Physiology & the Menstrual Cycle Flashcards
What changes can be seen to the myometrium towards the end of pregnancy?
Stretching increases muscle excitability & contractility.
Gap junctions are formed under the influence of oestrogen enabling transmission of electrochemical signals from cell to cell and a synchronized contraction wave
What changes can be seen to the cervix towards the end of pregnancy?
Decrease in collagen and an increase in water content enabling the cervix to soften & shorten- efface (cervix drawn up into the uterus) and dilate (ripen)
What changes can be seen to hormones towards the end of pregnancy?
Increased concentrations of oestrogen stimulate the production and release of prostaglandins.
Promotes the formation of oxytocin receptors so that the myometrium is more sensitive to oxytocin.
Prostaglandins and oxytocin are strong myometrial stimulants and play a major role in cervical ripening
What happens to CO in pregnancy?
Increases= inc HR & inc Stroke Vol
Dec in BP due to dec in vascular resistance
What happens to maternal blood in pregnancy?
More thrombotic
Increase in thrombotic factors in order to dec change of haemorrhage
What hormone is produced by the hypothalamus?
GnRH
What hormones are produced by the anterior pituitary?
Gonadotrophin’s:
FSH
LH
What does GnRH stimulate?
Inc in FSH & LH
What are the functions of oestrogen?
- STIMULATES production of GnRH
- Maintenance of accessory glands & organs
- Bone & muscle regulation
- Secondary sex characteristics
What are the functions of Progesterone?
- INHIBITS production of GnRH
- Growth of endometrium
Is GnRH released continuously?
No
Released in a pulsatile manner every 1-2hours
Continuous= loss of ability to cause LH & FSH release
When in life is GnRH released/ not released?
Released: Puberty
Not released: Pregnancy (suppressed by prolactin)
Disrupted in PCOS
Affected by hypothalamic-pituitary disease
Low in childhood
What is the role of inhibin?
-Inhibitory effect on FSH
What are the names of the 2 phases of the menstrual cycle? How long do they last?
Both 14days
Follicular Phase
Luteal Phase
What are the steps that occur in the follicular phase?
1) Ovary contains many primary follicles with the potential to become ovum. They have a large central oocyte surrounded by several small follicular cells.
2) Ovarian follicles stimulated to grow & one will emerge as dominant, eventually being release by the ovum
3) Due to FSH up to 20 primary follicles are stimulated to grow becoming secondary follicles
4) As they grow the number of follicular cells increases rapidly & the follicular cells differentiate into Granulosa cells
5) One follicle becomes dominant (Graffian/tertiary follicle)
6) Graffian releases oestrogen which positively feeds back by stimulating the production of more GnRH as well as having important effects on muscle & bone metabolism
7) LH rise causes the follicle to suspend meiosis I and in doing so the oocyte splits in 2 releasing one large egg and one small polar body
8) The oocyte is released from the ovum into the fallopian tube
What marks the start of the luteal phase?
When oocyte is released into the fallopian tube
What are the steps in the luteal phase?
1) The empty follicle remains in the ovary as the Corpus Luteum
2) LH stimulation causes it to slowly secrete progesterone in increasing amounts for 7days.
3) Progesterone is responsible for the build up & maintenance of the endometrium.
4) In the absence of fertilisation the corpus luteum will produce progesterone & oestrogen for 14days as it slowly degrades.
If fertilisation occurs, what happens to the corpus luteum?
The implanted embryo will produce hCG which stimulates the corpus luteum to continue producing progesterone to maintain the endometrium (eventually taken over by the placenta). Corpus luteum= Corpus Luteum Graviditatis
What happens from day 1-11 of the menstrual cycle?
FSH & LH production gradually falls
Stimulate follicle to produce oestrogen which in turn inhibits FSH & LH production
What happens from day 12-14 of the menstrual cycle?
High levels of oestrogen stimulate the production of high levels of FSH & LH (negative feedback loop reversed)
When is the corpus luteum created?
Ovulation
What hormone surge causes ovulation to occur?
LH
What happens if the LH surge is not great enough?
Anovulation- no ovum released
What happens from day 15-28 of the menstrual cycle?
Corpus luteum secrets progesterone, oestrogen & inhibin keeping levels of FSH & LH low. As corpus luteum output falls FSH & LH rise reducing inhibition of the anterior pituitary= START OF THE NEXT CYCLE. Activation of several primary follicles to begin development.
