Menstrual Cycle Flashcards
The menstrual cycle= 2 phases separated by ovulation
Describe the phases of the menstrual cycle.
Day 1= first day of menses
Days 1 to 14 = follicular phase: follicle grows - dominated by oestradiol production from dominant follicle, then ovulation occurs
After ovulation, ‘empty’ follicle (granulosa & theca cells) becomes CL, which produces progesterone = luteal phase
The key controller of the menstrual cycle is feedback along the HPG axis, which varies throughout the cycle. Explain how this occurs during each of the four phases of the cycle.
Late luteal:
Mid-follicular:
Late follicular:
Mid-luteal:
Late luteal: CL dies, so pg production drops. This removes neg feedback, but causes the inter-cycle rise in FSH
Mid-follicular: ↑ FSH stimulates antral follicle growth. E2 produced (theca, aromatase, GCs). E2 negatively feeds back to HPG - this ↓ FSH, which kills other follicles
Late follicular / early luteal: dominant follicle produces mucho E2. When oestradiol >300pmol for 48hrs, neg feedback switches to positive –>LH surge, ovulation
Mid-luteal: theca & granulosa remnants form CL + produces progesterone–> neg feedback by pg reduces GnRH, LH & FSH
What is the importance of the inter cycle rise?
The inter-cycle rise-and-fall in FSH allow selection of the dominant follicle‼️:
Raised FSH recruits a group of antral follicles at the right stage to continue their growth
1 follicle from this group will be j at the right growth stage to survive the subsequent decline in FSH
It has the lowest FSH threshold (highest affinity for FSH), + will become dominant to ovulate. This= selection, and can occur in either ovary
3 reasons why dominant follicle is able to survive?
Dominant survives the drop in FSH bc:
- has more FSHr so it has increased sensitivity to FSH
- has more GCs. This increases E2 production because of increased aromatase levels (200x more E2 in DF than in others)
- It acquires LHr in its granulosa cells, so it can continue to grow due to LH. LHr gene is switched on by FSH
Other follicles do not acquire LHr/have no stimulant when FSH levels fall –therefore they die
A surge in LH triggers ovulation cascade. Describe the process of ovulation
First, hay dramatic BF increase to follicle
Appearance of apex/stigma on ovary wall, where dominant follicle begins to emerge
Proteases + i.mediator release then break down the ovary wall
12-18 hrs after LH peak, the cumulus-oocyte complex (oocyte, ZP & cumulus cells) is released
Follicular fluid may pour into Pouch of Douglas
Egg ‘collected’ by fimbria of uterine (Fallopian) tube, moves down tube by peristalsis + action of cilia.
What happens to the nucleus of the oocyte in response to the LH surge?
Why is the first division unequal?
In response to LH surge, the oocyte nucleus in the DF completes the 1st meiotic division
This division is uneven; ½ chromosomes end up in the oocyte (big cytoplasm), and ½ end up in a small package called the 1st polar body.
Oocyte is now a secondary oocyte
The 1st polar body= now irrelevant + will not divide again, whilst the secondary oocyte starts 2nd meiotic division before arresting (meiosis 2 only occurs in fertilisation)
The 1st division is unequal bc the oocyte needs all the organelles, esp mitochondria for energy!
How long does the oocyte spend in the uterine tube?
Drescribe the formation of the corpus luteum
what happens if a pregnancy occurs? vs no pregnancy?
The oocyte spends 2-3 days in uterine tube, where it may meet a sperm or pass during menses
After ovulation, the follicle collapses & gives rise to the CL (yellow body)
CL–> huge increase in pg production (and a rise in oestradiol)
CL contains many LHr, so it is supported by low levels of LH
If a pregnancy occurs then hCG (from syncytiotrophoblast of embryo), also binds to LHr to maintain it. If no pregnancy, no hCG is produced & LH levels fall, so the CL will die in 14 days.
3 ways we can use the negative feedback system of the HPG axis clinically?
Continuous GnRH analogue dosing reduces gonadotrophins- eg COCP prevents LH & FSH release by providing constant neg feedback (via E2 or progesterone), preventing follicle growth (FSH) + ovulation (LH-mediated).
Pulsatile LH/FSH injections can be used for infertility
Clomid can also be used to treat infertility - It blocks oestrogen receptors, thus disrupting negative feedback along the HPG axis
The HPG axis is acc v complex - 3 things which can affect the menstrual cycle?
- Nutrition affects HPGA. The body needs to be fit to reproduce (ie have certain body fat %) or the cycle is ‘switched off’
- Obesity leads to insulin resistance, which can also switch off the cycle
- Cortisol/stress hormones can cause amenorrhoea
Due to the way follicles grow, we don’t always see the effects of the above issues until a few cycles later
How do we write about menstrual cycle in notes?
how much can a regular cycle vary?
Menstruation lasts 3-8 days, written in notes as 7/28 or 5-6/27-32
The numbers before and after the slash represent the number of days for menstruation and the total length of the menstrual cycle, respectively.
Regular cycle should have no more than 4 days variation from month to month
Signs of ovulation?
0.5-1°C increase in basal body temp - If monitoring body temp to track ovulation, a temp chart must be kept from day 1 of LMP as temp fluctuations are normal
Other signs of ovulation include:
- Tender breasts
- Bloating
- Light spotting
- Changes in cervical mucus (below)
- Slight pain or aching on one side of the abdomen
Ovulation Prediction Tests?
how long does fertile period span & how long can egg survive for? vs how long sperm survives for
- Urine tests which predict ovulation detect the LH surge - 12-18 hours after the surge in LH, ovulation occurs
- Some kits also detect E3G (a urinary metabolite of oestrogen)
The fertile period spans 6 days & egg survives up to 24 hrs after ovulation
The lifespan of sperm is ~1.5 days outside the body, though it can be as much as 5 days
Sperm survival depends on the type and quantity of mucus within cervix, + quality of the sperm
