L7: Menstrual Cycle and Menopause Flashcards
Consequences and culprits behind disruption to the hypothalamic-pituitary-ovarian axis:
- Affects secondary sexual characteristics and fertility
- Caused by….
- Stress, low body weight, excess exercise
- Pituitary adenoma, Sheehan syndrome
- POI, PCOS
What is the broad function of the menstrual cycle?
- Maturation of follicle, ovulation
- Shed previous endometrium, then proliferate and preparation of the next one in advance of implantation
- Developing corpus luteum after ovulation
What are the phases of the menstrual cycle?
- Follicular
- Luteal
Outline the endocrine pathway for ovulation:
- Hypothalamus releases GnRH into capillary beds -> travels down to pituitary gland
- FSH and LH stimulate -> travel to gonads
- LH surge prompts follicle rupture and release of oocyte (differing effect on leydig cells in males)
- FSH stimulates follicle development -> should occur one at a time through follicular phase
What process maintains basal oestrogen levels in menstruating women?
- Release of oestrogen by the dominant follicle
- An egg will be stimulated to develop every few days by FSH (fluctuates)
- Here, the granulosa cells will start to increase in number, forming primary follicles
Follicle development:
- Primary follicles: Growing number of GCs
- Antral follicles: FSH responsive (threshold must be reached for ovulation to proceed -> progress to graafian stage (oestrogen dependent)
Describe the feedback loops regulating oestrogen throughout the follicular phase:
- Negative feedback occurs during follicular phase under low oestrogen
- Positive feedback occurs at higher concentrations near the end of this phase (positively induces anterior pituitary)
- This triggers the release of more FSH and LH -> stimulates further oestrogen production and thus ovulation threshold of FSH is eventually reached
Describe the meiotic changes triggered by ovulation:
- First meiotic division completes
- Cell arrests at metaphase in meiosis 2
- Meiosis will only be completed upon fertilisation
How are FSH and LH regulated after ovulation?
- Suppressed
- Stops any ongoing follicular development
- Avoids twins developing asynchronously
What happens to the follicle after it has ruptured and released the oocyte?
- It will fold down into the corpus luteum
- This will produce progesterone to sustain the developing embryo for the first 14 days of development
- Production peaks at day 7
- The corpus luteum contains lots of lipid-rich lutein cells
- Progesterone prevents uterine lining from being cycled out
- The corpus luteum itself is maintained by hCG secreted by the blastocyst
How does AMH affect IVF cycles?
- Produced by GCs of follicle
- Higher AMH increases chance of success in IVF cycles
How does the combined pill affect the menstrual cycle?
- Enacts a constant level of oestrogen and progesterone
- This triggers negative feedback on levels of FSH and LH
- Prevents development of follicles and LH surge -> anovulatory phenotype
What hormonal test may inform perimenopause in patients?
- Basal FSH and LH day 2-4
- If elevate, may be perimenopausal
What is the hormonal trigger for menstruation? (Day 1-5)
- Fall in progesterone
- Stops maintaining uterine lining
- Leads to spasm of spiral arterioles, ischaemic necrosis of endometrium and thus uterine contraction occurs from fundus to cervix -> period released
Describe the events of the proliferative phase (Day 5 - 14):
- Oestrogen levels begin to rise, causing proliferation of the endometrium and stroma
- This thickens, increasing metabolic activity and upregulating PRs
- During this phase, contraction occurs from cervix to fundus (facilitating sperm transport)
