Download 10/2016

Fifth stage
‫أسماء السنجري‬.‫د‬
Gynecology
Lec-1
5/10/2016
Normal development of the female genital tract
The student at the end of this lecture should be able :
.1-
Describe the normal development of the internal and external genital organs
2-.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
- 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)
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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 part
as 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 the
uterus 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.
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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 the cloacal 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.
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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 week by 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 give rise 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 themselves with the pregranulosa cells are disintegrate.
Follicular development will become evident by 28 week of intrauterine life .
SH.J
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