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 gland The bulbourethral glands or Cowper's glands (named for English anatomist William Cowper) are two small exocrine and accessory glands in the reproductive system of many male mammals. They are homologous to Bartholin's glands in females. The bul ...

s (Cowper's). The phallic portion gives rise to the spongy (bulbar) part of the urethra and the

urethral gland The urethral or periurethral glands (also Littré glands after Alexis Littré) are glands that branch off the wall of the urethra of mammals. The glands secrete mucus and are most numerous in the section of the urethra that runs through the penis. ...

s (Littré's). In females, the pelvic part of the UG sinus gives rise to the

sinovaginal bulb The sinovaginal bulb is a transitional structure in the development of female genitalia, and is one of a pair of endodermal outgrowths of the urogenital sinus, which later fuse to form the lower part of the vagina In mammals and other anim ...

s, 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

s form as two solid

evagination Endodermic evagination relates to the inner germ layers of cells of the very early embryo, from which is formed the lining of the digestive tract, of other internal organs, and of certain glands, implies the extension of a layer of body tissue to f ...

s of the UG sinus. Cells in these bulbs divide to form a solid

vaginal plate In mammals and other animals, the vagina (: vaginas or vaginae) is the elastic, muscular reproductive organ of the female genital tract. In humans, it extends from the vulval vestibule to the cervix (neck of the uterus). The vaginal introit ...

, 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 gland In female human anatomy, Skene's glands or the Skene glands ( , also known as the lesser vestibular glands or paraurethral glands) are two glands located towards the lower end of the urethra. The glands are surrounded by tissue that swells with ...

s 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 A persistent cloaca is a symptom of a complex anorectal congenital disorder, in which the rectum, vagina, and urinary tract meet and fuse, creating a cloaca, a single common channel. Signs and symptoms Cloacas appear in a wide spectrum of variati ...

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 The human urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressu ...

meet and fuse, creating a

, a single common channel.

Other animals

In many mammals (excluding

homonid The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); ''Gorilla'' (the e ...

s 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