Editing Excretion (section)

=== Animals ===
[[File:Uric Acid.svg|left|thumb|Chemical structure of [[uric acid]].]]

In animals, the main excretory products are [[carbon dioxide]], [[ammonia]] (in [[ammoniotelic]]s), [[urea]] (in [[ureotelic]]s), [[uric acid]] (in [[uricotelic]]s), [[guanine]] (in [[Arachnida]]), and [[creatine]]. The liver and kidneys [[clearance (medicine)|clear]] many substances from the [[blood]] (for example, in [[Renal physiology#Filtration|renal excretion]]), and the cleared substances are then excreted from the body in the [[urine]] and [[feces]].<ref>{{cite journal | vauthors = Weiner ID, Mitch WE, Sands JM | title = Urea and Ammonia Metabolism and the Control of Renal Nitrogen Excretion | journal = Clinical Journal of the American Society of Nephrology | volume = 10 | issue = 8 | pages = 1444–58 | date = August 2015 | pmid = 25078422 | pmc = 4527031 | doi = 10.2215/CJN.10311013 }}</ref>

[[Aquatic animal]]s usually excrete [[ammonia]] directly into the external environment, as this compound has high [[solubility]] and there is ample water available for dilution. In [[terrestrial animal]]s, ammonia-like compounds are converted into other nitrogenous materials, i.e. [[urea]], that are less harmful as there is less water in the environment and ammonia itself is [[toxic]]. This process is called detoxification.<ref>{{Cite web|title=Excretion - General features of excretory structures and functions|url=https://www.britannica.com/science/excretion|access-date=2021-02-05|website=Encyclopedia Britannica|language=en}}</ref>

==== Birds ====
[[File:Feces and uric-acid.jpg|thumb|250px|White cast of uric acid defecated along with the dark feces by a [[lizard]]. Insects, birds and some other reptiles also use a similar mechanism.]]

[[Bird]]s excrete their nitrogenous wastes as [[uric acid]] in the form of a paste. Although this process is metabolically more expensive, it allows more efficient [[water]] retention and it can be stored more easily in the [[egg (bird)|egg]]. Many avian species, especially [[seabird]]s, can also excrete salt via specialized nasal salt glands, the saline solution leaving through nostrils in the [[beak]].{{Citation needed|date=January 2025}}

==== Insects ====
In [[insect]]s, a system involving [[Malpighian tubule]]s is used to excrete [[metabolic waste]]. Metabolic waste diffuses or is actively transported into the tubule, which transports the wastes to the intestines. The metabolic waste is then released from the body along with fecal matter.{{Citation needed|date=January 2025}}

The excreted material may be called ''ejecta''.<ref name="EOS1887">{{cite journal | vauthors = Carmichael J | title = Gastro-Intestinal Disorder in Sucklings | journal = The Transactions of the Edinburgh Obstetrical Society | volume = 12 | issue = | pages = 164–173, 169 | date = 1887 | pmid = 29613104 | pmc = 5487197 | doi = | url = | location = Edinburgh  | publisher = Oliver and Boyd  }}</ref> In [[pathology]] the word ejecta is more commonly used.<ref>{{cite book | chapter-url = https://www.oxfordreference.com/view/10.1093/acref/9780199891573.001.0001/acref-9780199891573-e-2074 | chapter = Ejecta | title = Oxford English Dictionary | publisher = Oxford University Press | edition = 2nd | date = 1989 }}</ref>