View source for Gonad

{{Short description|Gland that produces sex cells}}
{{for|the cartoon character|Buster Gonad}}

{{Cleanup|reason=Writing does not cover the subject in a clear and concise manner.|date=May 2012}}
{{Infobox anatomy
|Name = Gonad
| Image       = Ovaries of Cyprinus carpio.png
| Caption     = A pair of ovaries of  ''[[Cyprinus carpio]]'' (common carp) placed in dissecting dish
}}

A '''gonad''', '''sex gland''', or '''reproductive gland'''<ref>{{cite web|url=http://dictionary.reference.com/browse/sex+gland?r=66|title=the definition of sex gland|website=Dictionary.com|access-date=8 May 2018|url-status=live|archive-url=https://web.archive.org/web/20150722180541/http://dictionary.reference.com/browse/sex+gland?r=66|archive-date=22 July 2015}}</ref> is a [[Heterocrine gland|mixed gland]] and [[sex organ]] that produces the [[gamete]]s and [[sex hormone]]s of an organism. [[Female]] reproductive cells are [[egg cell]]s, and [[male]] reproductive cells are [[sperm]].<ref>{{cite web|url=http://www.macmillandictionary.com/dictionary/american/gonad|title=gonad (noun) American English definition and synonyms - Macmillan Dictionary|website=www.macmillandictionary.com|access-date=8 May 2018|url-status=live|archive-url=https://web.archive.org/web/20180508154610/http://www.macmillandictionary.com/dictionary/american/gonad|archive-date=8 May 2018}}</ref> The male gonad, the [[testicle]], produces sperm in the form of [[Spermatozoon|spermatozoa]]. The female gonad, the [[ovary]], produces egg cells. Both of these gametes are [[haploid]] cells. Some [[hermaphroditic]] animals (and some humans{{px2}}{{mdash}}{{hsp}}see [[Ovotesticular syndrome]]) have a type of gonad called an [[ovotestis]].

== Evolution ==
{{Main|Evolution of sexual reproduction}}
It is hard to find a common origin for gonads, but gonads most likely [[evolved independently]] several times.<ref>{{Cite book|last=Schmidt-Rhaesa|first=Andreas |chapter=13. Reproductive organs |chapter-url={{GBurl|iiwTDAAAQBAJ|p=252}} |title=The Evolution of Organ Systems|date=2007-08-30|publisher=Oxford University Press|isbn=978-0-19-856668-7 |oclc=190852859 |page=252 |quote=The diversity of modes in which gonads are formed makes it hard to substantiate a common origin of gonads. It appears to be more likely that gonads evolved independently several times.}}</ref>

== Regulation ==
The gonads are controlled by [[luteinizing hormone]] (LH) and [[follicle-stimulating hormone]] (FSH), produced and secreted by [[gonadotropic cell|gonadotropes or gonadotrophins]] in the [[anterior pituitary gland]].<ref>{{cite web|title=gonadotropin|url=http://medical-dictionary.thefreedictionary.com/gonadotropin|work=The Free Dictionary|publisher=Mosby's Medical Dictionary, 8th edition. Elsevier.|access-date=4 June 2012|year=2009}}</ref> This secretion is regulated by [[gonadotropin-releasing hormone]] (GnRH) produced in the [[hypothalamus]].<ref>{{cite web|title=Hormones of the Hypothalamus: Gonadotropin-releasing hormone (GnRH)|url=http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/H/Hypothalamus.html#GnRH|work=Kimball's Biology Pages|publisher=John W. Kimball (The Saylor Foundation)|access-date=4 June 2012|first=John W. |last=Kimball|date=12 February 2011|archive-url=https://web.archive.org/web/20120627085615/http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/H/Hypothalamus.html#GnRH|archive-date=27 June 2012}}</ref><ref name=Marieb>{{cite book | last = Marieb | first = Elaine | title = Anatomy & physiology | publisher = Benjamin-Cummings | page= 915 | year = 2013 | isbn = 978-0-321-88760-3 |oclc=43903780}}</ref>

==Development==
{{Main article|Development of the gonads}}

The gonads develop from three sources; the mesothelium, underlying mesenchyme and the primordial germ cells. Gonads start developing as a common primordium (an organ in the earliest stage of development), in the form of [[genital ridge]]s,<ref name="Larsen1">{{cite book |last1=Schoenwolf |first1=Gary C. |title=Larsen's human embryology |date=2015 |publisher=Elsevier |isbn=978-1-4557-0684-6 |oclc=862800082 |page=16 |edition=5th}}</ref> at the sixth week, which are only later [[sexual differentiation|differentiated]] to male or female [[sex organ]]s (except when they are not differentiated). The presence of the [[SRY]] [[gene]],<ref>{{cite web|title=Human Developmental Genetics|url=http://www.pasteur.fr/ip/easysite/pasteur/en/research/scientific-departments/developmental-biology/units-and-groups/human-developmental-genetics|work=Institut Pasteur|access-date=4 June 2012|archive-url=https://web.archive.org/web/20120505080019/http://www.pasteur.fr/ip/easysite/pasteur/en/research/scientific-departments/developmental-biology/units-and-groups/human-developmental-genetics|archive-date=5 May 2012}}</ref> located on the short arm of the [[Y chromosome]] and encoding the [[testis determining factor]], usually determines male sexual differentiation. In the absence of the SRY gene from the Y chromosome, usually the female sex (ovaries instead of testes) will develop. The [[development of the gonads]] is a part of the [[development of the urinary and reproductive organs]].{{cn|date=April 2025}}

==Disease==
{{Expand section|date=September 2022}}

The gonads are subject to many diseases, such as [[hypergonadism]], [[hypogonadism]], [[agonadism]], tumors, and cancer, among others.{{Citation needed|date=September 2022}}

==Aging==
===Ovarian aging===
A delay in having children is common in the developed world and this delay is often associated with ovarian [[female infertility]] and subfertility. Ovarian aging is characterized by progressive decline of the quality and number of [[oocyte]]s.<ref name = Park2021>{{cite journal |vauthors=Park SU, Walsh L, Berkowitz KM |title=Mechanisms of ovarian aging |journal=Reproduction |volume=162 |issue=2 |pages=R19–R33 |date=July 2021 |pmid=33999842 |pmc=9354567 |doi=10.1530/REP-21-0022 }}</ref> This decline is likely due, in part, to reduced expression of genes that encode proteins necessary for [[DNA repair]] and [[meiosis]].<ref>{{cite journal |vauthors=Yang Q, Mumusoglu S, Qin Y, Sun Y, Hsueh AJ |title=A kaleidoscopic view of ovarian genes associated with premature ovarian insufficiency and senescence |journal=FASEB J |volume=35 |issue=8 |article-number=e21753 |date=August 2021 |pmid=34233068 |doi=10.1096/fj.202100756R |doi-access=free }}</ref><ref>{{cite journal |vauthors=Turan V, Oktay K |title=BRCA-related ATM-mediated DNA double-strand break repair and ovarian aging |journal=Hum Reprod Update |volume=26 |issue=1 |pages=43–57 |date=January 2020 |pmid=31822904 |pmc=6935693 |doi=10.1093/humupd/dmz043 }}</ref> Such reduced expression can lead to increased [[DNA damage (naturally occurring)|DNA damage]] and errors in meiotic [[homologous recombination|recombination]].<ref name = Park2021/>

===Testicular aging===
The testes of older men often have [[sperm]] abnormalities that can ultimately lead to [[male infertility]].<ref name = Dong2022/>  These abnormalities include accumulation of DNA damage and decreased DNA repair ability.<ref name = Dong2022>{{cite journal |vauthors=Dong S, Chen C, Zhang J, Gao Y, Zeng X, Zhang X |title=Testicular aging, male fertility and beyond |journal=Front Endocrinol (Lausanne) |volume=13 |issue= |article-number=1012119 |date=2022 |pmid=36313743 |pmc=9606211 |doi=10.3389/fendo.2022.1012119 |doi-access=free}}</ref>  During spermatogenesis in the testis, spontaneous new mutations arise and tend to accumulate with age.<ref>{{cite book |vauthors=Cioppi F, Casamonti E, Krausz C |title=Genetic Damage in Human Spermatozoa |chapter=Age-Dependent De Novo Mutations During Spermatogenesis and Their Consequences |series=Adv Exp Med Biol |volume=1166 |pages=29–46 |date=2019 |pmid=31301044 |doi=10.1007/978-3-030-21664-1_2 |isbn=978-3-030-21663-4 }}</ref>

==See also==
{{Portal|Anatomy}}
* [[Gonadosomatic index]]
* [[Hypothalamic–pituitary–gonadal axis]]

==References==
{{Reflist}}

{{Endocrine system anatomy}}
{{Authority control}}

[[Category:Glands]]
[[Category:Endocrine system]]
[[Category:Human reproductive system]]
[[Category:Sex organs]]