Endocrine Control of Menstrual Cycle

Question 1

what are the hormones involved in female reproductive cycle produced by

Answer 1

• neurons in brain, pituitary gland, ovaries

Question 2

list relevant (ovarian) steroid hormones involved in female reproductive cycle

Answer 2

• oestrogen
• progesterone
  (produced in ovaries)

Question 3

list relevant protein hormones involved in female reproductive cycle & what produced by

Answer 3

• gonadotrophin releasing hormone (GnRH) - hypothalamus
• follicle stimulating hormone (FSH) - pituitary gland
• luteinising hormone (LH) - pituitary gland
• inhibin - produced in ovaries

Question 4

sources of environmental, metabolic and endocrine inputs that the brain receives as neuroendocrine input

Answer 4

• circadian cycle
• nutrition
• stress
• steroids (other hormones)
• many other cues
  can impact neurons

Question 5

which neurons are impacted by input into neuroendocrine system

Answer 5

• periventricular nucleus
• arcuate nucleus

Question 6

what can the periventricular and arcuate neurons do once received input

Answer 6

• interact w hypothalamus
• modulate production GnRH

Question 7

where does hypothalamus sit
where does pituitary gland sit

Answer 7

• hypothalamus: in brain
• pituitary gland: just below brain in skull

Question 8

what is GnRH produced by & where is it transported to

Answer 8

• produced by hypothalamus
• transported to pituitary gland

Question 9

at what point in cycle does pituitary gland respond to GnRH from hypothalamus & what is this response

Answer 9

• early in each new cycle
• responds by producing FSH & secreting into circulation

Question 10

what happens to secreted FSH early in cycle by pituitary gland

Answer 10

• secreted into circulation
• carried into ovaries
• ovarian follicles express FSH receptor and FSH binds
• promotes further growth and proliferation of follicular cells in follicles -> causes oocyte to simultaneously grow and mature

Question 11

does complete development of ovarian follicle occur in one 28 day cycle? what does occur?

Answer 11

• no
• last stages of folliculogenesis integrated in controlling menstrual cycle

Question 12

what do granulosa cells in follicle produce

Answer 12

• oestradiol (type of oestrogen)

Question 13

what is happening with regard to oestrogen from FSH release to follicles

Answer 13

• since follicles are growing with support of FSH -> incr granulosa cells
• increased oestrogen (oestradiol) secretion into blood
• secreted oestrgoen circulated back to brain & pituitary gland

Question 14

what does the secreted oestrogen from growing follicles in cycle allow for measurement of

Answer 14

=> oestrogen levels = measure of stage of follicle development

Question 15

describe how FSH suppression is reached after oestrogen release is stimulated from FSH early in cycle

Answer 15

• as cycle progressives, low but rising oestrogen levels (caused by granulosa cells of growing follicle) have negative feedback effect on both the cells of arcuate nucleus (for hypothalamus to release GnRH) and on pituitary gland -> suppressed FSH release

Question 16

does negative feedback from oestrogen that suppresses FSH slow down the growth of the dominant follicle & why / why not

Answer 16

• does not
• because its development causes it to gain FSH independence

Question 17

does negative feedback from oestrogen that suppresses FSH slow down the growth of the smaller follicles & why / why not

Answer 17

• yes
• smaller follicles are affected so that one or two dominant follicles emerge in each cycle -> continue to grow to pre-ovulatory stage of maturation

Question 18

what do larger dominant follicles produce as they continue to grow

Answer 18

• increasing levels of oestrogen

Question 19

as the dominant follicles grow and increasingly release oestrogen, what happens to oestrogen levels and what’s the result

Answer 19

• oestrogen levels rise in circulation
• higher oestrogen concentrations sensed by periventricular nucleus -> positive feedback on GnRH secretion

Question 20

what does the positive feedback by oestrogen on periventricular neurons for GnRH secretion lead to

Answer 20

• promoted secretion of LH from pituitary gland

Question 21

during what stage do follicles grow? what marks this stage?

Answer 21

• follicular phase
• start marked by gradual increase in FSH levels, followed by rise oestrogen levels later
• (progesterone levels stay low)

Question 22

list 4 phases of menstrual cycle in order

Answer 22

• menstrual phase
• follicular phase (early and late)
• ovulation
• luteal phase

Question 23

what does positive feedback effects of oestrogen on hypothalamus cause

Answer 23

• cause pulsatile release of GnRH from hypothalamus to increase in frequency and amplitude
• cause LH surge

Question 24

does oestrogen rise in follicular phase cause negative or positive feedback loop

Answer 24

both
- negative to hypothalamus (arcuate nucleus in brain in particular) & to pituitary gland
- positive to hypothalamus (periventricular nucleus in brain in particular)

Question 25

what is the link between GnRH pulses and patterns of LH release

Answer 25

- direct relationship

Question 26

in days, when does LH surge occur in cycle

Answer 26

- at midpoint of cycle ~day 14 of 28 day cycle (day 14 from time of last menstruation)

Question 27

what is considered start of cycle

Answer 27

- from time of last menstruation - includes bleeding days

Question 28

circulating LH from LH surge (~day 14 of cycle) is sensed by what cells to stimulate what

Answer 28

- sensed by granulosa cells (in ovary) - stimulate gene expression change that results in ovulation (release of oocyte; subsequent differentiation of remaining follicle to form corpus luteum)

Question 29

what does the corpus luteum secrete

Answer 29

- oestrogen (low levels) - progesterone at very high levels

Question 30

what does LH surge represent

Answer 30

- mid cycle - switching from follicular phase to luteal phase - ovulation occurs (day 14)

Question 31

what is follicular phase & what is it controlled by

Answer 31

- period when follicles growing - follicles controlling events thru hormones they secrete

Question 32

what is luteal phase & what is it controlled by

Answer 32

- preparing uterus for pregnancy by thickening uterine lining / endometrium (ie/ progesterone production) - controlled by corpus luteum thru hormones it secretes

Question 33

what phase occurs concurrently with follicular phase

Answer 33

menstrual phase

Question 34

provide approx days for each cycle

Answer 34

- menstrual cycle (day 1-5) - follicular phase (day 1-13) [early 1-7; late 8-13] - ovulation (day 14) - luteal phase (day 15-28)

Question 35

what does oestrogen produced by dominant ovarian follicle in later stages of follicular phase stimulate

Answer 35

- stimulates regeneration of endometrium - redeveloping its glandular and vascularised structure - to prime it to support implantation (that would occur in ensuing luteal phase)

Question 36

how is developed endometrium (from oestrogen produced from dominant follicle in late follicular phase) sustained in luteal phase

Answer 36

- rising oestrogen and progesterone levels from corpus luteum sustain developed endometrium

Question 37

what does high progesterone from corpus luteum induce in endometrium (in addition to sustaining its development)

Answer 37

- induces decidualisation - final stage of endometrium preparation for embryo implantation

Question 38

how is corpus luteum function sustained when implantation does occur

Answer 38

- developing placenta (trophoblast cells > cytotrophoblast cells) & uterus communicate -> produce hormones that help sustain function of corpus luteum (hCG by syncytiotrophoblast cells primarily maintain corpus luteum) -> this helps sustain uterine endometrium (CL keeps producing progesterone) and support embryo

Question 39

in non-pregnant cycle, corpus luteum regresses (no indication of implantation from hCG ie/ indicating a developing placenta), leading to what

Answer 39

- loss of trophic support for endometrium (no CL -> lack progesterone production) => menstruation occurs & cycle resets

Question 40

what event induces ovulation

Answer 40

LH surge