Repro 2 - Oestrous cycles (OOGENESIS (Formation of gametes within the…
Repro 2 - Oestrous cycles
Formation of gametes within the ovaries
Begins before females are even born
Primordial germ cells in early f. devel. Migrate from olk sac to ovaries. - OOGONIA
OOGONIA = Diploid (2n) stem cells - :heavy_division_sign: heavily to form millions of germ cells
! The ovaries are an ENDOCRINE gland!
Negative and positive feedback mechanisms which occur between ovaries and the HPA axis. (EXPLAIN THE LH SURGE?)
FSH, LH, ACTH, TSH, PROLACTIN, GH
LINK GnRH and LH - When GnRH pulsation increases, so will they as they ARE the gonadotrophic hormones
Negative feedback, as....
:arrow_up: GnRH, :arrow_up: FSH.
Ostrogen inhibits FSH, so less Oestrogen as fewer follicles, but less Oestrogen so more FSH
:arrow_up: GnRH :arrow_up: LH
Progesterone :red_cross: LH so -ve feedback
:heavy_plus_sign: Feedback too...
The dominant follicle will stimulate the surge centre of the brain and hypothalamus to release more GnRH due to more oestrogen. SO whilst it inhibits FSH, also :arrow_up: GnRH & hence LH etc
This is why you get an LH surge, as oestrogen supresses FSH
OVULATION :!!: ALWAYS follows LH surge. Marks end of follicular and start of luteal phase
Endocrine changes leading to ovulation
Firstly, GnRH produced by hypothalamus, (ANTERIOR PITUITARY) as told to do so by the surge centre of brain
GnRH :check: FSH and LH
FSH stimulates follicle development
LH stimulates corpus leuteal development
There has to be a dominant follicle
Produces Oestrogen, as all do
Stimulates LH as causes more GnRH to be secreted.
Increased LH causes SURGE
Surge in LH leads to ovulation!
Also causes inhibin to be secreted
Oestrous cycle of the women
Follicle maturation and Oocyte maturation are separate but important events
Follicles act as endocrine glands
BEFORE puberty - oocyte = Primary follice &
time, the follicle = Primary follicle
THEN... Secondary follicle, mature, OVULATION then Ovulated secondary oocyte