Female Reproductive System Flashcards
what are the gonadotropins? what regulates gonadotropin release?
FSH and LH
- released in response to pulsatile secretion of GnRH from preoptic nucleus of hypothalamus
- secretion regulated by neurotransmitters like endorphins, NP-Y, adrenergics
adrenarche
period of time around 7-9yo when adrenal cortex begins to mature into active steroidogenic tissue
- uptick in adrenal androgen secretion
- not a prereq for puberty! more like a supportive priming of gonadal/neuroendo tissues for growth/maturation
theories re: onset of puberty
- hypothalmic maturation: some signal causes GnRH-secreting neurons within preoptic nucleus of hypothal to turn on GnRH pulse generator
- gonadostat: a developmental switch in the gonadal-hypothal-pit axis decreases sensitivity to negative feedback by gonadal steroids, leading to start of pulsatile release
- nutitional influence: greater fat stores = more adipocytes = more leptin, might trigger early onset of menarche
menstrual cycle
- basic definition
- timeline
ovulation of one mature, viable oocyte during each 28-day reproductive/menstrual cycle
- follicular/proliferative phase: day 1-14
- ovulation: day 14
- luteal/secretory phase: day 15-28
regulated by ovarian-hypothalamic-pituitary axis
ovarian follicles
spheroid structures made up of one oocyte, theca cells, and granulosa cells
HORMONE FACTORIES: pump out stuff to foster growth/maturation of oocyte AND maintain feedback loops
- theca cells: outermost layer of follicle cells, 2 layers (theca interna/externa), vascularized
- basement membrane: separates TC and GC
- granulosa cells: surround oocyte
largest and most mature follicles = selected, preovulatory, Graafian follicles have large antrums filled with follicular fluid (rich in hormones/growth factors
GnRH pulse specifics for secretion of gonadotropins
- slow GnRH pulse frequency = FSH secretion
- rapid high amp GnRH = LH secretion
LH function
targets theca cells and GC to…
- induce steroidogenesis
- cause changes in GC function and structure that enable ovulation
- stimulates luteinization - differentiation between GC and theca cells
before ovulation: luteinization of selected follicle begins just prior to ovulation (LH spike)
after ovulation: stimulates luteinized GC and theca cells in corpus lutuem to produce estrogens/progesterone
FSH function
target GC cells to…
- convert aromatizable androgens (testosterone, androstenedione) into ESTROGENS - steroidogenesis
- regulate GC mitosis during follicular growth
- action is mediated by growth factors, cytokines, steroids secreted in response to FSH or LH
- key: cAMP/PKA cascade important for follicular cell responsiveness to FSH and LH
hypogonadotropic hypogonadism
characterized by low gonadotropins and suppressed gonadal fx
- failure to secrete sufficient levels of FSH and/or LH
- potential causes: lesions in neuroendo system, athletic overtraining
- could be attributed to normal LEVEL but abnormal CYCLING (rise/fall) of hormone
women: low serum estradiol, possibly low FSH and/or LH
ovarian follicular growth/devpt
- recruitment happens during follicular phase of each menstrual cycle
- whole process takes 3-4 cycles
- implication: there are groups of follicles at distinct stages of devpt in all women of repro age
- sequence: primordial, primary, secondary, tertiary (ANTRAL), and pre-ovulatory/dominant/Graafian
primordial follicles
follicles in arrested, immature state
- each contain…
- oocyte: arrested in meiotic prophase I (4n) - WILL NOT PROGRESS PAST THIS PHASE UNLESS OVULATED
-
single layer of squamous granulosa cells surrounding oocyte
- aka pre-GC because theyre non-steroidogenic
recruitment
entry of primordial follicles into growth phase - differentiation into primary and secondary follicles
- GC and oocyte are the first cells to grow/differentiate
- initial phase occurs independent of FSH
- dependent on oocyte-produced growth factors
- counter-modulated by AMH (anti Müllerian hormone, product of GC)
- ABSOLUTELY requires FSH later
development of preovulatory follicles
beyond recruitment/devpt to pre-antral phases, FSH and (later) LH required to sustain follicle
- distinct theca cells prob require LH secretion, happens at same time as vascularization
to get to more mature phases of development, need a jolt of FSH/LH, aka preovulatory gonadotropin surge
- causes cohorts of young follicles to grow/develop from preovulatory surge through approx mid luteal phase (AMH desensitizes small follicles’ GC from FSH effects)
- stop-and-go pattern of growth/maturation happens from cycle to cycle within a follicular cohort
- continues until dominant follicle is ovulated and other follicles undergo atresia
control of FSH and LH secretion: negative feedback
negative feedback by estradiol17beta
- low serum E2 levels exert negative feedback effect on hypothal/pituitary - suppress FSH and LH
summary: in early follicular phase, FSH and LH decreasing. pattern is maintained by low levels of E2
follicular selection and following events
around tertiary/antral stage, one follicle within recruited cohort is selected to differentiate further (aka dominant follicle)
- not sure how its selected BUT
- its GC express more FSH receptors
- start to make inhibin B: increase during mid-foll phase, fall at mid-cycle: blocks FSH secretion by pituitary further
theory: the increased # FSH receptors in the selected follicle allow it to get by with the low levels of FSH present, whereas the non-selected follicles cant, and therefore undergo atresia
describe the development of the dominant follicle after selection
selection of dominant follicle indirectly causes atresia of other sister follicles in the cohort (via GC cells’ secretion of inhibin B, drop in FSH…)
- dominant follicle grows, antrum becomes filled with follicular fluid, theca cells and GC proliferate
-
theca cells become androgen-producing cells (de novo steroidogenesis)
- turn cholesterol into androstenedione/testosterone
-
GC begin to express high levels of CYP19 (P450 aromatase) and 17betaHSD
- convert androgens into E2
-
theca cells become androgen-producing cells (de novo steroidogenesis)
processes are mediated by FSH and LH, and feedback from intraovarian growth factors/cytokins modulate gonadotropin action
developmental switch in E2 production
in advanced phase of antral follicle growth, seelcted follicle begins to make more E2
- leads to positive feedback effect on production/release of FSH and LH
- rising FSH induces expression of LH-receptors in GC - enables selected follicle to respond to both hormones
-
joint effect of FSH and LH…
- growth and diff of other younger cohorts
- increase in selected follicle steroidogenesis
- initial luteinization of selected follicle (GC cells start making progesterone in addtn to E2)
preovulatory gonadotropin surge [and role of inhibin B]
inhibin b secretion drops just before midcycle, which cuts out its feedback inhibition on activin
activin stimulates GSH secretion, leading to preovulatory surge
how is GnRH pulsatility interrupted?
combo of preovulatory levels of E2, rise in progesterone, rise in inhibin A by GC leads to disruption in GnRH pulsatility
- negative feedback on secretion of FSH (E2 dependent) and LH (progesterone dependent) via ERalpha and progesterone receptors in hypothalamus
- profound drop in gonadotropin secretion on ovulation
two-cell, two-gonadotropin mechanism
theca cells: produce androgens (androstenedione and testosterone)
GC cells: convert androgens from theca cells into E2, required for neuroendo feedback that leads to ovulation
AMH levels, follicular recruitment, and timeline of follicular reserves/devpt
AMH keeps younger cohorts of developing follicles from jumping into devpt too quick - serves as a marker of healthy growing follicles
serum AMH level parallels “level” of ovarian follicular reserve
follicle story:
- increase in recruitement through childhood, peaking at 14-15
- decline
AMH story:
- rises steadily through childhood, fluctuates around puberty, gets secondary increase through about 25, falls off steady after mid20s to undetectable levels around 40-45
ovulation:
hormone changes that precipitate it and their physical effects
dependent on gonadotropin surge; LH is the main player
- once GC begins to express LH receptors, FSH and LH stimulate GC to switch from near-exclusive E2 to production to joint E2 and progesterone production
- progesterone is thermogenic, accompanied by slight rise in temp
- LH stimulates production of prostaglandins and other cascades in GC to increase lysosomal enzyme levels
- collectively, causes intercellular GC connections and basal lamina integrity to drop
- angiogenesis (mediated by prostaglandins, growth factors, cytokines)
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ovulation:
exit of oocyte
- oocyte is released with surrounding layer of cumulus GC attached
- exits around fimbrae of oviduct and migrates down oviduct towards uterus
- changes in cAMP signaling in GC and oocyte trigger completion of meiosis I (first polar body extruded)
- what’s left (GC + theca cells) is stimulated by LH to become corpus luteum
corpus luteum
- hormones produced & fx
corpus luteum responds to LH to produce progesterone and E2 (both required for implanatation and early stages of preg)
- progesterone
- targets uterus, keeps myometrium from contracting, negative feedback on LH and some on FSH (at chronic elevated levels)
- inhibin A
- negative feedback on gonadotriopin secretion
- E2
- prolif and angiogenic effects in endometrium