Repro Session 2 Flashcards
Effect of oestrogen on GnRH secretion at moderate concentration?
reduces amount of GnRH released per pulse
Effect of oestrogen on GnRH secretion at high concentration?
promoted, producing a surge
what hormone reduces amount of FSH released in response to GnRH?
inhibin- produced by developing follicles in ovary granulosa cells, and seminiferous tubules, sertoli cells in testis
during antral phase of follicular development, what hormone do theca interna cells bind?
LH
during antral phase of follicular development, what hormone do granulosa cells bind?
FSH
action of FSH on granulosa cells?
develop enzymes to convert androgens secreted by theca interna to oestrogens
what happens to release of steroids by corpus luteum as it grows, for any given LH concentration?
it increases
what enhances the effects of LH acting upon leydig cells?
prolactin and inhibin
where does testosterone act to promote spermatogenesis?
sertoli cells
how does -ve feedback occur when testosterone levels rise?
testosterone inhibits GnRH secretion, reducing LH and FSH
reduces sensitivity of gonadotrophs to GnRH
so testosterone falls
what happens if spermatogenesis process too rapidly in terms of -ve feedback?
inhibin rises, and inhibin reduces secretion of FSH by acting on gonadotrophs in pituitary, and FSH is necessary to maintain Sertoli cells and make them responsive to tetosterone to promote spermatogenesis
what are the regulatory effects of testosterone?
maintenance of male internal genitali- prostate, seminal vesicles, vas deferens, epididymis
metabolic- anabolic action
behavioral- aggression, sexual activity
length of the luteal (waiting/secretory) phase?
14 days
how is sperm transport inhibited in the luteal phase?
action of progesterone on oestrogen primed cells, stimulating thickening and acidification of cervical mucus
which cells produce inhibins?
granulosa cells
sertoli cells
what happens to hormone secretion if conception occurs?
implanted embryo develops a placenta- secretes hCG- prevents corpus luteum regression, so oestrogen and progesterone continue to be secreted, supporting early wks of pregnancy, and maintaining suppression of ovarian cycle
what does the length of the luteal phase represent?
the lifespan of the corpus luteum
How does LH surge cause an ovum to be released?
LH stimulates collagenase which breaks down the theca externa (CT) of the pre-ovulatory follcle, so that it becomes weak and ruptures, releasing an ovum
why does progesterone increase prior to ovulation?
LH surge stimulates granulosa cells to secrete progesterone
where does oestrogen act via +ve feedback?
at both the hypothalamic neuroendocrine cells and anterior pituitary gonadotrophs
why does FSH also rise at when LH rises with the LH surge?
in response to GnRH signal
why is another LH surge prevented when the corpus luteum is formed during the luteal phase?
inhibitory effect of progesterone on the +ve feedback mechanism of oestrogen
how is the corpus luteum maintained in a normal cycle?
by LH
example of a drug that mimics action of dopamine, supressing release of prolactin?
bromocriptine
how is the corpus luteum maintained initially in pregnancy?
by hCG secretion from placenta
what is menstruation triggered by?
loss of progesterone support from corpus luteum
where does inhibin act?
on the anterior pituitary gland
why does FSH tend to rise more than LH at beginning of menstrual cycle?
low inhibin levels release FSH from selective inhibition at anterior pituitary
uterine cycle is produced by…?
gonadal steroids
use of LHRH (GnRH) agonists?
in metastatic prostate cancer to overwhelm anterior pituitary gland and so reduce testosterone secretion that is necessary for growth of prostate cancer, as GnRH release from hypothalamus is normally pulsatile