The urogenital sinus is a part of the human body only present in the

development of the urinary and reproductive organs The development of the urinary system begins during prenatal development, and relates to the development of the urogenital system – both the organs of the urinary system and the sex organs of the reproductive system. The development continues as ...

. It is the ventral part of the cloaca, formed after the cloaca 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 seg ...

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 urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters ...

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

urethra The urethra (from Greek οὐρήθρα – ''ourḗthrā'') is a tube that connects the urinary bladder to the urinary meatus for the removal of urine from the body of both females and males. In human females and other primates, the urethra con ...

, the prostate and the bulbourethral gland (Cowper's). The phallic portion gives rise to the spongy (bulbar) part of the urethra and the urethral glands (Littre's). Note that the penile part of the urethra originates from urogenital fold. 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, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...

. This process begins when the lower tip of the

paramesonephric ducts Paramesonephric ducts (or Müllerian ducts) are paired ducts of the embryo that run down the lateral sides of the genital ridge and terminate at the sinus tubercle in the primitive urogenital sinus. In the female, they will develop to form the fal ...

, the structures that will eventually form the

uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...

and

vaginal fornices The fornices of the vagina (sing. fornix of the vagina or fornix vaginae) are the superior portions of the vagina, extending into the recesses created by the vaginal portion of cervix. The word "fornix" is Latin for "arch". Structure There are t ...

, come in contact with the UG sinus. Shortly afterwards, the sinovaginal bulbs 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 ...

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

vaginal plate In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hym ...

, which extends and then canalizes (hollows) to form the inferior portion of the

. The female urogenital sinus also gives rise to the urethra and vestibule of the vagina.

Clinical significance

A urogenital sinus anomaly is also a rare

birth defect A birth defect, also known as a congenital disorder, 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 ca ...

women A woman is an adult female human. Prior to adulthood, a female human is referred to as a girl (a female child or Adolescence, adolescent). The plural ''women'' is sometimes used in certain phrases such as "women's rights" to denote female hum ...

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 varia ...

is a disorder where the

rectum The rectum is the final straight portion of the large intestine in humans and some other mammals, and the Gastrointestinal tract, gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the s ...

, and

urinary tract The 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 pressure, c ...

meet and fuse, creating a cloaca, a single common channel.

Other animals

In most mammals (excluding primates and species that have a cloaca), the urogenital sinus refers to the sinus in which the openings to the female's urethra and vagina are found. The urogenital sinus of non-primates is homologous to the

vulval vestibule The vulval vestibule (or vulvar vestibule or vestibule of vagina) is a part of the vulva between the labia minora into which the urinary meatus (urethral opening) and the vaginal opening open. Its edge is marked by Hart's line. It represents the ...

of primates.

Additional images

File:Gray1107.png, Enlarged view from the front of the left

Wolffian body The mesonephros ( el, middle kidney) is one of three excretory organs that develop in vertebrates. It serves as the main excretory organ of aquatic vertebrates and as a temporary kidney in reptiles, birds, and mammals. The mesonephros is included ...

before the establishment of the distinction of sex.

References

http://www.embryology.ch/anglais/ugenital/genitinterne04.html https://www.amboss.com/us/knowledge/Development_of_the_reproductive_system

External links

Urologyhealth.org page on Urogenital Sinus anomalies

Fetal pig dissection

AMBOSS
{{DEFAULTSORT:Urogenital Sinus Embryology of urogenital system

Clinical significance

Other animals

Additional images

See also

References

External links