2.2 The Menstrual Cycle Flashcards
What are the levels of FSH and LH like at the start of the menstrual cycle?
Low as there is no ovarian hormone production as the follicle is developing
Why do FSH levels rise early in the menstrual cycle?
Little inhibition at the anterior pituitary or hypothalamus. Little inhibin production
Where does the FSH bind to in the early menstrual cycle and what does this result in?
Binds to the granulosa cells
Aids follicular development so follicle can now produce oestrogen and inhibin
In the mid-follicular phase of development what affect does low oestrogen have on the anterior pituitary and hypothalamus?
Increases secretion of LH and FSH by negative feedback
Why in the mid-follicular phase of the menstrual cycle do LH levels rise but not FSH levels?
Inhibin release from the ovary is inhibiting FSH production
How does the body prepare for ovulation?
Oestradiol and inhibin rise rapidly
Progesterone production begins
Follicle cells respond to LH
What causes the surge in LH before ovulation?
Oestradiol is not dependent on FSH levels so LH levels surge
What happens in ovulation?
Meiosis I completes and meiosis II starts. Mature oocyte extruded through the capsule of the ovary
After ovulation how are LH levels reduced?
Large progesterone release from the corpus luteum decrease the oestrogen to progesterone ratio.
LH is suppressed by negative feebdack to the anterior pituitary and hypothalamus
What happens in the luteal phase of menstruation?
Corpus luteum produces progesterone, oestrogen and inhibin and waiting phase is started
What happens to the menstrual cycle if no fertilisation occurs?
Cycle starts again
Corpus luteum degenerates and hormone levels are decreased.
How long is a normal menstrual cycle?
21-35 days
Luteal phase is always 14 +/- 2 days
