The Menstrual Cycle

Question 1

What is the consequence of disruption of the hypothalamic-pituitary portal system?

Answer 1

high circulating prolactin

low FSH/LH

Question 2

To what stage in meiosis does the oocyte progress following release from the ovary?

Answer 2

from prophase II to arrest at metaphase II

Question 3

What is the normal duration of the menstrual cycle?

Answer 3

21-35 days

Question 4

What is GnRH?

Answer 4

Secreted by hypothalamus

Cause cells in AP to prod FSH and LH

Question 5

What is the role of FSH?

Answer 5

Bind granulosa cells = follicle maturation of primary follicles = secondary follicle

Theca interna appears = secondary follicles then prod low levels of oestrogen = inhib LH

Inhibin secretion begins = inhibits FSH = stops more follicles devel

Question 6

In the follicular phase what keeps LH levels low?

Answer 6

Due to rising levels of GnRH LH should be rising

However FSH causes the devel of the follicle which prod low levels of oestrogen = which inhib LH secretion

Question 7

After the first 10 days (mid-follicular phase) what affect does oestrogen have?

Answer 7

High levels now able to cause a +ve feedback = stim release of LH

FSH not released due to inhibin prod by the follicle

Question 8

What causes the LH surge?

Answer 8

+ve feedback from oestrogen levels that are now high

Continued release of GnRH

Question 9

What is the result of the LH surge?

Answer 9

Ovulation of the most mature follicle releasing the oocyte

Question 10

After the follicle ovulates what does it turn into?

Answer 10

Corpus luteum

Now luteinised = of yellow colour

Question 11

Outline the purpose of the corpus luteum

Answer 11

Secretes = oestrogen, inhibin, progesterone

Question 12

What is the role of inhibin?

Answer 12

-ve feedback = stops the secretion of FSH = as we don’t need anymore follicle maturing just yet

Question 13

Describe the function of progesterone

Answer 13

-ve feedback on GnRH = stop release of FHS/LH

Stimulate endometrial growth = for egg to implant if fertilised

Question 14

What causes the corpus luteum to degenerate?

Answer 14

Progesterone inhibiting a further rise in LH

Question 15

As the corpus luteum degenerates what does that cause?

Answer 15

Progesterone levels fall = GnRH not inhibited = new cycle

Endometrial lining sheds as not maintained by progesterone

Question 16

What are the 2 phases of the ovarian cycle?

Answer 16

Follicular = 0-14 days

Luteal = 14-28 days

Question 17

How does gamete prod vary males to females?

Answer 17

M = continuous

F = periodic, need to prepare for implantation, requires a waiting phase

Question 18

Explain the feedback mechanism in the female HPG axis

Answer 18

Oestrogen/progesterone allow switching from +/- feedback to allow for periodic ovulation

Question 19

Explain the feedback mechanism in the male HPG axis

Answer 19

-ve feedback by testosterone to control its levels

Question 20

What 2 cycles occur during menstruation?

Answer 20

Ovarian cycle

Uterine cycle

Question 21

What is the role of the endometrium?

Answer 21

Implantation site for fertilised egg

Question 22

Define ovulation

Answer 22

Release of gamete after LH surge

Question 23

What occurs during the ‘waiting stage’?

Answer 23

Pause, maintaining the endometrium until a signal is received to indicate that fertilsation has happened

further gamete devel suspended by LH suppression due to presence of progesterone

Question 24

What controls menstruation?

Answer 24

Gonadotrophins = act on ovary

Ovarian steroids = act on uterus, acting to control the cycle

Question 25

Explain the importance of the pulsatile release of GnRH

Answer 25

Absolute requirement for fertility

If agonist constantly present = receptors become desensitised = FSH/LH prod stops = gonadal steroid prod stops

Question 26

What is endometriosis?

Answer 26

Plaques of endometrium growing outside of the uterus

= express receptors for oestrogen/testosterone

= grow when hormones present = irritate peritoneum

Treat = continuous exposure to GnRH agonist = desensitisation = switches axis off

Question 27

What defines the start of the cycle?

Answer 27

First day of menstruation

Question 28

What is menstruation?

Answer 28

No ovarian hormonal support = endometrium is lost

Question 29

What is the myometrium?

Answer 29

Thick muscular wall of the uterus

Thickens/grows, but does not shed

Question 30

What is the endometrium?

Answer 30

Epithelial lining of the uterine cavity

Functional layer = hormone responsive

Basal layer = stem cell layer for functional layer to devel from

Question 31

What are the peripheral effects of oestrogen?

Answer 31

Stim bone/muscle growth

Stim endometrial growth

Maintains female secondary characteristics

Maintains glands – breasts

Question 32

How does the uterus change over the menstrual cycle?

Answer 32

Early proliferation = glands sparse

Late proliferation = functional layer doubled

Early secretory = endometrium at max thickness

Late secretory = gland adopt saw-tooth appearance

Question 33

If fertilisation does occur what are the next steps?

Answer 33

Human chorionic gonadotrophin is produced (equivalent to LH) by the syncytiotrophoblast = corpus luteum does not degenerate + HPG axis is not switched back on

Question 34

How can cycle length vary between diff individuals?

Answer 34

Due to variation in follicular phase length

Luteal phase strictly controlled 14 +/- 2 days