Week 2.2 - The menstrual cycle Flashcards Preview

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Flashcards in Week 2.2 - The menstrual cycle Deck (37)
1

In general, What effects do oestrogen have on the gamete and the endometrium?

-Prepare the gamete for ovulation
-Prepare the endometrium for implantation

2

What is the function of the luteal phase?

-Hold the system in pause and maintain the endometrium until a signal is received that fertilisation has happened

3

In what rhythm is GnRH released?

-Pulsatile release every hour

4

What are the functions of FSH and LH in the female?

-Promote follicular development
-Stimulate follicular cells to produce steroid hormones and inhibin
-ovulation

5

What control do the gonadal hormones have upon HPG axis?

-Both positive and negative feedback

6

When does oestrogen have positive feedback effects?

-When it is high titres by itself ie the follicular phase

7

When does oestrogen exert negative feedback?

-When it is at moderate titres ie luteal phase

8

What is the dominant steroid hormone in the luteal phase?

-Progesterone

9

Describe the ovarian steroid hormone levels at the start of the cycle

-No ovarian hormone production

10

Which hormone encourages follicular development at the start of the cycle?

-FSH

11

Why is it that ovarian hormones drop at the end of the cycle? What effect does this have on the HPG axis?

-Follicular cells are dying and thus stop producing oestrogen/progesterone
-This resets the HPG axis as all feedback is removed as the levels are too low.
-GnRH can now work normally, causing slow release of FSH and LH

12

What effect does resetting the HPG axis have on the ovary?

-Recruitment of small group of follicles within ovary independent of extragonadal signals. This starts follicular development

13

Which cells of the ovary do FSH act on?

-Granulosa cells

14

When does oestrogen secretion become possible from the developing follicle? Why?

-When theca interna has developed -> has LH receptors
-Oestrogen production depends on interaction between theca and granulosa cells

15

What hormone, besides oestrogen, begins to be secreted from the developing follicle?

-Inhibin

16

What drives the formation of a dominant follicle? (2 things)

-Follicular oestrogen now at a level where it can exert a positive feedback control at the hypothalamus and pituitary
-Follicular inhibin levels rise which selectively inhibits FSH production by anterior production

17

What is the consequence on gonadotropin levels of inhibin?

-Only see a rise in LH, FSH secretion inhibited

18

There is a rapid rise in oestrogen and inhibin at approximately day 12 (when the follicle is fully developed), what effect does this have on gonadotropin hormones?

-LH surge

19

Why does progesterone production begin after LH surge?

-Granulosa cells become responsive to LH as prior to this they only had FSH receptors

20

What effect does oestrogen exhibit on the sensitivity of anterior pituitary?why does this cause the LH surge?

-High levels of oestrogen increases sensitivity of anterior pituitary to GnRH
-Early follicular phase -> Oestrogen low-> anterior pituitary not very sensitive to GnRH -> slow release of LH
-Late follicular phase ->oestrogen high-> sensitivity of the anterior pituitary is increased -> LH surge.

21

How does LH contribute to ovulation?

-Causes increase in collagenase activity -> follucle membrane breakdown -> oocyte released
-Causes PG increase -> contraction of ovarian wall to help extrusion

22

What happens to the primary oocyte in the follicle just before ovulation?

-Meiosis 1 completes and meiosis II starts

23

What happens to the follicle after ovulation?

-Remains in the ovary and become leutinised under the control of LH (forms corpus luteum)

24

What is the function of the corpus luteum?

-Secrete oestrogen and progesterone from androgens in large quantities
-Inhibin still pruduced to inhibit FSH
-Suppresses LH secretion by putting the axis into pause as further gamete development is suspended due to negative feedback of oestrogen and progesterone

25

What happens to the corpus luteum in the absence of LH?

-Spontaneous regression

26

What happens to the hormone profile after the corpus luteum has regressed?

-The axis is reset and everything is at basal levels

27

What happens to the corpus luteum if fertilisation occurs?

-Syncytiotrophoblast produces hCG which has luteinising effect and maintains the corpus luteum until the placenta is sufficiently developed to take over oestrogen and progesterone production to control HPG (approx 4 months)

28

What are the two phases in ovarian cycle?

-Follicular
-Luteal

29

What are the two phases in the uterine cycle?

-Proliferative
-Secretory

30

What causes the proliferation of the endometrium?

-Oestrogen produced from ovary

31

What effect does progesterone have on the endometrium?

-Causes it to enter the secretory cycle where it becomes very glandular to allow implantation

32

What effect does oestrogen have in the follicular/proliferative phase?

-Increases mobility of uterine tube
-Thickening of endometrium
-Growth and motility of myometrium
-Thin alkaline cervical mucus
-Vaginal changes
-Changes in skin, hair and metabolism

33

What effect does progesterone have in the luteal/secretory phase?

-Further thickening of the endometrium to become glandular
-Thickening of myometrium but reduces motility
-Thick acid cervical mucus
-Changes in mammary tissue
-Increases in body temperature
-Metabolic and electrolyte changes

34

Why in the luteal phase, does the cervical mucus become thick and acidic?

-Limit polyspermy
-Prevent infection

35

What is the normal limit for menstrual cycle? How can it vary?

-21-35 days
-Luteal phase always 14 days (+/- 2 days) it is the follicular phase which varies

36

What is the ovarian cycle?

-Preparation of the gamete for ovulation

37

Describe the relationship between theca interna and granulosa cells in producing oestrogen

-Theca interna has receptors for LH which causes the production of androgens (androstenedione) which are precursors of eostrogen
-Granulosa cells have the enzyme aromatase which use the androgens secreted by theca interna to oestrogens