Fever
Fever Information
FEVER is an elevation of body temperature that exceeds
thenonnal daily variation and occurs in conjunction with an increase
in the hypothalamic set point-for example, from 37°C to 39°C. This
shift of the set point from "normothermic" to febrile levels very much
resembles the resetting of the home thermostat to a higher level in
order to raise the ambient temperature in a room. Once the hypothalamic setpoint is raised, neurons in the vasomotor center are activated
and vaso constriction commences. The individual first in fever notices vaso constriction in
the hands and feet. Shunting of blood away from the
periphery to the internal organs essentially decreases heat loss from
the skin, and the person feels cold.
For most fevers, body temperature
increases by 1 to 2°C. Shivering, which ncreases heat production from
the muscles, may begin at this time; however, shivering is not required
if heat conservation mechanisms raise blood temperature sufficiently.
Heat production from the liver also increases. In humans, behavioral
instinct (e.g.,putting on more clothing or bedding) lead to a reduction
of exposed surfaces, which helps raise body temperature.
A fever of > 41.5°C (106.7°P) is called hyperpyrexia. This extraordinarily high
fever can develop in patients with severe infections but
most commonly occurs in patients with central nervous system hemorrhages.
In the preantibiotic era, fever due to a variety of infectious
diseases rarely exceded 106°P, and there has been speculation that
this natural "thennal ceiling" is mediated by neuropeptides functioning
ascentral antipyretics.
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