Development of the female genital system
-
Upload
pukar-sapkota -
Category
Health & Medicine
-
view
64 -
download
3
description
Transcript of Development of the female genital system
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
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.
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
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
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
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
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
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
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
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
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
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
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
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
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