Menstrual Cycle

Question 1

when does the follicular phase occur?

Answer 1

• length can vary

~days 1-14

Question 2

when does ovulation occur?

Answer 2

day 14

Question 3

when does the luteal phase occur?

Answer 3

always 14 days before menses

Question 4

what hormones cause ovulation?

Answer 4

oestrogen-induced LH surge

Question 5

what hormone causes the luteal phase?

Answer 5

progesterone

Question 6

what uterine phase(s) occur days 1-14?

Answer 6

• menstrual

- proliferative

Question 7

what uterine phase(s) occur days 15-28?

Answer 7

secretory

Question 8

what does FSH bind to?

Answer 8

granulosa cells

Question 9

what are the actions of FSH?

Answer 9

• stimulates follicle growth
• allows conversion of androgens (from theca cells) → oestrogens
• stimulates inhibin secretion

Question 10

what does LH bind to?

Answer 10

theca cells

Question 11

what is the action of LH?

Answer 11

stimulates production & secretion of androgens

Question 12

what is the difference in GnRH secretion before and after the onset of puberty?

Answer 12

before - released at steady rate

after - released in pulses

Question 13

what effects does oestrogen have on the HPG axis?

Answer 13

moderate levels - negative feedback
high levels - (in absence of progesterone) positive feedback
in presence of progesterone - negative feedback

Question 14

what effect does inhibin have on the HPG axis?

Answer 14

inhibits FSH

Question 15

what are the phases of the ovarian cycle?

Answer 15

1. follicular
2. ovulation
3. luteal

Question 16

what is a follicle?

Answer 16

primary oocyte surrounded by granulosa and theca cells (stromal cells)

Question 17

summarise the follicular phase

Answer 17

Follicles begin to mature and prepare to release an oocyte

Question 18

what controls the maturation of the follicles?

Answer 18

• LH

- FSH

Question 19

what happens in days 1-10 of the follicular phase?

Answer 19

1. Theca cells develop receptors and bind LH
   
   • > Secrete androgen
2. Granulosa cells develop receptors and bind FSH
   
   • > Secrete aromatase - converts androgen → oestrogen

Question 20

what happens in days 10-14 of the follicular phase?1

Answer 20

1. follicles grow and oestrogen released in bloodstream
2. increased oestrogen acts as negative feedback signal to HPG axis
3. less FSH -> some follicles die
4. follicle with most FSH receptors continues to grow
5. high oestrogen acts as positive feedback signal to HPG axis
6. high levels of FSH & LH 1-2 days before ovulation

Question 21

what happens in ovulation?

Answer 21

1. LH surge
2. Follicle ruptures
3. Mature oocyte assisted to fallopian tube by fimbria

Question 22

how long does the mature oocyte remain viable in the fallopian tube?

Answer 22

~24 hours

Question 23

summarise the luteal phase

Answer 23

Remnant of the ovarian follicle becomes the corpus luteum

Question 24

what is the corpus luteum?

Answer 24

Leutinised theca & granulosa cells

Question 25

what happens in the luteal phase?

Answer 25

1. leutinised theca & granulosa cells continue to secrete androgen/produce oestrogen 2. low LH -> granulosa cells produce more progesterone than oestrogen 3. Progesterone acts as negative feedback signal on HPG axis 4. Leutinised granulosa cells begin secreting inhibin 5. Oestrogen levels decline ⇒ progesterone is the dominant hormone

Question 26

what is the effect of high levels of progesterone and low levels of oestrogen?

Answer 26

- signal ovulation has occurred | - helps to make endometrium receptive to implantation of fertilised gamete

Question 27

what are the phases of the uterine cycle?

Answer 27

1. menstrual 2. proliferative 3. secretory

Question 28

when does the menstrual phase occur?

Answer 28

days 1~5

Question 29

what is menses?

Answer 29

beginning of a new menstrual cycle

Question 30

summarise the proliferative phase

Answer 30

Changes in endometrium optimise chance of fertilisation

Question 31

what happens in the proliferative phase?

Answer 31

high oestrogen levels → thickening of endometrium → growth of endometrial glands → emergence of spiral arteries (to feed functional endometrium) → change the consistency of the cervical mucus (more hospitable to incoming sperm)

Question 32

what stimulates the proliferative phase?

Answer 32

high oestrogen levels

Question 33

when is the highest chance of fertilisation?

Answer 33

days 11-15

Question 34

when does the secretory phase occur?

Answer 34

days 15-28

Question 35

what happens on day 15 of the secretory phase?

Answer 35

high progesterone levels → spiral arteries coil and grow longer → uterine glands secrete more mucus

Question 36

what happens after day 15 of the secretory phase?

Answer 36

- cervical mucus thickens (less hospitable for sperm) - corpus luteum -> corpus albicans (levels of progesterone and oestrogen decrease) lowest progesterone levels → spiral arteries collapse → functional endometrial layer prepares to shed through menstruation