Influence of high temperatures on human organism

Introduction
High temperature of a human organism is by definition a temperature above normal, so before talking about the influence or effects of high temperature on a human we must define what “normal” body temperature is. “Normal” human blood temperature, or normothermia, is dependent on the location of the measurement as well as time of day and activity level of the person being measured. The reason why location affects the definition of normothermia is because different parts of the body have different measured temperatures. Measurement taken from inside the body cavity, such as rectal and vaginal, often are higher than external measurements such as skin temperature. The reason why time of day is also important to consider is the that the body temperature of a healthy person varies throughout the day by roughly 0.5 °C with slightly lower temperatures in the morning and slightly higher temperatures later in the afternoon and in the evening, as the body's needs and activities change. Although the normal human body temperature is variable, the widely accepted average core body temperature is 37.0 °C

Hyperthermia
Hyperthermia defines a process, in which the body heats up to significantly above normal Temperature (>37.5°), because of failure of the organism’s thermoregulation. The most common type of Hyperthermia is the so called Heat stroke.

A Heat stroke occurs, when the body is not able to properly dissipate heat by radiation or evaporation of sweat. This may be the case during exertion, very high outdoor air temperature, dehydration or air humidity. As a consequence, the organism starts to warm up to or above 41.1°. This state affects the body biochemically: Enzymes and other proteins will begin to function slower as they start to denature as a result of the extremely high temperature of the body. As a result of this Enzyme driven reactions (such as metabolic pathways) will not function properly. Consequently typical Symptoms of a heat stroke are a dry skin, small pupils and a high body temperature.

Hyperpyrexia
Hyperpyrexia is a state where the body temperature is extremely above normal, specifically greater than or equal to 41.5 °C (106.7 °F). A body temperature this high is considered a medical emergency as it may indicate a serious underlying condition or lead to severe side effects. Hyperpyrexia differs from hyperthermia in that in hyperpyrexia the body's thermoregulatory system sets the body temperature above the normal temperature, then generates heat to achieve this temperature, while in hyperthermia the body temperature rises above its set point as a result of an external source; to put it simply hyperthermia isn’t caused by a fever whereas hyperpyrexia is just an example of an extreme fever.

The most common cause is an intracranial haemorrhage. These affect the body initially the same way as Heat Stroke and develop into severe symptoms which include:
 * Sickness behaviour
 * Dry, hot, red skin
 * Extreme confusion
 * Fast shallow breathing
 * Weak, fast pulse
 * Dilated pupil’s
 * Loss of consciousness
 * Seizures.

These are symptoms caused by extreme vasodilation and the shutting down of metabolic pathways as a result of inhibited enzyme action. Since the body’s thermoregulatory system isn’t functioning properly during hyperpyrexia it is often fatal.