Transcript The development of genital tract

The development of
genital tract
By Dr. Eman fathi
The development of the reproductive
system It is a part of the stages of
sexual differentiation. Because its
location, to a large extent, overlaps
the urinary system, the development
of them can also be described
together as the development of the
urinary and reproductive organs.
The reproductive organs are
developed
from the intermediate mesoderm
on each side of the root of the
mesentery beneath the epithelium of
coelom. The male and female
reproductive systems follow a similar
pattern of development, with sexual
distinction coming about as a result of
the influence of hormones.
The permanent organs of the adult are preceded
by a set of structures which are purely
embryonic, and which with the exception of the
ducts disappear almost entirely before the end
of fetal life. These embryonic structures are the
Wolffian and Müllerian ducts, also known as
mesonephric and paramesonephric ducts,
respectively. The Wolffian duct remains as the
duct in males, and the Müllerian as that of the
female.
Contents •
In the outer part of the intermediate
mesoderm, between C5-T3 a series of short
evaginations from each segment grows
dorsally and extends caudally, fusing
successively to form the pronephric duct.
This continues to grow caudal ward until it
opens into the ventral part of the cloaca;
The mesonephric duct is what remains of
the pronephric duct after the atrophy of the
pronephros.
Three main stages during development
1.Differentiation of gonad (Sex determination)
2. Differentiation of internal genital organs
3. Differentiation of external genital organs
mesonephric/paramesonephric duct changes are
one of the first male/female differences that occur
in development, while external genitalia remain
indeterminate in appearance for quite a while
Sex determination takes place at the time of
fertilization through the coupling of two
gametes, either each with one X chromosome
(XX in females) or such with an X and a Y
chromosome (XY in males). Primarily, the male
(female) phenotype is determined by the
presence (or absence) of the Y chromosome
with its genes, even though genes on other
chromosomes are also involved
.
In addition to the(1) genetic factors,
(2)hormonal regulation also plays an
important role during the various
developmental steps.
During the first 6 weeks the genital system
is sex-indifferent and it is only then that
the gonads as well as the internal and
external genitalia form under hormonal
influence
Function of the testis
Normal female development does not depend on
gonadal hormones instead it occure due to
absence of testis
The testis have 3 endocrine functions :
1.secretion of (MIF)mullerian inhibiting factor
2.secretion of testosterone which directly
promotes wolffian development
3. secretion of testosteron which is converted to
(DHT) dihydrotetosterone by 5αreductase
in the external genitalia and promotes its
development
The first sign of development of reproductive •
organs (male or female) occurs during the fifth
week with the formation of the gonadal ridge. The
gonadal ridge continues to grow behind the
developing peritoneal membrane lining the
abdominal cavity. By the sixth week, string like
masses called primary sex cords form within the
enlarging gonadal ridge. In the female, the primary
sex cords will contribute to nurturing tissue of
developing ova
Development of the ovary
5th week of
gestation
Gonadal ridge
It will continue to
grow
6th week of
gestation
Mass called
primary sex
cord form
with in the
genital ridge
At 7th week of 9-10 weeks of
gestation
gestation
Identity of the
testis
Identity of
ovary
At 11th -12th
weeks of
gestation
germ cells
enter the
leptotene
stage of
prophase of
the 1st
meiotic
division
Development of gonads and ova
The primitive germ cells are first apparent in the
the yalk sac )endoderm )
From which they migrate to the gut and through
the mesentery to the genital ridge
The primitive gonads consist of Germ cells
thickened coelomic epithelium of genital ridge
By 5-6 weeks the epithelial element and germ cells
proliferate vigorously up to 14 weeks
The identity of the gonads is apparent in the testis
by 7 weeks, and 9-10 weeks in the ovary
The number of germ cells reach a maximum of
(7millions) in each ovary at 15-20 weeks , falling to 2
million at birth , and 400 000 by puberty
At 11-12 weeks the germ cells enter the leptotene
stage of prophase of the 1st meiotic division . They
remain in the prophase until ovulation occur
Early , ovary is attached to the inguinal fold and
uterus by gubernaculum along which it descend to its
definitive site
The cranial part of gubernaculum become the ovarian
ligament
And the caudal part become the round ligament
Development of uterus and fallopian
tubes
At 5-6 weeks the paramesonephric (mullerian)
duct develop at the lateral aspect of the
mesonephros , it extend caudaly to reach the
urogenital sinus at 9 weeks.
The wolffian develops before the mullerian and
gives out a pouch , the ureteric diverticulum
before entering the urogenital sinus and form a
separate opening , that’s why the wolffian duct
contribute to the ureter and trigon of the
bladder.
at 8 weeks both mullerian and wolfian
are present , at this point sex
differentiation will begin , wolffian
system degenerate due to lack of
testosterone .
The lower portion of mullerian duct
fuse to form uterus and cervix
while Separate as the fallopian tubes
the upper portion
Development of uterus and tubes
5 -6 weeks of
gestation
(mullerian)
duct develop
at the lateral
aspect of the
mesonephros
at 8 weeks
Both wolffian
and mullerian
are present .
From this
point
onwords
wolffian
disppear due
to absence of
tetosterone
and
amullerian
will continue
At 9 weeks
Mullerian
extend
caudaly to
reach the
urogenital
sinus
At 3rd month
fifth month
Fusion of
mullerian
duct fuse to
form uterus
and cervix
Separate as
the fallopian
tubes while
the upper
portion
a ring-like
constriction
marks the
position of
the cervix of
the uterus,
and after the
sixth month
the walls of
the uterus
begin to
thicken
Development of the vagina
Paired sinu vaginal bulbs on the posterior
aspect of the urogenital sinus fuse with
the lower end of the mullerian duct to
form the vaginal plate . At 1st the vagina
consist of solid mass which grows rapildy
and become canalized at 16-18 weeks . In
the mature vagina the upper 4/5 (four
fifth) derived from the mullerian duct and
the lower fifth develop from the urogenital
sinus
Formation of the vestibule
The urogenital sinus has 3 portions the
1.upper portion which will form the bladder
2. pelvic portion form the urethra
3. the lower(phalic portion) which will become
increasingly shallow to form the vestibule in
female and penile urethra in male.
The genital tubercle form the clitoris and the
genital fold form the labia minora , the genital
swelling become the labia majora
Female
Male
Primitive structure
Ovary
Testis
Un differentiated
gonads
Mullerian system
(paramesonephric)
Wolffian system
(mesonephric
Genital tubercle
Uterus , tubes , and
upper 4/5 of the vagina
Appendix testis and
prostetic utricle
Occasional remnant part Epidydimis vas deference
of the bladder and
, trigone of the bllader ,
prostetic urethra above
ureter (
the ejaculatory duct
Clitoris
Penis
Genital fold
Labia minora
Penile urethra
Genital swelling
labia majora and
bartholines gland
Scrotum and bulbourethral glands