6. Menstrual Cycle Flashcards
What are the aims of the menstrual cycle?
selects single oocyte regular spontaneous ovulation support (potential) fertilized embryo prepare the uterus endometrium lining growth
What is GnRH and LH/FSH release co-ordinated with?
Follicle growth
Hoq long is the menstrual cycle?
28 days
How long does the follicular phase last?
14 days (but can vary)
What happens in the follicular phase?
- Select dominant follicle
2. Follicle growth
What is the follicular phase dominated by?
Oestradiol (produced from dominant follicle)
How long is the luteal phase?
14 days (fixed) happens after ovulation
What is the luteal phase dominated by?
Progesterone (released by corpus luteum)
What is day 1 of the menstrual cycle?
bleed (first day of period)
What is the midpoint of the menstrual cyycle?
Ovulation of the selected dominant follicle= day 14
What is the corpus luteum
After egg has been released, whatever is left is the corpus luteum
releases progesterone
Whathappens to the corpus luteum if there is no fertilization or pregnancy?
corpus luteum dies
instigates new cycle to start
when corpus luteum dies,endometirum (lining of the womb) sheds and then get menstrual bleed
Other than androgens, oestrogens and progestogens, what are the other 2 proteins that act on the HPG acis?
activin and inhibin
What do activin and inhibin act on in the HPG axis?
pituitary
What kind of feedback is it in the luteal phase?
negative feedback (through progesterone)
What kind of feedback is it in the follicular phase?
Variable feedback
- negative feedback from luteal is released (so no negative feedback)
- negative feedback back to normal
- negative feedback to positive feedback switch
What happens in late luteal/early follicular phase?
- corpus luteum dies
- so less progesterone
- progesterone always makes negative feedback- so now no more negative feedback
- so FSH rises=INTERCYCLE RISE OF FSH
What is FSH needed for?
for antral follicle growth
What happens in the midfollicular phase?
- high FSH
- antral follicles can grow bc granulosa cells release oestrogen
- oestrogen act on pituitary and hypothalamus= negative feedback
- FSH drops
- lots of follicles die except dominant
What switches the feedback from negative to positive?
dominant follicle releases oestrogen (above 300pmol) for 48 hours
What happens in the midcycle stage?
oestrogen levels high
so LH surge
LH causes ovulation
What happens in the midluteal stae?
1, corpus luteum secrete progesterone
2. negative feedback again
What other sources of feedback affects the hypothalamic-ovarian axis?
- FAT SIGNALS (lepting, oestrol)
- INSULIN
- CORTISOL
In what condition, do women have high insulin levels (hyperinsulinaemia)?
polycystic ovary syndrome- the women can get insulin resistance- this affects follicle growth
How do fat signals feedback into the HPO axis?
They influence GnRH and gonadootrophins
What does the fall in FSH allow?
dominant follicle to be chosen
What is the window of opportunity?
when the FSH rises, the antral follicles can grow. when they reach right stage they are recturited into menstrual cycle and continue to grow
Where does follicle selection occur?
in either ovary
How does the dominant follicle survive?
has FSH receptors
gets LH receptors on granulosa cells
What receptors do theca cells have?
ONLY LH RECEPTORS= androgen and progesterone production
What receptors do granulosa cells have?
FSH
dominant follicle granulosa cells acquire LH receptors (mid follicular phase onwards)
Which cells take up cholestrol?
theca and granulosa
How many primordial follicles exist when a baby is born and how many get recruited to menstrual cycle?
4000 (in baby) to 400 (in cycle)
How long does the dominant follicle take to grow?
in 7 days from 7mm to 14mm diameter
Where does a follicle grow?
In the medulla of the ovary
When a dominant follicle is selected, where does it go?
to the cortex (of ovary)
What are the cascade of events during ovulation?
increase blood supply to follicle stigma on ovarian wall protease release (digest the wall)
What is extruded from the ovary wall?
oocyte with cumulus cells under high pressure= so fluid can pour into pouch of douglas (rectouterine)
How does the egg move down the tube?
peristalsis and cilia
How long does an oocyte stay a primary oocyte?
from foetal ovary to ovulation- arrested in first meiotic division
When does the nucleus of the oocyte complete first meiotic division?
after the LH Surge
What is the first polar body?
half of the chromosomes of the egg are put in this first polar body
What receptors does the corpus luteum have?
LH
What is the corpus luteum supported by?
LH and hCG (until placenta is established)
What does the corpus luteum secrete and what do they do?
PROGESTERONE: prepare endometrium controls fallopian tube cells OESTROGEN: endometrium health
How are periods written in clinical notes?
7/28 (7days menses/ 28 day cycle)
Why does the luteal phase only last 14 days?
because it depends on the demise of the corpus luteum
When is it best to have intercourse?
If cycle is regular, then bang in the middle
Where are androgens made?
only in theca cells
can be aromatised in granulosa cells to oestrogens
What things feed into the HPG axis?
- Nutritional systems
- Adipocytes via leptin
- Pancreas feeds into the cycle via insulin
- Liver feeds in via IGF-1
- Adrenals feed in e.g. corisol
- VEGF, TGF-beta also feed in
When is the dominant follicle selected?
midfollicular phase
How does a patient know when they are going to ovulate?
ultrasound monitoring- can see dominant follicle
ovulation sticks-detect LH (18 hours after LH surge there is ovulation) =EXPENSIVE
Why is oocyte stuck at first meiotic division at anaphase?
retain all its DNA and remain as large as possible.
What is the FSH threshold hypothesis?
One follicle from the group of antral follicles in ovary is just at the right stage at the right time….
This becomes the dominant follicle which goes onto ovulate
Known as “selection”
Can be in either ovary
What are the clinical applications of negative feedback?
Look at analogude- if thinking of treating early puberty or to delay early puberty or want to induce delayed puberty
Pulsatile treatment- gonadotrophin injections- pulsatile
HRT- in menopause
Part of fertility treatment- clomid-occupies oestrogen receptors- stops oestrogen binding to its receptors- stops negative feedback- allows follicles to grow up with endogenous FSH produced by women
