embryology of female genital system

3.  Gonadal development occurs slowly in females
 The X chromosmes bear genes for ovarian
development
 Autosomal gene also appears to play a role in
ovarian development
 Until 10th week: ovary cannot be identified
histologically

4.  Gonadal cords do not
become prominent.
 They extend into the medulla
and form rete ovarii, which is
rudimentary.
 Normally, it degenerates and
disappears as well as the
gonadal cords.

5.  Cortical cords extend from
 the surface epithelium of
the developing ovary into
 the underlying mesenchyme
 Time: early fetal period
 Epithelium: mesothelium-derived
 As the cortical cords
increase in size, primordial
germ cells are incorporated
in them
 Cords begin to break up
 forming primordial
follicles
 Time: about 16 weeks

6.  Formed at about 16 weeks
 Each consists of:
 Oogonium: derived from a primordial germ cell
 Surrounding it: a layer of flattened follicular cells
 Derived from surface epithelium
 Active mitosis of oogonia occurs during fetal
life producing thousands of primordial follicles
 No oogonia form postatally.
 Many oogonia degenerate before birth
 About 2 million remain enlarge to become primary
oocytes before birth

8.  Both male and female embryos have two pairs of genital ducts
 The mesonephric ducts (wolffian ducts) play an important
role in the development of the male reproductive system
 The paramesonephric ducts (mullerian ducts) have a leading
role in the development of the female reproductive system
 Till the end of sixth week, the genital system is in an
indifferent state, when both pairs of genital ducts are present

9.  The mesonephric ducts, which drained urine
from the mesonephric kidneys play a major
role in the development of male reproductive
system
The paramesonephric ducts
pass caudally, parallel to the
mesonephric ducts
The funnel shaped cranial ends of these ducts
open into the peritoneal cavity
The paramesonephric ducts play an essential role
in the development of the female reproductive
system

10.  Both the
paramesonephric
ducts pass caudally and
reach the future pelvic
region
 Cross ventral to the
mesonephric ducts

11. Fuse to form a Y-shaped
uterovaginal primordium in
the midline
This tubular structure projects
into the dorsal wall of the
urogenital sinus and produces an
elevation called sinus (muller)
tubercle

12.  In female embryos, the mesonephric ducts regress
because of the absence of testosterone
 Paramesonephric ducts develop because of the
absence of mullerian inhibiting substance (MIS)
 Female sexual development does not depend on the
presence of ovaries or hormones
 The paramesonephric ducts form most of the female
genital tract

13.  The caudal fused
portions of these ducts
form the uterovaginal
primordium
 It gives rise to uterus
and superior part of
vagina
The uterine tubes develop from
the unfused cranial part of the
paramesonephric ducts
 The endometrial stroma and myometrium are
derived from splanchnic mesenchyme

14.  Fusion of the paramesonephric ducts also
brings together a peritoneal fold that forms
the broad ligament
 Also forms two peritoneal compartments, the
rectouterine pouch and the vesicouterine
pouch

15.  Sinus tubercle induces the
formation of paired
endodermal outgrowths
called sinovaginal bulbs
 The sinovaginal bulbs fuse
to form a vaginal plate

16.  Later the central cells of the plate break down,
forming lumen of vagina
 The peripheral cells of the plate form the vaginal
epithelium

17.  Until the fetal life, the
lumen of the vagina is
separated from the
cavity of the urogenital
sinus by a hymen
 The hymen is formed by
invagination of the
posterior wall of the
urogenital sinus,
resulting from
expansion of the caudal
end of the vagina
 The hymen remains as a
thin fold of mucous
membrane just within
the vaginal orifice

19.  Estrogen produced by the placenta and fetal
ovaries appear to be involved in feminization
of indifferent external genitalia

20. •Growth of the primordial
phallus gradually ceases and
becomes clitoris
•The clitoris is relatively
large at 18 weeks
•It develops like a penis but
the urogenital folds do not
fuse, except posteriorly

21.  Urogenital folds fuses
posteriorly to form
the frenulum of the
labia minora
 The unfused parts of
the urogenital folds
form the labia minora
 The labioscrotal folds
fuse posteriorly to
form the posterior
labial commisure

22.  The labioscrotal folds
fuse anteriorly to form
the anterior labial
commisure and mons
pubis
 Most parts of the
labioscrotal folds
remain unfused and
form two large folds of
skin called labia majora
 Labia majora are
homologous to the
scrotum