The menstrual cycle Flashcards
When is the first day of menstruation?
on the 1st day of the menstrual cycle
What are the different Menstrual cycle phases?
Follicular Phase- first 14 days (variable)
Ovulation-mid cycle
Luteal Phase-last 14 days (constant)
Menstruation
What is the follicular phase?
First 14 days of menstrual cycle
-growth of follicles and selection of dominant follicle
Which hormone dominates the follicular phase?
Oestrogen
-feedback is variable on HPO axis
What is the Luteal phase?
Last 14 days of menstrual cycle
-remainder of empty follicle after ovulation is lutenised and becomes corpus luteum
Which hormone dominates the luteal phase?
Progesterone (from corpus luteum)
-exerts negative feedback on HPO axis
Describe the Steps of Menstrual cycle.
Late Luteal/Early Follicular
- no fertilisation, corpus luteum dies, no more progesterone production, no more -ve feedback on HPO axis, causing inter-cycle rise in FSH
- increase in FSH stimulates recruitment of antral follicles into menstrual cycle and further growth, producing oestrogen from granulosa cells
Mid-Follicular
- oestrogen exerts negative feedback on HPO axis
- drop in FSH causes antral follicle to die except dominant follicle
- dominant follicle grows in size and contains many granulosa cells which produce tons of oestrogen
Late Follicular
-when oestrogen levels sustained for 2 days (>300pmol), feedback switches to positive
Mid-cycle
- massive LH surge due to positive feedback from oestrogen
- LH surge induces completion of meiosis I and ovulation of cumulus-oocyte complex (day 14)
Mid-luteal
- remainder of follicle is luteinised by LH to become corpus luteum for progesterone production
- progesterone exerts negative feedback, reducing FSH+LH
How does the dominant follicle survive drop in FSH?
Increases FSH receptors
-to pick up declining levels of FSH
Increases number of granulosa cells
-more aromatase for oestrogen production
Acquiring LH receptors on granulosa cells
-LH receptor gene switched on by FSH and causes LH surge
What does the LH surge trigger?
completion of meiosis I & ovulation
What are the Steps of ovulation?
> blood flow to follicle increases
apex or stigma appearance on ovary wall
local release of proteases and inflammatory mediators
cause enzymatic breakdown of proteins in ovary wall
12-18 hours after LH surge, follicle wall digested and ovulation occurs with the release of cumulus-oocyte complex
What collects the egg after ovulation?
fimbrae of the fallopian tube
What happens after egg is collected by fimbrae?
progresses down the tube by peristalsis via action of cilia
What is the result of meiosis I completion in primary oocyte?
Unequal division of cytoplasm:
-small polar body extruded
-secondary oocyte containing majority of cytoplasm because egg needs mitochondria, proteins etc. to support fertilised embryo through early developmental stages until it attaches to placenta
>secondary oocyte enters meiosis II and arrests
Describe Corpus luteum formation.
remainder of the ruptured follicle (theca and granulosa) is luteinised by LH to become corpus luteum
-contains LH receptors, producing lots of progesterone (and oestrogen)
Describe the Effect of pregnancy on corpus luteum.
corpus luteum supported by LH and hCG (from imlpanting embryo) which also binds LH receptors
