The Menstrual Cycle Flashcards
T/F Duration of menstrual cycle is variable.
T 24-35 days
Duration of bleeding during menstrual cycle
<8 days
The two halves of the menstrual cycle are separated by what event?
ovulation
Which half of the menstrual cycle is variable in length?
follicular/proliferative stage –> development of follicle in ovary and proliferation of uterine lining
HPG axis
Hypothalamic GnRH –> Pituitary FSH and LH –> Ovarian estradiol and progesterone –> uterus
T/F GnRH has a long half life.
F –> short –> short travel path ensures that hormone is only useful at the nearby pituitary
T/F GnRH is released constitutively.
F –> pulsatile fashion –> frequency affects events (e.g. follicular phase = 60-90 min@low amp, luteal phase = 3-5 hours @high amp)
T/F gonadotropic hormones share the same beta subunit.
F –> same alpha subunit between FSH, LH, hCG, TSH but different beta subunits
T/F early development of follicles till secondary follicle stage is hormone independent
T –> only after puberty FSH can you have follicles growing beyond secondary follicle stage
By what day is a follicle selected to be dominant
8
At the beginning of the menstrual cycle there is a rise in ______ leading to recruitment of follicles.
FSH
3 functions of FSH
stimulates granulosa cell proliferation, stimulation of aromatase activity in granulosa cells (conversion of androgen to estrogen), and up regulation of LH/FSH receptors
Serum estradiol concentrations rise after stimulation by ____ and peak 1 day before ____.
FSH and ovulation
_____ results in negative feedback on pituitary and hypothalamus, reducing FSH levels.
estrogen
Once estradiol reaches a threshold estrogen feedback becomes stimulatory and results in increase in GnRH pulse frequency which increases ____
LH (and reexcites some FSH as well though not to original peak levels)
3 functions of LH
causes release of oocyte from follicle 36 hours after surge, leads to luteinization of granulosa cells and increased progesterone production, resumption of meiosis of oocyte and release of 1st polar body
In the ____ phase, estrogen and progesterone suppress gonadotropin release.
luteal
____ promotes growth and reconstruction of endometrium.
estrogen –> glands lined by low columnar epithelia and mitoses become prominent
effects of progesterone on uterus
limits growth, mitosis, DNA synthesis; increased tortuosity of glands/intensified coiling of spiral vessels, secretion of peptides and glycoproteins
The corpus luteum dgenerates after ___ days
14
Withdrawal of progesterone causes ___ endometrium to slough.
secreory
Why does FSH increase at the end of the cycle?
no more progesterone/estrogen negative feedback
If fertilization occurs, embryo begins making ___
hCG –> maintains corpus luteum
T/F progesterone and estrogen are continued to be secreted if there is fertilization
T
The parallel regulatory system for menstrual cycle involves what proteins?
activin and inhibin (TGF family)
functions of inhibin
reduce FSH synthesis, reduce pituitary gnrh receptors, increase LH receptors on theca cells
____ has one alpha and one beta subunit
inhibin
inhibin is produced by what cells?
granulosa
where is activin produced?
gonads and pituitary
functions of activin
enhance gnrh activity in pituitary and promotes granulosa proliferation/fsh receptors in follicle
