Menstrual Cycle Flashcards
What is the first phase of the cycle and what happens?
Follicular/proliferative
- GnRh -> FSH, LH
- Matures several primary follicles into secondary follicles
What cell types are present in secondary follicles?
- Theca Cells- produce testosterone, aromatised to oestrogen in the..
- Granulosa cells
What action does this oestrogen have?
=thickens the endometrium (by proliferation of basal cells) and thins the cervical mucus
-Oestrogen then supresses FSH by negative feedback (as oestrogen levels are below threshold)
(reduction in FSH ensures selection of the dominant follicle)
-Granulosa in the dominant follicle produce increasing levels of oestrogen, crossing a threshold to cause an LH surge
When does ovulation occur?
36 hours after the LH surger
always 14 days before the end
What happens in ovulation?
Meiosis 1 is resumed + completed
Secondary oocyte enters meiosis II and arrests at metaphase (would be completed at fertilisation)
-Tertiary follicle forms, follicle wall weakens -> ovulation
What is the final stage of menstruation and what happens
Luteal/secretory phase (prog dominant)
Follicle that has just released an oocyte undergoes lutenisation to form corpus luteum
- CL secrets oest+prog, prog causes change to endometrium
- negative feedback occurs to lower LH and FSH levels
If fertilisation occurs, what happens next?
release of hcg maintains the corpus luteum which will secrete prog until the placenta takes over. Then it becomes corpus albicans
If fertilistation does NOT occur, what happens next?
-luteolysis
Prog and Oest fall, removing negative feedback and restarting the cycle
What happens in the menstrual phase?
Extravastion and endometrial shedding due to falling prog levels
- occurs due to ischaemia, spasm of the spiral arterioles supplying it (PGE vasoconstriction, PGF Vasodilation)
- Fibrinolysis degrades fibrinogen to prevent clotting and ensures loss of endometrium
Average cycle length/bleed?
7 days of 21-35 days
