Excretion can be defined as the process of removal or expulsion of waste from the cells of the body of living organisms.
The different organs or parts of the body performing excretion form the excretory system.
The waste materials released out are known as excretory products.
In animals, there are two major categories of excretory products.
Carbonic excretory products: It includes carbon dioxide, which is exhaled out during respiration. In aquatic animals, it is diffused out through their skin, but in terrestrial animals, it is diffused out through the lungs.
Nitrogenous excretory products: The waste products which are formed as a result of protein metabolism, by the breakdown of amino acids are known as nitrogenous waste products. It mainly includes ammonia, uric acid, and urea.