Embryology - Legineds Flashcards
How do the genitals first appear?
As a thickening of the medial part of the mesonephric ridge (part of the mesonephros or early kidney)
Called the genital or gonadal ridge
What happens to the genital ridge after it forms?
It recieves germ cells that migrate from yolk sac to dorsal mesentery to primitive sex chords forming the Indifferent Gonad
Where do the primitive sex chords come from?
The mesenchyme of the genital ridges
They recieve germ cells from the yolk sac to form the indifferent gonad
What happens after formation of the indifferent gonad?
MEsonephric epithelium invaginates to form a Para-mesonephric duct
wheres the paramesonephric duct found?
Lateral to the mesonephros and indifferent gonad.
Opens into peritoneal cavity at one end and dorsal wall of urogenital sinus at the other
What happens to the indifferent Gonad?
Its at this point that the sexes diverge.
In women it forms the ovary
How does the body know to form an ovary rather than a testicle?
Ovaries are default
Only when a Y chromosome is present do testes form because it carries SDR Y (Sex Determining Region Y)
What happens to the mesonephric duct in women?
Degenerates
(In men it forms the vas deferens, epidydimis & seminal vesicles)
What happens to women’s paramesonephric duct?
Forms fallopian Tube, uterus, cervix & part of vagina.
In men it degenerates
What happens to urogenital sinus in women?
becomes the bladder and lower vagina
In men its the bladder, urethra and prostate
How do the primary sex cords start to become an ovary?
They degenerate leaving only the primordial germ cells then by 10 wks surface epithelium develops into secondary sex cords
So now you have secondary sex cords containing primordial germ cells, what happens next?
The germ cells bud off with a single surrounding layer of cortical cord cells
Giving you primordial follicles
At what stage do primordial follicles form?
~16 wks
How do we go from primordial follicles to the 2million+ follicles of a newborn?
Active mitosis.
By 7th month all have been formed
Some undergo follicular atresia so you have less by puberty
How many follicles develop per 28 day cycle (After puberty)?
12-15. But normally only 1 reaches maturity and ovulation
