sexual differentiation Flashcards
chromosomal sex
importance of the Y chromosome in mammalian sex differentiation
gonadal sex
development of the gonadal rise of intermediate mesoderm, origins and migrations of primordial germ cells
phenotypic sex
development of internal and external genitalia
gonadal ridge formation
forms on the medial aspect of the intermediate mesoderm in the region of the mesonephros
around week 5
important genes in gonadal ridge formation
WT1 (kidney and gonads)
SF1
LHX9
all act upstream of SRY
what occurs as the ridge descends through abdomen
concentration of ridge
testis or ovary forms from undifferentiated gonad
gene required for testis function
SRY/SOX9 from Y chromosome
lack causes ovary formation
germ cell migration
successful migration of germ cells into gonadal ridge important for ultimate functioning gonad
mis-directed primordial germ cells may develop into teratomas
where do germ cells develop
develop in epiblast and migrate to the gonadal ridge via the yolk sac and hind gut
what are the germ cells associated with
primitive sex cords - tissue of the gonadal ridge
primitive sex cords in males
sex cord cells proliferate by mitosis and surrounded the primordial germ cells to form testis cords
cells surrounding the germ cells differentiate into sertoli cells initiated by SRY
primordial germ cells called the prospermatogonia
primitive sex cords in female s
sec cords dissociate so the primordial germ cells are in ‘nests’ (primordial follicles). meiosis commences then arrests in foetus, follicles start to develop but undergo atresia until puberty
gonadal development in males
primordial cells concentrate in medulla, cortex regresses
medullary cords develop and contain spermatogonia and Sertoli cells -> seminiferous tubules and rete testes
leydig cells form and secrete testosterone
gonadal development in females
primordial follicles concentrate in the cortex of the developing ovary, medulla degenerates
cortex of indifferent gonads form ingrowths = cortical cords
oogonia proliferation
internal genitalia form from
mullerian (paramesonephric) ducts and wolffian (mesonephric) ducts
fate of ducts in females
mullerian duct maintained, forms the uterine tubes, uterus and upper part of vagina
wolffian ducts degenerate
wnt 4 importnat
fate of ducts in males
wolffian ducts differentiate to form the epididymus, vas deferens and seminal vesicles
prostate glands from urogenital sinus
mullerian duct degenerates
needs testosterone
what do Sertoli cells secrete to cause this duct differentiation
mullerian inhibiting substance
causes the mullerian ducts to regress
indifferent stage of external genitalia development
up to 8th week
genital tubercle -> phallus or clitoris
genital swelling -> scrotum or labia majora
male external development occurs when
androgens are produced from leydig cells
female external development occurs when
presence of ovary or lack of gonad
what is required to masculinise external genitalia
testosterone converted to dihydrotestosterone
converted by 5 alpha reductase in leydig cells
descent of testes
descent into scrotum
trans-abdominal, passing through inguinal canal
chemicals important for testicular descent
testosterone
DHT
mullerian inhibiting factor
members of hox gene family
wolffian duct in females
lack of testosterone causes complete duct regression
what is the gubernaculum
embryonic structure
aids the descent of the gonads
mesenchymal cord
between the caudal end of testis and scrotum
