The Menstrual Cycle Flashcards
What is the consequence of disruption of the hypothalamic-pituitary portal system?
high circulating prolactin
low FSH/LH
To what stage in meiosis does the oocyte progress following release from the ovary?
from prophase II to arrest at metaphase II
What is the normal duration of the menstrual cycle?
21-35 days
What is GnRH?
Secreted by hypothalamus
Cause cells in AP to prod FSH and LH
What is the role of FSH?
Bind granulosa cells = follicle maturation of primary follicles = secondary follicle
Theca interna appears = secondary follicles then prod low levels of oestrogen = inhib LH
Inhibin secretion begins = inhibits FSH = stops more follicles devel
In the follicular phase what keeps LH levels low?
Due to rising levels of GnRH LH should be rising
However FSH causes the devel of the follicle which prod low levels of oestrogen = which inhib LH secretion
After the first 10 days (mid-follicular phase) what affect does oestrogen have?
High levels now able to cause a +ve feedback = stim release of LH
FSH not released due to inhibin prod by the follicle
What causes the LH surge?
+ve feedback from oestrogen levels that are now high
Continued release of GnRH
What is the result of the LH surge?
Ovulation of the most mature follicle releasing the oocyte
After the follicle ovulates what does it turn into?
Corpus luteum
Now luteinised = of yellow colour
Outline the purpose of the corpus luteum
Secretes = oestrogen, inhibin, progesterone
What is the role of inhibin?
-ve feedback = stops the secretion of FSH = as we don’t need anymore follicle maturing just yet
Describe the function of progesterone
-ve feedback on GnRH = stop release of FHS/LH
Stimulate endometrial growth = for egg to implant if fertilised
What causes the corpus luteum to degenerate?
Progesterone inhibiting a further rise in LH
As the corpus luteum degenerates what does that cause?
Progesterone levels fall = GnRH not inhibited = new cycle
Endometrial lining sheds as not maintained by progesterone
What are the 2 phases of the ovarian cycle?
Follicular = 0-14 days
Luteal = 14-28 days
How does gamete prod vary males to females?
M = continuous
F = periodic, need to prepare for implantation, requires a waiting phase
Explain the feedback mechanism in the female HPG axis
Oestrogen/progesterone allow switching from +/- feedback to allow for periodic ovulation
Explain the feedback mechanism in the male HPG axis
-ve feedback by testosterone to control its levels
What 2 cycles occur during menstruation?
Ovarian cycle
Uterine cycle
What is the role of the endometrium?
Implantation site for fertilised egg
Define ovulation
Release of gamete after LH surge
What occurs during the ‘waiting stage’?
Pause, maintaining the endometrium until a signal is received to indicate that fertilsation has happened
further gamete devel suspended by LH suppression due to presence of progesterone
What controls menstruation?
Gonadotrophins = act on ovary
Ovarian steroids = act on uterus, acting to control the cycle
Explain the importance of the pulsatile release of GnRH
Absolute requirement for fertility
If agonist constantly present = receptors become desensitised = FSH/LH prod stops = gonadal steroid prod stops
What is endometriosis?
Plaques of endometrium growing outside of the uterus
= express receptors for oestrogen/testosterone
= grow when hormones present = irritate peritoneum
Treat = continuous exposure to GnRH agonist = desensitisation = switches axis off
What defines the start of the cycle?
First day of menstruation
What is menstruation?
No ovarian hormonal support = endometrium is lost
What is the myometrium?
Thick muscular wall of the uterus
Thickens/grows, but does not shed
What is the endometrium?
Epithelial lining of the uterine cavity
Functional layer = hormone responsive
Basal layer = stem cell layer for functional layer to devel from
What are the peripheral effects of oestrogen?
Stim bone/muscle growth
Stim endometrial growth
Maintains female secondary characteristics
Maintains glands – breasts
How does the uterus change over the menstrual cycle?
Early proliferation = glands sparse
Late proliferation = functional layer doubled
Early secretory = endometrium at max thickness
Late secretory = gland adopt saw-tooth appearance
If fertilisation does occur what are the next steps?
Human chorionic gonadotrophin is produced (equivalent to LH) by the syncytiotrophoblast = corpus luteum does not degenerate + HPG axis is not switched back on
How can cycle length vary between diff individuals?
Due to variation in follicular phase length
Luteal phase strictly controlled 14 +/- 2 days
