Warm blood life and fever...

[Externet]

Are all warm blooded animals regulated at 37 C ?

 

Why 37 ? Why fever does not go beyond 42 C ? Is it at 42 C the sickening microorganisms are 'killed' by the body thermal rise defense ?

 

In occasions with near 42 C fever, I have had allucinations, and after that, a relief/cured sensation. What goes on ? Did the fever actually killed the 'illness' ?

[tomgwyther]

No, dogs have a higher core temperature while cats are lower.

 

By increasing your body's temperature, you are attempting to sweat out the fever; 42 degrees is enough to make you sweat.

[Externet]

..."to sweat out the fever"... What is that ??

 

..."42 degrees is enough to make you sweat"... I thought sweat can happen at any body temperature. Can you explain ?

[Mokele]

Temperature does vary among endotherms, particularly with body size, aerobic scope, and descent. Birds have temperatures over 100F in some cases, while marsupials tend to have lower temperatures.

 

The purpose of fever has nothing to do with sweat. The idea is that increased temperature will cause denaturing of the pathogen's proteins, allowing your immune system to overpower it.

 

Interestingly, even cold-blooded organisms can have fevers. They just raise their body temperature higher than normal by basking in the sun longer and at hotter hours of the day - in effect, a behavioral fever.

[Paralith]

I thought the increased temperature of a fever was a result of the inflammatory reaction of your immune system. I don't think it's an actual defense mechanism, considering you can die if your fever goes too high. Your fever goes down when your immune system begins to "relax" as it were, having gotten the pathogens in your body to a more controllable level.

 

To the OP, at a certain temperature many of the proteins and other molecules your body depends on for survival change shape and no longer function the way they are supposed to.

 

oops, beat by Mokele. Interesting - though you would think that common pathogens would since have evolved to be able to function at the higher temperatures as well. Well, I would think that.

[GDG]

Fever is part of your immune response. Yes, inflammation causes the fever, due to the release of cytokines that have that activity, but it is not an accidental by-product.

 

Infection is a race between your immune system and the invading pathogens: the pathogens multiply rapidly. If they multiply rapidly enough, they can overwhelm your immune response. Your immune system (particularly lymphocytes - T cells, B cells, neutrophils, macrophages, etc.) also multiply rapidly after they are activated. Changing your body temperature affects the efficiency of the pathogen's enzymes, and (hopefully) slows them down a bit.

[SkepticLance]

The basic reason why evolution 'chooses' a specific temperature for warm blooded animals is to support enzyme action. Every enzyme has a specific temperature at which it works best. While evolution does result in certain creatures having enzymes that work at temperatures way off the optimum (eg fish that live under ice), the efficiency of those enzymes will never be as good as the efficiency of enzymes working at the optimum temperature.

 

Since different enzymes will be a little different in that optimum, the actual temperature that an animal maintains will vary to a minor degree between species. However, it should always be close to the human 37 Celsius.

 

At higher temperatures, enzymes lose efficacy, and can even be destroyed. It appears that bacteria, in general, have enzymes adapted to lower temperatures than human enzymes are. This means that humans can tolerate a slight increase in body temperature, which can kill many bacteria. Evolution has equipped us to go into fever when attacked by bacteria. This aids the recovery from illness.

[Mr Skeptic]

Body temperature is a big trade-off. A warmer body temperature means you need to spend more energy to maintain that temperature. The warmer you are, the more quickly chemical reactions happen (in general). However, rising temperatures also shakes up your enzymes, causing decreased efficiency and at higher temperatures denaturation. I think a warmer body temperature also gives increased speed/stamina (for creatures adapted to it, I mean).

 

As for fever, it usually reduces the rate at which pathogens can replicate. It also increases the efficiency of the immune system. Most of your cells are not going to be happy, especially for prolonged or high fevers. If your fever goes too high, your cells may start dying, and I think brain cells are among the first to go.

[Mokele]

The basic reason why evolution 'chooses' a specific temperature for warm blooded animals is to support enzyme action. Every enzyme has a specific temperature at which it works best. While evolution does result in certain creatures having enzymes that work at temperatures way off the optimum (eg fish that live under ice), the efficiency of those enzymes will never be as good as the efficiency of enzymes working at the optimum temperature.

 

Actually, enzymes are remarkable flexible, and can have very low optima. In geckos, nocturnal species can have muscle temperature optima in the low 70's, while diurnal species have more typical optima.

 

I think a warmer body temperature also gives increased speed/stamina (for creatures adapted to it, I mean).

 

That's currently one of the major theories, yes - increased basal metabolic rate in theory leads to increase maximal aerobic metabolic rate.

[SkepticLance]

Mokele

Enzymes can indeed be very flexible. Hence my example of fish under ice. However, the most efficient enzyme systems will be close to 37 C. Increased temperature leads to faster metabolism (basic chemistry), but too hot means damage to enzymes. A temperature close to, or at 37 C seems to be pretty optimum.

[Mr Skeptic]

Well, some enzymes do just fine above 100 C, but they have a lot of sulfur cross-linking to remain stable. But I think I know what you are getting at. The energy in folding an entire protein is about as much (usually less than) the energy to form one single chemical bond. I'm going to go ahead and guess that 37 C is approximately the temperature above which your average protein starts unfolding. I wonder, what do cold-blooded creatures think of being warmed to 37 C?

[Mokele]

However, the most efficient enzyme systems will be close to 37 C. Increased temperature leads to faster metabolism (basic chemistry), but too hot means damage to enzymes. A temperature close to, or at 37 C seems to be pretty optimum.

 

How much of that is due to laws of chemistry, and how much just due to lack of strong selection pressures in other directions due to the natural temperature range of our planet?

 

I wonder, what do cold-blooded creatures think of being warmed to 37 C?

 

Depends upon the creature. Fish cannot be warmer than the water (though some can warm certain parts of their body via muscle activity) since their gills effectively act as heat exchangers, most amphibians adapt to cooler temperatures to prevent dessication of their moist skin (except in the humid tropics), and most inverts are either too small to retain much heat (though some flying insects regionally heat their thorax to keep flight muscles warm) or use gills (see fish).

 

In contrast, most reptiles actually have field-active temperatures in the high 80's or low 90's, achieved by behavioral thermoregulation. This is probably why the only lineages of true endotherms both evolved from reptiles - reptiles already had enzymes "pre-set" to high temperatures, so all that was needed was a switch from external to internal heat.

Edited March 10, 2009 by Mokele