Embryology 5 - sex determination Flashcards
deck complete
sex in the initial development of embryos
same for both males and female, foundations for both sexes are created
where are the gonads developed
in the trunk of the body, around halfway between shoulder and pelvis
where does the germ line come from
the epiblast cells that were removed from the body around the time of gastrulation
where does the germ line end up
outside the body in the yolk sac - problem because germ line needs to be in the gonads
what is the mesentery
the sheet like connection between the gut and the rest of the body
how do germ cells invade the body
by use of the connection to the yolk sac, and the gut and its mesentery
what happens when the germ cells reach the level of the developing gonads
they move up the mesentery and then move across to enter the gonads themselves
chromosome constitution of females
XX
chromosome constitution of males
XY
what determines sex
a gene on the Y chromosome (SRY)
how does SRY act
primitive gonads consist of somatic cells and germ line cells
somatic cells express SRY if it is present
SRY forces somatic cells to develop into testis cells - otherwise they form ovary cells
what does the Y chromosome affect
only the production of testis. everything else stems from cues from the testis - communication by excreting androgenic hormones
key somatic differentials in females - Y2
mullerian ducts make oviducts, uterus, cervix uteri and upper vagina
wolffian ducts disappear
cloaca makes lower vagina
phallus develops into clitoris
labioscrotal folds remain separate and develop into labia
gonads remain internal
key somatic differentials in males - Y2
mullerian ducts disappear due to AMH - anti-mullerian hormone
wolffian ducts become vas deferens
cloaca does not become vagina
phallus develops into penis
labioscrotal folds fuse to become scrotum
gonads descend into scrotum
sexual dimorphism - external obvious differences between males and females
average height and mass
body shape
development of external genitalia
development of mammary glands
body hair pattern - extent varies with race
sexual dimorphism - differences between the male and female brain
example - gender specific sexual behaviours
androgen insensitivity
where chromosomes dont match external features
cause of androgen insensitivity
testosterone is a weak androgen meaning it only weakly stimulates androgen receptors
5⍺-reductase converted by tissues into 5⍺-dihydrotestosterone which stimulates androgen receptors strongly
what do XY children with deficient 5⍺-reductase produce
female presenting bodies
when do testosterone levels rise and to what level
beginning of puberty
high enough to act as an androgen even in absence of 5⍺-reductase
vast range of intersex phenotypes
generally children born with them undergo ‘corrections’ to conform with societal expectations of belonging clearly to one binary sex or another, even if they are at no clinical risk because of their phenotype
