Fetal Development of Sexual Anatomy Flashcards
Every mammalian fetus has the…
…anatomical precursors for BOTH sexes
Gonads
earliest sex structure to develop, same initial structure will become Testes or Ovaries
something has to trigger which direction it will take
(X or Y chromosomes)
Testis-Determining Factor (TDF)
Enzyme
genes turned on and the cells produce testosterone
gonads develop into testes
wolfian ducts transform into Vas Defrens
takes something extra to make the male
appears 6th - 8th week
Gentalia
same initial strucutre in all fetuses,
develop into male or female anatomy, depending on Androgens/Not
Wolfian and Muellerian ducts
in each fetus
their development depends on Androgens/Not
these become either Vas Defrens and Prostate
or
Fallopian Tubes and Uterus respectively
other system degenerates
Testosterone
first androgen triggered by TDF
genes controlling male/female body and brain development are
also present in BOTH sexes
Androgen-Insenstive
cells that respond to testosterone unresponsive
default female form taken despite presence of Y chromosome
to be fertile
takes 2 “Xs”
The “switch”
is one the male’s Y Chromosome
it signals production of the Testis-Determining Factor Enzyme
occurs during CRITICAL PERIOD of fetal development
genitals developed by
4th month
if testosterone is what’s required to masculinize a fetus, how does more estrogen somehow masculinizes fetuses?
the similarity between the chemical structure of estrogen and testosterone
testosterone gets into the cell and then it turns into the estrogen and the estrogen then has the masculinizing effect
if TDF is present =>
Male
Testes
tdf
differentiate, producing Androgens, including Testosterone => Wolffian ducts and male genitalia develop
also produce Anti-Muellerian Hormone
Alpha-Fetoprotein
produces by the fetus
it binds with estrogen so that it doesn’t play a role in determining the gender
fetus wants to determine its own gender: doesn’t want to be influenced by mother’s hormones
Anti-Muellerian Hormone
tdf
inhibits development of Muellerian system
if XY fetus is Androgen-Insensitive
its testes still produce Androgens and Anti-Muellerian Hormone, but since its Wolffian system’s androgen receptors are absent IT DOES NOT DEVELOP AND its Muellerian system is inhibited
so individual has no internal sex organs (infertile) except rudimentary, internal tests
external body develops as female, although without androgen stimulated pubic or secondary hair
If XX fetus is exposed to Testosterone during critical period…
…develops as male or semi-male form, sometimes infertile
some tendency for these individuals to be homosexual, tho per body, brain, and/or societal influences??
Testosterone enters fetal cells, where it is…
… converted (“aromatized”) into Estradiol (an Estrogen!) => male development
why doesn’t mom’s estradiol masculinize every fetus?
Alpha-Fetoprotein
Alpha-Fetoprotein
in fetal/infant blood, binds with Estrogen, preventing it from entering fetal cells (later inactivated)
Excessive Estrogens
e.g. DES, synthetic estrogen to prevent miscarriage
can overwhelm safeguard, masculinize fetus
