THE MENSTRUAL CYCLE Flashcards
What is the criteria for which women get menstrual cycles?
post pubertal post menopausal without POF healthy weight not pregnant not breast feeding
what is POF?
primary ovarian insufficiency - when ovaries stop working before 40
describe the mechanism of gonadotropin releasing hormone?
released from the hypothalamus and it binds to GnRH 1 receptors which can then elicit downstream signalling in the target cell. acts on the anterior pituitary to cause hourly pulses to make LH and FSH
describe how LH interacts with a cell?
it binds to the LH receptor which is a glycoprotein receptor
describe how FSH interacts with a cell?
it dimerises and binds to the FSH receptor which is a glycoprotein receptor
what are the 4 classes of steroids?
how do they differ?
oestrogen
progestogens
corticosteroids
androgens
by the number of carbons
what are steroid’s biochemical pre-curser?
cholesterol (from acetate)
what are hormone’s activity regulated by?
receptor levels
hormone production rate
binding proteins
clearance rate of hormones
describe the formation of oocytes?
gametes enter the first meiotic stage
eggs reach the stage of diplotene where they form a germinal vesicle
oocytes rest and meiosis stops
meiosis restarts at puberty
what is a primordial follicle
a primary oocyte surrounded by a layer of granulose cells, mesenchymal cells and membrane propia
describe the steps of primary follicle formation?
the primordial follicle grows and matures in around 70 days to form a primary follicle.
what is a primary follicle?
a fully grown oocyte but its still arrested in meiosis
describe the steps of pre-antral follicle formation?
primary follicle develops and granulosa cells proliferate to form layers- the outer layer becomes theca cells and oocyte gains the zone pellucid
describe the follicular trickle?
if the pre-antral follicles are growing at a pace that matches FSH and LH secretion levels then the follicle can be rescued from atresia and undergo significant growth to the pre-ovulatory phase
describe folliculogenesis?
a cavity forms within the granulose cells called the antrum. the antrum expands the oocyte. the oocyte retains a tight linked layer of specialised granulosa cells called cumulus cells
what is the length of the follicular phase of the ovarian cycle?
beginning on the first day of menses and ends on ovulation. 1-14
how is the follicular phase of the ovarian cycle characterised?
by the presence of a follicle
what is the length of the luteal phase of the ovarian cycle?
from ovulation to last day 14-28
how is the luteal phase of the ovarian cycle characterised?
when the corpus luteum is present
what is the corpus luteum?
the remnants of the follicle
what happens when GnRH stimulates the anterior pituitary?
FSH and LH are secreted.
what does LH act on?
LH receptor on the theca cells so they can make androgens
what does FSH act on?
FSH receptors on granulosa cells which causes expression of androgen aromatase (converts androgens to oestrogen). this causes a rise in oestrogen levels
what happens when oestrogen levels rise?
the release of LH and GnRH are slowed. = negative feedback
what do granulosa cells produce when oestrogen levels rise?
inhibin B to regulate FSH production
what stimulates follicular growth?
androgens having an anabolic effect on granulosa cell growth
what happens when follicular growth occurs?
AMH is produced which regulates growth of neighbouring follicles
what happens as plasma oestrogen levels surge past the threshold?
it overcomes the negative feedback effect and stimulates production of LH. now LH levels surge and can act on granulosa and theca cells to trigger ovulation.
what do granulosa cells release when ovulation is triggered?
progesterone
what is nuclear maturation of the oocyte?
reversing meiotic arrest and driving the progression of meiosis to prepare the egg for activation.
outline the basics of egg development?
oogonia undergo mitosis until bout 2-4 million form. oogonia then form a primary oocyte. these then begin meiosis 1 and stop in meiotic arrest from both till puberty.
at puberty, the second half of meiosis occurs and the oocyte splits to form a large secondary oocyte and a polar body (has hardly any cytoplasm)
sperm now fertilises egg and meiosis 2 occurs to form another oocyte and polar body.
what is oogenesis?
creation of eggs whilst in gestation
what is ovulation?
when an oocyte is pushed out of the ovary
describe the luteal phase of the ovarian cycle?
the ruptured follicle closes after releasing the egg and forms the corpus luteum, which produces increasing quantities of progesterone
outline the uterine cycle?
menstrual phase
proliferative phase
secretory phase
what happens in the menstrual phase?
shedding of uterine lining in absence of preganncy
what happens in the proliferative phase?
endometrium and myometrium regrow to prepare for possible pregnancy. cervical mural secretions change viscidity and pH
what happens in the secretory phase?
on day of ovulation, blood supply to endometrial tissue is remodelled, cervical secretions change, progesterone levels rise and prepare the endometrium for implantation
what are the effects of oestrogen?
maintains body temp
helps against memory loss
regulates production of cholesterol
stimulations maturation of ovaries and start of menstrual cycle, stimulates maturation of vagina and maintains a lubricated and thick vaginal lining, stimulates development of breast and prepares glands for future milk production, stimulates uterus maturation and prepares it to nourish a foetus, helps preserve bone density
