The Menstrual Cycle Flashcards
What is a normal cycle length?
24-32 days
It is not unusual to have fluctuations in cycle length. True or false?
True - some months may be 27 and others 31
Still = regular cycle
What is the mean menstrual blood loss?
37-43ml / cycle
40 ml = average
Occurs mostly in first 48 hours
What percentage of women lose more than 80ml per period?
9-14% = 90th centile
What percentage of those who lose more than 80ml are anaemic?
60-70%
Between what age are periods most regular?
Between 20-40 years
Are periods after menarche typically longer?
Yes
Are pre menopause periods typically shorter or longer?
Shorter
What factors affect menstrual blood loss?
Age - heaviness increases with age, especially fourth decade
Genetics
Parity has positive correlation ie more children likely heavier periods
At which point in the menstrual cycle is the woman most fertile?
Days 9-16
From 5 days before ovulation to 1-2 days after
Does a woman’s basal body temperature increase or decrease when a woman is about to ovulate?
Increase - occurs due to the LH surge
Indicates that ovulation likely to occur in next 24-48 hours
During ovulation what happens to the cervical mucus?
Thins - easier passage for sperm
Where are LH and FSH produced?
Anterior pituitary
What are the functions of progesterone?
Involved in many different processes
Causes endometrium to become more receptive to implantation of fertilised ovum - initiates secretory phase
Inhibits LH and FSH production via negative feedback
When does the menstrual phase occur in the cycle?
The very beginning
Begins with the breakdown of corpus luteum - ceases progesterone production
Loss of progesterone causes vasoconstriction of spiral arteries supplying the functional layer of the endometrium - becomes necrotic and lost through vagina, causing 3-5 days of bleeding
When does the proliferative phase occur?
Immediately after the menstrual phase - days 5-14
Increased levels of oestrogen driving repair and growth of functional endometrial layer
What are the effects of increased oestrogen in the follicular phase?
Thinning of cervical mucus
Thickening of endometrium
Is the entire endometrium shed during menstruation?
No only the functional layer (not the basal)
At what stage in the uterine cycle does the secretory phase occur?
Days 14-28
Begins after ovulation when ruptured Graafian follicle develops into corpus luteum - produced progesterone, causing endometrium to begin secreting substances that make uterus more receptive to implantation
From the eighth week of pregnancy, what is the primary source of progesterone?
The placenta
The corpus luteum is primary source at the start, but then it breaks down.
In a normal 28 day cycle when does the LH surge occur?
Days 11-13
Why does the LH surge occur?
Oestrogen levels reach a peak, causing positive feedback - LH surge
What does the LH surge do to the graafin follicle?
Causes the membrane to become thin and rupture
