Embryology of the External Genitalia Flashcards
From what are the indifferent genitalia formed?
urogenital sinus & surface ectoderm
What are the parts of the indifferent genitalia?
glans urogenital fold urogenital groove cloacal membrane lateral tubercle
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What androgen is responsible for formation of the male-specific genitalia?
dihydrotestosterone (NOT testosterone)
What happens to the cloacal membrane in female and male genitalia development?
female: disintegrates
male: fails to disintegrate
What ends up filling the labioscrotal swellings in female and male genitalia development?
female: fat
male: processus vaginalis and later testes migrate into the labioscrotal swellings
What happens to the urogenital fold in female and male genitalia development?
female: folds move apart laterally and grow
male: folds move together medially and fuse
How do the sinovaginal bulbs form and what do they become?
Sinovaginal bulbs are paired endodermal outgrowths of the wall of the fused paramesonephric ducts.
They fuse to form a vaginal plate, and the central cells of this plate break down, forming the vagina.
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How is the hymen formed?
by invagination of the posterior wall of the urogenital sinus
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Of what are the labia minora formed?
labia minora are the unfused parts of the urogenital folds
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Of what are the labia majora formed?
labia majora are the unfused parts of the labioscrotal folds
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How is the clitoris formed?
genital tubercle -> primordial phallus -> clitoris
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How is the penile raphe formed?
The urethral folds fuse with each other, and the surface ectoderm fuses in the median plane of the penis, forming the penile raphe.
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From what indifferent genitalia structure do the penile shaft and shaft of clitoris form?
lateral tubercle
Why does the male urethra end up at the tip of the penis and the female urethra end up in the vestibule?
female: urogenital sinus doesn’t quite reach the glans, and so the urethra doesn’t end in the glans
male: the urogenital sinus grows towards the glans, where it induces an “epithelial cord” within the glans to undergo apoptosis. This apoptosis MUST precede closure of the ventral portions of the urogenital sinus, otherwise urine builds up within the urethra, preventing closure.
How can hypospadias occur?
urethral folds do not fuse completely/correctly
