Session 4- Menstrual cycle Flashcards
Average length of cycle
21-35 days
What determines the length of cycle
Length of follicular phase
The menstrual cycle actually consists of two cycles in which organs…
Ovary and endometrium
Name the phases in each of the two cycles
Follicular and luteal, proliferative and secretory
Theca cells produce
Androgens and progestins
Granulosa cells produce
Inhibins and oestrogens
FSH stimulates
Granulosa cells
LH stimulates
Theca cells
Why does the menstrual cycle need a waiting phase?
See if fertilisation has occurred before deciding to start again
Main role of FSH
Grows follicles
What happens to LH and FSH after a dominant follicle is nominated?
FSH decreases due to inhibin negative feedback, LH doesn’t have this inhibition yet so get LH surge due to high oestrogen
What happens if there is continuous GnRH
GnRH receptors become desensitised (why GnRH agonist is useful for treating endometriosis)
What is main role of LH
Drives ovulation
What needs to happen before a follicle is capable of oestrogen secretion
FSH must develop follicle, then the theca interna forms, then oestrogen can be released (as well as inhibin)
After ovulation what happens to granulosa cells
They produce progesterone
After ovulation we want low FSH and low LH- so why not switch back to low oestrogen rather than having high oestrogen high progesterone?
Because we need to keep high oestrogen for maintaining endometrium until we know we aren’t pregnant
What does oestrogen cause in the endometrium
Proliferation
What do oestrogen and progesterone both cause the endometrium to do
Secrete
Describe layers of the uterus
Myometrium, endometrium (with basal layer and functional layer)
Which layer of endometrium is shed
Functional layer of endometrium
Does the myometrium also respond to oestrogen and progesterone?
Yes, but does not shed
Describe how the uterus changes over the cycle
Early proliferative: glands sparse and straight
Late proliferative: functional layer doubles and coiled glands
Early secretory: max endometrial thickness, very pronounced coiled glands
Late secretory: saw-tooth shaped glands
When is the only point that the endometrium has straight glands?
Early proliferative
If LH falls and hCG doesn’t come, what happens?
Corpus luteum regresses, big drop in oestrogen and progesterone
