Morphological Aspects of Differentiation Sexual

MORPHOLOGICAL ASPECTS OF DIFFERENTIATION SEXUAL The transformations of the urogenital system according to sex begin at the 8th week andcontinue during the development of the fetus during pregnancy and even beyond birth. Theyconcern all the constituents of the system: gonads, genital tracts, urogenital sinuses andexternal genitalia. Female differentiation 1. At the level of the gonad The primitive sex cords fragment very quickly into cell clusters in which some of theprimordial gonocytes are enclosed. At the 9th week, the elements of the somatic blastemalocated on the periphery give rise to a second push of cords called cortical sex cords whichin turn fragment and enclose the other gonocytes. The sexual cords located in the medullaryarea regress. The primordial gonocytes transform in the 5th month into oogonia which form, with the cellsderived from the sexual cords which surround them, the primordial follicles. The connections with the mesonephros are very thin and constitute the rete ovari whichrapidly regresses at the same time as the last mesonephrotic tubules, so that there is nolonger any continuity between the ovary and the urogenital sinus. These vestigial remainsare the origin of the Rosenmüller organ and can sometimes transform into a tumor. 2. The permanent genital tract ✪ The permanent genital tract develops from the Müllerian ducts while the Wolffian ducts regress completely. ✪ The head part of the Müllerian canal widens, remains open in the coelomic cavity and in contact with the ovary; it becomes the infundibulum of the tube (pinna). ✪ The middle part, which crosses the Wolff canal, forms the rest of the path of the trunk; at the time of the tilt of the ovary it causes a folding of the peritoneum which will become themesosalpinx. ✪ The caudal part, attached to its contralateral counterpart, with this forms the uterovaginal canal which will later be the origin of the uterus and the upper part of the vagina:

the uterine cavity becomes individualized in the 3rd month due to the resorption of themedian septum resulting from the adjoining area. The wall of the Müller ducts will be at theorigin of the endometrium, the mesenchymal elements located in contact with it willdifferentiate to give the myometrium and its connective envelope. Some Wolffian residuescan be locked in the myometrium (Gartner organ) the underlying narrowed region gives thecervical region the most caudal part is at the origin of the upper two thirds of the vagina. The development of the lower part of the vagina comes from the posterior wall of theurogenital sinus. Opposite the Müllerian tubercle, a posterior excrescence gives rise to twosmall evaginations joined together on the midline, the sinovaginal bulbs which proliferate atthe lower end of the uterovaginal canal. From the 3rd month this proliferation constitutes adense cellular plaque, the vaginal plaque. Between the 10th and 12th week, there is alowering of the lower part of the uterovaginal canal and the junction area with the wall of theurogenital sinus, the vaginal plate overhangs a flared area located opposite the uro slit.-genital, the vestibule. At the same time, this vaginal plate, through a phenomenon ofintraepithelial cleavage, widens to give the lower part of the vagina but the cavity remainsclosed: a thin tissue layer persists, the hymen, 3.The gubernaculum, due to the lateral development of the canal Utero-vaginal, is attached to the body of the uterus at the level of the area ofjunction with the uterine tube on each side. The upper segment between the lower pole ofthe ovary and the uterus becomes the utero-ovarian ligament and the lower segmentbetween the uterus and the labial region becomes the round ligament. Contrary to what isobserved in the male sex, the gubernaculum does not evolve subsequently during pre- andpost-natal development, the ovary remains at the level of the pelvic cavity and the vaginalprocess is obliterated before birth.