The document summarizes the development of the male and female genital systems from an indifferent stage. It describes how in males, the presence of SRY leads testes to develop from indifferent gonads, while in females without SRY ovaries develop. It outlines the development of testes, ovaries, male ducts including epididymis and vas deferens, and female ducts including uterus and vagina from indifferent ducts. External genitalia also develop differently in males under testosterone versus females.

1. Development of the male& female
genital system
By:-
Jwan Ali Ahmed AlSofi

2. List of Contents:
 Objectives
 Contents:
i. Introductory to the development of genital system
ii. Indifferent gonads: testis, ovaries
iii. Development of the genital ducts: male, & female
genital ducts
iv. External genitalia: male,& female
v. Clinical correlates.
 Summary or conclusion
 Question

3. PRIMORDIAL GERM CELLS
 Gametes are derived from primordial germ cells (PGCs)
 PGCs are formed in the epiblast during the 2nd week move
through the primitive streak during gastrulation  migrate to
the wall of the yolk sac  by the 3rd week reside among
endoderm cells in the wall of the yolk sac close to the allantois
 during the 4th week, these cells begin to migrate, by
amoeboid movement , from the yolk sac along the dorsal
mesentery of the hindgut toward the developing gonads,  at
the beginning of the 5th week , arrive and appear at the
primitive gonads in the 6thweek , invade the genital ridges.
 Mitotic divisions increase their number during their migration and also when
they arrive in the gonad.
 In preparation for fertilization, germ cells undergo gametogenesis, which
includes meiosis to reduce the number of chromosomes and
cytodifferentiation to complete their maturation.

5. Introductory to the development of
genital system:
 In the presence of SRY (sex determining
region) gene on the short arm of Y
chromosome, which contains testis –
determining factor protein (transcription factor
determining fate of indifferent gonads).If
present  male development occurs .
 In the absence of SRY gene the fetus develops
as a female.

6. Introductory to the development of
genital system
 All components go through an indifferent stage
in which they may develop into either male or
female.
 The gonads do not acquire male or female
morphological characteristics until the 7th wk .
 the sex of the embryo is determined genetically
 at the time of fertilization
 the gonads acquire male or female morphological
characteristics at the  7th week.

7. Introductory to the development of
genital system:
 Gonads appear initially as a pair of longitudinal
ridges during 5th wk .
 They are derives from 3 sources:
1- by proliferation of mesoderm epithelium lining the
posterior abdominal wall.
2- by condensation of underlying mesenchyme
3- germ cells that apear at 6th week.

9. Indifferent stage of the gonads
 Primordial germ cells originate from? epiblast
 Migration of germ cells through? primitive streak.
 Invading the genital ridges at beginning of 6th
week.
• If they fail to do so  the gonads do not develop.
(Hence, the primordial germ cells have an
inductive influence on development of the gonad
into ovary or testis.)

10. Indifferent stage of the gonads
 After the arrival of PGCs, each gonadal ridge
enlarges and frees itself from the mesonephros
by developing a mesentery which becomes the
mesorchium in a male and mesovarium in the
female.

11. Indifferent stage of the gonads
 As this occurs, the
epithelium of the genital
ridge proliferates and
epithelial cells penetrate
the underling
mesenchyme forming a
number of irregularly
shaped cords known as
primitive sex cords..

12. Indifferent stage of the gonads
 In both male and female
embryos, these cords are
connected to the surface
epithelium, and it is
impossible to differentiate
between the male and
female gonad, therefore
the gonad is known as
the indifferent gonad.
 The indifferent gonad
now consists of an
external cortex and
internal medulla.

13. Indifferent gonads
 In embryos with an XX sex chromosome, the cortex of the
indifferent gonad differentiates into an ovary and the medulla
regresses.
 In embryos with an XY sex chromosome, the medulla
differentiates into a testis and the cortex regresses.

14. Development of the testis
 In male fetus, the primitive sex cords continue
to proliferate & penetrate deep into the medulla
to form testis or medullary cords.
 Toward the hilum of the gland, the cords break
up into a network of tiny cell strands that latter
give rise to tubules of Rete testis.
 With further development a dense fibrous CT
separates testis cords from the surface
epithelium (Tunica albuginea).

16. Development of the testis
 Septa grow deeply from the tunica albuginea.
 The testis cords are composed of the PGCs & Sustentacular cells
of Sertoli (derived from the surface epithelium of the gland).
 Interstitial cells of Leydig:
– derived from the mesenchyme lie between the testis cords,
– it starts to produce Testosterone by 8th week.
– Testosterone production is stimulated by HCG.
 AMH or (MIS):
– is glycoprotein produced by the sustentacular cells (Sertoli cells);
– production continues until puberty, after which the levels are ↓.
– AMH suppresses development of the paramesonephric ducts,
which form the uterus and uterine tubes, exept for a small portion
at their cranial ends, the appendix testis

17. Development of the testis
 Testis cords remain solid until puberty, when
acquire a lumen they known as seminiferous
tubules.
 Once they are canalized, they join the rete
testis tubules, which intern enter ductuli
efferentes, which link the rete testis &
mesonephric ducts (ductus deferens).

18. Development of Testis

19. Development of the ovaries
 Two X chromosomes are required for the
development of the female. If the embryo
is genetically female, The PGCs carry an
XX sex chromosome and no Y
chromosome is present.
 The primitive sex cords extend into the
medulla as clusters containing groups of
primitive germ cells. Later they disappear
and are replaced by a vascular stroma
that forms the ovarian medulla.

21. Development of the ovaries
 Surface epithelium of the ovary,
unlike that of testis, continuous to
proliferate.
 In the 7th wk it gives rise to a 2nd
generation of cortical cords,
which penetrate the underlying
mesenchyme but remains close to
the surface.

22. Development of the ovaries
 In the 3rd month, the cords split into isolated
cell clusters, cells of these cluster continue to
proliferate & surround oogonium with a layer of
epithelial cell known as follicular cells forming
together primordial follicles.
 No oogonia form postnatally. Although
many oogonia degenerate before birth, the 2
million or so that remain will enlarge to become
primary oocytes before birth.

23. Indifferent genital ducts
 Indifferent stage: Both male and
female embryos have two pairs of
genital ducts:
 The mesonephric (Wolffian)
ducts will develop into MGD.
 The paramesonephric ducts
(mullerian ducts) developing into
FGD.

24. Genital ducts in the male
 the mesonephric ducts
persist and form the
main genital ducts.
1. As mesonephros regress,
a few excretory tubules
(epigenital tubules)
establish contact with rete
testis & latter will form
efferent ductules.
2. The excretory tubules
along the caudal pole
(paragenital tubules) will
not join rete testis, forming
paradidymis.

25.  Bellow entrance of efferent ductules,
the mesonephric ducts elongate &
become highly convoluted, forming
ductus epididymis.
 From tail of epididymis to the
outbudding of seminal vesicle, the
mesonephric duct gain a thick
muscular coat & form the ductus
deferens.
 Caudal end of each mesonephric duct
gives rise to the seminal vesicle.
 Part of mesonephric beyond the
seminal vesicle will form the
ejaculatory duct.
 Paramesonephric ducts in the male
degenerate except for a small portion
at their cranial ends forms the
appendix testes, under the influence
of AMH.
Genital ducts in the male

27. Development of the female
genital ducts
 In female embryo lacking a Y chromosome, the
mesonephric ducts regress because of the absence
of testosterone (secreted by?).
 The paramesonephric ducts develop because of:
1. the absence of Mullerian inhibitory substance
MIS(secreted by?).
2. Estrogens are also involved in stimulating PMD to form
uterine tubes, uterus, cervix, &upper vagina. Beside
differentiation of external genitalia.

28. Development of the
female genital ducts
 The paramesonephric ducts
form the main genital ducts of
the female. 3 parts of PMD :
 1-The cranial vertical portion of
this duct that opens into the
abdominal cavity.
 2-The horizontal part that
crosses the mesonephric duct
developing into the uterine tube.
 3-The caudal vertical fused
portions of these ducts form the
uterine canal and give rise to
the corpus and cervix of the
uterus and the upper portion of
the vagina.

30. Development of the vagina
 The vaginal epithelium is derived from the
endoderm of urogenital sinus.
 The vaginal fornices are derived from PMD.
 The fibro-muscular wall develops from the
surrounding mesenchyme.
 Two solid evaginations (sinovaginal bulb)
grow out from the pelvic part of the urogenital
sinus.
 They will proliferate & form a solid (vaginal
plate).
 the 5th month the vaginal outgrowth is entirely
canalized to form the lumen of the vagina.

31. Development of the vagina

33. Indifferent stage of external genitalia
 During the 3rd wk, mesenchymal cells from the primitive streak
migrate around the clocal membrane to form a pair of elevated
clocal folds.
 Cranial to cloacal membrane the folds unite to form genital
tubercle in both sexes.
 Caudaly, the folds are subdivided into urethral folds anteriorly,&
anal folds posteriorly.
 Another pair of elevation, the genital swellings becomes visible
on each side of the urethral folds. These swelling later form the
scrotal swelling in male and the labia majora in female.

34.  Is under the influence of testosterone.
 The genital tubercle soon elongates rapidly, forming
the phallus.
 As the phallus elongates, it pulls the urethral folds
forward to form the lateral walls of the urethral groove.
(This groove does not reach the most distal part of the
phallus, the glans.)
 The epithelial lining the groove , which originates in the
endoderm, will form the urethral plate.
 At the end of 3rd month, the two urethral folds close
over the urethral plate, forming the penile urethra.
 This canal does not extend to the tip of the phallus.
 At the tip of the glans of the penis, ectodermal cells
penetrate inward forming epithelial cord. This cord later
gains a lumen forming external urethral meatus.
 The scrotal swellings will move caudally, forming the
scrotum. The two are separated by the scrotal septum.
Development of male external genitalia

36. Development of the female external genitalia
 Estrogens stimulate development of EFG.
 The genital tubercle elongate slightly and becomes the
clitoris.
 Urethral folds do not fuse as in the male, but develope
into the labia minora.
 Genital swellings enlarge and form the labia majora,
which are homologous to the scrotum in male.
 The urogenital groove is open and forms the vestibule.

37. Descent of the testes
- Normally testes reach inguinal region by 12th week.
- Migrating through the canal by 28th weeks.
- Reach scrotum at week 33.
- What are the factors controlling testicular descent?
1. outgrowth of the extra-abdominal portion of the
gubernaculum produces intra-abdominal migration.
2. increase in intra-abdominal pressure due to organ growth
produces passage through the inguinal canal.
3. regression of the extra-abdominal portion of the
gubernaculum completes movement of testis into scrotum.
4. Hormones:androgens and MIS.

39. Clinical correlates of MRS:
 Cryptorchidism:
Sometime the testis does not continuous its
migration, but stop at certain point. This could
occur in the abdominal cavity, but usually in the
inguinal canal. The cause could be deficiency
of androgen.
An undescended testis is unable to produce
mature spermatozoa, most likely because of
high temperature in the abdominal cavity.

40. Clinical correlates of MRS:
 Congenital inguinal hernia:
The connection between the abdominal cavity
and the processus vaginalis in the scrotal sac
normally close in the 1st year after birth.
If this passageway remains open intestinal
loops may descend into the scrotum causing
congenital inguinal hernia.

41. Clinical correlates of MRS:
 Hydrocele: sometimes the obliteration of
the passageway is irregular, leaving
small cysts along its course. Later these
cysts may secrete fluid, resulting in the
formation of a hydrocele.
 Epispadias ?
 Hypospadias?

42. - In hypospadias, fusion of the urethral folds is
incomplete, and abnormal openings of the
urethra occur along the inferior aspect of the
penis, usually near the glans, along the shaft,
or near the base of the penis.
- In rare cases, the urethral meatus extends
along the scrotal raphe.
- When fusion of the urethral folds fails entirely,
a wide sagittal slit is found along the entire
length of the penis

43. Clinical correlates of FRS
 Duplication of the uterus
Results from failure of the fusion of the
inferior part of the paramesonephric
ducts in a local area or thougout their
line of fusion.
A- uterus didelphys: The uterus is
entirely double.
B- uterus arcuatus: here the
uterus is only slightly indented in the
middle. Only one vagina is present.

44. Clinical correlates of FRS
C- bicornuate uterus: Here the
uterus has two horns entering a
common vagina.
D- Uterus bicornis unicolis with one
rudementary horn:
– here there is atresia of one of the
paramesonephric ducts,
– the rudimentary horn lies as an appendage to
the well-developed side.
– Because its lumen usually does not
communicate with the vagina, complications
are common.

45. Clinical correlates of FRS
 Atresia of the cervix: here there is
atresia of both paramesonephric
ducts resulting in cervical atresia.
 Vaginal atresia:
– results if sinovaginal bulbs fail to
develop at all.
– A small vaginal pouch originating from
the paramesonephric ducts usually
surrounds the opening of the cervix.

46. Summary or Conclusion:
 In the presence of SRY gene on the short
arm of Y chromosome produces male
baby.
 All components of the MRS & FRS go
through an indifferent stage.

47. Questions?
 How the male and female sexual development
are regulated?
 What happen if the testes don descend into the
scrotum?