Development of female genital tract

1. DEVELOPMENT OF FEMALE
GENITAL TRACT
BY KARAN KUMAR
ROLL NO: 33
BATCH: 15TH

2. OUTLINE
 Development of Gonads
 Sex Determination
 Development of Ovaries
 Development of Genital Ducts
 Development of Vagina
 Development of External Genitalia

3. Development of Gonads
The gonads are derived from 3 sources:
 The mesothelium (mesodermal epithelium) lining the posterior
abdominal wall
 The underlying mesenchyme (embryonic connective tissue)
 The primordial germ cells

4. Indifferent Gonads
 The initial stages of gonadal development occur during the fifth
week
 A thickened area of mesothelium develops on the medial side of the
mesonephros
 Proliferation of this epithelium and the underlying mesenchyme
produces a bulge on the medial side of the mesonephros called
gonadal ridge

6. Indifferent Gonads
 Finger like epithelial cords or Gonadal cords
soon grow into the underlying mesenchyme
 The indifferent gonad now consists of an
external cortex and an internal medulla
 In embryos with an XX sex chromosome
complex, the cortex differentiates into an ovary
and the medulla regresses
 In embryos with an XY sex chromosome
complex, the medulla differentiates into a testis
and the cortex regresses

7. Primordial Germ Cells
 These large, spherical cells are visible early in the fourth
week among the endodermal cells of the yolk sac near
the allantois
 During folding of the embryo, the dorsal part of the yolk
sac is incorporated into the embryo
 With this the primordial germ cells migrate along the
dorsal mesentery of the hindgut to the gonadal ridges
 During the sixth week the primordial germ cells enter the
underlying mesenchyme and are incorporated in the
gonadal cords

9. Sex Determination
 Chromosomal and genetic sex is determined at fertilization
 It depends upon whether an X-bearing sperm or a Y-bearing sperm
fertilizes the X-bearing ovum
 The type of gonads develop is determined by the sex chromosome
complex of the embryo (XX or XY)

10. Sex Determination
 Before the seventh week, the gonads of the two
sexes are identical in appearance called
indifferent gonads
 Development of the male phenotype requires a
Y chromosome
 The SRY gene for a testes-determining factor
(TDF) has been localized in the sex-determining
region of the Y chromosome
 Two X chromosomes are required for the
development of the female phenotype

11. Sex Determination
 The Y chromosome has a testes-determining effect on
the medulla of the indifferent gonad
 The absence of a Y chromosome results in the formation
of an ovary
 Testosterone, produced by the fetal testes, determines
the maleness
 Primary female sexual differentiation in the fetus does
not depend on hormones
 It occurs even if the ovaries are absent

12. Development of Ovaries
 Gonadal development occurs slowly in female embryos
 The X chromosomes bear genes for ovarian development and an
autosomal gene also appears to play a role in ovarian
organogenesis
 The ovary is not identifiable histologically until about the 10th week

13. Development of Ovaries
 Gonadal cords do not become prominent but
they extend into the medulla and form a
rudimentary rete ovarii
 This structure and gonadal cords normally
degenerate and disappear
 Cortical cords extend from the surface
epithelium of the developing ovary into the
underlying mesenchyme during the early fetal
period

15. Development of Ovaries
 As the cortical cords increase in size, primordial germ cells are
incorporated in them
 At about 16 weeks these cords begin to break up into isolated cell
clusters called primordial follicles
 Each primordial follicle consists of an oogonium, derived from
primordial germ cell

16. Development of Ovaries
 Each oogonium is surrounded by a single layer of
flattened follicular cells derived from the surface
epithelium
 Active mitosis of oogonia occurs during fetal life
producing thousands of primordial follicles
 No oogonia form postnatally
 Many oogonia degenerate before birth
 About 2 million remain enlarge to become primary
oocytes before birth

18. Development of Ovaries
 After birth the surface epithelium of the ovary flattens to a
single layer of cells continuous with the mesothelium of the
peritoneum at the hilum of the ovary
 The surface epithelium of the ovary was formerly
inappropriately called the germinal epithelium
 The surface epithelium becomes separated from the follicles
in the cortex by a thin fibrous capsule called tunica albuginea
 As the ovary separates from the regressing mesonephros, it is
suspended by a mesentery called mesovarium

19. Development of Genital
Ducts
 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

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

23. Development of Genital
Ducts
 Both the paramesonephric ducts pass caudally
and reach the future pelvic region
 Cross ventral to the mesonephric ducts
 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

25. Development of Female
Genital Ducts & Glands
 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

26. Development of Female
Genital Ducts & Glands
 The uterine tubes develop from the unfused
cranial part of the paramesonephric ducts
 The caudal fused portions of these ducts form
the uterovaginal primordium
 It gives rise to uterus and superior part of vagina
 The endometrial stroma and myometrium are
derived from splanchnic mesenchyme

28. Development of Female
Genital Ducts & Glands
 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

29. Development of Vagina
 The vaginal epithelium is derived from the endoderm of the
urogenital sinus
 The fibromuscular wall of the vagina develops from the surrounding
mesenchyme
 Contact of the uterovaginal primordium with the urogenital sinus
forming the sinus tubercle

31. Development of Vagina
 Sinus tubercle induces the formation of paired
endodermal outgrowths called sinovaginal bulbs
 The sinovaginal bulbs fuse to form a vaginal
plate
 Later the central cells of the plate break down,
forming lumen of vagina
 The peripheral cells of the plate form the vaginal
epithelium

33. Development of Vagina
 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

35. Development of External
Genitalia
 Up to the seventh week of development the external genitalia are
similar in both sexes
 Distinguishing sexual characteristics begin to appear during the
ninth week
 External genitalia are not fully differentiated until the twelfth week

36. Development of External
Genitalia
 Early in the fourth week, proliferating
mesenchyme produces a genital tubercle in both
sexes at the cranial end of the cloacal membrane
 Labioscrotal swelling and urogenital folds soon
develop on each side of the cloacal membrane
 The genital tubercle soon elongates to form a
primordial phallus

38. Development of External
Genitalia
 When the urorectal septum fuses with the cloacal membrane, it
divides it into a dorsal anal membrane and a ventral urogenital
membrane
 The urogenital membrane lies in the floor of a median cleft, the
urogenital groove, which is bounded by urogenital folds

39. Development of External
Genitalia
 The anal and urogenital membranes rupture a week later forming
the anus and urogenital orifice, respectively
 In female fetus the urethra and vagina open into a common cavity
called vestibule

41. Development of Female
External Genitalia
 Estrogen produced by the placenta and fetal
ovaries appear to be involved in feminization of
indifferent external genitalia
 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

42. Development of Female
External Genitalia
 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

44. Development of Female
External Genitalia
 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

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