The Menstrual Cycle Flashcards
1
Q
What are the 4 stages of the menstrual cycle?
A
- menstrual phase
- follicular phase
- ovulation phase
- luteal phase
2
Q
What are the aims of the menstrual cycle?
A
- selection of a single oocyte
- regular spontaneous ovulation
- correct number of chromosomes in eggs
- cyclical changes in vagina, cervix + fallopian tube
- preparation of the uterus
- support of the fertilised dividing egg
3
Q
How often do humans ovulate each year?
A
12x / year
4
Q
How long is a typical cycle?
A
- typically 28 days (most are 30 days)
- day 1 = menses (bleeding starts)
- day 1-14 follicular phase
- day 14 = ovulation
- day 14-28 = luteal phase
5
Q
What is the follicular phase and when is it?
A
- growth of follicles up to ovulation
- dominated by oestradiol production from dominant follicle
- day 1 - 14
6
Q
What is the luteal phase and when is it?
A
- formation of corpus luteum from empty follicle
- dominated by progesterone production from corpus luteum
- day 14-28
7
Q
How does the luteal phase impact on the HPG axis?
A
- progesterone released
- -> negative feedback
8
Q
How does the follicular phase impact on the HPG axis?
A
- variable + more complex
- release/removal of negative feedback (like foot off the break)
- negative feedback then reinstated (oestrogen builds up, so reinstated)
- then switch from negative to positive feedback
9
Q
Describe the changes in the menstrual cycle
A
10
Q
What is the inter-cycle rise referring to?
A
- the rise in FSH
- occurs in late luteal / early follicular phase
- progresterone declines as the corpus luteum dies out
- therefore less negative feedback
- allowing for an increase in FSH
11
Q
Why is the inter-cycle rise (and fall) important?
A
- allows for selection of a single follicle
- as FSH increased, will recruit + accelerate growth of antral follicles
- as FSH declines, other follicles die
- selected follicle doubles in size every 24hrs + makes lots of E2
- this exerts -ve feedback on H-P to decrease FSH
12
Q
Raised FSH present a “window” of opportunity - what is the FSH threshold hypothesis?
A
- one follicle from the group fo antral follicles in ovary is just at the right stage at the right time…
- this becomes the dominant follicle -> goes onto ovulate
- known as selection
- can be in either ovary
13
Q
After the inter-cycle rise, why does the FSH drop?
A
- the dominant follicle releases oestradiol
- oestradiol levels rise
- reinstate negative feedback at pituitary
- causing FSH levels to fall
- prevents further follicle growth
14
Q
How does the dominant follicle survive the fall in FSH?
A
- as FSH falls
- LH increases
- dominant follicle acquires LH receptors on granulosa cells
- other follicles do not, so they lose their stimulant + die
15
Q
What receptors do Theca cells have?
A
- always have LHr
- never FSHr
- remember LH drives androgen + progesterone production from theca
16
Q
What receptors do granulosa cells have?
A
- have FSHr
- LHr acquired from mid-follicular phase onwards
- FSH + then LH drive oestrogen prod
17
Q
What causes ovulation?
A
- LH
- allows completion of meiosis I
- allows oocyte to enter meiosis II
18
Q
What is the process of steroidogenesis?
A
- all steroids originate from cholesterol
- made by sequential removal of C atoms
- by series of enzymes, which are distributed through cellular components of the follicle
19
Q
What other hormones are released aside from oestrogen + progesterone (and androgens) from the ovary that impact on the HPG axis?
A
- activin
- inhibin
- peptide hormones
20
Q
How long does menstruation (bleeding) last?
A
- starts day 1
- last 3-8 days
- written in notes as 7/28 or 5-6/27-32
- regular cycle should have no more than 4 days variation from month to month
21
Q
What is the lifespan of the corpus luteum?
A
- 14 days
- after 14 days CL will degenerate
- if a long cycle - then it’s to do with change in follicular phase
22
Q
What changes occur following dominant follicle selection?
A
- grows rapidly, doubling in diameter in 7 days from 7mm -> 14mm
- needs masses of growth factors, nutrients + steroids
- rapid neoangiogenesis
- oestrogen released from follicle into circulation
23
Q
What causes the massive release of LH from the pituitary?
A
- throughout follicular phase, E2 feedback was negative
- at end of follicular phase E2 levels raised for long enough -> feedback switches from negative to POSITIVE
- causes mass release of LH from pituitary
- exponential rise in LH in serum
24
Q
What does this mass release of LH trigger?
A
- triggers ovulation cascade
- egg is released
- results in changes in follicle cells -> luteinisation (formation of corpus luteum)
- E2 production falls + progesterone is stimulated
25
What are the cascade of events that result in ovulation?
* blood flow to follicle increases dramatically (inc in vasc perm increases intra-follicular pressure)
* appearance of apex or stigma or ovary wall
* local release of proteases
* enzymatic breakdown of protein of the ovary wall
26
How long after the peak in LH does ovulation occur?
12-18 hrs after peak of LH, hole appears in follicle wall + ovulation occurs
27
What happens next when the oocyte is released from the follicle during ovulation?
* oocyte w/ cumulus cells is extruded from ovary under pressure
* **follicular fluid** may pour into Pouch of Douglas
* egg collected by **fimbria** of fallopian tube (due to signal from fluid)
* egg progresses down tube by **peristalsis** + **action of cilia**
28
How does a patient work out when they are going to ovulate?
* if cycles are regular then it's easy
* but if cycles are irregular it's harder
* intercourse 2-3x/week is enough
* scanning by ultrasound best to detect ovulation
29
What hormone is primarily being detected by ovulation sticks?
* LH
* LH surge detected in urine
* that LH surge preceeds ovulation BUT need to have a lot of sticks
30
From its formation as a primary oocyte in the fetal ovary up until ovulation, the oocyte has been arrested in the first meiotic divison (meiosis I). What is beneficial about this?
This permitss the oocyte to retain all of the DNA + remain as large as possible during its long wait
31
What happens in terms of divison following the LH surge?
* LH surge
* -\> nucleus of oocyte in dominant follicle **completes meiosis I** but it _does not divide!_
32
Describe meiosis and extrusion of the polar body
* half of the chromosomes are put into a small package in the egg called the 1st polar body
* the egg is now called a secondary oocyte
* the 1st polar body plays no further part in the process + does not divide again
* oocyte begins the 2nd meiotic divison, but arrests again
33
Describe the life of a secondary oocyte
* unlike sperm, we only want a single oocyte
* the oocyte is the largest cell in the body (sperm are smallest, but fastest)
* oocyte has to support all of the early cell divisons of dividing embryo until it establishes attachment to placenta
* spends 2-3 days in uterine tube
34
How is the corpus luteum formed and maintained?
* after ovulation the follicle collapses
* corpus luteum is formed, 'yellow body'
* progesterone production increases greatly, also E2
* CL contains large # of LH receptors
* CL supported by LH and hCG ... if a pregnancy occurs
35
What are the secretions of the corpus luteum?
* progesterone
* oestradiol
36
What is the progesterone from the CL for?
* supports oocyte in its journey
* prepares endometrium
* controls cells in fallopian tubes
* alters secretions of cervix
(oestradiol also for endometrium)
37
What happens to the corpus luteum if fertilisation does not occur?
* if fertilisation does not occur, CL has finite lifespan of **14 days**
* removal of CL essential to initiate **new cycle**
* cell death occurs, vasculature breakdown, CL shrinks
* process not well understood
38
What info do you need to enter into a period tracker app?
* typical period + cycle length
* enter in symptoms of premenstrual syndrome
* app uses this info to predict future periods + ovulations days
* need to enter in a few months of data, to get accurate personalised data
39
Summary graph of hormone level changes throughout menstrual cycle
