Excretion is the removal of toxic waste products of metabolism from the body. The end-products of metabolism are either eliminated or conserved by an animal depending on its physiology. Carbon atoms are eliminated in carbon dioxide, hydrogen in water, and oxygen in carbon dioxide and water. Nitrogen which is the end-product of protein catabolism is found in large quantities. It is highly toxic and needs to be excreted as soon as it is formed, or converted into less toxic form before being eventually excreted.
In this you will learn how animals get rid of the toxic nitrogen. You will also study the structure and function of the excretory organs of various animals and also the mechanisms that -regulate kidney function. After that you shall study about osmoregulation, a process which maintains osmotic and ionic concentration of the body fluids. The processes of excretion and osmoregulation are performed by the same set of organs and maintain homeostasis. In this unit osmoregulatory function of the organs has also been dealt with at some places along with their excretory function.