development of the reproductive system Flashcards
what are the three primitive germ layers?
ectoderm - develops in skin
mesoderm- (paraxial- vertebrae, intermediate - urogenital structures, lateral)
endoderm- GIT and respiratory tubes
when does gastrulation occur?
day 16
what happens to the intermediate mesoderm?
condenses to form cylindrical structures creating the urogenital ridges.
They then organise into the nephrogenic cord which gives rise to urinary structures and the gonads
where does gonad development begin
in the yolk sac- lined with endoderm cells
how is the yolk sac connected to the embryo
via the vitelline duct
how to endoderm cells in the yolk sac become the primitive sex cords?
differentiate to primitive germ cells.
migrate along vitelline duct to the dorsal mesentery.
In week 6 they go to the genital ridge and settle in the epithelium
send signals to the ridge to self organise into an undifferentiated gonad of which the epithelium layer forms the primitive sex cords.
at what week does gonal differentiation occur
week 7
how do male gonads differentiate?
SRY region of the Y chromosome codes for testes determining factor
up regulating SOX9 which initiates testes development.
what happens to the primitive sex cords in males?
they become the medullary cords which carry germ cells into the mesoderm.
The medullary cord become 3 ductal structures: seminiferous tubules, straight tubules and the rete testes.
primordial germ cells into the seminiferous tubules and mature to become spermatogonia which then become sperm during puberty.
at what week do the cells in the walls of the seminiferous tubules become sertoli cells?
week 8
what do sertoli cells secrete
mullerian inhibiting factor
what do leydig cells secrete
testosterone
how do female gonads differentiate?
no SRY gene so no testes determining factor
WNT4 gene develops undifferentiated gonads into ovaries
what happens to the primitive sex cords in females?
they degenerate
the surface epithelium becomes cortical cords which form nests of follicular cells surrounding each primordial germ cell.
this is called a primordial follicle which becomes a primary then secondary oocyte.
from which embryological structure do the genital ducts originate from
nephrogenic duct
which embryological duct forms the male genital duct
mesonephric
which embryological duct forms the female genital duct
paramesonephric (mullerien)
how do the male genital ducts develop
mullerian inhibiting factor secreted from the sertoli cells degenerate the paramesonephric duct into the appendix testes
the mesonephric duct grows under the influence of testosterone forming: efferent ductules epididymus vas deferens seminal gland ejaculatory duct
what is the appendix testes
the degenerated paramesonephric duct
how do the female genital ducts develop
there is no testosterone so the mesonephric duct degenerates
no mullein inhibiting factor so the paramesonephric duct persists to form: fallopian tubes uterus cervix 1/3 vagina
what are the two sets of folds that form the undifferentiated external genetalia
urethral folds and labioscrotal swellings
there is also the genital tubercle which forms the primordial phallus
how does the male external genetalia develop
there are high levels of testosterone due to leydig cells
5-alpha-reductase converts testosterone to dihydrotestosterone (more potent) which masculinises the genetalia
urethral folds fuse along the midline to form the penile urethra
the primordial phallus elongates
the labioscrotal swellings fuse to form the scrotum
how does the female external genetalia develop
no testosterone so the urethral folds stay unfused forming the labia minora
the labioscrotal swellings fuse anteriorly to form the mons pubis and the labia majora
the primordial phallus shrinks to form the clitoris
what what week are the external genetalia done differentiating
week 12
