gonadal steroidogenesis W7

Question 1

HPG axis pathway?

Answer 1

hypothalamus secretes GnRH (gonadotropin releasing hormone) which travels to anterior pituitary gland and binds to GnRH receptors on gonadotroph cells. this stimulates production and release of LH and FSH (gonadotropins) which act on gonads (testes/ovaries) to produce androgens and oestrogens.

Question 2

HPG axis activity throughout life?

Answer 2

increase during foetal development, first postnatal months (mini-puberty), and puberty

Question 3

testosterone functions?

Answer 3

spermatogenesis
development of primary and secondary sexual characteristics
increasing libido
promoting bone and muscle growth

Question 4

testosterone negative feedback?

Answer 4

negative feedback on GnRH production in hypothalamus and FSH and LH production in anterior pituitary

Question 5

2 important cells types in the testes?

Answer 5

leydig cells (produce testosterone)
sertoli cells (control and facilitate production of mature sperm)

Question 6

what does FSH and LH stimulate in the testes

Answer 6

LH -> leydig cells (testosterone)
FSH -> sertoli cells (sperm)

Question 7

what cells in the testes does testosterone act on

Answer 7

sertoli cells (to promote spermatogenesis)

Question 8

what else does FSH promote the production of in sertoli cells? what is the effect of these? (males)

Answer 8

inhibin and activin
high testosterone leads to inhibin release, which negatively feeds back to hypothalamus and pituitary

low testosterone leads to activin release, which positively feeds back on the pituitary

Question 9

what do gonadotrophs stimulate in the ovaries?

Answer 9

production of mature gametes
synthesise and secrete estradiol and progesterone

Question 10

dominant follicle?

Answer 10

largest follicle in ovary during each menstrual cycle - that the oocyte is released from

Question 11

types of cells within follicles? which gonadotrophs act on these?

Answer 11

theca cells - LH
granulosa cells - FSH

Question 12

what do granulosa cells produce? what is their functions?

Answer 12

estradiol (stimulates preovulatory growth of the endometrium, level produced increases as follicle grows)
inhibin (inhibit FSH at anterior pituitary, hypothalamus)

Question 13

estradiol feedback?

Answer 13

moderate estradiol = negative feedback on hyp and pit
high estradiol and no progesterone = positive feedback on hyp and pit

Question 14

what causes the LH surge? Why is no more FSH produced at this moment?

Answer 14

high levels of estradiol exerting positive feedback on the pituitary
FSH not surged due to inhibin’s negative feedback on FSH production

Question 15

what does the corpus luteum produce?

Answer 15

estradiol and progesterone

Question 16

what occurs after ovulation in the dominant follicle?

Answer 16

dominant follicle -> corpus luteum
LH binds to theca cells in corpus luteum, this causes them to produce progesterone and androgens. androgens enter granulosa cells and are converted to estradiol.

Question 17

feedback effect of estradiol in the presence of progesterone?

Answer 17

negative effect on HPG axis

Question 18

effects of progesterone and estradiol?

Answer 18

prepare endometrium for pregnancy

Question 19

what occurs to the corpus luteum if there is no implantation?

Answer 19

regresses, withdrawal of progesterone and estradiol. menses (menstruation) occurs.