المحاضرة الأولى نساembryology of female genital system

Although genetic sex is determined at fertilization, gender is not apparent until

approximately the 12th week of embryonic life.

By the 6th week embryonic life, both male and female embryos start to develop

the following structures on either side of the midline:




1. Genital ridge (proliferation of coelomic epithelium)


2. Mesonephric (Wolffian) duct (lateral to the genital ridge)


3. Paramesonephric (Mullerian) duct which consists of:


• Upper vertical part lateral to the Wolffian duct.


• Middle horizontal part crosses in front of the Wollfian duct (Both upper and middle parts form the fallopian tube)


• Lower vertical part fuses with the similar part of the opposite side to form the utero-vaginal canal

(the upper part forms the body and cervix of the uterus while the lower part forms the upper 4/5 of the

vagina). The lower 1/5 of the vagina develops from the sino-vaginal bulbs in the posterior wall of the

uro-genital sinus.



N.B: The musculature of the uterus and vagina develops from the surrounding mesoderm. In male, the testis secretes Mullerian inhibitory factor (MIF) which causes atrophy and regression of the Mullerian ducts.




Origin and derivatives of the Mullerian ducts


****The coelomic epithelium lateral to the Wolffian duct is invaginated to form the Mullerian duct which grows


caudally, at first it is solid, but later it becomes canalized .


****It deviates more and more medially till it meets its fellow of the opposite side .


The septum between the 2 Mullerian ducts disappear .


****The proximal parts of the Mullerian ducts form

the fallopian tubes ,

**** while the distal parts meet together to form the body and cervix of the uterus and

the upper 4/5 ths of the vagina .

**** The stroma and muscles develop from the surrounding mesoderm .

****The fusion of the 2 Mullerian ducts brings together 2 peritoneal folds which become the broad

ligaments


****The Mullerian ducts reach the down to the urogenital sinus and at the meeting point , form the

Mullerian tubercle which meet a pair of endodermal sinovaginal bulbs which arise from the urogenital

sinus .

****The most lower portion of the uterovaginal canal becomes occluded by a solid core of tissue (the vaginal plate) , the origin of which is unclear .



This tissue elongates over the subsequent 2 months and canalizes by a process of central

desquamation, and the peripheral cells becomes the vaginal epithelium .


The ovary


Development of the ovary passes into three phases:

1st: Migration of the germ cells from the yolk sac to the posterior body wall at level of 10th thoracic

level to enter the Genital ridge.


2nd: the germ cells differentiate into oogonia then primary oocytes and become arrested until puberty.


3rd: descent of the ovary to reach the pelvis along a ligamentous cord called the gubernaculum that is
attached inferiorly to the inguinal region. The gubernaculum becomes incorporated into the uterine wall at the point of entry of the fallopian tube and persists in the adult as the ovarian ligament and the round ligament.



External genitalia

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• Clitoris develops from the genital tubercle (by slight elongation)
• Labia minora develop from the genital folds (by remaining separate)
• Labia majora develop from the genital swellings (by enlarging greatly)
• Vestibule develops from the lower most part of the urogenital sinus