Editing Excretion (section)

{{short description|Elimination by an organism of metabolic waste products}}
{{about|a biological process|a pharmacokinetics phase|Elimination (pharmacology)}}
[[File:Urinary System Large Unlabeled.jpg|thumb|Mammals excrete urine through the [[urinary system]].]]
'''Excretion''' is elimination of [[metabolic waste]], which is an essential process in all [[organism]]s. In [[vertebrate]]s, this is primarily carried out by the [[lungs]], [[Kidney (vertebrates)|kidneys]], and [[skin]].<ref name='beckett'>{{cite book | vauthors = Beckett BS | title = Biology: A Modern Introduction | publisher = [[Oxford University Press]] | year = 1987 | pages = 110 | isbn = 0-19-914260-2 }}</ref> This is in contrast with [[secretion]], where the substance may have specific tasks after leaving the [[Cell (biology)|cell]]. For example, [[placental mammals]] expel [[urine]] from the [[bladder]] through the [[urethra]],<ref name="Wake1992">{{cite book|author=Marvalee H. Wake|title=Hyman's Comparative Vertebrate Anatomy|url=https://books.google.com/books?id=VKlWjdOkiMwC&q=placental+mammal+urethra&pg=PA583|access-date=6 May 2013|date=15 September 1992|publisher=University of Chicago Press|isbn=978-0-226-87013-7|pages=583–}}</ref> which is part of the [[excretory system]]. [[Unicellular organism]]s discharge waste products directly through the surface of the cell.

During life activities such as [[cellular respiration]], several chemical reactions take place in the body. These are known as [[metabolism]]. These chemical reactions produce waste products such as [[carbon dioxide]], water, [[Salt (chemistry)|salts]], [[urea]] and [[uric acid]]. Accumulation of these wastes beyond a level inside the body is harmful to the body. The excretory organs remove these wastes. This process of removal of metabolic waste from the body is known as excretion.