Normal development of the female genital tract

Dr. asmaa A. al sanjary

Normal development of the female genital tract

The student at the end of this lecture should be able to:

Describe the normal development of the internal and external genital organs.
Determine the factors influencing normal sexual development.

Introduction

Following fertilization the normal embryo contains 46 chromosomes ,including 22 autosomes derived from each parent.
46XY embryo will develop as a male
46XX embryo will develop as a female
It’s the presence or the absence of the Y chromosome which determines whether the undifferentiated gonad becomes a testis or
an ovary.

The testis determining factor is on the Y

chromosome on a gene termed the SRY(sex
determining region of the Y chromosome).
This gene triggers testis formation from the
indifferent gonad.
Ovarian differentiation is determined by the
presence of 2 X chromosomes and the ovarian
determinant is located on the short arm of the
X chromosome.


Development of the Mullerian and and wolffian
Structures is under polygenic multifactorial
Inheritance and autosomal recessive gene may
also be involved.
The development of the differentiated gonad is
Fundamental for the development of the other
genital organs . This means the presence of the
testes leads to male genital organs and the
absence of an ovary leads to female genital
Organ.

Development of the genital organ

The genital organs and those of the urinary tract
arise in the intermediate mesoderm on either side
of the root of the mesentery beneath the epithelium
of the coelom.There is duct appear in association
of the pronephros(transient tubules in the cervical
region degenerate later),persists and extends
caudally to open at the cloaca called the
mesonephric(wolffian duct)


The mesonephros , the second primitive kidney develops as a swelling bulging into the dorsal wall of the coelom of the thoracic and upper lumber region.the mesonephros in the male persists in partas the excretory portion of the male genital system ; in the female only a small vestiges survive
The genital ridge in which the gonads of each sex
develop is visible as a swelling on the medial aspect of
the mesonephros . The paramesonephric duct which
forms much of the female genital tract develops as
In growth of the coelomic epithelium laterally , then
become a groove then as a tube below the surface

The uterus and the fallopian tube

The two paramesonephric ducts extend caudally until
they reach the urogenital sinus at about 9 weeks ’gestation.
the blind ends projects into the posterior wall of the sinus
to become the Mullerian tubrcule.
At the beginning of the third month the Mullerian and the
wolffian ducts and the mesonephric tubules are all present
and capable of development. In the female there is
degeneration of the wolffian system and marked growth of
the Mullerian system .In the male the opposite will occurs
as a result of the production of the Mullerian inhibitory
Substance(MIF) produced by the fetal testis.


The lower ends of the Mullerian ducts come together in the midline ,fuse and develop into theuterus and the cervix. The cephalic ends of the duct remain separate to form the fallopian tubes. Proliferation of the mesenchyme around the fused portion of the ducts form the thick muscular wall of the uterus and the cervix.

:The vagina

At the point of fusion of the paramesonephric duct to
the dorsal wall of the urogenital sinus as the Mullerian
tubercle there is marked growth of the tissues from
which the vagina will forms, known as the vaginal plate,
which extends between the cervix and the urogenital
sinus . Canalization of the vagina occurs and completed
around the 20th to 24th week gestation. Incomplete
canalization at any level result into a vaginal septum and
outflow tract obstruction.

The external genitalia:

The primitive cloaca becomes divided by a transverse
septum into an anterior urogenital portion and posterior
rectal portion .The urogenital portion of the cloacal
membrane breaks down and it’s divided into three
portions ; external expanded phallic part, a deeper narrow
pelvic part ,between it and the region of the Mullerian
Tubercle , and a vesicourethral part connected superiorly
into the allantois .


Externally in this region the genital tubercle forms a conical projection around the anterior part of thecloacal membrane .
Two pairs of swelling on the medial part(genital folds),
and lateral pairs (genital swelling) formed by
proliferation of mesoderm around the end of the
urogenital sinus . Development till 10 weeks is the same
in the male and female and differentiation occur later.

The vesicourethral portion of the urogenital sinus forms the bladder and urethra , the pelvic and the phallic portion forms the vestibule , the genital tubercle enlarge slightly and forms the clitoris ,the genital fold form the labia minora and the genital swelling enlarges to form the labia majora.

The gonads :

The primitive gonads appears in embryos at 5 weeks.
A proliferation of the coelomic epithelium on the medial
aspect of the urogenital ridge and grows into mesenchyme
(primary sex cord) and the gonads now have outer cortex
And inner medulla.
In embryos with XX complement , the cortex differentiate
to become the ovary and the medulla regresses.
The primordial germ cells develop by the 4th week in the
endodermal cells of the yolk sac and during the 5th week
they migrate along the dorsal mesentery of the hind gut to the
gonadal rigdes and become incorporated into the mesenchyme
and the primary sex cord by 6th week.






The testicular differentiation is evident by 7 weekby disappearance of the germ cells from the cortex and the cells differentiate into fibroblasts which form the tunica albuginea. The deeper parts of the sex cord giverise to the rete testis and the seminiferous and straight tubules.
In the ovary there is active growth of the sex cord forming the pregranulosa cells which surround the oocyte. There is active growth phase make the largest number of oocyte surrounded by pregranlosa cells
(7 million )at 20 weeks , at birth its about (2 million)

Those oocyte who fails to surround themselveswith the pregranulosa cells are disintegrate.
Follicular development will become evident
by 28 week of intrauterine life .

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