Hyperthermia is defined as the situation in which the body temperature is above normal levels of the thermostat set point. In hyperthermic situations, the thermoregulatory system is maximally effective, however, above a certain temperature it begins to lose sensitivity and effectiveness, and therefore the body is not capable of cooling. In other words: the heat sensors inform the hypothalamus about the raising temperature, but cooling activities are not sufficient.
This event leads to deregulation of the thermoregulatory centres in the hypothalamus and is called heat exhaustion. The individual will lose fluids due to excessive perspiration and must be provided with water, salts and a cool environment. Heat stroke describes a more severe situation of high uncontrollable body temperature and symptoms resulting from destruction of tissues like brain, liver, kidney and muscle. Treatment involves rapidly cooling of the whole body.
During hyperthermia the thermostat setpoint is raised.
Hyperthermia evokes a behaviour control of temperature: to look for a colder environment.
In hyperthermia, fluid loss and low blood volume do NOT result in hypotension, because the heat-loss centre constricts blood vessels.