Download Development of parts of Female Reproductive

Development Parts of Female Reproductive
System
LEARNING OBJECTIVES:
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At the end of the lecture, students should be able to :
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Know the precursor and migration of primordial germ cell
Define the location and division genital ridge
Mention the differentiation in development of male and female genital tract
Describe the development of female genital ducts
Discuss the development and differentiation of Paramesonephric ducts and
development uterus and vagina
Primordial Germ Cells:
 The primitive germ cells are developed from the Epiblastic cells
of germ layer during the second week of development.
 These cells reside in yolk sac.
 During the fourth week of development these primitive germ
cells migrate towards the cloaca.
 The cloaca has dorsal mesentery through it is suspended into
intra-embryonic cavity.
Migration of Primordial Germ Cells:
 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.
 The gondal ridge is formed by the proliferation of mesencymal cells in the
intermediate part of mesodermal layer of embryo.
Gonadal Ridge:
 The urogenital ridge is formed on the dorsal abdominal wall by
the proliferation of mesenchymal cells.
 These cell formed an elevated parallel ridge which extends above
downwards and divided into lateral part which develops into urinary system
and
 Medial part which develops into genital system.
Sex Determination:
 Chromosomal and genetic sex depends on whether an X-bearing
sperm or a Y-bearing sperm fertilizes the X-bearing oocyte.
 Before the seventh week, the gonads of the two sexes are identical in
appearance and are called Indifferent Gonads.
 It is the TDF regulated by the Y chromosome that determines
testicular differentiation.
 The absence of a Y chromosome results in the formation of an
ovary.
Development of the 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 approximately the
10th week.
 Gonadal cords do not become prominent, but they extend into the
medulla and form a rudimentary rete ovarii.
 This structure and the 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.
 This epithelium is derived from the mesothelium.
 As the cortical cords increase in size, Primordial Germ Cells are
incorporated in them.
 At approximately 16 weeks, these cords begin to break up into isolated cell
clusters-Primordial Follicles.
each of which consists of an oogonium, derived from a primordial germ cell,
surrounded by a single layer of flattened follicular cells derived from the
surface epithelium.
 Active mitosis of oogonia occurs during fetal life producing primordial
follicles.
 No oogonia form postnatally.
 Although many oogonia degenerate before birth, the two million or so that
remain enlarge to become primary oocytes before birth.
 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 becomes separated from the follicles in the cortex by
a thin fibrous capsule, the Tunica Albuginea.
 As the ovary separates from the regressing mesonephros, it is suspended by
a mesentery-the Mesovarium
Development of the Genital Ducts:
 The paramesonephric ducts (mullerian ducts) have a leading role in the
development of the female reproductive system.
 They develop lateral to the gonads and mesonephric ducts on each side from
longitudinal invaginations of the mesothelium on the lateral aspects of the
mesonephroi.
Paramesonephric Ducts:
The edges of these paramesonephric grooves approach each other and fuse
to form the paramesonephric ducts.
Uterovaginal Primordium.
The funnel-shaped cranial ends of these ducts open into the peritoneal
cavity.
Caudally, the paramesonephric ducts run parallel to the mesonephric ducts until
they reach the future pelvic region of the embryo.
Uterovaginal Primordium:
 Here they cross ventral to the mesonephric ducts, approach each
other in the median plane, and fuse to form a Y-shaped
uterovaginal primordium.
 This tubular structure projects into the dorsal wall of the urogenital
sinus and produces an elevation-the sinus tubercle.
Differentiation of Paramesonephric Ducts:
The paramesonephric ducts develop into the main genital ducts of the
female. Initially, three parts can be recognized in each duct:
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Cranial vertical portion that opens into the abdominal cavity,
Horizontal part that crosses the mesonephric duct
Caudal vertical part that fuses with duct of the opposite side.
Differentiation of Paramesonephric Ducts:
 With descent of the ovary, the first two parts develop into the
uterine tube and the caudal parts fuse to form the uterine canal.
 When the second part of the paramesonephric ducts moves
mediocaudally, the urogenital ridges gradually come to lie in a
transverse plane.
Development of Uterus:
 After the ducts fuse in the midline, a broad transverse pelvic fold is
established.
 This fold, which extends from the lateral sides of the fused
paramesonephric ducts toward the wall of the pelvis, is the broad
ligament of the uterus.
 The uterine tube lies in its upper border, and the ovary lies on its
posterior surface.
 The fused paramesonephric ducts give rise to the corpus (body) and cervix
of the uterus.
 They are surrounded by a layer of mesenchyme that forms the muscular coat
of the uterus, the myometrium, and its peritoneal covering, the perimetrium.
Development of Vagina:
 Shortly after the solid tip of the paramesonephric ducts reaches the
urogenital sinus, two solid evaginations grow out from the pelvic
part of the sinus.
 These evaginations, the sinovaginal bulbs, proliferate and form a
solid vaginal plate.
 Proliferation continues at the cranial end of the plate, increasing the
distance between the uterus and the urogenital sinus.
 By the fifth month, the vaginal outgrowth is entirely canalized.
 The wing-like expansions of the vagina around the end of the uterus, the
vaginal fornices, are of paramesonephric origin.
 Thus, the vagina has a dual origin, with the upper portion derived from the
uterine canal and the lower portion derived from the urogenital sinus.
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