Urogenital Sinus


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Related to Urogenital Sinus: Urogenital folds

Urogenital Sinus

 

the cavity into which the efferent ducts of the reproductive and excretory systems empty in many vertebrates. The urogenital sinus opens into the cloaca in elasmobranchs and holocephalans, in chelonians, and in monotremes; in vertebrates that have a reduced cloaca—polypterids, chondrosteans, and holosteans, males of lower teleosts, and viviparous mammals—the urogenital sinus opens directly to the outside.

The urogenital sinus in the mammalian embryo develops from the lower ventral section of the cloaca; the gonaducts and urinary bladder open into this section, as do the ureters of monotremes. In female eutherians (placental mammals) and in women, the urogenital sinus is greatly shortened, forming the vestibule of the vagina. The vestibule is inferior to and separated from the vagina in ungulates, rodents, prosimians, anthropoid apes, and women by a membranous structure called the hymen. In males of viviparous mammals and in men, the upper portion of the urethra develops from the urogenital sinus.

References in periodicals archive ?
The hymenal membrane separates the vaginal lumen from the urogenital sinus. Secondary to degeneration of the central epithelial cells, the hymen typically ruptures, leaving a thin fold of mucous membrane around the vaginal introitus.
An elective Caesarean section was performed and the newborn was treated early, the surgical act consisting of an excision of the cystic accessory phallic urethra with urogenital sinus septation and vaginoplasty.
These two cases, similar to the present cases, exhibited a severe phenotype with clitoromegaly, labial fusion, and/or single urogenital sinus at birth.
The formation of a urogenital sinus in these animals occurs due absence of an external vaginal ostium (Yalcinkaya et al., 1993; Browne et al., 2006; Glickman et al., 2006).
Affected females are born with enlarged clitoris, fused labioscrotal folds and a urogenital sinus which may become a phallic urethera.
The 18-day-old pig embryo has a well-defined genital tubercle (Figure 4-3), a swelling on the ventral surface between the umbilical cord and opening of the urogenital sinus. This will eventually form the male or female external genitalia.
"Embryologically, the vulva, distal vagina, trigone, and urethra are all derived from the urogenital sinus and contain the highest concentration of estrogen receptors.
The Sonic hedgehog (Shh) gene is expressed in the epithelium of the male urogenital sinus and is not regulated by testosterone.
The origin of SCEVs has been proposed to be from a possible embryonic remnant.[1] Although the embryologic development of the vagina is controversial, the hymenal ring appears to be derived from the urogenital sinus.[1,17,18] The greatest controversy exists on the relative contributions of the mullerian ducts and urogenital sinus to the development of the vagina.
The other two theories are that it is a mild anomaly of a midline abdominal wall closure defect, or that it is a congenital fistula of the primitive urogenital sinus (3,4).
The cause of hypospadias is not known, it is presumed that affected foetus may secret inadequate quantities of testosterone or that there may be inadequate conversion of testosterone to dihydrotestosterone in target tissues of urogenital sinus and external genitalia.