The urogenital sinus is a part of the human body only present in the development of the urinary and reproductive organs. It is the ventral part of the cloaca, formed after the cloaca separates from the anal canal during the fourth to seventh weeks of development.
Urogenital sinus of female human embryo of eight and a half to nine weeks old. (Urogenital sinus labeled at bottom.)
Stages in the development of the external sexual organs in the male and female. ("Opening of urogenital sinus" labeled in diagram D.)
|Gives rise to||urethra, bladder, vagina|
|Latin||sinus urogenitalis definitivus|
In males, the UG sinus is divided into three regions: upper, pelvic, and phallic. The upper part gives rise to the urinary bladder and the pelvic part gives rise to the prostatic and membranous parts of the urethra. The phallic portion gives rise to the penile urethra.
In females, the pelvic part of the UG sinus gives rise to the sinovaginal bulbs, structures that will eventually form the inferior two thirds of the vagina. This process begins when the lower tip of the paramesonephric ducts, the structures that will eventually form the uterus and vaginal fornices, come in contact with the UG sinus. Shortly afterwards, the sinovaginal bulbs form as two solid evaginations of the UG sinus. Cells in these bulbs divide to form a solid vaginal plate, which extends and then canalizes (hollows) to form the inferior portion of the vagina. The female urogenital sinus also gives rise to the urethra and vestibule of the vagina.
Enlarged view from the front of the left Wolffian body before the establishment of the distinction of sex.
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- Gerald N N Callahan. Between XX and XY: Intersexuality and the Myth of Two Sexes. Chicago Review Press, 2009. p. 182.
- Jenkins D, Bitner-Glindzicz M, Thomasson L, et al. (2007), "Mutational analyses of UPIIIA, SHH, EFNB2 and HNF1β in persistent cloaca and associated kidney malformations", J Pediatr Urol, 3 (1): 2–9, PMC , PMID 17476318, doi:10.1016/j.jpurol.2006.03.002.