Excretory System

The excretory system removes cellular wastes and helps maintain the salt-water balance in an organism. In providing these functions, excretion contributes to the body's homeostasis, the maintenance of constancy of the internal environment. When cells break down proteins, they produce nitrogenous wastes, such as urea. The excretory system serves to remove these nitrogenous waste products, as well as excess salts and water, from the body. When cells break down carbohydrates during cellular respiration, they produce water and carbon dioxide as a waste product. The respiratory system gets rid of carbon dioxide every time we exhale. The digestive system removes feces, the solid undigested wastes of digestion, by a process called elimination or defecation. Organisms living in fresh and salt water have to adjust to the salt concentration of their aqueous environment, and terrestrial animals face the danger of drying out. It is the job of the excretory system to balance salt and water levels in addition to removing wastes. Different organisms have evolved a number of organs for waste removal. Protozoans, such as Paramecium, have specialized excretory structures; flatworms, which lack a circulatory system, have a simple excretory organ; earthworms, grasshoppers, and humans, have evolved an excretory system that works with the circulatory system.