Development of the Female Genital System

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Development of the Female Genital System

• Bilal M. K. Marwa

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Development of Ovaries
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Development of ovaries

• 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

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• 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.

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• 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

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Primordial Follicles

• 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

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Development of Female Genital Ducts and glands
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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

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• 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
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• Both the paramesonephric ducts pass caudally and
  reach the future pelvic region
• Cross ventral to the mesonephric ducts

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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
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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

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• 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

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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

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Development of Vagina

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

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

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• 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

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Development of Female Genital Ducts and glands
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Development of Female External Genitalia

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

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• 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

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• 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

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• 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