What does the body do when it gets too cold?
- Contraction of hair erector muscles - this traps a layer of warm air at the skin that acts as extra insulation.
- Decreased rate of sweating - little or no energy is lost trying to evaporate sweat.
- Vasoconstriction - blood vessels near the surface of the skin called arterioles constrict (become narrower) allowing less blood to the skin surface and therefore less heat is lost by radiation.
- Shivering - nerve impulses are sent by the hypothalamus to the skeletal muscles to bring about rapid contractions that generate heat. Shivering therefore helps raise the body temperature.
- Increase in metabolic rate - the liver produces extra heat in order to raise the temperature of the body.
Negative feedback control brings about changes that help return the body to normal conditions. If the body temperature drops, negative feedback control raises the temperature back to normal. If the body temperature rises, negative feedback control lowers the temperature back to normal.
All of the methods to regulate body temperature mentioned so far are involuntary responses - we do not consciously decide to sweat or to shiver. In contrast, humans are also able to make voluntary responses, for example when we decide to take action to help regulate our body temperature.
Examples of voluntary responses when the environment is hot:
- removing clothes
- taking a cold drink
- opening a window
Examples of voluntary responses when the enivronment is cold:
- putting on extra clothes
- having a hot drink
- turning up the heating
