The process of selection is essential for homeostasis, it provides an exemption of the body from end-products of metabolism, which can no longer be used, alien and toxic substances and excess water, salts and organic compounds, arrived with the food or formed as a result of metabolism. Excretion is performed by many organs, but the main are human kidneys, lungs, skin, and digestive tract.
Ketter, T.A.; Frye, M.A.; Corá-Locatelli, G.; Kimbrell, T.A.; Post, R.M. (1999). Metabolism and Excretion of Mood Stabilizers and New Anticonvulsants . Cellular and Molecular Neurobiology, 19(4), pp. 511-512.
Spilsbury, L.; Spilsbury, R. (2008). Digestion and Excretion, p. 18.
Walsh, P.J.; Wright, P.A. (1995). Nitrogen metabolism and excretion. Pp. 215-216.