hormonal control of the menstrual cycle Flashcards
describe the pattern of FSH
Increases in early part of follicular phase, then steadily decreases throughout
remainder of cycle EXCEPT small midcycle peak
describe the pattern of LH
Constant during most of follicular phase, then large midcycle increase (LH surge)
peaking ~18h before ovula?on. Then rapid decrease with further slow decline
during the luteal phase.
describe the pattern of oestrogen
Low and stable for 1st week, increases rapidly in 2nd weeks, starts to decline before
LH peak. Then second increase due to corpus luteum in last few days of cycle.
describe the pattern of progesterone
Low level due to ovary release during follicular phase with small increase just
before ovula?on. Soon a[er ovula?on, large increase due to CL release, then
similar paPern to oestrogen.
describe the pattern of inhibin
similar to oestrogen
what does low concentration oestrogen inhibit
FSH and LH
what does inhibin do
inhibits secretion of FSH
what does a dramatic increase in oestrogen do
increases LH and FSH causing positive feedback of the LH surge which triggers ovulation
what does high progesterone in the presence of oestrogen do
inhibits FSH and LH during the luteal phase and pregnancy
what cells express receptors for FSH during the follicular phase of the menstrual cycle
granulosa cells
homologous to sertoli cells
what is the function of FSH
max conc during follicular phase
stimulates growth of medium sized follicles
what is the function of LH
stimulates steroid hormone synthesis by the corpus luteum
stimulates ovulation
what stimulates an increase in LH
increase in oestrodiol 17b (oestrogen) which is secreted by the dominant follicle
what cells are homologous to theca cells
Leydig
because they both synthesise androgens
what do theca cells do
synthesise androgens which are then converted to estrogens by granulosa cells in the follicle by diffusing across the basement membrane
what hormone stimulates granulosa cells to convert androstenedione to oestrodiol 17b
FSH
What causes the LH surge
dominant follicle secretes large amount of oestrogen which stimulates LH surge
this triggers ovulation of corpus luteum
mediated by granulosa cells
what are the effects of LH on the ovary
primary oocyte completes first meiotic division and undergoes cytoplasmic changes
antrum size and blood flow increased
granulosa cells release progesterone and decrease oestrogen
enzymes and prostaglandins break down the follicular membrane which rupture
corpus luteum forms
what are the functions of granulosa cells
nourish the oocyte
secrete chemical messengers
secrete antral fluid
site of action for oestrogen and FSH in the control of follicular development
expresses aromatase
secretes inhibin
site of action for LH during formation of the corpus luteum
what happens if there is no zygote implantation
no hCG
CL dies
progesterone and oestrogen decrease
what is the function of hCG
maintains CL which continues to secrete progesterone
what are the other effects of oestrogen
increases the motility of the fallopian tubes
causes proliferation of the endometrium
secondary sexual characteristics
what are the effects of progesterone
causes secretory activity in the endometrium
catabolic
cervical mucous increase
how does the combined pill work
inhibits FSH secretion by mimicking luteal phase no follicular growth no ovulation and no corpus luteum low oestrogen synthesis no build up of endometrium
what hormones causes the granulosa cells to proliferate and secrete oestrogen
FSH
what is the function of the theca externa
During ovulation, the surge in LH increases cAMP which increases progesterone and PGF2α production. The PGF2α induces the contraction of the smooth muscle cells of the theca externa, increasing intrafollicular pressure. This aids in rupture of the mature oocyte
what is the function of the theca interna
contains LH receptors
produces androgens which are then converted to oestrogens by the granulosa cells
what are granulosa cells homologous to
sertoli
they both convert androgens to oestrogens
