Our body undergoes different metabolic activities. These activities produce many substances of which some are useful for our body while the other are useless. If useless substances accumulated in our body, then they may become toxic and cause much harm to our body. The organs which help in the removal of these unwanted substances are known as excretory organs and the process of removal of unwanted harmful metabolic waste substances is called excretion.

The treatment which is used for a person with a machine which filters and cleans the blood when kidney is not working properly. This process is known as dialysis.

Each kidney has nearly one million complex tubular structures called nephrons, which are the functional units. Each nephron has two parts – the glomerulus and the renal tubule. Glomerulus is a tuft of capillaries formed by the afferent arteriole – a fine branch of renal artery. Blood from the glomerulus is carried away by an efferent arteriole.