2.1 - hypothalamic-pituitary-gonadal axis: androgens, testes, ovary Flashcards
what are the 3 phases of follicular development in the ovary?
antral phase
pre-ovulatory phase
after ovulation
during the antral phase of follicular development in females, what binds to LH and what binds to FSH?
cells of the theca interna bind LH
granulosa cells bind FSH
what happens after the cells of theca interna bind to LH in antral phase of follicular development?
LH stimulate thecal cells to produce androgens (mainly androstenedione)
what happens after granulosa cells bind to FSH in antral phase of follicular development?
FSH stimulates granulosa cells to develop enzymes which convert these androgens to oestrogens
what happens as the follicle grows during the antral phase of follicular development in the ovary?
more oestrogen are produced for a given gonadotrophic stimulation
what happens in the pre-ovulatory phase in female ovary?
LH receptors develop in outer layers of GRANULOSA cells
a ‘surge’ of LH will stimulate ovulation
what happens after ovulation in female ovary?
LH stimulates corpus luteum to secrete progesterone and oestrogen
what happens as the corpus luteum grows after ovulation in the female ovary?
more steroids are produced at a given LH concentration
in females, what do the events of the ovarian cycle influence?
the response to gonadotrophins
what is important in controlling the reproductive cycle of females?
the variation of ovarian cycle produces a so-called ‘ovarian clock’
in the testis, where does LH act? leading to?
LH acts upon Leydig cells to promote the secretion of testosterone
what are the effects of LH enhanced by in the testis (acting on Leydig cells)?
LH enhanced by prolactin and inhibin
which cells do testosterone act on? promotes what?
acts on Sertoli cells to promote spermatogenesis
testosterone acting on elsewhere in the body has what effect?
maintain the male reproductive system
what is FSH’s function in the testis?
maintains Sertoli cells and makes them responsive to testosterone
what maintains spermatogenesis and testosterone secretion?
LH and FSH at appropriate levels
males must produce sperm constantly and be ready to deliver them to the female. what does this require?
appropriate levels of FSH, LH and testosterone
how is appropriate levels of FSH, LH and testosterone in males achieved?
negative feedback
what happens as testosterone levels rise?
inhibit GnRH secretion, reducing production of LH + FSH (spermatogenesis + testosterone secretion not maintained, so testosterone levels fall, no inhibition, GnRH increases)
what happens if spermatogenesis proceeds too rapidly?
inhibin levels rise
enhance LH, secrete more testosterone, reduce LH + FSH, inhibition on spermatogenesis
where does inhibin act to reduce secretion of FSH?
on gonadotrophs in (ant) pituitary
what are the effects of gonadal steroids?
- determinative effects:
qualitative, only partly reversible if at all (mostly secondary sexual characteristics e.g. deepening of voice) - regulatory effects: highly reversible, rely on continuous hormonal stimulation for maintenance
what are the major determinative effects of testosterone?
deepening of voice
growth of facial, armpit, chest + pubic hair
what are the regulatory effects of testosterone?
- maintenance of male internal genitalia
- metabolic effects
- behavioural effects
what are the male internal genitalia?
prostate
seminal vesicles
vas deferens
epididymis
what are the metabolic effects of testosterone?
anabolic:
increase is muscle mass and strength, density + strength of bones
what are the behavioural effects of testosterone in male?
aggression, sexual activity
