What is the difference between excretion and egestion? Name three major organs of excretion in humans, the substances they excrete and the function of this excretion.

Excretion is the removal of toxic materials, waste products of metabolism and excess substances from organisms.

Egestion is the passing out of undigested food as faeces, through the anus.

Three major organs of excretion are the skin, kidneys and lungs.

Sweat glands in the skin produce sweat. This contains water, urea and salt. Excreting sweat helps keep the body cool in hot conditions.

The kidneys remove excess water, salts and urea to prevent a toxic build-up of these substances in the body.

The lungs remove excess carbon dioxide (and some water) when breathing out.