The female reproductive system develops from indifferent gonads that are initially the same in males and females. In the absence of the SRY gene, the gonads develop into ovaries containing primordial follicles. The paramesonephric ducts fuse to form the uterus and fallopian tubes, while the mesonephric ducts regress. The vagina develops from sinovaginal bulbs, and external genitalia are feminized under the influence of estrogen to form the clitoris and labia.

1. DEVELOPMENT OF THE FEMALE
REPRODUCTIVE SYSTEM
Atere Ahmad Jr.
MB;BS (ILORIN)

2. OUTLINE
 Introduction
 Development of the gonads: Indifferent gonads
 Development of the ovary
 Development of the uterus and fallopian tubes
 Congenital malformations of the uterus
 Development of the vagina
 Development of the external genitalia

3. INTRODUCTION

4. INTRODUCTION
 Development begins with fertilization, the process by
which the male gamete, the sperm, and the female
gamete, the oocyte, each harbouring a pair of sex
chromosomes, unite to give rise to a zygote, inheriting
any combination of the sex chromosomes.
 If the sex pair is XX, the individual is genetically female;
if the pair is XY, the individual is genetically male.

5. INTRODUCTION
 The reproductive system, its structure and function depends
largely on sex differentiation, a complex process that
involves many genes.
 However the key to sexual dimorphism is the Y
chromosome, which contains the testis-determining gene
called the SRY gene on its short arm (Yp11) that codes for
the SRY protein, the testis-determining factor (TDF).
 Under its influence, male development occurs; in its
absence, female development is established.

6. INTRODUCTION

7. DEVELOPMENT OF THE GONADS

8. INDIFFERENT 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

9. INDIFFERENT GONADS
 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.
 The initial stages of gonadal development occur during
the fifth week of intrauterine life
 The primitive gonads appear initially as a pair of
longitudinal ridges, the gonadal ridges. They are formed
by proliferation of the epithelium and a condensation of
underlying mesenchyme on the medial side of the
mesonephros.

11. INDIFFERENT GONADS
 Primordial Germ cells (PGC) fated to occupy the ridges
do not appear until the 6th week of development.

12. INDIFFERENT GONADS
 PGCs originate in the epiblast during the second week
of development, migrate through the primitive streak,
and by 3rd week reside among endoderm cells in the
wall of the yolk sac.

14.  In the fourth week, germ cells begin to migrate from
the endoderm lining of the yolk sac to the genital
ridges, via the dorsal mesentery of the hindgut. They
reach the genital ridges in the sixth week.

16. INDIFFERENT GONADS
 Simultaneously, the epithelium of the genital ridges
proliferates and penetrates the intermediate mesoderm to
form the primitive sex cords. The combination of germ
cells and primitive sex cords forms the indifferent gonad
– from which development into the testes or ovaries can
occur.
 If the PGCs fail to reach the ridges, the gonads do not
develop. Hence, they have an inductive influence on
development of the gonad into ovaries or testes.

18. INDIFFERENT GONADS
 If the embryo is genetically male, the primordial germ
cells carry an XY sex chromosome complex and under
influence of the SRY gene, the primitive sex cords
continue to proliferate and form the testis cords.
 In a female embryo, the XX sex chromosomes are present.
As there is no Y chromosome, there is no SRY gene to
influence development. Without it, the primitive sex
cords degenerate and do not form the testis cords.

19. DEVELOPMENT OF THE OVARIES

20. DEVELOPMENT OF THE OVARIES
 In the absence of the testis-determining factor, the
epithelium of the gonad continues to proliferate,
producing cortical cords. In the third month, these cords
break up into clusters, surrounding each oogonium
(germ cell) with a layer of epithelial cells called follicular
cells.
 Active mitosis of oogonia occurs during intrauterine life.
Majority of oogonia continue to divide but some of them
arrest their cell division in prophase of meiosis I and form
primary oocytes.

22. DEVELOPMENT OF THE OVARIES (CONT’D)
 By the 5th month of prenatal development the total number
of germ cells in the ovary reaches its maximum, estimated
at 7 million.
 At this time cell death begins and many oogonia as well as
primary oocytes degenerate and become atretic. No
oogonia forms postnatally.
 Only about 2 million germ cells remain at birth and 400,000
at puberty.
 A primary oocyte together with its surrounding follicular
cells is known as a primordial follicle.

23. DESCENT OF THE OVARIES
 While the gonads arise in the upper lumbar region, they
are each tethered to the labia by the gubernaculum – a
ligamentous structure formed from mesenchyme.
 As the body of the fetus grows, the ovaries become
more caudal. They pass through the inguinal
canal around the 28th week, and reach their final
destination just within the true pelvis, slightly below the
level of the pelvic brim. The gubernaculum becomes the
ovarian ligament and round ligament of the uterus.

25. DEVELOPMENT OF THE UTERUS AND
FALLOPIAN TUBES

26. DEVELOPMENT OF THE UTERUS AND
FALLOPIAN TUBES
 In the first weeks of urogenital development, all embryos
have two pairs of ducts, both ending at the cloaca. These
are the:
 Mesonephric (Wolffian) ducts
 Paramesonephric (Mullerian) ducts

27. DEVELOPMENT OF THE UTERUS AND
FALLOPIAN TUBES
 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

29. DEVELOPMENT OF THE UTERUS AND
FALLOPIAN TUBES
 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

31. DEVELOPMENT OF THE UTERUS AND
FALLOPIAN TUBES
 Both paramesonephric ducts pass caudally and reach the
future pelvic region, then cross ventral to the mesonephric
ducts
 They 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

33. DEVELOPMENT OF THE UTERUS AND
FALLOPIAN TUBES
 In female embryos, the mesonephric ducts regress because
of the absence of testosterone
 In the presence of estrogen and the absence of Mullerian
inhibiting substance (MIS) produced by Sertoli cells,
paramesonephric ducts develop into the main genital duct of
the female
 Initially 3 parts can be recognized:

34. DEVELOPMENT OF THE UTERUS AND
FALLOPIAN TUBES
 Cranial vertical part which opens within the coelomic
cavity.
 Mid horizontal part which crosses the mesonephric duct.
 Caudal vertical part which fuses in the midline with its
partner from the opposite side

36. DEVELOPMENT OF THE UTERUS AND
FALLOPIAN TUBES
 With the descent of ovaries into the pelvic inlet, the first two
parts of the duct on each side will develop into the
Fallopian tubes.
 The caudal fused parts will give rise to the fundus, body,
and cervix of the uterus as well as the upper part of the
vagina.
 The surrounding mesenchyme will form the myometrium
and perimetrium.

38. DEVELOPMENT OF THE UTERUS AND
FALLOPIAN TUBES
 Fusion of the paramesonephric ducts also brings together
a peritoneal fold that forms the broad ligament of the
uterus
 The uterus and the broad ligaments thus divide the pelvic
cavity into the uterorectal pouch and the uterovesical
pouch.

39. CONGENITAL MALFORMATIONS OF
THE UTERUS

40. CONGENITAL MALFORMATIONS OF THE UTERUS
 Lack of fusion of Paramesonephric ducts in a localized
area or throughout the length results in different types of
duplication of uterus.
 Uterus didelphys results from failure of fusion of the
inferior parts of paramesonephric ducts. The uterus is
entirely double and each one enters a separate vagina

42. CONGENITAL MALFORMATIONS OF THE UTERUS
 Uterus arcuatus is the least severe form in which there is
malfusion in the upper region of the vertical parts of
paramesonephric ducts and is represented by a slight
indentation in the middle of the fundus of uterus.
 Uterus bicornis is one of the more common anomalies in
which the malfusion involves only the superior part of the
paramesonephric ducts resulting in a double-horned
uterus entering a single vagina

44. CONGENITAL MALFORMATIONS OF THE UTERUS
 In patients with complete or partial atresia of one of the
paramesonephric ducts, the rudimentary part lies as an
appendage to the well-developed side as seen in Uterus
bicornis unicollis.
 If the atresia involves one side, an atresia of the cervix
may result
 If the sinovaginal bulbs fail to fuse or do not develop at
all, a vaginal atresia develops

46. DEVELOPMENT OF THE VAGINA

47. DEVELOPMENT OF THE VAGINA
 During the 7th week of intrauterine life, the solid tip of
fused paramesonephric ducts reaches the dilated pelvic
part of the urogenital sinus
 Contact of the uterovaginal primordium with the urogenital
sinus forms the sinus tubercle
 The sinus tubercle induces the formation of paired
endodermal outgrowths called sinovaginal bulbs

49. DEVELOPMENT OF THE VAGINA
 The sinovaginal bulbs subsequently fuse to form a vaginal
plate
 Later the central cells of the plate break down, forming the
lumen of the vagina
 The peripheral cells of the plate form the vaginal
epithelium
 The fibromuscular wall of the vagina develops from the
surrounding mesenchyme
 Four wing-like expansions of the fused paramesonephric
duct will encircle the cranial part of the vaginal plate.
They will become the vaginal fornices.

51. DEVELOPMENT OF THE 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
 At the time of birth (perinatal period), this hymen usually
ruptures in the middle and remains as a thin fold of
mucous membrane just within the vaginal orifice.

53. ANOMALIES OF VAGINA DEVELOPMENT
 Failure of canalization of the vaginal plate will lead to
vaginal atresia.
 If the middle portion of the hymen fails to get thin
down during the last weeks of intrauterine life, there
would be failure of rupture of hymen during the time
of birth resulting in an imperforate hymen.

55. DEVELOPMENT OF EXTERNAL
GENITALIA

56. 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

57. DEVELOPMENT OF EXTERNAL GENITALIA
 In the third week, mesenchyme cells originating in the
region of the primitive streak migrate around the cloacal
membrane to form a pair of slightly elevated cloacal folds
 Cranial to the cloacal membrane, the folds unite to form the
genital tubercle.
 Caudally, the folds are subdivided into urethral folds
anteriorly and anal folds posteriorly

59. DEVELOPMENT OF EXTERNAL GENITALIA
 In the meantime, another pair of elevations, the genital
swellings, becomes visible on each side of the urethral
folds.
 Estrogen produced by the placenta and fetal ovaries
appear to be involved in feminization of indifferent
external genitalia
 The genital tubercle thus elongates only slightly and
forms the clitoris

60. DEVELOPMENT OF EXTERNAL GENITALIA
 The genital swellings later enlarge to form the labia
majora in the females.
 They fuse anteriorly to form the anterior labial
commisure and mons pubis
 Fuse posteriorly to form the posterior labial commisure

62. DEVELOPMENT OF EXTERNAL GENITALIA
 The urethral folds do not fuse, except posteriorly, and
develop into the labia minora.
 The posterior fusion forms the frenulum of the labia
minora
 The urogenital groove remains open and forms the
vestibule of the vagina, a common cavity into which the
urethra and vagina open.

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