Core body temperature stays close to 37 °C, usually between 36.5 and 37.5 °C. The hypothalamus acts as the thermostat, comparing body temperature with a set point.
Making heat
Heat comes from metabolism, especially in the liver and muscles. Shivering raises heat production quickly when the body is cold.
Losing heat
The body loses heat by radiation, conduction, convection and evaporation of sweat. When the air is hotter than the skin, sweating is the only way to cool down.
Responses to heat and cold
In heat, skin vessels dilate and sweat glands become active. In cold, skin vessels constrict to keep heat in the core, and shivering starts.
Fever and heat stroke
Pyrogens from infection raise the hypothalamic set point, so the body feels cold and shivers until it reaches the new temperature. In heat stroke the set point is normal, but heat loss fails.
| Process | How heat leaves | Example |
|---|---|---|
| Radiation | Infrared heat to cooler surroundings | Uncovered skin in a cold room |
| Conduction | Direct contact with a cooler surface | Lying on cold ground |
| Convection | Moving air or water | Wind or a fan |
| Evaporation | Sweat turning into vapor | Sweating during exercise |
At the bedside
Measure temperature accurately and note the method, since oral, axillary and tympanic readings differ. Remove wet clothing in hypothermia and cool rapidly in heat stroke.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).