2.1 - hypothalamic-pituitary-gonadal axis: androgens, testes, ovary

Question 1

what are the 3 phases of follicular development in the ovary?

Answer 1

antral phase
pre-ovulatory phase
after ovulation

Question 2

during the antral phase of follicular development in females, what binds to LH and what binds to FSH?

Answer 2

cells of the theca interna bind LH

granulosa cells bind FSH

Question 3

what happens after the cells of theca interna bind to LH in antral phase of follicular development?

Answer 3

LH stimulate thecal cells to produce androgens (mainly androstenedione)

Question 4

what happens after granulosa cells bind to FSH in antral phase of follicular development?

Answer 4

FSH stimulates granulosa cells to develop enzymes which convert these androgens to oestrogens

Question 5

what happens as the follicle grows during the antral phase of follicular development in the ovary?

Answer 5

more oestrogen are produced for a given gonadotrophic stimulation

Question 6

what happens in the pre-ovulatory phase in female ovary?

Answer 6

LH receptors develop in outer layers of GRANULOSA cells

a ‘surge’ of LH will stimulate ovulation

Question 7

what happens after ovulation in female ovary?

Answer 7

LH stimulates corpus luteum to secrete progesterone and oestrogen

Question 8

what happens as the corpus luteum grows after ovulation in the female ovary?

Answer 8

more steroids are produced at a given LH concentration

Question 9

in females, what do the events of the ovarian cycle influence?

Answer 9

the response to gonadotrophins

Question 10

what is important in controlling the reproductive cycle of females?

Answer 10

the variation of ovarian cycle produces a so-called ‘ovarian clock’

Question 11

in the testis, where does LH act? leading to?

Answer 11

LH acts upon Leydig cells to promote the secretion of testosterone

Question 12

what are the effects of LH enhanced by in the testis (acting on Leydig cells)?

Answer 12

LH enhanced by prolactin and inhibin

Question 13

which cells do testosterone act on? promotes what?

Answer 13

acts on Sertoli cells to promote spermatogenesis

Question 14

testosterone acting on elsewhere in the body has what effect?

Answer 14

maintain the male reproductive system

Question 15

what is FSH’s function in the testis?

Answer 15

maintains Sertoli cells and makes them responsive to testosterone

Question 16

what maintains spermatogenesis and testosterone secretion?

Answer 16

LH and FSH at appropriate levels

Question 17

males must produce sperm constantly and be ready to deliver them to the female. what does this require?

Answer 17

appropriate levels of FSH, LH and testosterone

Question 18

how is appropriate levels of FSH, LH and testosterone in males achieved?

Answer 18

negative feedback

Question 19

what happens as testosterone levels rise?

Answer 19

inhibit GnRH secretion, reducing production of LH + FSH (spermatogenesis + testosterone secretion not maintained, so testosterone levels fall, no inhibition, GnRH increases)

Question 20

what happens if spermatogenesis proceeds too rapidly?

Answer 20

inhibin levels rise

enhance LH, secrete more testosterone, reduce LH + FSH, inhibition on spermatogenesis

Question 21

where does inhibin act to reduce secretion of FSH?

Answer 21

on gonadotrophs in (ant) pituitary

Question 22

what are the effects of gonadal steroids?

Answer 22

1. determinative effects:
   qualitative, only partly reversible if at all (mostly secondary sexual characteristics e.g. deepening of voice)
2. regulatory effects: highly reversible, rely on continuous hormonal stimulation for maintenance

Question 23

what are the major determinative effects of testosterone?

Answer 23

deepening of voice

growth of facial, armpit, chest + pubic hair

Question 24

what are the regulatory effects of testosterone?

Answer 24

1. maintenance of male internal genitalia
2. metabolic effects
3. behavioural effects

Question 25

what are the male internal genitalia?

Answer 25

prostate
seminal vesicles
vas deferens
epididymis

Question 26

what are the metabolic effects of testosterone?

Answer 26

anabolic:

increase is muscle mass and strength, density + strength of bones

Question 27

what are the behavioural effects of testosterone in male?

Answer 27

aggression, sexual activity