Repro 2.2 The Menstrual Cycle Flashcards
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?
Steroids
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?
LH
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
clomiphene
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?
bromocriptone
