Editing Hyperthermia (section)

==Pathophysiology==
[[File:fever-conceptual.svg|thumb|upright=1.6|A summary of the differences between hyperthermia, [[hypothermia]], and fever.<br />Hyperthermia: Characterized on the left. Normal body temperature (thermoregulatory set-point) is shown in green, while the hyperthermic temperature is shown in red. As can be seen, hyperthermia can be considered an increase above the thermoregulatory set-point.<br />Hypothermia: Characterized in the center: Normal body temperature is shown in green, while hypothermic temperature is shown in blue. As can be seen, hypothermia can be conceptualized as a decrease below the thermoregulatory set-point.<br />Fever: Characterized on the right: Normal body temperature is shown in green. It reads "New Normal" because the thermoregulatory set-point has risen. This has caused what was the normal body temperature (in blue) to be considered hypothermic.]]

A [[fever]] occurs when the [[body temperature|core temperature]] is set higher, through the action of the pre-optic region of the [[anterior hypothalamus]]. For example, in response to a [[bacteria]]l or [[virus|viral]] infection, certain white blood cells within the blood will release [[pyrogens]] which have a direct effect on the anterior hypothalamus, causing body temperature to rise, much like raising the temperature setting on a [[thermostat]].

In contrast, hyperthermia occurs when the body temperature rises without a change in the heat control centers.

Some of the gastrointestinal symptoms of acute exertional heatstroke, such as vomiting, diarrhea, and gastrointestinal bleeding, may be caused by barrier dysfunction and subsequent [[endotoxemia]]. Ultraendurance athletes have been found to have significantly increased plasma endotoxin levels. Endotoxin stimulates many inflammatory cytokines, which in turn may cause multiorgan dysfunction. Experimentally, monkeys treated with oral antibiotics prior to induction of heat stroke do not become endotoxemic.<ref>Lambert, Patrick. "Role of gastrointestinal permeability in exertional heatstroke". ''Exercise and Sport Science Reviews.'' '''32'''(4): 185-190. 2004</ref>

There is scientific support for the concept of a temperature set point; that is, maintenance of an optimal temperature for the metabolic processes that life depends on. Nervous activity in the [[Preoptic area|preoptic-anterior hypothalamus]] of the brain triggers heat losing (sweating, etc.) or heat generating (shivering and muscle contraction, etc.) activities through stimulation of the autonomic nervous system. The pre-optic anterior hypothalamus has been shown to contain warm sensitive, cool sensitive, and temperature insensitive neurons, to determine the body's temperature setpoint. As the temperature that these neurons are exposed to rises above {{cvt|37|C}}, the rate of electrical discharge of the warm-sensitive neurons increases progressively. Cold-sensitive neurons increase their rate of electrical discharge progressively below {{cvt|37|C}}.<ref>{{cite web|last=Byrne|first=J.H.|title=Neuroscience Online: An Electronic Textbook for the Neurosciences|url=http://nba.uth.tmc.edu/neuroscience/|publisher=Department of Neurobiology and Anatomy, The University of Texas Medical School at Houston (UTHealth)|access-date=13 January 2013}}</ref>