Editing Glans penis (section)

== Development ==
{{Main|Development of the reproductive system}}
[[File:Development of Male External Genitalia.png|left|thumb|298x298px|Development of external genitalia in the male embryo]]
The glans develops as the terminal end of a [[Primordial phallus|phallic]] structure, called the [[genital tubercle]], which forms in the [[embryo]] regardless of [[sex]] during the early weeks of [[pregnancy]].<ref name="George, Wilson">{{Cite book|chapter-url=https://www.sciencedirect.com/science/article/pii/B9780407003668500083|title=Fetal Physiology and Medicine|last=W.George, D.Wilson|first=Fredrick, Jean|chapter=2 - Sexual Differentiation|year=1984|pages=57–79|publisher=Butterworth-Heinemann|doi=10.1016/B978-0-407-00366-8.50008-3|isbn=978-0-407-00366-8|edition=Second, Revised|access-date=2022-09-23|archive-date=2022-09-22|archive-url=https://web.archive.org/web/20220922095406/https://www.sciencedirect.com/science/article/pii/B9780407003668500083|url-status=live}}</ref> Initially undifferentiated, the tubercle develops into a penis during the [[development of the reproductive system]] depending on the exposure to [[male hormones]], such as [[androgen]]s. In mammals, [[sexual differentiation]] is determined by the [[sperm]] that carries either an [[X chromosome|X]] or a [[Y chromosome|Y]] (male) [[chromosome]].<ref>{{Cite book |last1=Arulkumaran |first1=Sabaratnam |url=https://books.google.com/books?id=lRaWcRYx_7YC&pg=PP1 |title=Oxford Desk Reference: Obstetrics and Gynaecology |last2=Regan |first2=Lesley |last3=Papageorghiou |first3=Aris |last4=Monga |first4=Ash |last5=Farquharson |first5=David |date=2011-06-23 |publisher=OUP Oxford |isbn=978-0-19-162087-4 |language=en}}</ref> The Y chromosome contains a sex-determining gene ([[SRY]]) that encodes a [[transcription factor]] for the protein TDF (testis determining factor) and triggers the creation of [[testosterone]] for the embryo's development into a male.<ref name=":0">{{Cite book |last1=Schünke |first1=Michael |url=https://books.google.com/books?id=NK9TgTaGt6UC&pg=PP1 |title=Thieme Atlas of Anatomy: General Anatomy and Musculoskeletal System |last2=Schulte |first2=Erik |last3=Lamperti |first3=Edward D. |last4=Schumacher |first4=Udo |date=2006 |publisher=Thieme |isbn=978-1-58890-387-7 |language=en}}</ref><ref>{{Cite web |last1=Hake |first1=Laura |last2=O'Connor |first2=Clare |name-list-style=amp |title=Genetic Mechanisms of Sex Determination {{!}} Learn Science at Scitable |url=http://www.nature.com/scitable/topicpage/genetic-mechanisms-of-sex-determination-314 |url-status=live |archive-url=https://web.archive.org/web/20170819121941/http://www.nature.com/scitable/topicpage/genetic-mechanisms-of-sex-determination-314 |archive-date=2017-08-19 |access-date=2022-09-23 |website=nature.com |language=en}}</ref>  

Although the sex of the infant is [[Sex-determination system|determined]] from the moment of [[Fertilisation|conception]],<ref name="George, Wilson"/> the complete external differentiation of the organs begins about eight or nine weeks after conception.<ref>Merz, Eberhard; Bahlmann, F. (2004). Ultrasound in Obstetrics and Gynecology. Vol. 1. Thieme Medical Publishers. {{ISBN|978-1-58890-147-7}}.</ref> Some sources state that the process will be completed by the twelfth week,<ref>{{Cite book|chapter-url=https://www.sciencedirect.com/science/article/pii/B9780750611718500088|title=Introduction to Clinical Reproductive Endocrinology|last=C.L.Lachelin|first=Gillian|chapter=Chapter 4 - Sexual differentiation|year=1991|pages=36–41|publisher=Butterworth-Heinemann|doi=10.1016/B978-0-7506-1171-8.50008-8|isbn=978-0-7506-1171-8|access-date=2022-09-23|archive-date=2022-09-22|archive-url=https://web.archive.org/web/20220922095404/https://www.sciencedirect.com/science/article/pii/B9780750611718500088|url-status=live}}</ref><ref>Merz, Eberhard; Bahlmann, F. (2004). Ultrasound in Obstetrics and Gynecology. Vol. 1. Thieme Medical Publishers. {{ISBN|978-1-58890-147-7}}</ref> while others state that it is clearly evident by the thirteenth week and that the sex organs are fully developed by the sixteenth week.<ref name=":0"/>

Both the penis and clitoris develop from the same [[Tissue (biology)|tissues]] that become the glans and [[Body of penis|shaft]] of the penis and this shared embryonic origin makes these two organs [[Homology (biology)|homologous]] (different versions of the same structure).<ref name=":0"/><ref>{{Cite book |last=Sloane |first=Ethel |url=https://books.google.com/books?id=kqcYyk7zlHYC&pg=PP1 |title=Biology of Women |date=2002 |publisher=Delmar Thomson Learning |isbn=978-0-7668-1142-3 |language=en}}</ref> In the [[female]] fetus the absence of testosterone will stop the growth of the phallus causing the tubercle to shrink and form the clitoris. In the [[male]] fetus the presence of a Y chromosome leads to the development of the [[Testicle|testes]], which secrete a large amount of hormones called androgens. These hormones will cause the [[Virilization|masculinization]] of the phenotypically indifferent organs.<ref name="George, Wilson"/> When exposed to testosterone, the genital tubercle elongates to form the [[Human penis|penis]]. By fusion of the [[urogenital folds]]—elongated spindle-shaped structures that contribute to the formation of the [[Primary urethral groove|urethral groove]] on the belly aspect of the genital tubercle—the [[urogenital sinus]] closes completely to form the [[spongy urethra]] and the labioscrotal swellings unite to form the [[scrotum]].<ref>Sloane, Ethel (2002). Biology of Women. Cengage Learning. {{ISBN|978-0-7668-1142-3}}. Archived from the original on 13 June 2013. Retrieved 27 October 2015. </ref><ref name=":0"/> The secretion of testosterone during this phase plays a decisive role in the final shaping of the penis. After birth, testosterone levels drop significantly until [[puberty]].