EXCRETORY SYSTEM

Excretion is defined as the process of removing or ejecting material that has no further utility, especially from the body.
   


In other words, excretion can be defined as the removal of metabolic waste from the body.

Importance of excretion.


1. Excretion helps to maintain water balance in the body.

2. The excretory products are harmful to the body and so must be removed.

3. Some are poisonous and must never be allowed to accumulate within the body.

4. Excretion also helps to maintain salt balance i.e homeostasis in the body.

Excretory system or organs of some organisms.
1. Protozoa e.g Amoeba uses Contractile vacuole.

2. Annelids (earthworm) use  Nephridia

3. Insects uses  malphighian tubules.

4. Fishes use Kidneys
5. Amphibians e.g toad use  kidneys
6. Reptiles use   kidneys
7. Birds use  kidneys or lungs.
8. Mammals  use    kidneys, skin, liver and lungs.
9. Flowering plants   use   stomata and lenticels.

Excretory system and their waste product.
1. Contractile vacuole: carbondioxide and water.
2. Flame cells: ammonia, water.
3. Nephridia: water, urea and carbondioxide.
4. Kidneys: urine containing urea salt, water and uruc acid.
5. Liver: bile salts, urea and water.
6. Stomata and lenticels: water, carbondioxide and oxygen.
7. Lungs: co₂, water vapour.
8. Gills: co₂, water and urea.

Excretion in mammals.

There are four types of excretory organs used by mammals. These are: lungs, skin, liver and kidneys. The lungs excrete water vapour and carbondioxide, the liver excretes bile pigment called Bilirubin (from haemoglobin's). The skin excretes water, salt and urea through sweat while the kidney excretes water, mineral salts, urea, uric,acid and creatinine. In mammals, kidneys are the major excretory organs.



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