Lecture 1 - Menstrual cycle Flashcards
What is the purpose of the menstrual cycle
generate oocyte
facilitate fertilisation
optimise endometrium for implantation
protect developing embryo
What are the divisions of the menstrual cycle
Follicular - 1-14 (menstrual pahse and proliferative phase)
Luteal phase - 14-28 (secretory phase)
Effects of the menstrual cycle
ovarian
endometrial
fallopian
cervical
Describe the endocrine control of the menstrual cycle
Hypothalamus releases GnRh which stimulates AP to release FSH and LH which acts on ovary to produce oestrogen.
Oestrogen release is a negative feedback mechanism on Hypothalamus and pituitary
What is GnRH and its structure
decapeptide
secreted by mid basal hypothalamic neurons
transported to pituitary hypophyseal portal blood system
What affects secretion of GnRh
time zone exercise weight/loss/gain anxiety time zone
What are fsh and lh
glycoproteins
Actions of FSH
Stimulates follicular activity
promotes estradiol production from granulosa cells
LH actions
stimulates follice to release egg
promotes development of corpus luteum and production of progesterone
When is negative feedback not applicable
near mid-cycle when high levels of E2 triggers release of LH (+VE feedback) - ovulation
primordial follicles
degenerate as you grow older
450 follicles develop and produce an egg
no new produced
Stages of follices
primordial - primary/preantral- secondary - preovulatory - ovulation
at what day is the egg released
day 14
What occurs during follicular development
proliferation of granulosa cells - antrum (fluid)
gap junctions and cytoplasmic processes allows communication and passage of nutrients
proliferation of thecal cells
theca interna - secrete circulating oestrogen - highly glandular and vascularised
theca externa - fibrous capsule
What do the theca interna secrete
androgens and oestrogen
what to androgens convert to
estradiol 17- beta in granulosa
what happens in the luteal phase?
granulosa cells undergo luteinisation. forms the corpus luteum which releases progesterone and oestradiol 17 Beta
What happens when there is no fertilisation
corpus luteum degnenrates and fibroses to become corpus albicans
What happens in the proliferative phase?
secretion of estradiol (E2)
Endometrium thickens
increase in stroma and gland cells, blood vessels
endometrium 2-3 mm thick
What happens during the secretory phase
progesterone dominant hormone
increased secretion of lipids and glycogen
increase in blood supply
optimal conditions for implantation
What occurs during menstruation
vasodilation - vasospasms of BV
increase PGF2 alpha - blood supply cuts off
necrotic outer layers of endometrium separate from uterus
separate tissue and blood initiate uterine contractions
What does the cervix produce
mucous from columnar glands
midcycle
inelastic during luteal phase - protect embryo, prevents microbial ingress
critical to pregnancy
How does oral contraception work?
combined oral contraceptive - contains estradiol and progestagen steady levels of oestrogen and progesterone inhibit GnRh/FSH and LH Thin endometrium tenacious mucus
