Development of female genitalia

Development
Of
Female Genital
System
Department of Gynecology and Obstetrics

Genital System
Development Of Indifferent Gonads
Development Of Genital Ducts
External Female Genitalia Internal Female Genitalia

Sex differentiation is the complex process that
involves many genes, including some that are
autosomal. The key to sexual dimorphism is Y
chromosome which contains testis determining
gene called the SRY gene (sex determining
region on Y) gene on it’s short arm (Yp11).
The SRY protein is the testis determing factor
under it’s influence male development occurs,
and it’s absence leads to female development.
Genital System

Although the sex of the embryo is determined
genetically at the time of fertilization. The gonads
do not acquire male or female morphological
characteristics until the 7th week of
development.

DEVELOPMENT OF GONADS
Gonads appear initially as a pair of longitudinal ridges,
the genital or gonadal ridges. They are formed by
proliferation of the epithelium and a condensation of
underlying mesenchyme. Germ cell do not appear in the
genital ridges until the sixth week of development.
The gonads are derived from three sources:
•The primordial germ cells (Epiblast)
•The mesothelium(mesodermal epithelium) lining the
posterior abdominal wall
•The underlying mesenchyme( embryonic connective
tissue)

INDIFFERENT GONADS
The initial stages of gonadal development occur
during the fifth week when a thickened area of
mesothelium develops on the medial side of the
mesonephors i.e. from lining mesothelium of
posterior abdominal wall.
Proliferation of this epithelium and the underlying
mesenchyme produces a bulge on the medial side of
the mesonephros- The gonadal ridge.
Fingerlike epithelial cords- the gonadal cords soon
grow into the underlying mesenchyme.

Primordial germ cells which are large spherical sex
cells become visible early in the fourth week among the
endodermal cells of yolk sac near the origin of allantois
and migrated through primitive streak to reach
endodermal cells
They migrate along the dosal mesentery of the hind
gut to gonadal ridges during 6th week and and invade the
genital ridges ..
Then proliferation of genital ridge occurs and epithelial
cells penetrate the underlying mesenchyme and form a
cords gonadal cords (primitive sex cords).
 In both male and female embryos, these cords are
connected to surface epithelium and it is impossible to
differentiate between the male and female gonad hence
called indifferent gonads.

The indifferent gonads differentiate into cortex
and medulla.
Medulla regresses in embryos with an XX sex
chromosome complex whereas in XY sex
chromosome complex, medulla differentiate into
testis but cortex regresses.
Thus, indifferent gonads is defined as the
gonads developed before the 7th week which are
identical in appearance in both the sexes.

Development of genital ducts
Both male and female embryos have two pairs of
genital ducts in period of indifferent gonadal state :
A. Mesonephric duct (wolffian ducts) and
B. paramesonephric ducts (mullerian ducts)
The paramesonephric ducts have a leading role in the
development of female reproductive system

The paramesonephric duct develop lateral to the
gonads and mespnephric duct which play essential
role in the development of female reproductive
system.
The para mesonephric duct from each side form
longitudinal invagination of the mesothelium on the
lateral aspect of the mesonephric duct
The funnel shaped cranial end of these ducts open
into peritoneal cavity .
The paramesonephric duct pass caudally, parallel to
the mesonephric duct until they reach the further
pelvic region of the embryo.

They cross ventrally to the mesonephric duct approach
each other in midline and fuse to form Y shaped
uterovaginal primodium. (future uterovaginal canal)
In the other hand
This tubular structure project into the dorsal
(posterior)wall of urogenital sinus and produce an
elevation the sinus (muller) tubercle (paramesonephric
tubercle) in which the combined tip of paramesonephric
duct projects
The mesonephric ducts regress because of the absence
of testosterone and the paramesonephric ducts develops
because of the absence of MIS(mullerian inhibiting sbstnc)

The uterine tube develop from the non fused cranial
parts of the paramesonephric ducts.
The caudal fused portion of this ducts forms the
uterovaginal primodium, as name indicate it gives rise to
uterus and superior part of the vagina
The endometrium stroma and myometrium derived
from splanchnic mesenchyme (surrounding connective
tissue)
Fusion of paramesonephric ducts also bring together a
peritoneal fold that form the broad ligament and two
peritoneal compartments the retrouterine pouch and
vesicouterine pouch… (picture)

Development Of Ovaries
Gonadal development occur slowly in female embryo
Gonadal sex cords(primitive sex cord) dissociate into
irregular cell clusters and extend into the medulla and form
a rudimentary rete ovary in absence of TDF (testis
determining factor) later they disappera and replaced by
vascular stroma- ovarian medulla
 surface epithelium of female gonad continue proliferate
and at the 7th week give rise to cortical cords,

As the cortical cord increase in size primodial germs
cells are incoperate in them.
At about 16 weeks these cords begins and break up to
isolated cell clusters called primodial follicles each of
which consist of an oogonium, derived from primodial
germ cells surrounding by a single layer of flattened
follicular cells derived from surface epithelium .
Active mitosis of oogonia occurs during fetal life
producing thousands of follicles.
Although many oogonia degenerate before birth two
million or so that remain enlarge to become primary
oocytes after birth

The surface epithilum becomes separated from the
follicles in the cortex by the thin fibrous capsule the
tunica albugina
As the ovary separates from the the regressing
mesonephrons it is suspended by a mesentry the
mesovarium.

Development of female external genitalia
The external genital organs start developing almost
simultaneously with the development of the internal
genital organs.
Feminization of the indifferent external genitalia is
produced by the placenta and fetal ovaries (estrogenic
effect)
The endodermal cloaca is divided by urorectal
septum and forms dorsally rectum and anal canal, and
ventrally urogenital sinus
The site of origin female external genitalia is from the
urogenital sinus.

The urorectal septum contains a pair of
paramesonephirc ducts close to the midline and a pair
of mesonephric ducts laterally.
The vertical portion, known as urogenital sinus,
differentiates into three parts:
1. Upper vesicourethral : major pat of female urethra.
2. Middle pelvic: unite with caudal end of the two
paramesonephhric ducts in the midline and forms
epithelium of the vagina, Bartholin’s gland and the
hymen.
3. The lower phallic: contributes to vestibule of vagina.

Development of vagina
It develops from two main sources
1. Upper 1/3rd: lower part of fused paramesonephric duct
(utero vaginal canal)
2. Lower 2/3rd: Sinovaginal bulbs (evagination from pelvic
part of urogenital sinus)
Two solid evaginations, sivovaginal bulbs proliferate and
form a solid vaginal plate.
It develops cranially and fully canalized by the end of 5th
month
The vaginal fornices develop from the paramesonephric
duct caudally.
The lumen of vagina remains separated from the urogenital
sinus by a thin tissue plate hymen

In the third week of development
mesenchymal cell from primitive streak migrate
to cloacal membrane to form cloacal folds
Cranial end of fold unite to form genital
tubercle
In the mean time genital swelling become
visible which later become labia majora
The genital tubercle elongate only slightly and
form the clitoris.
Urethral fold do not fused and developed into
labia minora.

Urethral fold do not fused and developed into labia
minora.
Urogenital groove opens and form the vestibule

Clinical correlates
Uterine and vaginal defect:
result from lack of fusion of the paramesonephric duct in local
area or throughout their normal line of fusion.
Double uterus (uterus didelphys) :failure of fusion of inferior
part of paramesonephric duct
Uterus arcuatus: uterus is divided internally by thin septum
Bicornuate uterus: duplication involves only the superior part of
body of uterus
Bicornuate uterus with a rudimentary horn: one
paramesonephric duct is retarded in its growth and doesn’t fuse
with other
Unicornuate uterus: one paramesonephric duct fails to develop
Cervical atresia: failure of canalization of cervix
Vaginal atresia: due to imperforate hymen or transverse septum

Anomalies of uterine tube: infrequent
Accessory ostia
Complete and segmental absence
Duplication of duct
Lack of muscular layer and failure of tube to
canalize

Interesting Fact
Although the genital tubercle doesn’t elongate
extensively in the female it is larger than male
during the early stage of the development infact
using the tubercle length as a criteria (USG) has
resulted in mistake in identification of sexes
during the 3rd and 4th month of gestation.

Development of female genitalia

Development of female genitalia

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