Physiology of the Menstrual Cycle

Question 1

What are the two functions of ovaries?

Answer 1

1) Hormone production

2) Oocyte release - menstruation, reproduction

Question 2

Describe the hypothalamic-pituitary-ovarian axis

Answer 2

• Hypothalamus → GnRH → anterior pituitary → LH, FSH → gonads → sex hormones → negative feedback to hypothalamus and pituitary

Question 3

What causes cramps?

Answer 3

The drop in progesterone

Question 4

Describe how the number of eggs drops over time

Answer 4

1) Before birth - 7 million
2) At birth - 2 million
3) First period - 0.5 million eggs
4) Menopause - no eggs

Question 5

What is menarche?

Answer 5

The onset of menstruation

Question 6

What do ovulation kits measure?

Answer 6

The level of LH (LH surge) in urine to predict when ovulation occurs

Question 7

What does the corpus luteum secrete?

Answer 7

Progesterone (and oestrogen)

Question 8

Why is LH called so?

Answer 8

Bc it acts on the corpus luteum

Question 9

How much thicker does the lining get during the follicular/proliferative phase?

Answer 9

11-14mm

Question 10

Describe the ovarian cycle

Answer 10

1) Follicular phase (D1-10) - hormones signal 10-20 follicles to grow in ovaries, oestrogen matures one oocyte
2) Ovulatory phase (D11-14) - oocyte undergoes cell division, follicle wall thins and ruptures, oocyte enters abdominal cavity near timbre of fallopian tube
3) Luteal phase (D14-28) - oestrogen levels drop, egg travels through the fallopian tube towards the uterus

Question 11

How does oestrogen feedback change in the cycle?

Answer 11

First half of the cycle oestrogen is associated with positive feedback, but in the second half, it is associated with negative feedback

Question 12

What can you see in a transvaginal scan?

Answer 12

The follicle/corpus luteum

Question 13

Describe the motility of the oocyte during ovulation

Answer 13

1) Shortly before ovulation, fimbriae begin to sweep over the surface of ovaries
2) Once the oocyte is in the tube, it is propelled by cilia and fallopian tube contractions

Question 14

When does implantation begin?

Answer 14

By day 6-7 after ovulation (D21)

Question 15

Where do gonadotropins act?

Answer 15

Directly on ovaries

Question 16

What are the roles of oestrogen?

Answer 16

1) Promotes maturation of reproductive organs
2) Development during puberty
3) Regulates the menstrual cycle
4) Pregnancy

Question 17

What are the roles of progesterone?

Answer 17

1) Promotes breast development
2) Maintains the uterine lining
3) Regulates the menstrual cycle
4) Sustains pregnancy

Question 18

What is the FSHR?

Answer 18

Follicle stimulating hormone receptor - transmembrane receptor that interacts with FSH and represents a GPCR

Question 19

What are the 4 phases of the menstrual cycle?

Answer 19

1) Menstrual phase
2) Proliferative phase
3) Late proliferative phase
4) Secretory phase

Question 20

Describe the menstrual phase of the menstrual cycle

Answer 20

D1-5 → the functional layer of the endometrium becomes detaches from the uterine wall, resulting in bleeding (menses)

Question 21

Describe the proliferative phase of the menstrual cycle

Answer 21

D6-14 → GnRH, FSH, LH
→ Follicular development
→ Increasing levels of oestrogen
→ Endometrium begins to proliferate and thicken, tubular glands and spiral arteries form
→ Stimulation of progesterone receptor synthesis in endometrial cells

Question 22

Describe the late proliferative phase of the menstrual cycle

Answer 22

D13-14 → the glands are long and tortuous due to the active growth
→ Stroma is gradually becoming oedematous

Question 23

Describe the secretory phase of the menstrual cycle

Answer 23

D15-22 → rising levels of progesterone
→ Enlargement of glands which begin secreting mucus and glycogen in preparation for implantation of the fertilised ovum
→ Increased fluid (oedema) in the stroma

Question 24

What is the menstrual cycle?

Answer 24

Series of cyclic changes in the endometrium in response to changes in levels of ovarian hormones

Question 25

What % of women with regular cycles are on their fertile window on any given day of their cycle between days 6-21?

Answer 25

At least 10%

Question 26

What is defined as a regular cycle?

Answer 26

A cycle that has no more than 4 days variation from month to month

Question 27

What is day 1 of the menstrual cycle?

Answer 27

The first day of bleeding

Question 28

How long does menstruation last?

Answer 28

3-8 days, written as 7/28 or 5-6/27-32

Question 29

Describe oogenesis before ovulation

Answer 29

• At birth all primordial oocytes are arrested at prophase I of meiosis I
• The majority of the follicles/oocytes undergo atresia from birth to menopause
• Meiosis I generates a secondary oocyte and the first polar body dies
• Secondary oocyte arrests at metaphase II of meiosis II (just before it ovulates)

Question 30

When does meiosis II occur in oogenesis?

Answer 30

Meiosis II only completes when the egg is fertilised at which poiunt the second polar body is extruded to prevent triploidy

Question 31

What happens alongside oogenesis?

Answer 31

Folliculogenesis (follicular development) which can take 300+ days and ovulation

Question 32

What are the 3 stages of the ovarian cycle?

Answer 32

1) Follicular phase
2) Ovulation
3) Luteal phase

Question 33

What are the 3 stages of the uterine cycle?

Answer 33

1) Menstruation
2) Proliferative phase
3) Secretory phase