Why does the human body need such a high temperature?

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Main Question or Discussion Point

If our body temperature falls below 30 degrees C or so, it stops functioning properly and we die.
30 C seems still a rather warm temperature for normal chemical reactions to be able to occur, and in most environmental conditions inhabited by men it still represents a temperature gradient compared to the cooler external environment.
Which metabolic processes or chemical reactions fail at such temperatures? Why do we need such a high body temperature to function properly?

And a related question: By now life has evolved a wide spectrum of solutions to cope with a relatively wide range of external temperatures, from Tardigrades or frogs who can survive in freezing temperatures (or warm blooded animals of course) to thermophile bacteria who can survive over-boiling temperatures, but for simpler very early life to develop, which is the range of temperatures believed to be needed?
 

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  • #2
Doug Huffman
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Biological whys are a step onto the slippery slope of teleology. I suspect lower temperatures cause too slow reactions to survive. Here the temperature is about zero at the moment, and a usually deadly reptile would just be easy picking food.
 
  • #3
Pythagorean
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In neurons, current in and out of the cell is mediated by ion channels. The time "constant" of channel kinetics is extremely sensitive to temperature and changes in the time constant can lead to a different time course for currents which can lead to a different effective threshold for neuron firing.

I don't know how much of an effect this would be, or how it would emerge in the whole organism. There may be metabolic or physical consequences that come first or are more deleterious.
 
  • #4
Andy Resnick
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No, I was not really asking that, although it might be related. Do you mean that physical body functioning does not need such a high temperature, and that our requirement for high body temperature happens only because we need significant brain activity to keep our body functioning? So that it is actually only the brain, and not the rest of the body, which needs such a high temperature to keep on working? If that's the case this might be in line with the previous reply by Pythagorean.

In other words, do you suggest that when our body temperature drops below 30 C it is our brain which ceases to work properly (causing the failure of metabolic processes controlled by the brain) and not a failure of the metabolic processes themselves due to insufficient temperature?
 
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  • #6
Doug Huffman
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Nerve function is similar through out the human body.
 
  • #7
Ygggdrasil
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All enzymes (as well as other functional molecules like channels) in the body have evolved to work optimally at 37oC, and changing the temperature can alter their rates as well as their stability. Because the rates of many enzymes must match with the rates of other processes and changing the temperature can have unequal effects on different enzymes, changing the temperature of the body will have disastrous effects on many processes in the body (at low temperatures, reactions won't happen fast enough, and at high temperatures, enzymes will start unfolding).

This is not to say that all enzymes have to work at 37oC. Different organisms have evolved different optimal temperatures for their enzymes. For example, arctic shrimp have enzymes evolved for cold temperatures while thermophilic bacteria have enzymes optimized for high temperatures. Thus, another question may be why did humans (and other similar mammals) evolve to have a core body temperature above the ambient temperature?

The answer to this may simply be that it is easier for the body to warm itself in cold environments that it would be to shed excess heat in warm environments. Metabolic processes generate a lot of heat which will keep the body warm, and the body can expend energy for the specific task of generating heat. Removing heat, however, relies solely on heat exchange with the environment which is probably fairly inefficient means to cool a body with a relatively low surface area to volume ratio.
 
  • #8
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Thanks to all, but I'm still missing a reasonable enough answer. Which human metabolic reactions precisely fail to occur at temperatures around 30 C causing death? If that's what happens of course, some posts suggest that temperature is not the issue for the metabolic processes and reactions sustaining our life, but only for the functioning of the neurological system supporting fundamental metabolic processes.
 
  • #9
Evo
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You are asking about hypothermia. Hypothermia is dangerously low body temperature, below 95 °F (35 °C).

Severe
As the temperature decreases, further physiological systems falter and heart rate, respiratory rate, and blood pressureall decrease. This results in an expected heart rate in the 30s at a temperature of 28 °C (82 °F).[11]

Difficulty speaking, sluggish thinking, and amnesia start to appear; inability to use hands and stumbling are also usually present. Cellular metabolic processes shut down. Below 30 °C (86 °F), the exposed skin becomes blue and puffy, muscle coordination very poor, and walking almost impossible, and the person exhibits incoherent/irrational behavior, including terminal burrowing (see below) or even stupor. Pulse and respiration rates decrease significantly, but fast heart rates (ventricular tachycardia, atrial fibrillation) can also occur. Atrial fibrillation is not typically a concern in and of itself.[1]Major organs fail. Clinical death occurs.
http://en.wikipedia.org/wiki/Hypothermia#Signs_and_symptoms

Many changes to physiology occur as body temperature decreases. These occur in the cardiovascular system leading to the Osborn J wave and other dysrhythmias, decreased CNS electrical activity, cold diuresis, and non-cardiogenic pulmonary edema.[42]

Research has shown that glomerular filtration rate (GFR) decreases as a result of hypothermia.[43] In essence, Hypothermia increases http://en.wikipedia.org/w/index.php?title=Preglomerular_vasoconstriction&action=edit&redlink=1 [Broken], thus decreasing both renal blood flow (RBF) and GFR.[44]
http://en.wikipedia.org/wiki/Hypothermia#Pathophysiology
 
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  • #10
Pythagorean
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As far as the nosology is concerned, hypothermia is more of a symptom-based disease classification, whereas the OP is asking about the pathology (mechanism) of hypothermic death.
 
  • #11
Evo
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As far as the nosology is concerned, hypothermia is more of a symptom-based disease classification, whereas the OP is asking about the pathology (mechanism) of hypothermic death.
That's covered in the wiki article. If he wants more in depth details of what happens with the shutdown of organs as body temperature decreases, he can look up the symptoms listed in the wiki.
 
  • #12
Pythagorean
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Thanks to all, but I'm still missing a reasonable enough answer. Which human metabolic reactions precisely fail to occur at temperatures around 30 C causing death? If that's what happens of course, some posts suggest that temperature is not the issue for the metabolic processes and reactions sustaining our life, but only for the functioning of the neurological system supporting fundamental metabolic processes.
Yggg's post is probably the most informed. It suggests that there's no single enzyme failure; that in cold temperature many operate at suboptimal speeds which causes systemic failures (i.e. higher level processes begin failing as at least one of their dependent enzymes). Since there are so many enzymes underlying biofunction and they are spatially distributed throughout the body, I'm not sure it would be accurate to pinpoint one enzyme, as the specific details of the body's temperature loss (such as does the brain reach 28 first or the heart?) will affect which enzyme (or set of enzymes) is affected first.
 
  • #13
Ygggdrasil
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Thanks to all, but I'm still missing a reasonable enough answer. Which human metabolic reactions precisely fail to occur at temperatures around 30 C causing death? If that's what happens of course, some posts suggest that temperature is not the issue for the metabolic processes and reactions sustaining our life, but only for the functioning of the neurological system supporting fundamental metabolic processes.
The question is somewhat akin to asking, what components of a radio fail if you dunk it in a bathtub full of water. Hypothermia will induce multi-system organ failures, so as Pythagorean says, it's probably difficult to determine which organs failures (or combinations of failures) are most responsible for death. Skimming through the wikipedia article suggests to me respiratory or heart failure, which could be due to dysfunction of channels that signal breathing and heart beat.

There has been research on using hypothermia as a medical tool to limit damage to tissues during heart attacks or stroke, so you may be able to find more information by digging through the medical literature. For example, here's an article that pops up from a quick google search.

And a related question: By now life has evolved a wide spectrum of solutions to cope with a relatively wide range of external temperatures, from Tardigrades or frogs who can survive in freezing temperatures (or warm blooded animals of course) to thermophile bacteria who can survive over-boiling temperatures, but for simpler very early life to develop, which is the range of temperatures believed to be needed?
That's a good question that for which we don't have a good answer. Jack Szostak has an http://www.nature.com/scientificamerican/journal/v301/n3/full/scientificamerican0909-54.html speculating that the best environment would have been a volcanic pool with a temperature gradient that could drive convection that could shuttle the protocells between warm and cold temperatures for different reactions to take place. He also notes that many essential nutrients like phosphate are poorly soluble at cold temperatures, necessitating warmer environments. This is, of course, pure speculation, but it would make sense for such environments to exist and to be plausible spots for the origin of life. Other researcher, however, have a number of other ideas (for example, I remember one seminar where the speaker speculated that life originated in shallow pools that would periodically dry up, concentrating the reagents to allow chemistry to occur, then be rehydrated later).
 
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  • #14
Andy Resnick
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<snip>In other words, do you suggest that when our body temperature drops below 30 C it is our brain which ceases to work properly (causing the failure of metabolic processes controlled by the brain) and not a failure of the metabolic processes themselves due to insufficient temperature?
No, at least I don't think that's what I meant. What I meant was that considering torpor/hibernation means re-evaluating what you define as 'body functioning'. Hibernation is not simply sleep-

"Hibernators’ lungs become covered with a thick deposit of mucus and collagen like those seen in people with asthma, and their brains show changes that resemble those of early-stage Alzheimer’s. Some species lose memory during hibernation. Most surprising of all, some show symptoms of sleep deprivation when they finally wake."

"As their body temperature drops, hibernators also remove the lymphocytes (white blood cells) from their blood and store them in the lymph nodes. And within 90 minutes of awakening, these reappear. This damping down of the immune system prevents a general inflammation in the body during rewarming – the very thing that would cause humans and other non-hibernators to suffer kidney damage."

http://www.bbc.com/future/story/20140505-secrets-behind-the-big-sleep

In humans, hypothermia can (intentionally or not) be helpful as a survival strategy- surgery, being submerged in a cold lake, etc. As you can see, there are many unanswered questions.
 
  • #15
its bcuz most enzymes in our body work best at 37 degree celsius . enzyme is a catalyst for metabolic reaction, if we cannot provide the optimum temperature for enzyme,it will slow down the metabolic reaction rate
 
  • #16
lower temperature --> less kinetic energy of enzyme and substrate -->the chance of formation of enzyme-substrate complex decrease -->lower reaction rate(e.g respiration ,reaction that break down harmful substances(H2O2),etc) --> deaths of organisms

hope this can help
 
  • #17
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Yes all the replies helped, TX
 
  • #18
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lower temperature --> less kinetic energy of enzyme and substrate -->the chance of formation of enzyme-substrate complex decrease -->lower reaction rate(e.g respiration ,reaction that break down harmful substances(H2O2),etc) --> deaths of organisms

hope this can help
May I know if all kinetic energy of enzyme and substrate come from respiration (ATP) or do they occur as a result of heat from the surrounding environment? I'm thinking that at 30 Celsius.. all atoms and molecules vibrate because they are not at absolute zero.. so do enzyme Brownian motion occurs because they are not at absolute zero temperature or all due to ATP process?
 
  • #19
the temperature of surrounding is usually lower that our body,which means heat will lose from the body to the surrounding.
 
  • #20
Ygggdrasil
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May I know if all kinetic energy of enzyme and substrate come from respiration (ATP) or do they occur as a result of heat from the surrounding environment? I'm thinking that at 30 Celsius.. all atoms and molecules vibrate because they are not at absolute zero.. so do enzyme Brownian motion occurs because they are not at absolute zero temperature or all due to ATP process?
All enzymes use thermal energy (i.e. energy derived from collisions with molecules in their environment) to provide the activation energy required for the chemical reaction to occur. If the chemical reaction is thermodynamically favorable (i.e. the products have a lower free energy than the reactants), thermal energy is sufficient for the enzyme to perform its function. If the chemical reaction is not thermodynamically favorable, the enzyme's action must be powered by another thermodynamically favorable process, such as the hydrolysis of ATP.
 
  • #21
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All enzymes use thermal energy (i.e. energy derived from collisions with molecules in their environment) to provide the activation energy required for the chemical reaction to occur. If the chemical reaction is thermodynamically favorable (i.e. the products have a lower free energy than the reactants), thermal energy is sufficient for the enzyme to perform its function. If the chemical reaction is not thermodynamically favorable, the enzyme's action must be powered by another thermodynamically favorable process, such as the hydrolysis of ATP.
But where does the thermal energy of the enzymes come from? They say heat occurs by convection, conduction or IR radiation.. so even though the surrounding has lower temperature than the body. It is not at absolute zero.. and IR radiation from surrounding travels to our body as well as conduction from air. Are these environmental heat transferred to the enzymes and what make the enzymes able to do thermal Brownian motion?
 
  • #22
Ygggdrasil
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But where does the thermal energy of the enzymes come from? They say heat occurs by convection, conduction or IR radiation.. so even though the surrounding has lower temperature than the body. It is not at absolute zero.. and IR radiation from surrounding travels to our body as well as conduction from air. Are these environmental heat transferred to the enzymes and what make the enzymes able to do thermal Brownian motion?
I'm not quite sure I understand your question. Are you asking how the body maintains its temperature above that of the environment? Are you asking where Brownian motion comes from?
 
  • #23
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I'm not quite sure I understand your question. Are you asking how the body maintains its temperature above that of the environment? Are you asking where Brownian motion comes from?
Let's take the example of the dna replication, it does so by Brownian motion... that's how the nucleutides found their way to each other. Do their Brownian movement comes from the energy of ATP or from the ambient temperature of the body? In other words.. does the body maintain its temperature because of ATP or because the environment is not near absolute zero and conduction and IR radiation goes to the body.

When we are deep in Antarctica. We need thick clothes to avoid the cold from the environment to get into the body. So this means the body cellular machineries need cooperation from the environment. But do they depend on the environment partly to get heat.

Or let's take extreme example of a human completely naked deep in Antarctica with zero Celsius environment. If his body is packed with mitochondria and can manufacturer massive ATPs. Would this be enough to maintain the temperature of the body to avoid it becoming frozen?

Last example. Let's say the dna or enzymes are unfrozen. When they are warmed. Would they begin to move because of increased temperature or because of ATP?
 
  • #24
Ygggdrasil
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1. Temperature is defined as the average kinetic energy of molecules in a system. Molecules inside of our body (at a temperature of 37oC) will have an average kinetic energy of 4.3 x 10-21 J, which for a small molecule (say 330 Da, the average weight of a nucleotide) gives an average speed of 88.6 m/s (of course, these molecules frequently collide with each other, so they do not move in straight lines at these speeds). So, by virtue of not being at absolute zero, these molecules are moving around in our cells (which helps them find other molecules to react with) and their collisions can provide energy to make chemical reactions happen. So, at the proximate level, thermal energy provides the kick to initiate many chemical reactions in our bodies.

2. What maintains the body's temperature above the ambient temperature? Here, the answer is metabolism (not just the energy from ATP as the process of generating ATP from food also generates heat). Most of these metabolic processes that break down food generate heat because the products have a lower amount of chemical potential energy than the reactants. This excess potential energy is released as heat into the body, keeping the body warm (this is, for example, why warm-blooded animals tend to eat more food than cold-blooded animals; warm-blooded animals need to literally burn calories in order to maintain their core body temperature). Many animals can even uncouple the breakdown of food from the generation of ATP in order to produce heat more efficiently. So, ultimately, all of the thermal energy in our bodies derives from the calories we consume.
 

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