View Full Version : Body temperature.


John99
11-21-08, 05:34 PM
How does the human body maintain approximately 98.6F?

It is easy to see how temperature can come down but where does the heat come from when ambient temp is much lower?

What is the source of heat in humans? I know about differences between warm blooded and cold blooded. What generates the heat in warm blooded creatures, specifically humans.

John99
11-21-08, 06:33 PM
I assume, perhaps, that the commonly held belief is that food, working as a fuel source, and possibly digestive processes generates heat but is that true? I dont think so.

John99
11-21-08, 06:59 PM
13 people viewed this and no one has an explanation?

madanthonywayne
11-21-08, 08:57 PM
How does the human body maintain approximately 98.6F?

It is easy to see how temperature can come down but where does the heat come from when ambient temp is much lower?

What is the source of heat in humans? I know about differences between warm blooded and cold blooded. What generates the heat in warm blooded creatures, specifically humans.
Our body is only about 20% efficient, so 80% of the calories we use go towards generating heat. Usually, this heat is simply waste, but when it's cold outside our body attempts to keep more of this heat by constricting peripheral blood vessels, "goose bumps" (intended to fluff up fur to hold more heat), and shivering which increases your metabolic rate from a base for a sitting person of 50 Cal/m 2 hr to about 250 Cal/m 2 hr.

Read-Only
11-21-08, 09:40 PM
13 people viewed this and no one has an explanation?

I haven't seen it until just now.

The first method is simply to increase the rate of metabolism (besides reducing perspiration, which is the actual first). The second is to reduce the amount of blood flowing near the skin. And if the temp drops too much, involuntary shivering starts.

John99
11-22-08, 05:23 AM
All the information we can obtain the better. I am asking specifically about the heat source whereas the methods of maintaining body, temperature is interesting albeit secondary.

For reference think of a wood stove.

http://www.northerntool.com/images/product/images/172892_lg.jpg

The stove is cold and it just exists. You take a few pieces of wood and you throw it into the hole, arrange it in a way as to facilitate combustion, specifically in a way as to maintain combustion for the usable lifetime of the wood.

Once the fire begins you feel the stove gradually getting warmer. When the fire is blazing and the apex of heat radiation is achieved the stove becomes
extremely hot. As the supply of fuel is exhausted the stove reflects this in a lowering of temperature.

When a human walks into a room with a temp of 72F the body maintains it's temperature of 98.6F (or around that). If the temperature of the room fluctuated withing a range of 40F the temperature of the human will remain constant.

The human stays in this room (really a small living space) for days and maintains it's temperature even with varying amounts of food intake.

Taken to an extreme the subject will now forgo food intake for a prolonged period of time AND the temperature in the room will remain a constant (consistant) 65F. Of course the first response of the reader will be 'the subject will shiver and maintain it's temperature that way'. Of course, however, that is NOT the question. What I am asking is what physical process produces the 98F body temperature.

John99
11-22-08, 05:31 AM
Here is something i found:

http://hypertextbook.com/facts/LenaWong.shtml

"For decades it was thought that the normal body temperature was 98.6 F. This number was calculated from a study in Germany which reported normal at 37 C. What was not known was that this number was an average rounded to the nearest degree. In other words it was only accurate to two significant digits, not the three we have with 98.6. Scientists today know that normal is actually 98.2 plus or minus 0.6, that is to say anything in the range of 97.6 to 98.8 should be considered normal."

I will continue to add links that may be even more pertinent in relation to my specific question.

Sciencelovah
11-22-08, 05:40 AM
Obviously human (or other animals) can maintain their body temperature because there are heat production inside the human body. You are asking about the heat source? You might be interested with a topic of thermoregulation (http://en.wikipedia.org/wiki/Thermoregulation), which is the ability of an organism to keep its body temperature within certain boundaries, even when temperature surrounding is very different.

The heat is mainly produced by the liver and muscle contractions, but that is not the only heat production process. Any 'mechanical' activity including thinking produce heat. Actually, the heat itself is a heat loss, which is the conversion of mechanical energy spent in activities into heat. The source of energy itself is mainly from food. For example, by consuming carbohydrates you can get 4 calories of energy per gram. So in short the process is more or less:

Food intake ---> food cooking (metabolism) ----> mechanical activity (thinking, breathing, moving, etc) ----> heat loss (preservation of body temperature)

John99
11-22-08, 05:46 AM
Thank you. I will look at the link but do you have an answer?


...can maintain their body temperature because there are heat production inside the human body. You are asking about the heat source? You might be interested with a topic of thermoregulation, which is the ability of an organism to keep its body temperature within certain boundaries, even when temperature surrounding is very different.

What is the heat source? 98F is relatively hot.

John99
11-22-08, 05:51 AM
Let me say that the only organ i can think of that may radiate heat is the heart. Obviously blood alone will not produce heat but acts as a conduit and perhaps a heat exchanger, specifically it flows through the veins while reacing the outermost extremities becoming cooler\colder (losing temperature). This is especially evident in low ambient temperature.

Sciencelovah
11-22-08, 05:55 AM
Thank you. I will look at the link but do you have an answer?


What is the heat source? 98F is relatively hot.


I'm not sure if I can do the calculation, for sure there are other people that can. The conversion of energy content in a food into heat and then into temperature, I mean. To maintain the temperature, we are continuously consume food. The further mechanism to keep the temperature constant itself can be found in that link (but citation is needed):


In hot conditions

1. Sweat glands under the skin secrete sweat (a fluid containing mostly water with some dissolved ions) which travels up the sweat duct, through the sweat pore and onto the surface of the skin. This causes heat loss by evaporation; however, a lot of essential water is lost.
2. The hairs on the skin lie flat, preventing heat from being trapped by the layer of still air between the hairs. This is caused by tiny muscles under the surface of the skin called erector pili muscles relaxing so that their attached hair follicles are not erect. These flat hairs increase the flow of air next to the skin increasing heat loss by convection. When environmental temperature is above core body temperature, sweating is the only physiological way for humans to lose heat.
3. Arterioles Vasodilation occurs, this is the process of relaxation of smooth muscle in arteriole walls allowing increased blood flow through the artery. This redirects blood into the superficial capillaries in the skin increasing heat loss by radiation and conduction.

Note: Most animals can't sweat efficiently. Cats and dogs only have sweat glands on the pads of their feet. Horses and humans are two of the few animals capable of sweating. Many animals pant rather than sweat, this is because the lungs have a large surface area and are highly vascularised. Air is inhaled, cooling the surface of the lungs and is then exhaled losing heat and some water vapour.

In cold conditions

1. Sweat stops being produced.
2. The minute muscles under the surface of the skin called erector pili muscles (attached to an individual hair follicle) contract (piloerection), lifting the hair follicle upright. This makes our hairs stand on end which acts as an insulating layer, trapping heat. This is what also causes goose bumps since humans don't have very much hair and the contracted muscles can easily be seen.
3. Arterioles carrying blood to superficial capillaries under the surface of the skin can shrink (constrict), thereby rerouting blood away from the skin and towards the warmer core of the body. This prevents blood from losing heat to the surroundings and also prevents the core temperature dropping further. This process is called vasoconstriction. It is impossible to prevent all heat loss from the blood, only to reduce it. In extremely cold conditions excessive vasoconstriction leads to numbness and pale skin. Frostbite only occurs when water within the cells begins to freeze, this destroys the cell causing damage.
4. Muscles can also receive messages from the thermo-regulatory center of the brain (the hypothalamus) to cause shivering. This increases heat production as respiration is an exothermic reaction in muscle cells. Shivering is more effective than exercise at producing heat because the animal remains still. This means that less heat is lost to the environment via convection. There are two types of shivering: low intensity and high intensity. During low intensity shivering animals shiver constantly at a low level for months during cold conditions. During high intensity shivering animals shiver violently for a relatively short time. Both processes consume energy although high intensity shivering uses glucose as a fuel source and low intensity tends to use fats. This is why animals store up food in the winter.[citation needed]

It's about my lunch time, btw. Then I have to do something. Later!

John99
11-22-08, 06:03 AM
To maintain the temperature, we are continuously consume food.

That does not seem to be correct. The reason i say this is that assuming food as a fuel source then wouldnt there be a corresponding loss of heat or increase in heat with the amount of food intake?

As i said previously, taken to an extreme and doing without food (fuel) there is no gradual lowering of heat. Even at the point whereas the stomach contains no food.

Read-Only
11-22-08, 06:06 AM
Let me say that the only organ i can think of that may radiate heat is the heart. Obviously blood alone will not produce heat but acts as a conduit and perhaps a heat exchanger, specifically it flows through the veins while reacing the outermost extremities becoming cooler\colder (losing temperature). This is especially evident in low ambient temperature.

I've answered your question COMPLETELY.

John, do you honestly NOT know what the word "metabolism" is and means? If not, read about it in Wikipedia - evidently, you've got a lot to learn about the subject.

Asguard
11-22-08, 06:08 AM
john as read only and mad have said the heat in the body comes in the form of in efficencies in ATP usesage and possable its creation. Futher it heat can be formed from ambient suroundings in the form of ingestion of hot liquids ect. Lastly friction itself in the joints and musles produces heat.

I disagree with Mad that its an unintended process. Rather, regulation of heat is very important for the body. For instance emzimes have a specific temp where they will activate or work to there optium. If this temp isnt maintained the emzimes dont work or (if to high) they denature. This is why the body produces fevers, bacteria are less protected than the cells of the body and there for by boosting the heat the body can denature the protines and emzimes of the invader or even cause them to premiturly activate causing digestion of the bacteria itself. Not the most precise method maybe but a method nun the less.

Further mechanical digestion itself can produce heat from the many chemical reactions which take place in the gut

Lastly the body is full of chemical reactions apart from just ATP construction and use (fuel load for want of a better term), pH reactions for instance produce heat as a bi-product and these happen all the time in our bodies.

As to how we keep it in thats easy, fat is a VERY poor conductor of heat. This is why fat stores (atipose tissue) are near the skin (sub cut) for the main. The skin's capillary bed flows ABOVE the sub cut fat cells, this alows the body to decide to send blood to the skin in order to radiate it away (as well as convection and conduction). If, however it wishes to CONCERVE heat it diverts the blood surplie away from the superfical cap bed and there by forces the heat to travel through the adipose tissue to escape. As this is hard to do the heat is conserved in the body

John99
11-22-08, 06:19 AM
Asguard, are you saying that your belief is that food is the primary or main factor in producing heat in the human body?

John99
11-22-08, 06:40 AM
I've answered your question COMPLETELY.

John, do you honestly NOT know what the word "metabolism" is and means? If not, read about it in Wikipedia - evidently, you've got a lot to learn about the subject.



The first method is simply to increase the rate of metabolism (besides reducing perspiration, which is the actual first). The second is to reduce the amount of blood flowing near the skin. And if the temp drops too much, involuntary shivering starts.

That is WHY i am ASKING - What the initial source is. The FUEL.

Read-Only
11-22-08, 07:01 AM
That is WHY i am ASKING - What the initial source is. The FUEL.

The food is the fuel, John - it's just as simple as that! Food is broken down by digestion inro simple sugars like glucose - and the body uses that for energy by 'burning" (oxidizing) it. The process produces heat as a byproduct.

Surely you understand what oxidizing does to a substance.

John99
11-22-08, 07:23 AM
The food is the fuel, John - it's just as simple as that! Food is broken down by digestion inro simple sugars like glucose - and the body uses that for energy by 'burning" (oxidizing) it. The process produces heat as a byproduct.

The temperature is close to 100F, which is pretty high.

The stomach empties of food after approx. 3.5hrs. Nine hours later and the body shows no signs of temperature variance.

Read-Only
11-22-08, 07:57 AM
The temperature is close to 100F, which is pretty high.

The stomach empties of food after approx. 3.5hrs. Nine hours later and the body shows no signs of temperature variance.

Of course! The temperature is regulated by activity which in turn is regulated by the hypothalamus gland. You should read up on that, too.

Tell me - and be honest - are you actually reading ANYTHING I've been suggesting or are you just blindly continuing to ask questions while putting forth no effort of your own????

If you aren't too lazy to do so, read THIS: http://thalamus.wustl.edu/course/hypoANS.html

John99
11-22-08, 08:30 AM
If you aren't too lazy to do so, read THIS: http://thalamus.wustl.edu/course/hypoANS.html

There ya go.

Sciencelovah
11-22-08, 11:03 AM
Actually everyone else has answered it. I'm just going to try it in my layman way. :-P


That does not seem to be correct. The reason i say this is that assuming food as a fuel source then wouldnt there be a corresponding loss of heat or increase in heat with the amount of food intake?

As i said previously, taken to an extreme and doing without food (fuel) there is no gradual lowering of heat. Even at the point whereas the stomach contains no food.


The temperature is close to 100F, which is pretty high.

The stomach empties of food after approx. 3.5hrs. Nine hours later and the body shows no signs of temperature variance.


Actually our body works just like a machine. Imagine a car. One liter of gasoline contains about 8 million calories. Depends on its speed and its efficiency, car can travel various km with just 1 liter of gasoline. I think if I remember correctly (with my father's car), if it runs with speed about 80 km/hr, it can travel about 30 km with 1 liter of gasoline.

Now, 1 cup of rice contains about 220,000 calories. If everything we eat a day is more or less equal to 4-5 cups of rice, it produces already about 1 million calories (about 1/8 of 1 liter gasoline). The different is that, we don't have to run about 80 km/hr and carrying 4 people or heavy stuffs, so we need less energy.

When a car run, it is also hot or warm as a result of inefficiency of combustion. And so does our body. As long as we breath, having metabolism, etc, it 'runs' like a car. It's only cold (equal to surrounding temperature) when it is 'switched off' (dead), just like a car.

Source of calorie data: http://www.tinajuanfitness.info/articles/111803.htm

madanthonywayne
11-22-08, 02:45 PM
The temperature is close to 100F, which is pretty high.

The stomach empties of food after approx. 3.5hrs. Nine hours later and the body shows no signs of temperature variance.Perhaps you're unaware that the human body can store energy in the form of gycogen and fat. So, whether we've eaten recently or not, our metabolism still keeps right on chugging along generating energy and heat. Therefore, there is no sudden drop in body temperature 3.5 hours after eating.

The exception to this would be during starvation when the body has used up its store of energy:

Deep body temperature and locomotor activity of rats fed a reduced food amount (n = 9) and of starved rats (n = 9), were measured by implanted transmitters. Both groups were then refed ad libitum. The reduction in body temperature was significant for both groups, but larger in the starved rats than in the food restricted rats. http://cat.inist.fr/?aModele=afficheN&cpsidt=1727854

One other thing I might add is that this is going on in every cell in your body, so the heat doesn't come from any one place, but from everywhere. Some areas produce more heat than others, but heat is a byproduct of our metabolism and it is produced in every living cell of our bodies.

Asguard
11-22-08, 05:51 PM
Read Only, i wouldnt really call ATP production "oxydisation". The chemical reactions are much more complex than that

Read-Only
11-22-08, 06:03 PM
Read Only, i wouldnt really call ATP production "oxydisation". The chemical reactions are much more complex than that

That's a separate function entirely, Asguard, and unrelated directly to metabolism.

Asguard
11-22-08, 06:24 PM
ok i will bite:p

carbohydrates are hyrdolased to monosarcorides (mostly glucose and fructose) by specific emzimes for instance lactanaise.

The glucose is then transported to either the cells or stored by the liver. If its transported to the cells it is transfered to the mitocondria.

i was going to go through the chemical reaction but i cant rember it off the top of my head, and i didnt go through the whole proccess in my essay and the wikipedia link on cellular respiration is just dead wrong

If you can great but which point in the proccess would you call "oxydisation"? The only time oxygen is actually used in the proccess is to split H+ from NADH to form H2O (4 NADH bind to 2 O2 molicules)

Read-Only
11-22-08, 07:02 PM
ok i will bite:p

carbohydrates are hyrdolased to monosarcorides (mostly glucose and fructose) by specific emzimes for instance lactanaise.

The glucose is then transported to either the cells or stored by the liver. If its transported to the cells it is transfered to the mitocondria.

i was going to go through the chemical reaction but i cant rember it off the top of my head, and i didnt go through the whole proccess in my essay and the wikipedia link on cellular respiration is just dead wrong

If you can great but which point in the proccess would you call "oxydisation"? The only time oxygen is actually used in the proccess is to split H+ from NADH to form H2O (4 NADH bind to 2 O2 molicules)

It's very simple, really. Oxidation occurs when the body 'burns' the glucose to produce energy. The waste products are the familar CO2 and water.;)

Asguard
11-22-08, 11:33 PM
um how much do you know about celular respiration?
There is no "burn" in the body, glucose is chemically changed into purvic acid and then through the citric acid cycle into 36? (could be 34) highly charged ATP molicules which the body then uses to do work. Glucose itself is never burnt because it never does any work, its energetic bonds are transfered to a compleatly different molicule

If we look at ANAROBIC respiration there IS no oxygen in the system so there for how could the molicule "burn" or oxydise? The answer is it doesnt, it produces lactic acid insted of H2O in the proccess of ATP production. However this is a waste of glucose (and toxic to most cells except skelital mussle cells which can survive this for up to 1/2 hour or so)

MetaKron
11-23-08, 03:28 AM
Glucose itself is never burnt because it never does any work

Glucose doesn't have to do work to be burnt. It is oxidized to produce the ATP molecules, and that means that it is burnt. Yes, I had to look that up.