2.2 - the menstrual cycle: lecture Flashcards
describe the gamete production in males
continuous
describe the gamete production in females
- tract needs to prepare for implantation
- needs to build in a ‘waiting phase’
therefore, gamete production needs to be periodic
effects of oestrogen on hypothalamus and AP in terms of feedback? (female)
can be positive or negative depending on the concentration
low - inhibit LH/FSH
high - positive feedback (LH surge)
effects of testosterone on hypothalamus and AP in terms of feedback? (males)
negative feedback on hypothalamus and AP
what does menstrual cycle refer to? (umbrella term)
both ovaries and endometrium
what are the stages of menstrual cycle?
preparation
ovulation
waiting
what is the preparation stage of the menstrual cycle?
preparation of gamete = ovarian cycle
preparation of endometrium = uterine cycle
what happens in the ovulation stage of the menstrual cycle?
release of the gamete
what happens in the waiting stage of the menstrual cycle?
pause, maintaining the endometrium until a signal is received to indicate that fertilisation has happened (from conceptus)
what are the control over the menstrual cycle?
- gonadotrophins acting on ovary (produce steroid hormones - LH, FSH)
- ovarian steroids:
acting on tissues of reproductive tract (endometrium)
act to control cycle (follicular + luteal phase)
describe the HPO axis in females
GnRH produced by hypothalamus –> AP –> release gonadotrophins (FSH, LH) –> ovary
what is the effect of gonadotrophins acting on ovaries?
- promoting follicular development
2. production of ovarian hormones: steroid (oestrogen, progesterone), inhibin
what is the HPO axis controlled by?
effects of gonadal hormones
negative AND positive
what are the stages of the endometrial cycle?
menses
proliferative phase
secretory phase
what happens at the start of the menstrual cycle?
no ovarian hormone production
early development of follicles begin
low steroid and inhibin levels - therefore little inhibition at hypothalamus + AP
what happens to FSH levels at the start of the menstrual cycle?
free form inhibition (low steroid and inhibin, as follicle development only just beginning, so little inhibition at hypothalamus + AP)
FSH levels rise
what does FSH bind to in females?
granulosa cells
what are the effects of FSH?
follicular development continues
theca interna appears (outer layer)
what happens as follicle continues to develop?
capable of oestrogen secretion
inhibin secretion begins (inhibits FSH - for 1 dominant follicle, as female are born with all follicles)
what are the stages of development of an oocyte into an ovum?
primary oocyte (4n DNA) –> primordial follicle –> primary follicle –> secondary follicle –> early tertiary follicle –> graafian follicle –> ovulated ovum
difference between primordial follicle and primary follicle?
primary follicle has zona pellucida (protein outer)
cells change from pregranulosa –> granulosa
difference between primary follicle and secondary follicle?
theca cells appear in secondary follicle
difference between secondary follicle and early tertiary follicle?
theca cells differentiate to theca interna and externa antrum appears (space between theca and granulosa cells) BM under theca cells
when is first meiotic division completed?
between early tertiary follicle and graafian follicle
difference bewteen early tertiary follicle and Graafian follicle?
secondary oocyte (2n DNA) and first polar body (2n DNA) present in Graafian follicle
what are the stages undergone by Graafian follicle to turn into ovulated ovum?
beginning of second meiotic division
FERTILISATION
completion of second meiotic division (POST fertilisation)
what are the structures present in an ovulated ovum?
corona radiata
second polar body
what is the purpose of the mid-follicular phase?
need 1 dominant follicle
need to prevent recruitment of any further follicles
what are the hormonal changes that happen in mid-follicular phase?
- gonadotrophin levels can rise further (LH)
- follicular inhibin rising - selective inhibition on FSH by AP
(dissociate FSH + LH, cause LH surge)
what are the hormonal changes that occur in preparation for ovulation? (think oestradiol)
circulating oestradiol + inhibin rise rapidly (from follicle, positive feedback)
oestradiol production no longer dependent on FSH (inhibin)
surge in LH
what are the changes to progesterone in prepartion for ovulation?
progesterone production begins: granulosa cells become responsive to LH
(LH receptors develop on the outside of granulosa cells)
what happens to GnRH in preparation for ovulation?
modulation of GnRH pulse generator
pulse gets more rapid
how does high oestradiol affect GnRH?
high oestradiol enhances sensitivity of AP gonadotrophs to GnRH
(in late follicular phase - just before ovulation)
what happens to meiosis in ovulation?
meiosis I completes
meiosis II begins (but pause until fertilisation then complete)
when does ovulation occur?
about 3 hours post LH surge
what happens in ovulation?
mature oocyte extruded through the capsule of the ovary
release oocyte into fallopian tube
what are the oestrogen changes of mid-follicular phase?
follicular oestrogen now at concentration where it exerts POSITIVE feedback at hypothalamus AND AP
what happens to the follicle after ovulation?
the follicle is luteinised
what does a luteinised follicle post ovulation secrete? what does this result in?
oestrogen and progesterone in large quantities
(inhibin continues to be produced - suppresses FSH, prevent another follicle from developing before the corpus luteum is broken down - further gamete development suspended: waiting phase established)
what happens to LH post ovulation? why?
LH is suppressed - further gamete development suspended (prevent LH surge): waiting phase established
negative feedback due to presence of progesterone (on hypothalamus and AP)
what happens in the waiting phase?
endometrium build lining and wait for signal from oocyte (fertilised = conceptus)
LH suppressed by progesterone from luteinised follicle
inhibin suppresses FSH
what are the hormones produced in luteal phase?
corpus luteum produces progesterone and oestrogens from androgens
CL produces inhibin (no FSH): promotes production of progesterone (why?)
what happens as a result of the hormones produced by CL in luteal phase? why?
CL regresses spontaneously in the absence of a further rise in LH (progesterone suppresses)
what happens at the end of the menstrual cycle? leading to?
absence of further rise in LH, corpus luteum regresses
dramatic fall in gonadal hormones (FSH + LH)
relieving negative feedback (on AP + hypothalamus)
cycle starts again
(IF fertilisation has NOT occurred)
