#101 Homeostasis

Homeostasis is the maintenance of a constant internal environment, which is vital for an organism to stay healthy. Fluctuations in temperature, water levels and nutrient concentrations … could lead to death.

Temperature regulation is one homeostatic function. Mammals and birds are warm-blooded – they maintain a constant body temperature despite external environment changes.

Human maintain a body temperature of 37⁰C – we have mechanisms to lose heat when we get too hot, and ways of retaining heat when we get too cold.

A section through human skin. 

The hypothalamus coordinates temperature control

The hypothalamus (part of brain) acts like a thermostat. It detects t^o of the blood running through it.

If t^o > or < 37⁰C, it sends electrical impulses, along nerves, to parts of the body which function in regulating body t^o.

When you are cold, body produces and saves heat

- shivering: muscles contract and relax spontaneously ---> produces heat ---> warms blood

- vasoconstriction: arterioles near skin become narrower so little blood can flow through them (the blood flows through the deep-lying capillaries instead)---> conserve heat

- metabolism may increase ---> release energy

- hair stands up. In human, it just produces ‘goose pimples’. But in hair animals (cat), it acts as an insulator: trap a thicker layer of warm air next to the skin, prevent skin from loosing more warmth.  

When you are hot, the body loses more heat:

- sweating: droplets of sweat evaporate, cooling the body

- vasodilation: more blood flows near skin surface ---> lose heat

- hair lies flat.

Common misconceptions

Remember that the process of vasodilatation and vasoconstriction happen only in arterioles – they do not happen in capillaries or veins. When writing about the process, make sure you refer to arterioles.