Lesson: Chapter 6 — Human body processes

6.3. Excretion and the urinary system 1 of 3

What excretion is

Metabolism in the cells makes waste the body cannot use, and some of it is poisonous. Removing that waste is excretion.

Excretion

Excretion is the removal from the body of the waste products of metabolism.

Excretory organ	What it removes
Kidneys	Urine: water, urea, salts
Lungs	Carbon dioxide and water vapour
Skin	Sweat: water, salts, a little urea
Liver	Bile pigments, sent out with the bile

Egestion is not excretion

Most of the faeces is undigested food that never entered the cells, so removing it is not excretion. It is egestion.