The urogenital sinus is a body part of a human or other

placental Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguished ...

only present in the development of the urinary and reproductive organs. It is the ventral part of the cloaca, formed after the

cloaca A cloaca ( ), : cloacae ( or ), or vent, is the rear orifice that serves as the only opening for the digestive (rectum), reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles, birds, cartilagin ...

separates from the

anal canal The anal canal is the part that connects the rectum to the anus, located below the level of the pelvic diaphragm. It is located within the anal triangle of the perineum, between the right and left ischioanal fossa. As the final functional s ...

during the fourth to seventh weeks of development. In males, the UG sinus is divided into three regions: upper, pelvic, and phallic. The upper part gives rise to the

urinary bladder The bladder () is a hollow organ in humans and other vertebrates that stores urine from the Kidney (vertebrates), kidneys. In placental mammals, urine enters the bladder via the ureters and exits via the urethra during urination. In humans, the ...

and the pelvic part gives rise to the prostatic and membranous parts of the

urethra The urethra (: urethras or urethrae) is the tube that connects the urinary bladder to the urinary meatus, through which Placentalia, placental mammals Urination, urinate and Ejaculation, ejaculate. The external urethral sphincter is a striated ...

, the

prostate The prostate is an male accessory gland, accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation. It is found in all male mammals. It differs between species anatomically, chemica ...

and the bulbourethral glands (Cowper's). The phallic portion gives rise to the spongy (bulbar) part of the urethra and the urethral glands (Littré's). 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 In mammals and other animals, the vagina (: vaginas or vaginae) is the elastic, muscular sex organ, reproductive organ of the female genital tract. In humans, it extends from the vulval vestibule to the cervix (neck of the uterus). The #Vag ...

. This process begins when the lower tip of the paramesonephric ducts, the structures that will eventually form the

uterus The uterus (from Latin ''uterus'', : uteri or uteruses) or womb () is the hollow organ, organ in the reproductive system of most female mammals, including humans, that accommodates the embryonic development, embryonic and prenatal development, f ...

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, vestibule, Skene's glands and

Bartholin's gland The Bartholin's glands (named after Caspar Bartholin the Younger; also called Bartholin glands or greater vestibular glands) are two pea-sized compound racemose glands, compound alveolar glandsManual of Obstetrics. (3rd ed.). Elsevier. pp. 1-16. . ...

Clinical significance

A urogenital sinus anomaly is also a rare

birth defect A birth defect is an abnormal condition that is present at birth, regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can range from mild to severe. Birth de ...

women A woman is an adult female human. Before adulthood, a female child or adolescent is referred to as a girl. Typically, women are of the female sex and inherit a pair of X chromosomes, one from each parent, and women with functional u ...

where the

and

both open into a common channel. A persistent cloaca is a disorder where the

rectum The rectum (: rectums or recta) is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. Before expulsion through the anus or cloaca, the rectum stores the feces temporarily. The adult ...

, and urinary tract meet and fuse, creating a

, a single common channel.

Other animals

In many mammals (excluding homonids and some rodents), the urogenital sinus refers to the sinus in which the openings to the female's urethra and vagina are found. However, this term may also apply to some male mammals.

Additional images

File:Gray1107.png, Enlarged view from the front of the left Wolffian body before the establishment of the distinction of sex.

References

Sources

External links