Excretory Organs

The main organs of excretion are:

The lungs (water and CO₂)
The skin (water and salts)
The kidneys (urea, salt and water) These excretory organs maintain homeostasis.

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Excretion is the removal of metabolic wastes from the body.

These excretory organs help to:

Regulate body temperature
Control osmosis
Control the concentration of body fluids
Remove the waste products of metabolic reactions.

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Homeostasis: the maintenance of a constant internal environment.

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Metabolism: The sum of all the chemical reactions in the body.

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Exam Tip Excretion vs Egestion One of the common areas of confusion for students is the difference between excretion and egestion.

Excretion is the removal of metabolic wastes from the body. These wastes include substances like urea, carbon dioxide, and salts, which are by-products of the body's metabolic processes.
Egestion is the removal of undigested food waste from the body. This is not the same as excretion, as it involves the elimination of materials that were never absorbed into the body's cells.

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