1) Between weeks 1-6 of development, the reproductive systems of female and male embryos are indistinguishable, even though the genotype is established at fertilization. By week 12, some sex characteristics emerge and by week 20 differentiation is complete. 2) The indifferent gonads develop from an elevation in the intermediate mesoderm called the urogenital ridge. Primordial germ cells migrate into the indifferent gonad, with male cells colonizing the medulla and female cells the cortex. 3) The SRY gene on the Y chromosome causes the indifferent gonad to develop into testes. Testes produce testosterone and MIF, directing phenotypic male development, while lack of these hormones results in female

1. Reproductive System
Session 1
Origin of the Sexes
Lecture 2
Dr. Abdulghafoor
Development of Male and
Female Reproductive System
1

2. Indifferent Embryo
‫فقط‬ Power point ‫ا‬‫لمحاضرة‬‫تحتوي‬‫ملفات‬‫صوتية‬‫يمكن‬‫تشغيلها‬‫بنظام‬
• Between week 1 and 6, female and male
embryos are phenotypically indistinguishable,
even though the genotype (XX or XY) of the
embryo is established at fertilization.
• By week 12, some female and male
characteristics of the external genitalia can be
recognized.
• By week 20, phenotypic differentiation is
complete.
2

3. Indifferent Embryo
• Powerpoint ‫المحاضرة‬‫تحتوي‬‫ملفات‬‫صوتية‬‫يمكن‬‫تشغيلها‬‫بنظام‬‫فقط‬
• The indifferent gonads develop in a longitudinal elevation or
ridge of intermediate mesoderm called the urogenital ridge
• Primordial germ cells arise from the lining cells in the wall of
the yolk sac at weeks 3-4.
• At week 4-6, primordial germ cells migrate into the indifferent
gonad.
 Male germ cells will colonise the medullary region and the
cortex region will atrophy.
 Female germ cells will colonise the cortex of the primordial
gonad so the medullary cords do not develop.
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4. 4

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6. 6

7. • Phenotypic differentiation is determined by the Sry
gene (sex determining region on Y).
• which is located on the short arm of the Y chromosome.
The Sry gene encodes for a protein called testes-
determining factor (TDF).
1. As the indifferent gonad develops into the testes, Leydig
cells and Sertoli cells differentiate to produce
Testosterone and Mullerian-inhibiting factor (MIF),
respectively.
3. In the presence of TDF, testosterone, and MIF, the
indifferent embryo will be directed to a male phenotype.
4. In the absence of TDF, testosterone, and MIF, the
indifferent embryo will be directed to a female
phenotype.
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8. 8

9. 9
The components of the indifferent embryo
that are remodeled to form the adult female
and male reproductive systems are:
1. Gonads
2. Paramesonephric (Mullerian) duct
3. Mesonephric (Wolffian) duct
4. Phallus
5. Urethral folds
6. Genital swellings

10. 10

11. Indifferent Embryo Adult Female Adult Male
Gonads
Ovary, Primordial Follicles,
Rete Ovarii
Testes, Seminiferous
Tubules, Tubuli Recti, Leydig
Cells, Sertoli Cells
Paramesonephric Ducts
Uterine Tubes, Uterus,
Cervix, Upper Third of
Vagina*, Hydatid of
Morgagni
Appendix Testes
Mesonephric Ducts
Appendix Vesiculosa, Duct of
Gartner
Epididymis, Ductus
Deferens, Seminal Vesicles,
Ejaculatory Duct, Appendix
Epididymis
Mesonephric Tubules Epoophoron, Paroophoron
Efferent Ductules,
Paradidymis
Phallus Clitoris
Glance and Body of the
Penis
Urethral Folds Labia Minora Ventral Aspect of the Penis
Genital Swellings Labia Majora, Mons Pubis Scrotum
• * Lower two-thirds develops from vaginal plate of urogenital sinus
• Structures written by red color refers to vestigial structures

12. Genital Ducts in the Sixth Week A: Male; B: Female
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Genital ducts in the sixth week in the male A and female B. The mesonephric and
paramesonephric ducts are present in both. Note the excretory tubules of the
mesonephros and their relation to the developing gonad in both sexes.

13. A:Genital ducts in the female at the end of the second month
B: Genital ducts after descent of ovary
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Genital ducts in the female at the end of the second month. Note the paramesonephric
(müllerian) tubercle and formation of the uterine canal. B. Genital ducts after descent of
the ovary. The only parts remaining from the mesonephric system are the epoophoron,
paroophoron, and Gartner’s cyst.

14. A: Genital ducts in the male in the fourth month.
B: Genital ducts after descent of the testis.
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15. Testes
1. The gubernaculum extends from the
testes to the genital swellings (forming
the gubernaculum testes in the adult
male, which anchors the testes within
the scrotal sac).
2. The processus vaginalis forms the
tunica vaginalis in the adult male.
3. Cryptorchidism???
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16. Descent of the testis: A. During the 2nd month; B. In
the middle of the 3rd month; C. In the 7th month;
D. Shortly after birth.
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17. Descent of the Ovary and Testes
• The ovaries and testes develop within the
abdominal cavity but later descend into
the pelvis and scrotum, respectively.
• This descent involves the gubernaculum
(a band of fibrous tissue) and the
processus vaginalis (an invagination of
peritoneum).
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18. Development of Prostate Gland
The prostate gland develops from
multiple outgrowths of the prostatic
urethra.
Dihydrotestosterone (DHT) is the main
mediator of prostatic growth in males.
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19. External Genitalia
Indifferent Stage
A. Approximately 4 weeks; B. Approximately 6 weeks
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20. External Genitalia in the Male
A. Development of external genitalia in the male at 10 weeks; B. Transverse
sections through phallus during formation of penile urethra; C. Newborn
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21. Development of the External Genitalia in the
Female:- A: at 5 months; B: in the newborn
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22. Internal and External Genitalia of
the Male
• Internal
– Testis
– Epididymis
– Ductus deferens
– Seminal glands
– Ejaculatory ducts
– Prostate
– Bulbourethral glands
• External
– Glans penis
– Shaft of Penis
• Scrotum
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23. Drawing showing the coverings of the testes that are
derived from constituents of the abdominal wall
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24. Main Reproductive Hormones
Produced by Hormone
Hypothalamus Gonadotrophin Releasing Hormone (GnRH)
Prolactin Releasing Hormone (PRH)
Prolactin Inhibiting Hormone (PIH)
Posterior Pituitary Oxytocin
Anterior Pituitary Follicle Stimulating Hormone (FSH)
Luteinising Hormone (LH)
Prolactin
Testes Testosterone
Inhibin
Mullerian Inhibiting Hormone (MIH)
Ovaries Oestrogen
Progesterone
Inhibin
Placenta Human Chorionic Gonadotrophin (hCG)
Human Placental Lactogen (hPL)
Oestrogen
Progesterone
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25. Structure of the Testis, Including the Main
Compartments and Cells Types
• The testis (testicles) are the male gonads. They are
paired, ovoid reproductive glands that produce
spermatozoa and male hormones, primarily
testosterone. The testis are suspended in the scrotum by
the spermatic cords.
• Visceral layer of the tunica vaginalis.
• Parietal layer of the tunica vaginalis.
• Internal spermatic fascia.
• There is a small amount of fluid between the two
layers, in the cavity of the tunica vaginalis, allowing
the testis to move freely in the scrotum.25

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27. • Tunica albuginea
• Mediastinum of
the testis
• Seminiferous
tubules
• Straight tubules
• Rete testis
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28. The Process of Spermatogenesis
• Spermatogonia → spermatozoa.
• Germ cells colonise the sex cords in the
primordial gonad.
• These cords connect with the rete testis, the
epididymis and the vas deferens. Before birth, the
germ cells proliferate by mitosis to form
spermatogonia stem cells.
• These begin mitosis to maintain a population of
self-regenerating stem cells that remain available
up to and beyond the age of 70, to allow for
continuous sperm production at a high rate.
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29. Sex cord
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30. • At puberty, the cords hollow out to form the
seminiferous tubules, where sperms are
produced. Each testis has 250-750 tubules, which
empty into the rete testis, and from there form the
epididymis.
• A1 Spermatogonia (diploid 2n)→ A1
Spermatogonia and type B Spermatogonia
(diploid 2n)
• B Spermatogonia (fixed number of mitotic
divisions typically 64) → Primary
Spermatocytes (diploid 4n) … all linked
together by cytoplasm bridges.
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31. • Primary Spermatocytes (push their way towards the
lumen of the tubule ) → meiosis (M)
M1: two secondary spermatocytes (haploid 2n)
M2: four Spermatids (haploid 1n)
• Each A1 Spermatogonium yields up to 256
spermatids.
• Spermatids are re-modelled to form sperm by
Spermiogenesis, and the cytoplasmic bridges
between them are broken down before they are
released into the tubule lumen to be washed down to
the rete testis by fluid secreted from Sertoli cells
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32. Spermiogenesis
Series of changes resulting in transformation of
spermatids to spermatozoa.
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33. Sex Cord and Seminiferous Tubules
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34. • Spermatogenesis takes about 70 days and new
groups of A1 spermatogonia arise every 16 days,
meaning four spermatogenic processes are going
simultaneously.
• Production is continuous because different
sections along the length of the tubule begin the
process at different times, so some part is always
releasing sperm. A spermatogenic ‘wave’ of
production sweeps along the length of the
tubule.
• Spermatozoa finally mature during progress
through the epididymis
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37. 37
Spermiogenesis
(1) formation of the acrosome, which covers half of the nuclear
surface and contains enzymes to assist in penetration of the egg
and its surrounding layers during fertilization
(2) condensation of the nucleus;
(3) formation of neck, middle piece, and tail;
(4) shedding of most of the cytoplasm as residual bodies that are
phagocytized by Sertoli cells.

38. Sertoli Cells
• Associated with Seminiferous Tubules
• Spermatozoa support, nutrition and development
Leydig (Interstitial) Cells
• Cells in the interstitial tissue
• Secrete testosterone
The tubules are separated from the surrounding
interstitial tissue by the blood testis barrier.
Why?
38

39. Hypospadias and Epispadias
Hypospadias showing the various
locations of abnormal urethral orifices
Epispadias combined with exstrophy of
the bladder. Bladder mucosa is exposed
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40. LANGMAN”S Medical
Embryology
PROBLEMS TO SOLVE???
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