Editing Testicle (section)

==Structure==
===Appearance===
[[File:Male and female gonads 1.png|thumb|Male gonad (testes, left) and female gonad ([[ovaries]], right)]]

Males have two testicles of similar size contained within the [[scrotum]], which is an extension of the [[abdominal wall]].<ref name="Steger">{{Cite book|last1=Steger|first1=Klaus|last2=Weidner|first2=Wolfgang|title=Practical Urology: Essential Principles and Practice|chapter=Anatomy of the Male Reproductive System|chapter-url=https://books.google.com/books?id=A9m8TkdCUqEC&pg=PA57|date=2011|publisher=Springer Science & Business Media|isbn=978-1-84-882034-0|pages=57–59|access-date=2022-06-01|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629155358/https://books.google.com/books?id=A9m8TkdCUqEC&pg=PA57|url-status=live}}</ref> Scrotal asymmetry, in which one testicle extends farther down into the scrotum than the other, is common. This is because of the differences in the vasculature's anatomy.<ref name="Steger"/> For 85% of men, the right testis hangs lower than the left one.<ref name="Steger"/> 

===Measurement and volume===
The volume of the testicle can be estimated by palpating it and comparing it to [[ellipsoid]]s (an [[orchidometer]]) of known sizes. Another method is to use calipers, a ruler, or an [[ultrasound]] image to obtain the three measurements of the x, y, and z axes (length, depth and width). These measurements can then be used to calculate the volume, using the formula for the volume of an ellipsoid: 
:<math>Volume = \frac{4}{3} \cdot \pi \cdot \frac{length}{2} \cdot \frac{width}{2} \cdot \frac{depth}{2}</math>
:<math>\approx length \cdot width \cdot depth \cdot 0.52</math>

However, the most accurate calculation of actual testicular volume is gained from the formula:<ref name="Lao">{{Cite book|last1=Lao|first1=Michael|last2=Smith|first2=Shannon|last3=Gilbert|first3=Bruce R.|title=Practical Urological Ultrasound|chapter=Male Reproductive Ultrasound|chapter-url=https://books.google.com/books?id=QU8AEAAAQBAJ&pg=PA298|date=2020|publisher=Springer Nature|isbn=978-3-03-052309-1|page=298|access-date=2022-07-05|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629155354/https://books.google.com/books?id=QU8AEAAAQBAJ&pg=PA298|url-status=live}}</ref>

:<math>\approx length \cdot width \cdot depth \cdot 0.71</math>

An average adult testicle measures up to {{convert|5|×|2|×|3|cm|in|frac=4|abbr=on}}. The [[Tanner scale#Genitals (male)|Tanner scale]], which is used to assess the maturity of the male genitalia, assigns a maturity stage to the calculated volume ranging from stage I, a volume of less than 1.5&nbsp;cm<sup>3</sup>; to stage V, a volume greater than 20&nbsp;cm<sup>3</sup>. Normal volume is 15 to 25&nbsp;cm<sup>3</sup>; the average is 18&nbsp;cm<sup>3</sup> per testis (range 12–30&nbsp;cm<sup>3</sup>).<ref name="Steger"/>

The number of spermatozoa an adult human male produces is directly proportional to testicular volume, as larger testicles contain more seminiferous tubules and [[Sertoli cells]] as a result.<ref name="Rhoades">{{Cite book|last1=Rhoades|first1=Rodney A.|last2=Bell|first2=David R.|title=Medical Physiology: Principles for Clinical Medicine|date=2012|publisher=Lippincott Williams & Wilkins|isbn=978-1-60-913427-3|page=681|url=https://books.google.com/books?id=1kGcFOKCUzkC&pg=PA681|access-date=2022-07-05|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629155405/https://books.google.com/books?id=1kGcFOKCUzkC&pg=PA681|url-status=live}}</ref> As such, men with larger testicles produce on average more sperm cells in each [[ejaculate]], as testicular volume is positively correlated with semen profiles.<ref>{{cite journal | doi=10.1155/2013/145792 | doi-access=free | title=Relationship between Testicular Volume and Conventional or Nonconventional Sperm Parameters | year=2013 | last1=Condorelli | first1=Rosita | last2=Calogero | first2=Aldo E. | last3=La Vignera | first3=Sandro | journal=International Journal of Endocrinology | volume=2013 | pages=1–6 | pmid=24089610 | pmc=3780703 }}</ref>

===Internal structure===
[[Image:transversetestis.png|thumb|Transverse section through the left side of the scrotum and the left testis]]

====Duct system====
The testes are covered by a tough fibrous shell called the [[Tunica albuginea of testis|tunica albuginea]].<ref name="Cho">{{Cite book|last1=Cho|first1=S|last2=Bae|first2=J.H.|title=Clinical Regenerative Medicine in Urology|chapter=Penis and Testis|chapter-url=https://books.google.com/books?id=J9s1DwAAQBAJ&pg=PA281|date=2017|publisher=Springer|isbn=978-9-81-102723-9|page=281|access-date=2022-06-01|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629155730/https://books.google.com/books?id=J9s1DwAAQBAJ&pg=PA281|url-status=live}}</ref> Under the tunica albuginea, the testes contain very fine-coiled tubes called [[seminiferous tubule]]s.<ref name="Cho"/> The tubules are lined with a layer of cells ([[germ cell]]s) that develop from [[puberty]] through old age into [[sperm]] [[cell (biology)|cells]] (also known as [[spermatozoa]] or male [[gamete]]s).<ref name="Cho"/> The developing sperm travel through the seminiferous tubules to the [[rete testis]] located in the [[mediastinum testis]], to the [[efferent ducts]], and then to the [[epididymis]] where newly created sperm cells mature ([[spermatogenesis]]).<ref name="Pocock">{{Cite book|last1=Pocock|first1=Gillian|last2=Richards|first2=Christopher D.|last3=Richards|first3=David A.|title=Human Physiology|date=2018|publisher=Oxford University Press|isbn=978-0-19-873722-3|page=766|url=https://books.google.com/books?id=NcQ9DwAAQBAJ&pg=PA766|access-date=2022-06-02|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629155730/https://books.google.com/books?id=NcQ9DwAAQBAJ&pg=PA766|url-status=live}}</ref> The sperm move into the [[vas deferens]], and are eventually expelled through the [[urethra]] and out of the [[External urethral orifice (male)|urethral orifice]] through muscular contractions.<ref name="Pocock"/>

====Primary cell types====
Within the seminiferous tubules, the germ cells develop into [[spermatogonia]], [[spermatocyte]]s, [[spermatid]]s and spermatozoa through the process of spermatogenesis. The gametes contain DNA for fertilization of an [[ovum]].<ref>[https://books.google.com/books?id=FoSiGTXn6BUC&q=testes+OR+testis+OR+testicle+OR+testicles Histology, A Text and Atlas] {{Webarchive|url=https://web.archive.org/web/20230629155731/https://books.google.com/books?id=FoSiGTXn6BUC&q=testes+OR+testis+OR+testicle+OR+testicles |date=2023-06-29 }} by Michael H. Ross and Wojciech Pawlina, Lippincott Williams & Wilkins, 5th ed, 2006{{page needed|date=April 2022}}</ref> Sertoli cells{{Snd}}the true epithelium of the seminiferous epithelium, critical for the support of germ cell development into spermatozoa. Sertoli cells secrete [[inhibin]].<ref name="Huhtaniemi">{{Cite book|last=Huhtaniemi|first=Ilpo|title=Encyclopedia of Endocrine Diseases|date=2018|publisher=Academic Press|isbn=978-0-12-812200-6|page=667|url=https://books.google.com/books?id=nVh7DwAAQBAJ&pg=RA1-PA667|access-date=2022-06-02|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629155732/https://books.google.com/books?id=nVh7DwAAQBAJ&pg=RA1-PA667|url-status=live}}</ref> [[Peritubular myoid cells]] surround the seminiferous tubules.<ref name="Schlegel">{{Cite book|last1=Schlegel|first1=P.N.|last2=Katzovitz|first2=M.A.|title=Urologic Principles and Practice|chapter=Male Reproductive Physiology|chapter-url=https://books.google.com/books?id=bNHHDwAAQBAJ&pg=PA50|date=2020|publisher=Springer Nature|isbn=978-3-03-028599-9|page=50|access-date=2022-06-02|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629155757/https://books.google.com/books?id=bNHHDwAAQBAJ&pg=PA50|url-status=live}}</ref>

Between tubules (interstitial cells) exist [[Leydig cells]]<ref name="Bitzer">{{Cite book|last1=Bitzer|first1=Johannes|last2=Mahmood|first2=Tahir A.|title=Handbook of Contraception and Sexual Reproductive Healthcare|date=2022|publisher=Cambridge University Press|isbn=978-1-10-895863-9|page=16|url=https://books.google.com/books?id=WWtYEAAAQBAJ&pg=PA16|access-date=2022-07-05|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629155732/https://books.google.com/books?id=WWtYEAAAQBAJ&pg=PA16|url-status=live}}</ref>{{Snd}}cells localized between seminiferous tubules that produce and secrete [[testosterone]] and other [[androgen]]s important for [[puberty]] (including [[secondary sexual characteristics]] like facial hair), [[Human sexual activity|sexual behavior]], and [[libido]]. Sertoli cells support spermatogenesis.<ref name="Miell">{{Cite book|last1=Miell|first1=John|last2=Davies|first2=Zoe|title=Clinical Biochemistry: Metabolic and Clinical Aspects|chapter=Reproductive function in the male|chapter-url=https://books.google.com/books?id=2FkXAwAAQBAJ&pg=PA451|date=2014|publisher=Elsevier Health Sciences|isbn=978-0-70-205478-5|page=451|access-date=2022-07-05|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629160234/https://books.google.com/books?id=2FkXAwAAQBAJ&pg=PA451|url-status=live}}</ref> Testosterone controls testicular volume.

Immature Leydig cells and interstitial [[macrophage]]s and [[epithelial cells]] are also present.

====Blood supply and lymphatic drainage====
The testis has three sources of arterial blood supply: the [[testicular artery]], the [[cremasteric artery]], and the [[artery to the ductus deferens]].<ref name="Goldenberg">{{Cite book|last1=Goldenberg|first1=Etai|last2=Benjamin|first2=Tavya G.R|last3=Gilbert|first3=Bruce R.|title=Practical Urological Ultrasound|chapter=Scrotal Ultrasound|date=2020|publisher=Springer Nature|isbn=978-3-03-052309-1|page=80|chapter-url=https://books.google.com/books?id=QU8AEAAAQBAJ&pg=PA80|access-date=2022-07-06|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629160234/https://books.google.com/books?id=QU8AEAAAQBAJ&pg=PA80|url-status=live}}</ref> Blood supply and [[lymphatic drainage]] of the testes and scrotum are distinct:
* The paired testicular arteries arise directly from the [[abdominal aorta]] and descend through the [[inguinal canal]], while the scrotum and the rest of the external genitalia is supplied by the [[internal pudendal artery]] (a branch of the [[internal iliac artery]]).<ref name="Steger 2"/><ref name="Tortora">{{Cite book|last1=Tortora|first1=Gerard J.|last2=Nielsen|first2=Mark|title=Principles of Human Anatomy|date=2017|publisher=John Wiley & Sons|isbn=978-1-11-944446-6|page=486|url=https://books.google.com/books?id=e0rcDwAAQBAJ&pg=PA486|access-date=2022-07-06|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629160234/https://books.google.com/books?id=e0rcDwAAQBAJ&pg=PA486|url-status=live}}</ref>
* The testis has collateral blood supply from the cremasteric artery (a branch of the [[inferior epigastric artery]], which is a branch of the [[external iliac artery]]), and the artery to the ductus deferens (a branch of the [[inferior vesical artery]], which is a branch of the internal iliac artery).<ref name="Pua">{{Cite book|last1=Pua|first1=Bradley B.|last2=Covey|first2=Anne M.|last3=Madoff|first3=David C.|title=Interventional Radiology: Fundamentals of Clinical Practice|date=2018|publisher=Oxford University Press|isbn=978-0-19-027625-6|page=533|url=https://books.google.com/books?id=edB2DwAAQBAJ&pg=PA533|access-date=2022-07-06|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629160235/https://books.google.com/books?id=edB2DwAAQBAJ&pg=PA533|url-status=live}}</ref><ref name="Berney">{{Cite book|last1=Berney|first1=Daniel M|last2=Ulbright|first2=Thomas M.|title=Genitourinary Pathology: Practical Advances|chapter=Anatomy of the Testis and Staging of its Cancers: Implications for Diagnosis|date=2015|publisher=Springer|isbn=978-1-49-392044-0|page=436|chapter-url=https://books.google.com/books?id=97RnBwAAQBAJ&pg=PA436|access-date=2022-07-06|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629160304/https://books.google.com/books?id=97RnBwAAQBAJ&pg=PA436|url-status=live}}</ref> Therefore, if the testicular artery is ligated, e.g., during a Fowler-Stevens [[orchiopexy]] for a high undescended testis, the testis will usually survive on these other blood supplies.<ref name="Aboumarzouk">{{Cite book|last=Aboumarzouk|first=Omar M.|title=Blandy's Urology|date=2019|publisher=John Wiley & Sons|isbn=978-1-11-886336-7|page=747|url=https://books.google.com/books?id=WsaKDwAAQBAJ&pg=PA747|access-date=2022-07-06|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629160244/https://books.google.com/books?id=WsaKDwAAQBAJ&pg=PA747|url-status=live}}</ref>
* Lymphatic drainage of the testes follows the testicular arteries back to the [[paraaortic lymph nodes]], while lymph from the scrotum drains to the [[inguinal lymph nodes]].<ref name="Steger 2"/><ref name="Berney"/>

====Layers====
[[File:Layers of the Scrotum.ogg|thumb|3D anatomy of the layers surrounding the testis]]

Many anatomical features of the adult testis reflect its developmental origin in the [[abdomen]]. The layers of tissue enclosing each testicle are derived from the layers of the anterior [[abdominal wall]].<ref name="Steger"/> The [[cremasteric muscle]] arises from the [[internal oblique muscle]].<ref name="Steger"/><ref name="Tubbs">{{Cite book|last1=Tubbs|first1=R. Shane|last2=Shoja|first2=Mohammadali M.|last3=Loukas|first3=Marios|title=Bergman's Comprehensive Encyclopedia of Human Anatomic Variation|date=2016|publisher=John Wiley & Sons|isbn=978-1-11-843068-2|page=1393|url=https://books.google.com/books?id=U_0dDAAAQBAJ&pg=PT1393|access-date=2022-06-03|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629160506/https://books.google.com/books?id=U_0dDAAAQBAJ&pg=PT1393|url-status=live}}</ref>

====The blood–testis barrier====
{{main|Blood–testis barrier}}
Large molecules cannot pass from the blood into the lumen of a seminiferous tubule due to the presence of [[tight junction]]s between adjacent Sertoli cells.<ref name="Steger 2">{{Cite book|last1=Steger|first1=Klaus|last2=Weidner|first2=Wolfgang|title=Practical Urology: Essential Principles and Practice|chapter=Anatomy of the Male Reproductive System|chapter-url=https://books.google.com/books?id=A9m8TkdCUqEC&pg=PA63|date=2011|publisher=Springer Science & Business Media|isbn=978-1-84-882034-0|page=63|access-date=2022-06-05|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629160505/https://books.google.com/books?id=A9m8TkdCUqEC&pg=PA63|url-status=live}}</ref> The spermatogonia occupy the basal compartment (deep to the level of the tight junctions) and the more mature forms, such as primary and secondary spermatocytes and spermatids, occupy the adluminal compartment.<ref name="Steger 2"/>

The function of the blood–testis barrier may be to prevent an [[auto-immune]] reaction.<ref name="Steger 2"/> Mature sperm (and their [[antigen]]s) emerge significantly after immune tolerance is set in infancy.<ref name="Steger 2"/> Since sperm are antigenically different from self-tissue, a male animal can react immunologically to his own sperm. The male can make antibodies against them.<ref name="Steger 2"/>

Injection of sperm antigens causes inflammation of the testis (auto-immune orchitis) and reduced fertility.<ref name="Steger 2"/> The blood–testis barrier may reduce the likelihood that sperm proteins will induce an immune response.<ref name="Wiser">{{Cite book|last1=Wiser|first1=Herbert J.|last2=Sandlow|first2=Jay|last3=Kohler|first3=Tobias S.|title=Male Infertility: Contemporary Clinical Approaches, Andrology, ART & Antioxidants|chapter=Causes of Male Infertility|chapter-url=https://books.google.com/books?id=W8pplg2vbEUC&pg=PA8|date=2012|publisher=Springer Science & Business Media|isbn=978-1-46-143335-4|page=8|access-date=2022-07-10|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629160509/https://books.google.com/books?id=W8pplg2vbEUC&pg=PA8|url-status=live}}</ref>

===Temperature regulation and responses===
[[Carl Richard Moore]] in 1926 <ref name="Moore 1926 pp. 4–50">{{cite journal |last=Moore |first=Carl R. |date=1926 |title=The Biology of the Mammalian Testis and Scrotum |journal=The Quarterly Review of Biology |volume=1 |issue=1 |pages=4–50 |doi=10.1086/394235 |issn=0033-5770}}</ref> proposed that testicles were external due to [[spermatogenesis]] being enhanced at temperatures slightly less than core body temperature outside the body. The spermatogenesis is less efficient at lower and higher temperatures than 33&nbsp;°C. Because the testes are located outside the body, the smooth tissue of the scrotum can move them closer or further away from the body.<ref name="Cho"/> The temperature of the testes is maintained at 34.4&nbsp;°C, a little below body temperature, as temperatures above 36.7&nbsp;°C impede spermatogenesis.<ref name="Steger"/><ref name="Cho"/> There are a number of mechanisms to maintain the testes at the optimum temperature.<ref name="Coad">{{Cite book|last1=Coad|first1=Jane|last2=Pedley|first2=Kevin|last3=Dunstall|first3=Melvyn|title=Anatomy and Physiology for Midwives E-Book|date=2019|publisher=Elsevier Health Sciences|isbn=978-0-70-206665-8|pages=53–54|url=https://books.google.com/books?id=YnetDwAAQBAJ&pg=PA53|access-date=2022-06-17|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629160508/https://books.google.com/books?id=YnetDwAAQBAJ&pg=PA53|url-status=live}}</ref>

The cremasteric muscle covers the testicles and the [[spermatic cord]].<ref name="de Jong">{{Cite book|last=de Jong|first=M. Robert|title=Sonography Scanning E-Book: Principles and Protocols|date=2020|publisher=Elsevier Health Sciences|isbn=978-0-32-376425-4|page=343|url=https://books.google.com/books?id=BvcCEAAAQBAJ&pg=PA343|access-date=2022-06-05|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629160507/https://books.google.com/books?id=BvcCEAAAQBAJ&pg=PA343|url-status=live}}</ref> When this muscle contracts, the cord shortens and the testicles move closer up toward the body, which provides slightly more warmth to maintain optimal testicular temperature.<ref name="de Jong"/> When cooling is required, the cremasteric muscle relaxes and the testicles lower away from the warm body and are able to cool.<ref name="de Jong"/> Contraction also occurs in response to [[Stress (biology)|physical stress]], such as blunt trauma; the testicles withdraw and the scrotum shrinks very close to the body in an effort to protect them.<ref name="Song">{{Cite book|last1=Song|first1=David H|last2=Neligan|first2=Peter C|title=Plastic Surgery E-Book: Volume 4: Trunk and Lower Extremity|date=2017|publisher=Elsevier Health Sciences|isbn=978-0-32-335707-4|page=293|url=https://books.google.com/books?id=cR0xDwAAQBAJ&pg=PA293|access-date=2022-06-10|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629160507/https://books.google.com/books?id=cR0xDwAAQBAJ&pg=PA293|url-status=live}}</ref>

The [[cremasteric reflex]] will reflexively raise the testicles. The testicles can also be lifted voluntarily using the [[pubococcygeus]] muscle, which partially activates related muscles.

===Gene and protein expression===
{{Further |Bioinformatics#Gene and protein expression}}

The [[human genome]] includes approximately 20,000 protein coding genes: 80% of these [[Gene expression|genes are expressed]] in adult testes.<ref name="Uhlén 1260419">{{Cite journal|last1=Uhlén|first1=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|journal=Science|language=en|volume=347|issue=6220|pages=1260419|doi=10.1126/science.1260419|issn=0036-8075|pmid=25613900|s2cid=802377}}</ref> The testes have the highest fraction of tissue type-specific genes compared to other organs and tissues.<ref name="Djureinovic 476–488">{{Cite journal|last1=Djureinovic|first1=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|journal=MHR: Basic Science of Reproductive Medicine|volume=20|issue=6|pages=476–488|doi=10.1093/molehr/gau018|pmid=24598113|issn=1360-9947|doi-access=free}}</ref> About 1000 of them are highly specific for the testes,<ref name="Uhlén 1260419"/> and about 2,200 show an elevated pattern of expression. A majority of these genes encode for proteins that are expressed in the seminiferous tubules and have functions related to spermatogenesis.<ref name="Djureinovic 476–488"/> Sperm cells express proteins that result in the development of [[flagella]]; these same proteins are expressed in the female in cells lining the [[fallopian tube]] and cause the development of [[cilia]]. Sperm cell flagella and fallopian tube cilia are [[Homology (biology)|homologous]] structures. The testis-specific proteins that show the highest level of expression are [[protamine]]s.<ref name="Hammoud">{{Cite book|last1=Hammoud|first1=S|last2=Carrell|first2=D.T.|title=Biennial Review of Infertility: Volume 2, 2011, Volume 2;Volume 2011|chapter=The Emerging Role of the Sperm Epigenome and its Potential Role in Development|chapter-url=https://books.google.com/books?id=4LgOGlCK_FMC&pg=PA184|date=2011|publisher=Springer Science & Business Media|isbn=978-1-44-198456-2|page=184|access-date=2022-06-16|archive-date=2023-06-29|archive-url=https://web.archive.org/web/20230629160804/https://books.google.com/books?id=4LgOGlCK_FMC&pg=PA184|url-status=live}}</ref>