Menstrual Cycle (Normal Physiology,Menopause and Pre-menstrual dysphoric syndrome)) Flashcards
Name the two phases in the menstrual cycle
Follicular phase
Luteal phase
Average length of menstrual cycle?
28 days.
What pituitary axis controls the menstrual cycle?
Hypothalamus-pituitary-gonadal axis
Describe how the female HPG axis works
- Hypothalamus secretes GnRH
- GnRH travels down anterior pituitary gland and bind to receptor on gland
- This promotes release of LH and FSH from the anterior pit
- LH and FSH travel in blood stream to the ovaries
- LH and FSH bind to the ovaries, stimulating production of oestrogen and inhibin.
- Increasing levels of oestrogen and inhibin have negative feedback effect on hypothalamus and anterior pit
- This leads to decreased production of GnRH, LH< FSH.
- This results in decreased production of oestrogen and inhibin.
Name hormones involved in menstrual cycle
GnRH, LH, FSH, Oestrogen, Progesterone, Inhibin, activin
Describe release of hormones in female HPO axis
Pulsatile manner
Why is HPO axis in females pulsatile?
- Persistent presence of GnRH would lead to desensitisation of its receptors on gonadotrophs (in ant pit gland).
- So FSH and LH production would cease
- Gonadal steriod production would cease
What type of feedback do oestrogen, progesterone and inhibin have on pituitary and hypothalamus?
NEGATIVE
Describe the early follicular phase (days 0-5 of the menstrual cycle)
No ovarian hormone production (i.e no oestrogen and inhibin made)
Granulosa cells (endocrine cells in ovary) secrete activin
* This incerases FSH production, and have increase FSH receptors on granulosa cells
* Reduced production of androgens by theca cells at this point (so less oestrogen is made).
Collectively, this increases FSH levels, so:
* to stimulate follicle growth
* theca interna appears
* enhanced aromatase function –> so the follicle is now capable of enhanced oestrogen production
The follicle with the most FSH = the dominant follicle - sometimes called Graafian follicle.
Dominant Follicle/Graafian follicle’s granulosa cells switch from producing activin to producing inhibin
Describe the late follicular phase (days 5-14 of the menstrual cycle)
Dominant follicle/Graafian follicle granulosa cells** produce oestrogen and inhibin **
Oestrogen:
* Increases FSH receptors on the follicle (so the dominant follicle continues to grow)
* Initially exert negative feedback to reduce FSH production
* Increases LH receptors on granulosa cells to prep for ovulation
Inhibin:
* **Reduces FSH **production
* Helps LH to increase theca cells androgen production (androgens are converted to oestrogen)
Oestrogen and inhibin continue to rise.
How is FSH important in the production of oestrogen?
FSH enhances the function of aromatase.
Aromatase converts androgen –> oestrogen
Describe what happens in the ovulatory phase (day 14)
Oestrogen rises (independent of FSH)
High levels of oestrogen exert positive feedback on the hypothalamus and anterior pituitary
Results in a surge in LH production
There is no rise in FSH, due to presence of inhibin
Granulosa cells start secreting **progesterone **
How do high levels of LH change the membrane of the Graafian follicle?
Membrane becomes thinner.
Follicle ruptures releasing oocyte
What happens after follicle rupture? (but before luteal phase begins)
Secondary oocyte matures into mature ovum
Mature ovum is released into peritoneal space
It is taken into the fallopian tube via the fimbriae.
Describe the luteal phase of the menstrual cycle
Starts once ovulation has occured.
LH and FSH now stimulate remaining Graffian follicle to develop into corpus luteum (i.e. follicle is luteinised)
Corpus luteum produces progesterone (also secretes oestrogen and inhibin but that’s not as important)
Oestrogen and progesterone exert **negative feedback on LH **
Levels of FSH and LH fall, so corpeus luteum dedgenerates.
Degeneration of corpus luteum results in loss of progesterone production.
Falling progesterine levels** trigger mensturation** - then we are back to start of early follicular phase!
In the luteal phase, progesterone levels increase. What does this result in?
- Endometrium becoming receptive to implantation of blastocyst
- negative feedback causing decreased LH and FSH
- increase in woman’s basal body temperature
Which hormones are needed to maintain corpeus luteum?
FSH and LH
(That’s why when they fall in the luteal phase, the C.L degenerates)
What happens if an ovum is fertilised?
ie. what hormones, what happens to corpeus luteum
Fertilised ovum produced hCG, which has similar function to LH
hCG prevents degeneration of corpus luteum = get continued production of progesterone
Continued production of progesterone = prevent menstruation
What takes over role of corpus luteum from ~8 weeks gestation
Placenta
What are the three phases of the uterine cycle?
Menstrual
Proliferative
Secretory
Name for inside lining of uterus?
Endometrium
What are two layers of endometrium?
Functional layer
basal layer
Describe the growth of the functional layer of the endometrium
Grows thicker in response to oestrogen
Is shed in menstruation
Describe the basal layer of the endometrium
Forms the foundation from which the functional layer develops
(is not shed!)