what is excretion

Excretion is the process by which metabolic waste is eliminated from an organism/13%3A_Human_Biology/13.43%3A_Excretion). It is an essential process in all forms of life and is one of the major ways the body maintains homeostasis/13%3A_Human_Biology/13.43%3A_Excretion). In vertebrates, excretion is primarily carried out by the lungs, kidneys, and skin/13%3A_Human_Biology/13.43%3A_Excretion). The kidneys are considered the main organs of excretion, and their primary function is the elimination of excess water and wastes from the bloodstream by the production of urine/13%3A_Human_Biology/13.43%3A_Excretion). The large intestine eliminates solid wastes that remain after the digestion of food, while the liver breaks down excess amino acids and toxins in the blood/13%3A_Human_Biology/13.43%3A_Excretion). The skin eliminates excess water and salts in sweat, and the lungs exhale water vapor and carbon dioxide/13%3A_Human_Biology/13.43%3A_Excretion). In unicellular organisms, waste products are discharged directly through the surface of the cell, while in insects, a system involving Malpighian tubules is used to excrete metabolic waste.