See soorce fer Testicle

{{fixscots}}
{{Infobox anatomy
| Name        = Testicle
| Latin       = testis
| GraySubject = 258
| GrayPage    = 1236
| Image       = Figure_28_01_03.JPG
| Caption     = Inner wirkins o the testicles.
| Width       = 400
| Image2      = Gray1144.png
| Caption2    = Diagram o male (human) testicles
| ImageMap    = 
| MapCaption  = 
| Precursor   = 
| System      = 
| Artery      = [[Testicular artery]]
| Vein        = [[Testicular vein]], [[Pampiniform plexus]]
| Nerve       = [[Spermatic plexus]]
| Lymph       = [[Lumbar lymph nodes]]
| MeshName    = 
| MeshNumber  = 
| Code        = 
| Dorlands    = eight/000107530
| DorlandsID  = Testicle
}}
The '''testicle''' (frae [[Laitin]] ''testiculus'', diminutive o ''testis'', meanin "witness" o [[virility]],<ref>{{cite web|url=http://onlinelibrary.wiley.com/doi/10.1046/j.1464-410X.2002.02783.x/abstract |title=Blackwell Synergy |publisher=Blackwell Synergy |accessdate=2010-10-25}}</ref> [[Grammatical nummer|plural]] ''testes'') is the male [[gonad]] in [[ainimal]]s. Lik the [[ovary|ovaries]] tae which they are [[homology (biology)|homologous]], testes are components o baith the [[reproductive seestem]] an the [[endocrine seestem]]. The primary functions o the testes are tae produce [[spermatozoon|sperm]] ([[spermatogenesis]]) an tae produce [[androgens]], primarily [[testosterone]].

==Structur==
===Appearance===
[[File:Male and female gonads 1.png|thumb|Male gonads (testes, left) an female ([[ovaries]], richt)]]
Males hae twa testicles o seemilar size conteened within the [[scrotum]], that is an extension o the abdominal wall. Scrotal asymmetry is nae unusual: ane testicle extends forder doun intae the scrotum nor the ither due tae differences in the anatomy o the vasculatur.

===Meisurment===
The vollum o the testicle can be estimatit bi palpating it an comparin it tae [[ellipsoids]] o kent sizes. Anither method is to use calipers (an [[orchidometer]]) or a ruler aither on the person or on an [[ultrasoond]] eemage tae obteen the three meisurments o the x, y, an z axes (lenth, deepth an weenth). Thir measurements can then be uised tae calculate the vollum, uisin the formula for the vollum o an [[ellipsoid]]: 4/3 π × (lenth/2) × (weenth/2) × (deepth/2).

The dimensions o the average adult testicle are up tae 2&nbsp;inches lang, 0.8&nbsp;inches in breidth, an 1.2&nbsp;inches in hicht (5 × 2 × 3&nbsp;cm). The [[Tanner scale#Genitals (male)|Tanner scale for the maturity o male genitals]] assigns a maturity stage tae the calculatit vollum rangin frae stage I, a vollum o less nor 1.5&nbsp;ml; tae stage V, a vollum greater nor 20&nbsp;ml. Normal vollum is 15 tae 25 ml; the average is 18&nbsp;cm³ per testis (range 12&nbsp;cm³ to 30&nbsp;cm³.<ref>[https://books.google.com/books?id=LZsrznAqKnEC&printsec=frontcover&dq=andrology&sig=du3-cvy3ozj6KnifCoXuH2hzpbg#PPA92,M1]" By E. Nieschlag, Hermann M. Behre, H. van. Ahlen, Andrology: Male Reproductive Health and Dysfunction"</ref>

===Internal structur===
[[Image:transversetestis.png|thumb|right|Transverse section throu the left side o the scrotum an the left testis.]]

====Duct seestem====
The testes are kivert bi a teuch membranous shell cried the [[tunica albuginea (testicles)|tunica albuginea]]. Within the testes are verra fine coiled tubes cried [[seminiferous tubules]]. The tubules are lined wi a layer o cells ([[germ cells]]) that develop frae [[puberty]] throu auld age intae [[sperm]] [[cell (biology)|cells]] (kent as [[spermatozoa]] or male [[gametes]] forby). The developin sperm travel throu the seminiferous tubules tae the [[rete testis]] locatit in the [[mediastinum testis]], tae the [[efferent ducts]], an then tae the [[epididymis]] whaur newly creatit sperm cells matur (see [[spermatogenesis]]). The sperm muive intae the [[vas deferens]], an are eventually expelled throu the [[urethra]] an oot o the [[Freemit urethral orifice (male)|urethral orifice]] throu muscular contractions.

====Primary cell teeps====
;Within the [[seminiferous tubules]]:
* Here, [[germ cells]] develop intae [[spermatogonia]], [[spermatocytes]], [[spermatids]] an [[spermatozoon]] throu the process o spermatogenesis. The gametes conteen DNA for fertilisation o an ovum<ref>[https://books.google.com/books?id=FoSiGTXn6BUC&printsec=frontcover#v=onepage&q=testes%20OR%20testis%20OR%20testicle%20OR%20testicles&f=false Histology, A Text and Atlas] by Michael H. Ross and Wojciech Pawlina, Lippincott Williams & Wilkins, 5th ed, 2006</ref>
* [[Sertoli cells]] – the true epithelium o the seminiferous epithelium, creetical for the support o germ cell development intae spermatozoa.  Sertoli cells secrete [[inhibin]].<ref>{{cite journal |vauthors=Skinner M, McLachlan R, Bremner W |title=Stimulation of Sertoli cell inhibin secretion by the testicular paracrine factor PModS |url=https://archive.org/details/sim_molecular-and-cellular-endocrinology_1989-10_66_2/page/239 |journal=Mol Cell Endocrinol |volume=66 |issue=2 |pages=239–49 |year=1989 |pmid=2515083 |doi=10.1016/0303-7207(89)90036-1}}</ref>
* [[Peritubular myoid cells|Peritubular]] [[myoid cells]] surroond the seminiferous tubules.<ref>Arch Histol Cytol. 1996 Mar;59(1):1–13</ref>

;Atween tubules (intersteetial cells)
* [[Leydig cells]] – cells localized atween [[seminiferous tubules]] that produce an secrete [[testosterone]] an ither [[androgen]]s important for [[sexual development]] an [[puberty]], [[seicontar sexual chairacteristics]] lik facial hair, [[Human sexual activity|sexual behaviour]] an [[libido]], supportin spermatogenesis an [[erection|erectile function]]. Testosterone controls testicular vollum forby.
* Present as weel are:
** Immatur Leydig cells
** Intersteetial [[macrophages]] an [[epithelial cells]].

====Bluid supplee an lymphatic drainage====
Bluid supplee an [[lymphatic drainage]] o the testes an scrotum are distinct:
* The paired [[testicular arteries]] arise directly frae the [[abdominal aorta]] an strynd throu the [[inguinal canal]], while the scrotum an the rest o the freemit genitalia is supplee'd bi the [[internal pudendal artery]] (itsel a branch o the [[internal iliac artery]]).
* The testis haes collateral bluid supply frae 1. the [[cremasteric artery]] (a brainch o the [[inferior epigastric artery]], that is a branch o the [[external iliac artery]]), an 2. the [[artery tae the ductus deferens]] (a brainch o the [[inferior vesical artery]], that is a brainch o the [[internal iliac artery]]). Tharefore, if the testicular artery is ligatit, e.g., in a Fowler-Stevens [[orchiopexy]] for a heich undescendit testis, the testis will uisually survive on thir ither bluid supplies.
* Lymphatic drainage o the testes follaes the testicular arteries back tae the [[paraaortic lymph nodes]], while lymph frae the scrotum drains tae the [[inguinal lymph nodes]].

====Layers====
Mony anatomical featurs o the adult testis reflect its developmental oreegin in the [[abdomen]]. The layers o tishie enclosin ilk testicle are derived frae the layers o the anterior [[abdominal waw]]. Notably, the [[cremasteric muscle]] arises frae the [[internal oblique muscle]].

====The bluid–testis barrier====
Muckle molecules canna pass frae the bluid intae the lumen o a seminiferous tubule due tae the presence o [[ticht junctions]] atween adjacent [[Sertoli cells]]. The spermatogonia are in the basal compartment (deep tae the level o the ticht junctions) an the mair matur forms such as primar an seicontar spermatocytes an spermatids are in the adluminal compairtment.

The function o the [[bluid–testis baurier]] (reid heichlicht in diagram abuin) mey be tae prevent an [[auto-immune]] reaction. Matur sperm (an thair [[antigen]]s) arise lang efter immune tolerance is established in infancy. Tharefore, syne sperm are antigenically different frae ''sel'' tishie, a male ainimal can react immunologically tae his awn sperm. In fact, he is capable o makkin antibouks against them.

Injection o sperm antigens causes inflammation o the testis (auto-immune orchitis) an reduced fertility. Sicweys, the bluid–testis baurier mey reduce the likeliheid that sperm proteins will induce an immune response, reducin fertility an sae progeny.

===Temperatur regulation===
Spermatogenesis is enhanced at temperaturs slichtly less nor core bouk temperatur.<ref name=":0">{{Cite journal|last=Mieusset|first=R|last2=Bujan|first2=L|last3=Mansat|first3=A|last4=Pontonnier|first4=F|date=1992|title=Hyperthermie scrotale et infécondité masculine|url=http://www.urofrance.org/fileadmin/documents/data/PU/1992/PU-1992-00020031/TEXF-PU-1992-00020031.PDF|journal=Progrès en Urologie|language=French|issue=2|pages=31–36|doi=|pmid=|access-date=|archive-date=2016-03-03|archive-url=https://web.archive.org/web/20160303171952/http://www.urofrance.org/fileadmin/documents/data/PU/1992/PU-1992-00020031/TEXF-PU-1992-00020031.PDF|url-status=dead}}</ref> The [[spermatogenesis]] is less efficient at lawer an heicher temperaturs nor 33&nbsp;°C.<ref name=":0" /> Acause the testes are locatit ootside the bouk, the smuith tishie o the scrotum can muive them closer or forder awey frae the bouk.<ref name=":0" /> The temperatur o the testes is mainteened at 35 degrees Celsius (95 degrees Fahrenheit), i.e. twa degrees ablo the bouk temperatur o 37 degrees Celsius (98.6 degrees Fahrenheit). Heicher temperaturs affect [[spermatogenesis]].<ref>{{Cite book|url=https://www.worldcat.org/oclc/19493880|title=Concepts of human anatomy and physiology|last=1942-|first=Van De Graaff, Kent M. (Kent Marshall),|date=1989|publisher=Wm. C. Brown Publishers|others=Fox, Stuart Ira.|year=|isbn=0697056759|edition=2nd|location=Dubuque, Iowa|pages=936|oclc=19493880}}</ref> Thare are a nummer o mechanisms tae mainteen the testes at the optimum temperatur.<ref name=":0" />

===Gene an protein expression===
{{Further |Bioinformatics#Gene an protein expression}}
The [[human genome]] includes approximately 20,000 protein codin genes: 80% o thir [[Gene expression|genes are expressed]] in adult testes.<ref name="Uhlén 1260419">{{Cite journal|last=Uhlén|first=Mathias|last2=Fagerberg|first2=Linn|last3=Hallström|first3=Björn M.|last4=Lindskog|first4=Cecilia|last5=Oksvold|first5=Per|last6=Mardinoglu|first6=Adil|last7=Sivertsson|first7=Åsa|last8=Kampf|first8=Caroline|last9=Sjöstedt|first9=Evelina|date=2015-01-23|title=Tissue-based map of the human proteome|url=http://science.sciencemag.org/content/347/6220/1260419|journal=Science|language=en|volume=347|issue=6220|pages=1260419|doi=10.1126/science.1260419|issn=0036-8075|pmid=25613900}}</ref> The testes have the heichest fraction o tishie teep-speceefic genes compared tae ither organs an tishies:<ref name="Djureinovic 476–488">{{Cite journal|last=Djureinovic|first=D.|last2=Fagerberg|first2=L.|last3=Hallström|first3=B.|last4=Danielsson|first4=A.|last5=Lindskog|first5=C.|last6=Uhlén|first6=M.|last7=Pontén|first7=F.|date=2014-06-01|title=The human testis-specific proteome defined by transcriptomics and antibody-based profiling|url=https://academic.oup.com/molehr/article/20/6/476/2883144/The-human-testis-specific-proteome-defined-by|journal=MHR: Basic science of reproductive medicine|volume=20|issue=6|pages=476–488|doi=10.1093/molehr/gau018|issn=1360-9947}}</ref> aboot 1000 o them are heichly speceefic for the testes,<ref name="Uhlén 1260419"/> an aboot 2,200 shaw an elevatit pattern o expression here. A majority o thir genes encode for proteins that are expressed in the [[seminiferous tubule]]s an hae functions relatit tae [[spermatogenesis]].<ref name="Djureinovic 476–488"/><ref name="atlas">{{cite web|title=The human proteome in testis - The Human Protein Atlas|url=http://www.proteinatlas.org/humanproteome/testis|website=www.proteinatlas.org}}</ref> Sperm cells express proteins that result in the development o  [[flagella]]; thir same proteins are expressed in the female in cells linin the [[fallopian tube]], an cause the development o [[cilia]]. In ither wirds, sperm cell flagella an Fallopian tube cilia are ''[[Homology (biology)|homologous]]'' structurs. The testis-specific proteins that shaw the heichest level o expression are [[protamine]]s.

==Development==
Thare are twa phases in that the testes growe substantially; namely in embryonic an pubertal age.

===Embryonic===
In mammalian development, the gonads are at first capable o acomin aither [[ovary|ovaries]] or testes.<ref>Online textbook: "[https://www.ncbi.nlm.nih.gov/books/NBK9983/?depth=2 Developmental Biology]" 6th ed. By Scott F. Gilbert (2000) published by Sinauer Associates, Inc. of Sunderland (MA).</ref> In humans, stairtin at aboot week 4 the gonadal rudiments are present within  the [[intermediate mesoderm]] adjacent tae the developin neers. At aboot week 6, [[sex cords]] develop within the formin testes. Thir are made up o early Sertoli cells that surroond an nurtur the [[germ cell]]s that migrate intae the gonads shortly afore sex determination begins. In males, the sex-speceefic gene [[SRY]] that is foond on the Y-chromosome ineetiates sex determination bi dounstream regulation o sex-determinin factors, (sic as GATA4, SOX9 an AMH), that leads tae development o the male phenoteep, includin directin development o the early bipotential gonad doun the male path o development.

Testes follae the "path o strynd" frae heich in the posterior fetal abdomen tae the inguinal ring an ayont tae the [[inguinal canal]] an intae the [[scrotum]]. In maist cases (97% full-term, 70% [[preterm]]), baith testes hae stryndit bi birth. In maist ither cases, anerly ane testis fails tae strynd ([[cryptorchidism]]) an that will probably express itsel within a year.

===Pubertal===
The testes growe in response tae the stairt o [[spermatogenesis]]. Size depends on lytic function, sperm production (amoont o spermatogenesis present in testis), [[interstitial fluid]], and [[Sertoli cell]] fluid production.

==Clinical signeeficance==
{{anchor|Disease}}

===Pertection an injure===
{{Further|Testicular pain}}
* The testicles are weel kent tae be verra sensitive tae impact an injure. The pyne involved traivels up frae ilk testicle intae the abdominal cavity, via the [[spermatic plexus]], that is the primar nerve o ilk testicle. This will cause pyne in the hip an the back. The pain uisually goes away in a few minutes.
* [[Testicular torsion]] is a medical emergency.
* [[Testicular ruptur]] is a medical emergency caused bi blunt force impact, shairp edge, or piercin impact tae ane or baith testicles.
* Penetratin injuries tae the scrotum mey cause [[castration]], or pheesical separation or destruction o the testes, possibly alang wi pairt or aw o the penis, that results in tot sterility if the testicles are nae reattached quickly.
* Some [[jockstrap]]s are designed tae provide support tae the testicles.<ref>{{cite web|url=https://www.amazon.com/Suspensory-Jockstrap-Scrotal-Testicle-Support/dp/B0050HR23Q|title=Amazon.com: Suspensory Jockstrap for Scrotal/Testicle Support by FlexaMed: Health & Personal Care|website=www.Amazon.com|access-date=25 January 2018}}</ref>

===Diseases an condeetions===
{{Infobox disease
 | Name            = Testicular disease
 | Image           =
 | Caption         =
 | DiseasesDB      =
 | ICD10           = {{ICD10|E|29||e|20}}, {{ICD10|N|43||n|40}}-{{ICD10|N|44||n|40}} 
 | ICD9            = {{ICD9|257}}, {{ICD9|603}}-{{ICD9|604}} 
 | ICDO            =
 | OMIM            =
 | MedlinePlus     =
 | eMedicineSubj   =
 | eMedicineTopic  =
 | MeshID          = D013733
}}
* [[Testicular cancer]] an ither [[neoplasms]] – Tae impuive the chances o catchin possible cases o [[testicular cancer]] or ither heal issues early, regular [[testicular sel-examination]] is recommendit.
* [[Varicocele]], swalt vein(s) frae the testes, uisually affectin the left side,<ref>{{cite web|url=http://kidshealth.org/teen/sexual_health/guys/varicocele.html |title=Varicocele |publisher=Kidshealth.org |access-date=25 October 2010}}</ref> the testis uisually bein normal
* [[Hydrocele testis]], swallin aroond testes caused bi accumulation o clear liquid within a membranous sac, the testis uisually bein normal
* [[Spermatocele]], a retention cyst o a tubule o the [[rete testis]] or the heid o the [[epididymis]] distendit wi barely watyery fluid that conteens [[spermatozoa]]
* [[Endocrine disorders]] can n aw affect the size an function o the testis.
* Certaint inheritit condeetions involvin mutations in key developmental genes impair testicular strynd an aw, resultin in abdominal or inguinal testes that remeen nonfunctional an mey acome cancerous. Ither genetic condeetions can result in the loss o the [[Wolffian ducts]] an allou for the persistence o [[Müllerian ducts]]. Baith excess an deficient levels o [[estrogen]]s can disrupt [[spermatogenesis]] an cause infertility.<ref>{{Cite journal
| last1 = Sierens | first1 = J. E.
| last2 = Sneddon | first2 = S. F.
| last3 = Collins | first3 = F.
| last4 = Millar | first4 = M. R.
| last5 = Saunders | first5 = P. T.
| title = Estrogens in Testis Biology
| doi = 10.1196/annals.1336.008
| journal = Annals of the New York Academy of Sciences
| volume = 1061
| pages = 65–76
| year = 2005
| pmid = 16467258
| pmc =
}}</ref>
* [[Bell-clapper deformity]] is a deformity in that the testicle is nae attached tae the scrotal waws, an can rotate freely on the spermatic cord within the tunica vaginalis. It is the maist common unnerlyin cause o testicular torsion.
* [[Orchitis]] inflammation o the testicles
* [[Epididymitis]], a pynefu inflammation o the epididymis or epididymides frequently caused bi bacterial infection but whiles o unkent oreegin.
* [[Anorchia]], the absence o ane or baith testicles.
* [[Cryptorchidism]] or "unstryndit testicles", when the testicle daes nae strynd intae the scrotum o the infant boy.

Testicular enlairgement is an [[sensitivity an speceeficity|unspeceefic]] sign o various testicular diseases, an can be defined as a testicular size o mair nor 5&nbsp;cm ([[Anatomical terms o location#Axes|lang axis]]) x 3&nbsp;cm (short axis).<ref>[https://books.google.com/books?id=safNmcP3lakC&pg=PA559 Page 559] in: {{cite book|title=Introduction to Vascular Ultrasonography|author=John Pellerito, Joseph F Polak|edition=6|publisher=Elsevier Health Sciences|year=2012|isbn=9781455737666}}</ref>

[[Blue baws]] is a slang term for a temporar fluid congestion in the [[testicles]] an [[prostate]] region caused bi prolanged [[sexual arousal]].

[[Testicular prostheses]] are available tae mimic the appearance and feel o ane or baith testicles, whan absent as frae injury or as treatment in association to [[gender dysphoria]]. Thare hae been some instances o thair implantation in dugs an aw.<ref>{{cite web|url=http://www.neuticles.com|title=Neuticles.com|website=www.Neuticles.com|access-date=25 January 2018}}</ref>

===Effects o exogenous hormones===
Tae some extent, it is possible tae chynge testicular size. Short o direct injury or subjectin them tae adverse condeetions, e.g., heicher [[temperatur]] nor thay are normally accustomed tae, thay can be shrunk bi competin against their intrinsic hormonal function throu the uise o externally admeenistered steroidal hormones. [[Steroids]] taken for muscle enhancement (especially [[anabolic steroids]]) eften hae the undesired side effect o testicular shrinkage.

Seemilarly, stimulation o testicular functions via [[gonadotropin|gonadotropic-lik hormones]] mey enlarge thair size. Testes mey shrink or atrophy in [[Hormone therapy|hormone replacement therapy]] or throu [[chemical castration]].

In aw cases, the loss in testes vollum corresponds wi a loss o spermatogenesis.

==Society an cultur==
{{Main|Testicles as fuid}}
Testicles o a male cauf or ither fermstockin are cuiked an eaten in a dish whiles cried [[Rocky Mountain oysters]].<ref>{{cite web|url=http://news.bbc.co.uk/2/hi/uk_news/england/devon/3651400.stm|title=Reviving a very delicate delicacy|date=13 September 2004|publisher=|access-date=25 January 2018|via=news.BBC.co.uk}}</ref>

{{Main|Sex selection}}

As early as 330 BC, [[Aristotle]] prescrived the ligation (tyin aff) o the left testicle in men wishin tae hae boys.<ref>Hoag, Hannah. [http://dfire.org/x1405.xml I'll take a girl, please... ''Cherry-picking from the dish of life'']. Drexel University Publication. {{webarchive |url=https://web.archive.org/web/20110831122518/http://dfire.org/x1405.xml |date=August 31, 2011 }}</ref> In the Middle Ages, men that wantit a boy whiles haed thair left testicle remuived. This wis acause fowk believed that the richt testicle made "boy" sperm an the left made "girl" sperm.<ref>{{cite web|url=http://genetics.thetech.org/ask/ask76|title=Understanding Genetics|website=Genetics.TheTech.org|access-date=25 January 2018|archive-date=2013-11-09|archive-url=https://web.archive.org/web/20131109115247/http://genetics.thetech.org/ask/ask76|url-status=dead}}</ref>

==Etymology==
Ane theory aboot the etymology o the wird ''testis'' is based on [[Roman law]]. The oreeginal [[Laitin]] wird ''testis'', "witness", wis used in the firmly established legal principle "''Testis unus, testis nullus''" (ane witness [equals] na witness), meanin that testimony bi ony ane person in coort wis tae be disregairdit unless corroboratit bi the testimony o at least anither. This led tae the common practice o producin twa witnesses, bribed tae testify the same wey in cases o lawsuits wi ulterior motives. Syne siv "witnesses" ayeweys came in pairs, the meanin wis accordinly extendit, eften in the diminutive (''testiculus, testiculi'').

Anither theory says that ''testis'' is influenced bi a lend translation, frae Greek ''parastatēs'' "defender (in law), supporter" that is "twa glands side bi side".<ref>[[The American Heritage Dictionary of the English Language]], Fourth Edition</ref>

==Ither ainimals==

===Freemit appearance===
In [[shairk]]s, the testicle on the richt side is uisually mair muckle, an in mony bird an mammal species, the left mey be the larger. The primitive [[jawless fish]] hae anerly a single testis, locatit in the midline o the bouk, awtho even this forms frae the fusion o paired structurs in the embryo.<ref name=VB/>

In [[saisonal breeder]]s, the wecht o the testes eften increases in the breedin saison.<ref name="Johnson2012">{{cite book|author=A.D. Johnson|title=Development, Anatomy, and Physiology|url=https://books.google.com/books?id=yAJMlA0FkAUC&printsec=frontcover#v=onepage&q=%22seasonal%20breeders%22&f=false|date=2 December 2012|publisher=Elsevier|isbn=978-0-323-14323-3}}</ref> The [[Dromedary#Testicles|testicles o a dromedary camel]] are {{convert|7|-|10|cm|in|abbr=on}} lang, {{convert|4.5|cm|in|abbr=on}} deep an {{convert|5|cm|in|abbr=on}} in weenth. The richt testicle is eften smawer nor the left.<ref name=anatomy>{{cite book|last=Mukasa-Mugerwa|first=E.|title=The Camel (Camelus dromedarius): A Bibliographical Review|pages=11–3}}</ref> The testicles o a male reid tod atteen thair greatest wecht in December–Februar.<ref name="s537">{{Harvard citation no brackets|Heptner|Naumov|1998|p=537}}</ref> Spermatogenesis in male [[gowden jackal]]s occurs 10–12 days afore the females enter [[estrus]] an, in this time, males' testicles treeple in wecht.<ref name="h154">{{Harvard citation no brackets|Heptner|Naumov|1998|pp=154–155}}</ref>

===Location===

====Internal====
The basal condeetion for mammals is tae hae internal testes.<ref>[http://www.ias.ac.in/article/fulltext/jbsc/035/01/0027-0037] {{Webarchive|url=https://web.archive.org/web/20180225094002/http://www.ias.ac.in/article/fulltext/jbsc/035/01/0027-0037 |date=2018-02-25 }}</ref> Thare are some [[marsupial]]s wi freemit testes<ref name="Tyndale-BiscoeRenfree1987">{{cite book|author1=Hugh Tyndale-Biscoe|author2=Marilyn Renfree|title=Reproductive Physiology of Marsupials|url=https://books.google.com/books?id=HpjovN0vXW4C&printsec=frontcover#v=onepage&q=testes&f=false|date=30 January 1987|publisher=Cambridge University Press|isbn=978-0-521-33792-2}}</ref> an Boreoeutherian mammals wi internal testes, sic as the rhinoceros.<ref name="rhinoresourcecenter.com">Schaffer, N. E., et al. "[http://www.rhinoresourcecenter.com/pdf_files/125/1258623199.pdf Ultrasonography of the reproductive anatomy in the Sumatran rhinoceros (Dicerorhinus sumatrensis)] {{Webarchive|url=https://web.archive.org/web/20170923194033/http://www.rhinoresourcecenter.com/pdf_files/125/1258623199.pdf |date=2017-09-23 }}." Journal of Zoo and Wildlife Medicine (1994): 337-348.</ref> [[Cetaceans]] sic as whauls an dowphins hae internal testes an aw.<ref name="researchgate.net">Rommel, Sentiel A., D. Ann Pabst, and William A. McLellan. "[https://www.researchgate.net/profile/Sentiel_Rommel/publication/286334625_Functional_Anatomy_of_the_Cetacean_Reproductive_System_with_Comparisons_to_the_Domestic_Dog/links/567295cb08aeb8b21c70cea0.pdf Functional anatomy of the cetacean reproductive system, with comparisons to the domestic dog]." ''Reproductive Biology and Phylogeny of Cetacea''. Science Publishers (2016): 127–145.</ref> As freemit testes wad increase drag in the watter thay hae internal testes that are keepit cuil bi special circulatory seestems that cuil the arterial bluid gaein tae the testes bi placin the arteries near veins bringin cuiled venous bluid frae the skin.<ref name="uncwweb.uncw.edu">Rommel, Sentiel A., D. Ann Pabst, and William A. McLellan. "[http://uncwweb.uncw.edu/mmsp/documents/Rommeletal1998ReproductiveThermoregulation.pdf Reproductive Thermoregulation in Marine Mammals: How do male cetaceans and seals keep their testes cool without a scrotum? It turns out to be the same mechanism that keeps the fetus cool in a pregnant female] {{Webarchive|url=https://web.archive.org/web/20170923194115/http://uncwweb.uncw.edu/mmsp/documents/Rommeletal1998ReproductiveThermoregulation.pdf |date=2017-09-23 }}." American scientist 86.5 (1998): 440-448.</ref><ref name="Pabst, D. Ann 1998">Pabst, D. Ann, Sentiel A. Rommel, and WILLIAM A. McLELLAN. "Evolution of thermoregulatory function in cetacean reproductive systems." The Emergence of Whales. Springer US, 1998. 379-397.</ref>

====Freemit====
[[Boreoeutheria]]n laund mammals, the muckle group o mammals that includes humans, hae freemitised testes.<ref name="MillsMarchant-Forde2010">{{cite book|author1=D. S. Mills|author2=Jeremy N. Marchant-Forde|title=The Encyclopedia of Applied Animal Behaviour and Welfare|url=https://books.google.com/books?id=vrueZDfPUzoC&pg=PA293&lpg=PA293&dq=%22boreoeutherian+OR+boreoeutheria%22+(testes+OR+testicles)+-wikipedia+-%22There+are+also+some+Boreoeutherian+mammals%22&source=bl&ots=u8GpQB33iQ&sig=lPj-8H-lJSSbyOA3bxrCu7k3L-U&hl=en&sa=X&ved=0ahUKEwjtt4eaqIbSAhVIlpAKHV5XA2gQ6AEINjAF#v=onepage&q=%22boreoeutherian%20OR%20boreoeutheria%22%20(testes%20OR%20testicles)%20-wikipedia%20-%22There%20are%20also%20some%20Boreoeutherian%20mammals%22&f=false|year=2010|publisher=CABI|isbn=978-0-85199-724-7|pages=293–}}</ref> Thair testes function best at temperaturs lawer nor thair core bouk temperatur. Thair testes are locatit ootside o the bouk, suspendit bi the spermatic cord within the scrotum.

Thare are several hypotheses why maist boreotherian mammals hae fremmit testes that operate best at a temperatue that is slichtly less nor the core bouk temperatur, e.g. that it is stuck wi enzymes evolved in a caulder temperatur due tae freemit testes evolvin for different raisons, that the lawer temperatur o the testes semply is mair efficient for sperm production.

1) ''Mair efficient''. The clessic hypothesis is that cuiler temperatur o the testes allous for mair efficient fertile [[spermatogenesis]]. In ither wirds, thare are na possible enzymes operatin at normal core bouk temperatur that are as efficient as the anes evolved, at least nane appearin in our evolution so faur.

Houiver, the quaisten remeens why birds despite haein verra heich core bouk temperaturs hae internal testes an did nae evolve freemit testes.<ref name=bio>[http://www.biolreprod.org/content/56/6/1570.full.pdf BIOLOGY OF REPRODUCTION 56, 1570–1575 (1997)- Determination of Testis Temperature Rhythms and Effects of Constant Light on Testicular Function in the Domestic Fowl (Gallus domesticus)] {{webarchive|url=https://web.archive.org/web/20150923190501/http://www.biolreprod.org/content/56/6/1570.full.pdf |date=2015-09-23 }}</ref> It wis ance theorised that birds uised their [[air sacs]] tae cuil the testes internally, but later studies revealed that birds' testes are able tae function at core bouk temperatur.<ref name="bio"/>

Some mammals that hae [[saisonal breedin]] cycles keep thair testes internal till the breedin saison at that pynt thair testes strynd an increase in size an acome freemit.<ref>{{cite web |url=http://www.askabiologist.org.uk/answers/viewtopic.php?id=653 |title=Ask a Biologist Q&A / Human sexual physiology – good design? |publisher=Askabiologist.org.uk |date=4 September 2007 |access-date=25 October 2010 |archive-date=2010-10-27 |archive-url=https://web.archive.org/web/20101027155029/http://askabiologist.org.uk/answers/viewtopic.php?id=653 |url-status=dead }}</ref>

2) ''Irreversible adaptation tae sperm competeetion''.  It haes been suggestit that the auncestor o the boreoeutherian mammals was a smaw mammal that required verra muckle testes (aiblins raither lik thae o a [[hamster]]) for [[sperm competeetion]] an sicweys haed tae place its testes ootside the byle.<ref>{{cite web |url=http://old.richarddawkins.net/videos/865-the-human-body-as-an-evolutionary-patchwork/comments |title='The Human Body as an Evolutionary Patchwork' by Alan Walker, Princeton.edu |publisher=RichardDawkins.net |date=2007-04-10 |access-date=25 October 2010 |deadurl=yes |archiveurl=https://web.archive.org/web/20131109120731/http://old.richarddawkins.net/videos/865-the-human-body-as-an-evolutionary-patchwork/comments |archivedate=9 November 2013 |df= }}</ref> This led tae enzymes involved in spermatogenesis, spermatogenic [[DNA polymerase beta]] an [[recombinase]] activities evolvin a unique temperatur optimum, slichtly less nor core bouk temperatur. Whan the boreoeutherian mammals then diversifee'd intae forms that war muckler an/or did nae require intense sperm competeetion thay still produced enzymes that operatit best at cuiler temperaturs an haed tae keep thair testes ootside the bouk. This poseetion is made less parsimonious bi the fact that the [[kangaroo]], a non-boreoeutherian mammal, has freemit testicles. The auncestors o kangaroos micht, separately frae boreotherian mammals, hae been subject to hivy sperm competeetion an sicweys developit freemit testes, houiver, kangaroo freemit testes are suggestive o a possible adaptive function for freemit testes in muckle ainimals.

3) ''Protection frae abdominal cavity pressure changes''. Ane argiement for the evolution o freemit testes is that it pertects the testes frae abdominal cavity pressur chynges caused bi jimpin an gallopin.<ref>{{cite web|url=https://www.newscientist.com/article/mg15120432.000-science--bumpy-lifestyle-led-to-external-testes.html|title=Science : Bumpy lifestyle led to external testes|publisher=}}</ref>

''4) Pertection against [[DNA damage (naiturally occurrin)|DNA damage]]''.  Mild, transient scrotal heat stress causes DNA damage, [[infertility|reduced fertility]] an abnormal embryonic development in mice.<ref name="pmid18390691">{{cite journal |vauthors=Paul C, Murray AA, Spears N, Saunders PT |title=A single, mild, transient scrotal heat stress causes DNA damage, subfertility and impairs formation of blastocysts in mice |journal=Reproduction |volume=136 |issue=1 |pages=73–84 |year=2008 |pmid=18390691 |doi=10.1530/REP-08-0036 |url=}}</ref>  DNA strand breaks war foond in [[spermatocyte]]s recovered frae testicles subjectit tae 40&nbsp;°C or 42&nbsp;°C for 30 meenits.<ref name="pmid18390691" />  Thir findings suggest that the freemit location o the testicles provides the adaptive benefit o pertectin spermatogenic cells frae heat-induced DNA damage that coud itherwise lead tae [[infertility]] an [[germline mutation]].

===Size===
[[Image:Rabbit testis.jpg|thumb|right|Cross section o rabbit testis, photographed in bricht field microscopy at 40× magnification.]]
The [[Monogamy in animals#Testis size|relative size o testes]] is eften influenced bi [[matin seestem]]s.<ref name="Pitcher,Dunn,Whittingham,2005">{{cite journal | last1 = Pitcher | first1 = T.E. | last2 = Dunn | first2 = P.O. | last3 = Whittingham | first3 = L.A. | year = 2005 | title = Sperm competition and the evolution of testes size in birds | url = | journal = Journal of Evolutionary Biology | volume = 18 | issue = | pages = 557–567 | doi=10.1111/j.1420-9101.2004.00874.x}}</ref> Testicular size as a proportion o bouk wecht varies widely. In the mammalian kinrick, there is a tendency for testicular size tae correspond wi multiple mates (e.g., harems, [[polygamous|polygamy]]). Production o testicular ootput sperm an spermatic fluid is lairger in [[polygamous]] ainimals, possibly a [[Sperm competeetion|spermatogenic competeetion]] for survival. The testes o the [[richt whaul]] are likely tae be the maist muckle o ony animal, ilk wechtin aroond 500&nbsp;kg (1,100&nbsp;lb).<ref>{{cite web |url=http://animaldiversity.ummz.umich.edu/site/accounts/information/Eubalaena_glacialis.html |author=Crane, J. |author2=Scott, R.  |year=2002 |title=Eubalaena glacialis |work=Animal Diversity Web |access-date=1 May 2009}}</ref>

Amang the [[Hominidae]], [[gorilla]]s hae little [[female promiscuity]] an sperm competeetion an the testes are smaw compared to bouk wecht (0.03%). [[Chimpanzee]]s hae heich promiscuity an muckle testes compared tae bouk weight (0.3%). Human testicular size faws atween thir extremes (0.08%).<ref name=Shackelford>{{Cite journal | last1 = Shackelford | first1 = T. K. | last2 = Goetz | first2 = A. T. | doi = 10.1111/j.1467-8721.2007.00473.x | title = Adaptation to Sperm Competition in Humans | url = https://archive.org/details/sim_current-directions-in-psychological-science_2007-02_16_1/page/47 | journal = Current Directions in Psychological Science | volume = 16 | pages = 47 | year = 2007 | pmid =  | pmc = }}</ref>

===Internal structur===

Unner a teuch membranous shell cried the [[tunica albuginea (testicles)|tunica albuginea]], the testis o [[amniote]]s, as well as some [[teleost]] fish, conteens verra fine coiled tubes cried [[seminiferous tubules]].

[[Amphibian]]s an maist fish dae nae possess seminiferous tubules. Instead, the sperm are produced in spherical structures cried ''sperm ampullae''. Thir are saisonal structurs, releasin thair contents in the breedin saison, an then bein reabsorbed bi the bouk. Afore the next breedin saison, new sperm ampullae begin tae form an ripen. The ampullae are itherwise essentially identical tae the seminiferous tubules in [[heicher vertebrates]], includin the same range o cell teeps.<ref name=VB>{{cite book |author=Romer, Alfred Sherwood|author2=Parsons, Thomas S.|year=1977 |title=The Vertebrate Body |url=https://archive.org/details/vertebratebody0000rome_a5a9|publisher=Holt-Saunders International |location= Philadelphia, PA|pages= [https://archive.org/details/vertebratebody0000rome_a5a9/page/385 385]–386|isbn= 0-03-910284-X}}</ref>

==Gailerie==
<gallery class="center">
File:Slide4aaaaaa.JPG|Testicle
File:Slide2CC.JPG|Testicle
Image:Hanging testicles.JPG| Testicle hangin on cremaster muscle. Thir are twa halthy testicles. Heat causes them tae descend, allouin cuilin.
Image:Human_Scrotum.JPG| A healthy [[scrotum]] conteenin normal size testes. The scrotum is in ticht condition. The eemage shaws the textur an aw.
 Image:Testicle-cat.jpg|Testicle o a cat: 1: Extremitas capitata, 2: Extremitas caudata, 3: Margo epididymalis, 4: Margo liber, 5: Mesorchium, 6: Epididymis, 7: testicular artery an vene, 8: Ductus deferens
 Image:Illu testis surface.jpg|Testis surface
 Image:Illu testis cross section.jpg|Testis cross section
 Image:Gray1148.png|The richt testis, exposed bi layin appen the tunica vaginalis.
 Image:Rabbitttestis100x2.jpg|Microscopic view o Rabbit testis 100×
 File:Slide8eee.JPG|Testicle
</gallery>

==References==
{{Reflist}}

[[Category:Glands]]
[[Category:Endocrine seestem]]
[[Category:Mammal male reproductive seestem]]
[[Category:Testicle| ]]
[[Category:Scrotum]]