cells against skin cells, etc.

It appears that body heat is mostly chemical, according to the above posts.

Enola Straight
09-29-2003, 09:45 AM
I think what he's asking is how the body knows how to maintain precicely 98.6 deg. F.

Uncommon Sense
09-29-2003, 10:53 AM
The 98.6 deg.F. is a function of all of the chemical reactions and friction.
There is a lot of heat given off by the internal organs such as the heart, liver, and also the digestive track as it breaks down the food we eat. The vascular system helps regulate the overall body temp by channelling heat from the internals to the extremeties. All of these systems together produce the 98.6 degrees in a healthy adult.

Uncommon Sense
09-29-2003, 10:58 AM
The 98.6 deg.F. is a function of all of the chemical reactions and friction.
There is a lot of heat given off by the internal organs such as the heart, liver, and also the digestive track as it breaks down the food we eat. The vascular system helps regulate the overall body temp by channelling heat from the internals to the extremeties. All of these systems together produce the 98.6 degrees in a healthy adult.

09-29-2003, 11:01 AM
Ask this guy: http://napa.ufl.edu/2003news/bodytemp.htm

Thudlow Boink
09-29-2003, 11:05 AM
Nitpick: "precisely 98.6 degrees" may not be precisely the right number (see this thread (http://boards.academicpursuits.us/sdmb/showthread.php?threadid=196338)).

09-29-2003, 05:04 PM
Your body (and the body of pretty much any other living thing) basically burns food, in the same general way as a bonfire, candle or gasoline engine -- taking a complex molecule with carbon, oxygen and hydrogren and breaking it down with more oxygen to get carbon dioxide and water and energy (heat). Your body (just like a gasoline engine) diverts some of the energy to move its muscles, build up other big molecules and other things, but most of the energy still turns into heat. Just like in a car engine, friction does create some heat, but mostly it's the unused heat from the oxidation reaction.
This 'burning' takes place in every single cell in your body, so heat is produced everywhere, all the time. Cells that are working harder (muscle cells while you're running and so on) need to burn fuel more quickly, so they end up with more waste heat.
So you could I guess stop eating the things that power your body, and you would eventually stop creating heat, at least until decomposition set in. But you wouldn't be around to notice.

The human body has a thermostat that decides when it's getting too hot or too cold, and makes the body do lots of different things to get back to the right temperature, including sweating, shivering, reducing or increasing blood flow to outlying areas where it will lose more heat, and telling your concious mind that you're cold and it might be a good idea to put on a sweater.

A fever is your body deciding that it's got an infection, and while turning up the temp a little bit is going to make the body's cells unhappy, the higher heat is going to make the nasty infecting bacteria even more unhappy. So it just sets the same thermostat to a slightly higher temperature. Kind of like turning down the heat in your apartment in order to encourage the friend staying on your couch to move on already - it bothers you, but you hope it bothers them more. Once they're out, you put the heat back to a comfy level.

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