Session 4: The Menstrual Cycle

Question 1

Why is gametogenesis periodical in women?

Answer 1

Because it takes time to prepare the uterus for the implantation of a fertilised oocyte.

Question 2

What is the fundamental difference of the HPG axis in men and women?

Answer 2

In men testosterone produces negative feedback to the hypothalamus and anterior pituitary gland to inhibit release of GnRH and LH/FSH In women oestrogen can either produce negative feedback or positive feedback depending on the level of oestrogen. Low levels of oestrogen causes negative feedback. High levels of oestrogen causes positive feedback.

Question 3

How long does a typical menstrual cycle last?

Answer 3

21-35 days

Question 4

What controls the menstrual cycle?

Answer 4

Gonadotrophins (LH & FSH) acting on the ovaries. Ovarian steroids acting on tissue in the reproductive tract and also control the cycle.

Question 5

Explain the frequency of release of GnRH.

Answer 5

It is released in a pulsatile fashion.

Question 6

Why is it important that the GnRH release is pulsatile?

Answer 6

It is very key in fertility, because the receptors can become desensitised if they are overexposed to this hormone.

Question 7

Explain endometriosis.

Answer 7

A condition where ectopic endometrial tissue can develop. This leads to significant pain.

Question 8

Give a common management for endometriosis.

Answer 8

Giving continuous GnRH to such patients can switch the axis off and desensitise the patient to GnRH and alleviate their symptoms.

Question 9

Give another situation where giving continuous GnRH can be beneficial.

Answer 9

In precocious puberty when you want to temporarily halt this axis.

Question 10

Explain the HPO-axis.

Answer 10

GnRH from hypothalamus. Goes to AP -> LH and FSH LH and FSH act on the ovary. This leads to promotion of follicular development and production of ovarian hormones such as oestrogen and inhibin. Depending on levels of oestrogen it is negative feedback or positive feedback.

Question 11

Function of FSH.

Answer 11

Acts at the ovary to allow the follicles to develop at the start of the menstrual cycle in order to nurture and sustain the development of the gamete.

Question 12

What do the follicles produce?

Answer 12

Oestrogen and inhibin.

Question 13

Function of LH.

Answer 13

Responsible for ovulation.

Question 14

The menstrual cycle can be divided into two ‘sub-cycles’. Which?

Answer 14

The ovarian cycle The uterine cycle

Question 15

The ovarian cycle can be further divided into two phases. Which?

Answer 15

The follicular phase The luteal phase

Question 16

Explain the follicular phase.

Answer 16

Preparing a follicle to be ready for ovulation. Small number of follicles will begin to develop. FSH causes granulosa cells to proliferate and development of theca interna and externa. This follicle start to produce oestrogen from granulosa cells and the theca cells. Lead to a rise in oestrogen levels. The levels of oestrogen levels are still relatively low and this will cause negative feedback on hypothalamus and AP. Follicles develop into a Graafian follicle ready for ovulation. The Graafian follicle gets bigger and produce more oestrogen. Oestrogen levels rise and starts to exert positive feedback instead in hypothalamus and AP. At this point inhibin also rises. This leads to a LH surge whereas FSH won’t rise as much. The LH surge cause ovulation.

Question 17

Why is inhibin important in the development of the Graafian follicle?

Answer 17

Inhibin suppress release of FSH to prevent stimulation of more than one dominant follicle.

Question 18

Explain the luteal phase.

Answer 18

Happens after ovulation. ‘Waiting to see if fertilisation and implantation has occurred. After ovulation the follicle still has the granulosa and theca cells. This becomes the corpus luteum. Corpus luteum produce oestrogen and progesterone. High levels of oestrogen would cause positive feedback usually but the progesterone promotes negative feedback of oestrogen. Without fertilisation and LH the corpus luteum will regress. This leads to a drop in levels of oestrogen, progesterone and inhibin.

Question 19

How long is the luteal phase usually?

Answer 19

14 days. Corpus luteum has set lifespan of 14 days.

Question 20

The uterine cycle can be further divided into two phases as well. Which?

Answer 20

Proliferative phase Secretory phase

Question 21

What separates the proliferative phase from the secretory phase in relation to the ovarian phases?

Answer 21

Proliferative phase is before ovulation making it align with the follicular phase. Secretory phase is after ovulation making it align with the luteal phase.

Question 22

The uterus has two linings. Which?

Answer 22

Myometrium and endometrium

Question 23

What is the myometrium?

Answer 23

The muscular wall of the uterus

Question 24

What is the endometrium?

Answer 24

The epithelial lining of the uterine cavity.

Question 25

The endometrium can be further divided into what?

Answer 25

The functional layer and the basal layer.

Question 26

Function of the functional layer.

Answer 26

Sheds during menstruation

Question 27

Function of the basal layer.

Answer 27

Allows this to regrow at the start of a new cycle

Question 28

Explain the proliferative phase.

Answer 28

Endometrium will proliferate and thicken in response to oestrogen that is being produced by the ovary. Simple, straight glands within the endometrium will become coiled and the functional layer will double in size as the endometrium continues to develop.

Question 29

Explain the secretory phase.

Answer 29

After ovulation the glands that have been produced in the proliferative stage then become secretory under the influence of progesterone. When the corpus luteum begin to fall the glands then lose their structure and the endometrium becomes ready to shed its functional layer if implantation has not occurred.

Question 30

What happens instead if fertilisation occurs?

Answer 30

Syncytiotrophoblasts will start to produce hCG which acts as gonadotrophin.

This has the same function as LH and the hCG will maintain the corpus luteum which wil ltherefore maintain the pregnancy by producing oestrogen.

This function will later be taken over by the placenta.

Question 31

Functions of oestrogen in promotion of feritilisation.

Answer 31

Proliferation of endometrium and myometrium

Fallopian tube motility

Thin alkaline cervical mucus

Question 32

Function of progesterone in menstrual cycle.

Answer 32

To sustain a viable prengancy.

Secretory function of endometrium

Reduction of motility of myometrium

Thich acidic cervical mcuus to prevent further entry of sperm.