Excretion and Excretory Organs

The metabolic reactions occurring in an animal body produce certain nitrogen-containing materials which are of no use in the cells. These are called nitrogenous waste materials. They are mainly formed from the breakdown of proteins and nucleic acids. They become toxic if allowed to accumulate in the body. Therefore, these materials must be removed from the body for healthy life. The elimination of nitrogenous waste products from the animal body to regulate the composition of the body fluids and tissues is called excretion.

Various metabolic activities generate nitrogenous materials which need to be removed. It is an essential process in all forms of life.

1.0Excretory organs/structures in animals:

The organs which remove the waste products of metabolism from the animal body are called excretory organs. In single-celled organisms like amoeba, waste products are discharged directly by diffusion through the surface of the cell. The multicellular organisms utilize more complex excretory methods.

• The ammonotelic organisms are those which excrete ammonia e.g., most aquatic animals like bony fishes, tadpole stage in frog.

• The ureotelic organisms are those which excrete urea e.g., cartilaginous fishes like sharks, frogs and mammals.

• The uricotelic organism are those which excrete uric acid e.g., reptiles, birds and insects.

There are some other organs such as lungs, liver, intestine and skin, that remove certain metabolic waste e.g., CO₂, sweat, oil etc. They are known as accessory or additional excretory organs.

2.0How does skin help in the regulation of body temperature?

The thin layer of fat cells in the dermis of the skin insulates the body. The contraction of smooth muscles attached to hairs results in goosebumps and creates an insulating blanket of warm air. Also, sweat produced by sweat glands uses excess body heat to evaporate, providing a cooling effect.

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