Your cells work best when the temperature inside your body is 37 degrees Celsius (98.6 degrees Fahrenheit). Thermoregulation is a homeostatic function that enables you to maintain this core temperature independent of how hot or cold your surroundings are.
Humans regulate body temperature via a combination of internal processes and external actions. The latter includes behavioural responses, such as heading for shade when we’re exposed to too much Sun.
If that doesn’t help, the body also has a number of automatic responses that help regulate temperature. The main organ involved is the skin, which is controlled by the autonomic nervous system. When your surroundings heat up, the brain triggers a series of chemicals which tell your blood vessels to dilate (widen).
This not only brings warm blood to the surface of the skin where it can more easily radiate heat away, but it also releases sweat through the pores. The body emits heat to vaporise the moisture from the skin, cooling us in the process.
Conversely, when your surroundings grow cold, your blood vessels constrict (narrow), reducing the flow of blood to the surface. The hairs on your skin stand on end and you may shiver and get goosebumps as the skin’s arrector pili muscles contract, pulling the hairs erect to trap air near the skin’s surface.