Repro: The menstrual cycle Flashcards
Why is the waiting phase after ovulation important?
Gives the conceptus time to travel down the fallopian tube
Takes 14 days to produce a measurable signal to indicate that fertilisation has happened and pregnancy should continue
What are the stages of the ovarian cycle?
The follicular phase: the recruitment and growth of the follicles, then one dominant follicle is chosen to produce the gamete
The luteal phase: the dominant follicle is leuteinized to form a corpus luteum
What are the stages of the uterine cycle?
Menses: shedding of the endometrium
Proliferative phase: the endometrium becomes thicker
Secretory phase: the endometrium is made glandular to secrete substances needed if implantation occurs
When are meiosis 1 and 2 complete?
Meiosis 1 completes at ovulation and meiosis 2 completes if the oocyte is fertilised
What embryonic structure produces human chorionic gonadotrophin?
The synctiotrophoblast - appears in the 2nd week
What is the function of human chorionic gonadotrophin?
Analogous to LH so maintains the corpus luteum and signals for it to keep producing progesterone
When does the corpus luteum regress if fertilisation occurs?
Maintained by HCG (now called the corpus luteum graviditatis)
The placenta eventually is able to take over secreting progesterone and the corpus albicans is formed
What phase is responsible for variations in the length of the menstrual cycle?
The follicular phase
The luteal phase is strictly controlled to 14 days +/- 2 days
Why is exclusively breastfeeding a form of birth control?
High levels of prolactin inhibit FSH
What levels of oestrogen are needed for positive feedback and therefore the LH surge?
200pg/mL for approx 50 hours
Therefore not enough oestrogen, or oestrogen not high for long enough can be a cause of infertility
What is the blood supply to the uterine wall?
A pair of uterine arteries form radial artery branches which supply the myometrium
There then branch straight and spiral arteries which supply the endometrium.
At the menses the blood supply is lost so the endometrium becomes ischaemic and sloughs off
How much blood loss during the menses is associated with anaemia?
60-70% of women losing >80ml per cycle are anaemic
This is about of the female menstruating population
What are some causes of menorrhagia? (Heavy periods)
- abnormal clotting
- fibroids
- cancer
- progesterone contraception
- 60% of cases are dysfunctional uterine bleeding - which is unknown cause
What is endometrial ablation?
Burning the endometrium to make it thinner
Has a good success rate in reducing heavy periods
Is the entire endometrium shed during menstruation?
No - the functional layer is shed however the basal layer remains and provides stem cells so the functional layer can regrow
