2.2 the menstrual cycle: control of the menstrual cycle

Question 1

what are the oestrogen, progesterone and inhibin levels like at the beginning of the menstrual cycle?

Answer 1

low

Question 2

where is GnRH secretion released from?

Answer 2

inhibition

Question 3

how are the FSH and LH levels like at the beginning of the menstrual cycle?

Answer 3

LH + FSH tend to rise
FSH rises more
as low inhibin levels release FSH from selective inhibin at pituitary

Question 4

what causes follicles to grow in the menstrual cycle?

Answer 4

FSH, followed by LH

Question 5

what happens to oestrogen and inhibin secretion as the follicle begins to grow under the influence of FSH and LH?

Answer 5

oestrogen and inhibin secretion rises

Question 6

how is FSH secretion inhibited?

Answer 6

selectively inhibited by inhibin

Question 7

what does rising oestrogen lead to?

Answer 7

stimulation of GnRH and hence LH secretion

Question 8

at about 12-14 days into the cycle, what stimulates the LH surge?

Answer 8

positive feedback of rising oestrogen stimulates LH surge

Question 9

what influences the positive feedback of rising oestrogen stimulating LH surge?

Answer 9

environmental factors influence precise timing

Question 10

what does LH surge produce?

Answer 10

ovulation

Question 11

what happens to oestrogen during LH surge and ovulation?

Answer 11

oestrogen levels fall dramatically

Question 12

what forms spontaneously from LH surge and ovulation?

Answer 12

corpus luteum

Question 13

what does LH promote after ovulation?

Answer 13

oestrogen and progesterone secretion from corpus luteum

Question 14

what happens as corpus luteum grows after ovulation?

Answer 14

more steroids are secreted

Question 15

what happens to oestrogen after ovulation? why?

Answer 15

rising oestrogen levels do NOT exert positive feedback on LH

because progesterone levels are also rising

Question 16

what happens to corpus luteum 14 days after ovulation? why?

Answer 16

in the absence of pregnancy, the corpus luteum regresses spontaneously

Question 17

what happens to progesterone and oestrogen levels 14 days after ovulation?

Answer 17

fall

Question 18

what happens as progesterone and oestrogen levels fall 14 days post ovulation?

Answer 18

triggers menstrual bleed

Question 19

what happens when menstrual bleed is trigger 14 days after ovulation?

Answer 19

relieving inhibition on FSH and LH, so triggering the development of new follicles and the beginning of a new cycle

Question 20

what happens if conception has occurred? (in terms of implanted embryo)

Answer 20

the implanted embryo develops a placenta which secretes human chorionic gonadotrophin (hCG)

Question 21

what is the function of hCG?

Answer 21

prevents regression of the corpus luteum

Question 22

what happens if corpus luteum is maintained by hCG?

Answer 22

continues to secrete oestrogen and progesterone

Question 23

what is the function of the oestrogen and progesterone secreted by corpus luteum?

Answer 23

support early weeks of pregnancy

maintaining suppression of ovarian cycle

Question 24

what are the durations of the follicular and luteal phases influenced by?

Answer 24

the ovary
(the time it takes for follicle to mature, and lifespan of corpus luteum)

Question 25

what is the transition between the follicular and luteal phase controlled by?

Answer 25

the brain via the LH surge

Question 26

overall there is a complex interaction between which organs in the menstrual cycle?

Answer 26

hypothalamus, pituitary and ovary