Development of the reproductive tracts Flashcards
When does embryonic development occur?
4th week
Which embryonic layer gives rise to the urogenital tract?
intermediate mesoderm
What decides if the foetus is male or female?
Karyotype (if there is a Y chromosome). This decides the path taken for development.
What is the common origin of the urinary, GI and reproductive tract?
Cloaca - this is a dilated structure at the end of the hindgut
What is the urogenital ridge?
Region on intermediate mesoderm giving rise to both embryonic kidneys and gonads
What is the gonad derived from?
Intermediate mesoderm and primordial germ cells.
How do the primordial germ cells arise?
Arise from the yolk sac and migrate into the retroperitoneum, along the dorsal mesentery
What is the differences between the development of the gonads with / without a Y?
With a Y = Testes
- Medullary cord develops
- No cortical cords
- Thick tunica albuginea
Without a Y = Ovary
- Medullary cord degenerates
- Cortical cord develops
- No tunica albuginea
Why does the Y chromosome make males male?
Because of the expression of the SRY gene. This causes development of the: -Testes -Testicular hormones -Internal genitalia
What happens in X chromosome gametes?
Absence of Y chromosome leads to female development.
- Gonad (ovary)
- Internal genitalia - duct system
What are the mesonephric ducts?
Ducts that develop the embryonic kidney
Where do the mesonephric and paramesonephric ducts end?
Urogenital sinus part as of the cloaca
What hormones do the males produce and what effect do these have?
Mullerian inhibiting hormone - suppress malarian (paramesonephric) duct development
Androgens - supporting Wolffian (mesonephric) duct
What happens if the males hormones are not produced?
No testes producing Mullerian inhibiting hormone - so no suppression of Mullerian / Paramesonephric duct development
No testes producing androgens - Wolffian (mesonephric) duct degenerates
What happens if exogenous androgen but no testes?
Exogenous androgen supports mesonephric duct formation but, no testis so no MIH so, the paramesonephric duct also develops. (So person has both ducts)
What happens if AIS?
AIS = androgen insensitivity syndrome
- Receptors for testosterone won’t work so the Wolffian ducts dont survive and the MIH is present so Mullerian ducts degenerate.
- This means that neither duct develops.
Where does the mesonephric duct drain?
Into urogenital sinus which becomes the bladder
What does the mesonephric duct turn into?
Vas deferens and epidydimis
It migrates and descends.
What do the paramesonephric ducts form?
The two paramesonephric ducts meet in the midline and fuse at the urogenital sinus to form the uterus
What happens to the redundant paramesonephric duct? Why?
It degenerates because the testes secrete MIH. This occurs in XY embryo. In these people, androgen secretion also supports the mesonephric duct.
What happens to the redundant mesonephric duct? Why?
It degenerates because no androgens are produced as there are no testes. This occurs in XX embryos and also means that there is no MIH and ovaries develop.
What are the basic components of the external genetalia?
Genital tubercle
Genital folds
Genital folds
How does the male external genitalia develop?
GT elongates and genital folds fuse under influence of dihydrotestosterone to form the spongy urethra. This then becomes the glans penis
How does the female external genitalia develop?
No fusion of the genital folds - remain open so development of the labia majora and minors.
Genital tubercle develops into clitoris.
Urethra opens into vestibule.
