Repro 2.2 The Menstrual Cycle Flashcards Preview

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Flashcards in Repro 2.2 The Menstrual Cycle Deck (45):

What is the reproductive cycle?

A series fo physiological changes surrounding ovulation


What purpose of the first phase of the reproductive cycle?

The ovaries, reproductive tract and other systems are prepared for ovulation so to maximise the chance of fertilisation


What is the purpose of the waiting phase?

If fertilisation occurs, the conceptus is initially too small to signal its presence so the waiting phase allows time for an appropriate chemical signal from the developing placenta during which physiological changes occur in preparation for a potential pregnancy


WHat are the phases of the menstrual cycle?

The initial phase is known as the follicular or proliferative phase
The waiting phase is the luteal or secretory phase


What coordinates the phases of the menstrual cycle?

Gonadotrophins and gonadal steroids


When is the menstrual cycle deemed to begin?

The first day of the menstrual bleed although this is physiologically the end of the previous cycle


How long are the phases?

Follicular - usually 12-14 days but variable
Luteal - 14 days exactly


How is the early follicular phase characterised? (relative levels of hormones)

High titres of FSH and LH
Low but rising titres of oestradiol
Very low levels of progesterone


What are the relative levels of hormones in the later follicular phase and what results?

FSH levels fall
LH levels rise
Oestrogen levels rise dramatically - this is followed by the LH surge and ovulation


What are the relative levels of hormones in the early luteal phase?

Low FSH and LH
Rising titres of oestradiol and progesterone


What are the relative levels of hormones in the late luteal phase?

Low FSH and LH
High oestradiol and progesterone (progesterone higher)


What happens to the hormone levels at the end of the luteal phase and what is the result?

Progesterone then oestrogen titres fall and menstruation begins (progesterone lower)


What effects do the rising titres of oestrogen have on the fallopian tubes?

Stimulate secretion and muscular contraction
Growth and motility of fallopian cillia


What effects do the rising titres of oestrogen have on the myometrium?

Stimulate growth and motility


What effects do the rising titres of oestrogen have on the endometrium?

Increase in number and size of glandular invaginations. The cells secrete watery fluid conducive to sperm (supports travel and provides nutrients)


What effects do the rising titres of oestrogen have on secretion of cervical mucus?

Stimulates secretion of thin and alkaline mucus conducive to sperm transport


What effects do the rising titres of oestrogen have on vaginal epithelium?

Increased mitotic activity


What effects do the rising titres of oestrogen have on metabolism?

Mildly anabolic effects, depresses appetite and maintains bone structure


What is the effect of progesterone on oestrogen primed cells of the fallopian tube?

Reduces fallopian tube motility, secretion and cilia activity


What is the effect of progesterone on oestrogen primed cells of the myometrium?

Stimulates further thickening but reduced myometrial motility


What is the effect of progesterone on oestrogen primed cells of the endometrium?

Stimulates further thickening and increased secretion
Development of the spiral arteries


What is the effect of progesterone on oestrogen primed cells of the cervical mucus?

Stimulates thickening and acidification inhibiting sperm transport - blocks off the uterus from the outside world


What is the effect of progesterone on metabolism?

Mildly catabolic metabolic change
Elevates basal body temperature
Promotes changes in salt and water retention which may in combination with oestrogen lead to net sodium and water retention (weight gain and bloating)


What is the result of a sudden fall in progesterone and oestrogen?

Elaborate secretory epithelium of the endometrium collapses - this is apoptotic cell death. This is shed as a menstrual bleed, spiral arteries contract to reduce bleeding


What controls the uterine cycle?



Why does FSH rise more than LH at the beginning of the menstrual cycle?

Low inhibin levels release FSH from selective inhibin at the pituitary


What causes the follicle to grow?

FSH followed by LH


Why is the timing of the LH surge not fixed?

Influenced by environmental factors e.g. stress, light


What happens after ovulation?

Oestrogen levels fall dramatically
Spontaneous formation of the corpus luteum


What hormone promotes oestrogen and progesterone secretion from the corpus luteum?



Why is there no increase in LH despite the increase in oestrogen from the corpus luteum?

Growing corpus luteum also releases more progesterone


How long does the corpus luteum "live"?

14 days unless fertilisation occurs in which case hCG from the placenta maintains it


How does a new cycle begin?

Removal of oestrogen and progesterone by regression of the corpus luteum removes negative feedback so FSH and LH increase


What does maintenance of the corpus luteum do?

Supports early weeks of pregnancy and suppresses ovarian cycle


What does testosterone feedback on in the male?

LH and GnRH


What happens to hormone levels at the beginning of menopause?

Ovary secretes significantly less oestrogen causing a rise in LH and FSH (more because of fall in inhibin)
Return to lower levels several years later


What happens to concentrations of LH and FSH in pregnancy?

Placenta begins to secrete oestrogen and progesterone independently of LH and FSH. Negatively feedsback decreasing LH and FSH.


Name an anti-oestrogen drug



What does clomiphene do?

Exerts a weak oestrogen effect, sufficient to achieve uptake and binding to oestrogen receptors. It also inhibits the process of receptor replenishment, reducing their number. Thus the hypothalamic pituitary axis is blinded to endogenous oestrogen level in circulation. This results in and increase in GnRH and FSH and LH


What would be the effects on gonadotrophin secretion of a constant moderate dose of a progesterone like drug?

Enhance positive feedback of oestrogen -> decrease FSH and LH
Inhibit positive feedback and therefore LH surge -> no ovulation (dose must be high enough)

(Also affects cervical mucus inhibiting sperm transport)


What would happen to the concentration of LH, FSH, TSH, GH and ACTH? What happens to prolactin?

Decrease - concentration of releasing hormones decreases due to dilution by general circulation (loss of short portal system)
Prolactin concentrations increase - loss of inhibitory effects of dopamine - released from hypothalamus


What drug acts like dopamine?

Bromocriptine - inhibits prolactin


What drugs antagonise dopamine?

haloperidol, metoclopramide and domperidone


What effect does prolactin have on fertility?

Suppresses fertility - increasing prolactin levels will produce a spectrum ranging from inadequate luteal phase function to an ovulation and amenorrhoea with complete GnRH suppression (fertility always affected)


What drug can be given to improve fertility?