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What is the physical mechanism that causes temperature to rise during a fever? I know that somehow the hypothalamus "orders" to increase the standard body temperature regulation, and this should stimulate mitochondria to produce more ATP. Is that right?

Is this the only heating physical mechanism (through increasing production of ATP) that acts during a fever?

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From Wikipedia: "The [hypothalamus] ultimately orchestrates heat effector mechanisms via the autonomic nervous system. These may be: (1) Increased heat production by increased muscle tone, shivering and hormones like epinephrine; (2) Prevention of heat loss, such as vasoconstriction. In infants, the autonomic nervous system may also activate brown adipose tissue to produce heat (non-exercise-associated thermogenesis, also known as non-shivering thermogenesis). Increased heart rate and vasoconstriction contribute to increased blood pressure in fever." –  Alan Boyd Nov 5 '12 at 20:47

2 Answers 2

Cytokine production in the body resets the thermoregulatory centre in the hypothalamus to a higher temperature. As a result, your muscles begin to contract violently (rigors) to generate more heat until you equilibrate to the new setpoint. Hope this helps.

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Yes but just to mention the reset is to a higher temperature. From 37 to 38 for example. –  AndroidPenguin Jun 11 '13 at 13:57
    
@AndroidPenguin Thanks for pointing that out-its a higher temperature. I'll edit my answer. –  John Jun 11 '13 at 14:30

As John mentioned, pyrokines such as IL1 and TNF affect the hypothalamus. Your hypothalamus is a thermostat, similar to central heating for example. So when you set your core temperature higher, your body thinks it is cold. To warm up it does several things:

  • Vasoconstriction directs blood to the core body and prevents heat loss
  • Brown fat break down in infants makes heat
  • Shivering which requires respiration which produces a lot of heat. Metabolism also increases in other ways - this is why it is commonly advised to increase food consumption during illness
  • We wrap up warm - an often overlooked mechanism that is incredibly important.
  • Limited piloerection: if we are hairy our hair will stand up attempting to create a barrier for heat loss
  • We stop sweating (breaking of a fever or when the hypothalamus is reset to normal causes us to sweat)
  • Hormonal regulation via (nor)adrenaline/epinephrine, thyroxine - these are related to the increased metabolism.
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