L7: the menstrual cycle

Question 1

Describe the function of GnRH

Answer 1

Released in pulses from the hypothalamus, stimulating the release of FSH and LH from the anterior pituitary
Pulsatile release – receptors can become desensitised if they are over exposed to this hormone

Question 2

Describe endometriosis

Answer 2

Ectopic endometrial tissue can develop (can be anywhere in the body), leading to significant pain
Giving continuous GnRH can ‘switch the axis off’ to alleviate their symptoms
-can also be given in situations such as precocious puberty

Question 3

Describe the function of FSH

Answer 3

Acts at the ovary to allow the follicles to develop at the start of the menstrual cycle
Follicles also produce oestrogen and a hormone called inhibin -> selectively involved in negative feedback of FSH at the anterior pituitary

Question 4

Describe the function of LH

Answer 4

Responsible for ovulation

‘LH surge’ = key factor that drives ovulation

Question 5

What is the ovarian cycle?

Answer 5

Describes the changes that affect the ovaries during the menstrual cycle
2 halves: follicular phase & luteal phase

Question 6

Describe what happens in the follicular phase

Answer 6

All about preparing a follicle to be reading for ovulation
At the start -> small number of follicles begin to develop -> FSH levels start to rise
Number of granulosa cells increases -> causes development of theca interna & externa cells
These produce oestrogen -> oestrogen rises (lower levels = negative feedback on hypothalamus & anterior pituitary)
Follicles will then develop into a Graafian follicle, oestrogen levels rise further (high levels = positive feedback)
Levels of LH & inhibin rise (therefore LH rises considerably more than the levels of FSH prior to ovulation)
Phase can be variable in length – precise timing of ovulation can vary from individual to individual

Question 7

Describe what happens in the luteal phase

Answer 7

Phase after ovulation & is where the repro system is waiting to see if fertilisation & implantation has occurred
Corpus luteum forms – produce oestrogen & progesterone
Negative feedback at the hypothalamus and anterior pituitary
Corpus luteum has lifespan of 14 days -> no implantation -> oestrogen, progesterone & inhibin drop, allowing the cycle to start again
Luteal phase is always constant = typically 14 days long

Question 8

What is the uterine cycle?

Answer 8

Describes the effects on the uterus

Can be divided into the proliferative phase & secretory phase

Question 9

Describe what happens in the proliferative phase

Answer 9

Endometrium will proliferate and thicken in response to oestrogen produced by the ovary
Simple, straight glands within the endometrium, but as this part of the cycle continues, the glands become coiled and the functional layer doubles in size

Question 10

Describe what happens in the secretory phase

Answer 10

Ovulation has occurred -> glands produced become secretory under the influence of progesterone
Towards the end of this stage -> hormones from the corpus luteum begin to fall -> glands lose their structure and endometrium becomes ready to shed its functional layer if implantation has not occurred

Question 11

What happens if implantation occurs?

Answer 11

Trophoblast produces hCG – acts as a gonadotrophin and has the same function as LH
hCG will maintain the corpus luteum -> maintain the pregnancy by producing oestrogen and progesterone (later this function is taken over by the placenta)

Question 12

List the functions of oestrogen

Answer 12

Intended to promote fertilisation:

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

Question 13

List the functions of progesterone

Answer 13

Intended to sustain a viable pregnancy:

1) Secretory function of endometrium
2) Reduction of motility of myometrium (assumed fertilisation has occurred)
3) Thick, acidic cervical mucus to prevent further entry of sperm