Menstrual Cycle Flashcards
What are the aims of the menstrual cycle?
- selection of a single oocyte
- spontaneous ovulation
- correct number of chromosomes in eggs
- preparation of the uterus
- support of the fertilised egg
- cyclical changes in cervix and vagina and fallopian tube
what 2 phases can the menstrual cycle be split into?
follicular and luteal
what are the follicular and luteal phases separated by?
ovulation
when does the menstrual cycle begin?
day 1 - bleeding
next 14 days are follicular phase, then ovulation, then next 14 days are luteal
what does the empty follicle form?
the corpus luteum
what is the follicular phase and what is it dominated by?
- growth of follicles up until ovulation
- dominated by oestrogen production from the dominant follicle
what is the luteal phase and what is it dominated by?
- formation of the corpus luteum form the empty follicle,
- dominated by progesterone production from the corpus luteum
what happens on day 14?
ovulation!
the dominant follicle ovulates the egg, which is picked up by the Fallopian tube. the remainder of the follicle becomes the corpus luteum, and the luteal phase begins.
which phase does oestrogen dominate in?
the follicular phase
which phase does progesterone dominate in?
the luteal phase
menstrual cycle full
luteal phase, corpus luteum is there and is secreting progesterone. progesterone exerts negative feedback on the HPG axis, suppressing gonadotrophin secretions. when the CL dies, exertion is lifted. leads to a selective rise in FSH, which recruits early antral follicles from the cohort, follicles at the right size at that point in the cycle. these follicles grow and secrete oestrogen which then inhibits the HPG axis. negative feedback means FSH drops preventing follicle growth, all the antral follicles die apart from the dominant follicle. dominant follicle grows at an exponential rate, increase in number of granulosa cells, very rich theca, lots of growth factors and starts to produce tons and tons of oestrogen. When you have lots of oestrogen being produced over a sustained amount secretes loads of oestrogen. sustained high levels of oestrogen (48 hrs) means there is a switch from negative to positive feedback, LH surge!
Triggers completion of meiosis 1, start of meiosis 2 and ovulation of dominant follicle and lutinization. formation of CL and progesterone production, negative feedback all over again.
why is the inter cycle rise and fall of FSH important?
allows selection of a single follicle, a dominant follicle which will eventually ovulate
How does the dominant follicle survive the fall in FSH?
As FSH falls, LH increases. Dominant follicle acquires LH receptors - LHR gene is switched on by FSH.
Increases sensitivity to FSH through increased FSH receptors, increased numbers of granulosa cells
wha does the corpus luteum have?
both luteinised granulosa and theca cells
ovulation occurs via cascade of events:
- blood flow to the follicle increases dramatically
- appearance of apex in ovary wall
- release of enzymes and inflammatory mediators
- enzymatic degradation of protein in ovary wall
- sticky cumulus oocyte complex extruded from the ovary
- follicular fluid may go into pouch of Douglas
- egg collected by the fimbrae of the Fallopian tube
- egg travels down the tube via cilia and peristalsis
how many hours after the LH peak does ovulation occur?
12-18 hrs
how does egg progress down the Fallopian tube?
by peristalsis and action of cilia
why is the cumulus oocyte complex sticky?
- to ensure it’s picked up by the fallopian tube
- protect it from any harsh environment
what does the oocyte complete meiosis 1 in response to?
the LH surge
what happens during the oocyte cell divisions after the LH surge
- nucleus of the dominant follicle completed its first meiotic division, forming a secondary oocyte and a polar body, where half the chromosomes are
- oocyte beings 2nd meiotic division but arrests
when is meiosis 2 completed?
sperm touching the oocyte (fertilisation)
as soon as 1 sperm penetrates through the layers what happens?
- zona pellucida changes and doesn’t allow other sperm to enter - prevents polypsermy
- the 1 sperm brings its DNA in, meiosis II can be completed and fusion and fertilisation can occur
corpus luteum
- yellow body, collapsed follicle
- produces progesterone (and oestrogen)
- has large number of LH receptors, where both LH and beta-HCG bind
- needs beta-HCG to keep it alive
if theres no pregnancy what happens to the corpus luteum?
it dies
functions of progesterone secretions from the CL?
- maintains the CL
- prepares oocyte in its journey
- alters cervical secretions
- prepares endometrium
function of oestrogen secretion from the CL?
endometrium
what can be used as fertility treatment?
clomid
-disrupts negative feedback in the HPG axis
what is OCP?
drug
- constant negative feedback of HPG axis
- no FSH or LH release
symptoms of ovulation?
- Tender breasts
- Abdominal bloating
- Light spotting
- Changes in cervical mucus
- Slight pain or ache on one side of the abdomen
