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Author Topic: What causes a fever?  (Read 5145 times)

Offline tweener

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What causes a fever?
« on: 21/04/2004 04:20:51 »
When a person has an infection, they run a fever.  What causes the rise in body temperature?  I have never heard any explanation other than "the body is trying to fight the infection", which doesn't explain anything.

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Offline cuso4

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Re: What causes a fever?
« Reply #1 on: 21/04/2004 08:44:43 »
The heat is produced from the chemical reaction in the body. Normally the body carries out thermal regulation to keep the body temperature at about 37 degrees C. In the case of an infection, the brain increases the set temperature in the body (say 39 degrees), so the body doesn't start cooling down until the internal temperature exceed 39 degrees. And yes this mechanism is body trying to fight the infection.

Chris, please correct me if I'm wrong.

Angel
 

Offline chris

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Re: What causes a fever?
« Reply #2 on: 21/04/2004 10:34:37 »
Angel you are right. Body temperature is regulated within the hypothalamus in the base of the brain. This area of the nervous system orchestrates the various mechanisms we have to gain or lose heat including shivering, vaso-constriction (when blood vessels supplying the extremeties clamp down to reduce blood flow and hence heat loss), sweating and metabolic rate.

Certain factors (called pyrogens), which are produced by the immune system as it deals with the causative agents of an infection, cause an adjustment in the hypothalamic 'thermostat', pushing up metabolic rate and boosting body temperature. How these pyrogens work is not well understood but presumably it involves substances called prostaglandins because drugs like aspirin and paracetamol inhibit prostaglandin synthesis and are very effective at lowering temperature.

Some people have suggested that the higher temperature in some way disadvantages the bugs although it is hard to see why. If this were the case the bugs would merely adapt, over time, to tolerate a higher temperature.

One the whole, spiking a fever probably either directly increases the efficiency of the immune system response, or is a side effect of a generalised rise in metabolic rate as the body mobilises resources to tackle the infection and the toxins that it produces.

In energy terms, fighting an infection is a costly business - the body needs to rapidly synthesise millions of antibodies (proteins) to neutralise the infectious agent and the toxins it produces, multiply millions of white blood cells, remove dead cells, mop up bugs and viruses from the circulation and break them down. This produces huge amounts of heat !

Chris

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« Last Edit: 21/04/2004 10:36:00 by chris »
 

Offline Quantumcat

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Re: What causes a fever?
« Reply #3 on: 21/04/2004 14:27:00 »
Why do people often feel cold when they're quite warm during a fever?

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Offline nilmot

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Re: What causes a fever?
« Reply #4 on: 22/04/2004 11:06:17 »
May be because you perspirate and vasodilate so you loss too much heat in a short time.

Tom
 

Offline Donnah

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Re: What causes a fever?
« Reply #5 on: 22/04/2004 20:03:15 »
quote:
Originally posted by chris

...drugs like aspirin and paracetamol inhibit prostaglandin synthesis and are very effective at lowering temperature.

Chris


Does ibuprofen lower body temperature or blood pressure?  Does it inhibit prostaglandin synthesis?
 

Offline chris

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Re: What causes a fever?
« Reply #6 on: 23/04/2004 02:46:20 »
Yes, Ibuprofen is an NSAID (new sort of aspirin in disguise) and hence works in an analogous way (via cyclooxygenase inhibition - the rate-limiting step in prostaglandin synthesis).

Chris

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Offline Donnah

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Re: What causes a fever?
« Reply #7 on: 23/04/2004 20:02:35 »
Thanks Chris, you NSAID it.  LOL
« Last Edit: 23/04/2004 20:03:03 by Donnah »
 

Offline tweener

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Re: What causes a fever?
« Reply #8 on: 23/04/2004 21:25:42 »
Thanks everyone.  This is very enlightening!

Once when I was sick and running a fever, my pulse rate was steady at 104.  I suppose this is due to the increased metabolic rate and the need to increase circulation to do all the things that Chris was talking about in fighting the infection.

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Re: What causes a fever?
« Reply #8 on: 23/04/2004 21:25:42 »

 

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