Menstrual Cycle

Question 1

How long is the typical menstrual cycle?

Answer 1

21-35 days.

Question 2

Explain the normal differences in men and women reproductively.

Answer 2

Both HPG axis’ start in the hypothalamus making GnRH which stimulates FSH and LH in the anterior pituitary gland.
In the female LH and FSH works to stimulate the making of oestrogen and progesterone which have negative or positive feedback results depending on the stage in the females cycle.
In men, LH and FSH stimulate the formation of testosterone which then always negatively feedback the anterior pituitary and hypothalamus.

Question 3

Describe the release of GnRH.

Answer 3

Released by the hypothalamus in pulses, stimulating the release of FSH and LH from the anterior pituitary gland.

Question 4

Why does GnRH need to be released in pulses?

Answer 4

GnRH receptors become desensitised if they are over exposed to GnRH

Question 5

Describe Endometriosis.

Answer 5

Ectopic endometrial tissue develop, leading to significant pain.

Question 6

How to treat endometriosis.

Answer 6

Continuous GnRH switches off the axis to alleviate symptoms.

Question 7

When else can continuous GnRH be given.

Answer 7

To treat precocious puberty to halt the axis temporarily.

Question 8

What are the actions of FSH?

Answer 8

1. Acts at the ovary to allow follicles to develop and start the menstrual cycle (first day of menstruation) to sustain the development of the gamete.
2. Produce oestrogen and inhibin to selectively be involved in -ve feedback of FSH at the APG.

Question 9

What is the action of LH?

Answer 9

1. Ovulation as the LH surge is what drives ovulation.

Question 10

What are the 2 stages of the Ovarian Cycle?

Answer 10

1. Follicular Phase.

2. Luteal Phase.

Question 11

Describe, in stages the Follicular Phase of the Ovarian Cycle.

Answer 11

1. Small number of follicles begin to develop.
2. No inhibition of the hypothalamus or anterior pituitary gland so FSH rise.
3. FSH increases the number of granulosa cells.
4. Increases granulosa cells develops theca interna and externa cells.
5. Follicle can now produce oestrogen from both granulosa cells and theca interna and external cells.
6. Oestrogen levels rise.
7. Low levels of oestrogen cause negative feedback at the hypothalamus and anterior pituitary.
8. Follicle will become Graafian with a large antrum, which is now ready to released in ovulation.
9. Oestrogen rise further, which causes a positive feedback effect on the hypothalamus and APG, increasing LH.
10. As follicle develops inhibin also rises from the granulosa cells.
11. Inhibin inhibits FSH stimulation so LH will rise and FSH will not.

Question 12

Can the Follicular Phase of the Ovarian Cycle vary in length?

Answer 12

Yes, thus the precise timing of ovulation can vary from individual to individual.

Question 13

What happens in preparation for ovulation?

Answer 13

1. Circulating oestradiol and inhibin rise rapidly.
2. Oestradiol production is no longer dependent on FSH.
3. Surge in LH production.
4. Progesterone production begins and granulosa cells become responsive to LH.
5. GnRH is modulated.

Question 14

Describe, in stages the Luteal Phase of the Ovarian Cycle.

Answer 14

1. Granulosa and theca cells become vascularised to form the corpus luteum (lutein= the yellow/cold pigmentation). The corpus luteum produces oestrogen and progesterone. Progesterone inhibits the high oestrogen effects on the hypothalamus and APG of positive feedback.
2. Corpus Luteum has a set lifespan of 14 days to see whether implantation of a fertilised oocyte has occurred.
3. If fertilisation hasn’t occurred it will regress and thus levels of oestrogen, progesterone and inhibin will drop. This allows the cycle to start again.

Question 15

Is the Luteal Phase of the Ovarian Cycle different between people?

Answer 15

No, the lifespan is 14 days so it is 14 days long.

Question 16

What is the name of the 2 phases of the uterine cycle.

Answer 16

1. Proliferative Phase.

2. Secretory Phase.

Question 17

Describe the Proliferative Phase of the Uterine Cycle.

Answer 17

1. The endometrium will proliferate and thicken in response to oestrogen produced by the ovary. The glands within the endometrium are simple and straight.
2. As the endometrium continuous to proliferate and thicken these glands become coiled and the functional layer doubles in size.

Question 18

Describe the Secretory Phase of the Uterine Cycle.

Answer 18

1. Once ovulation has occurred the glands that have been produced in the proliferative stage then come secretory under the influence of progesterone.
2. Towards the end of this stage, hormones from the corpus luteum begin to fall and the glands lose their structure. The endometrium becomes ready to shed its functional layer if implantation have no occurred.

Question 19

Describe the wall of the Uterus.

Answer 19

1. Outer most layer of myometrium made of musculature.
2. Basal Endometrium Epithelial Lining provides a source from which a new functional layer can develop.
3. Functional Endometrium Epithelial Lining is hormone responsive and shed if no pregnancy occurs.

Question 20

What happens if Implantation does occur?

Answer 20

The outer cell mass (syncytiotrophoblast) produces hormone chorionic gonadotrophin which functions the same as LH.
hCG maintains the corpus luteum which will thus maintain pregnancy by producing oestrogen and progesterone.
This function will later be taken over by the placenta.

Question 21

Describe the functions of oestrogen.

Answer 21

1. Proliferation of endometrium.
2. Proliferation of myometrium.
3. Fallopian tube motility.
4. Thin, alkaline cervical mucus.

Question 22

Describe the functions of progesterone.

Answer 22

1. Secretory function of endometrium.
2. Reduction of motility of myometrium, assuming that fertilisation has already occurred.
3. Thick, acidic cervial musics to prevent further entry of sperm.