Repro Phys I Flashcards
(28 cards)
Function of ovarian cortex and ovarian medulla
Cortex = where oocytes and corpus luteum develop
Medulla = inner stroma with large vasculature
HPG/HPO axis
Hypthalamus releases GnRH –> ant pituitary releases FSH and LH (similar structure to TSH) –> LH binds theca cells to make androstenedione and FSH binds granulosa cells to make estrogen and ovarian peptides
GnRH pulsatility before and after puberty
Constant/non-pulsatile before puberty
Pulsatile beings in puberty
When is GnRH sensitivity highest in life?
During childhood/before puberty (little amount of sex steroid can act as negative feedback to the hypothalamus and anterior pituitary, pulsatility later in life decreases sensitivity of HPG axis to sex steroids)
End results of FSH and LH release
Follicular development
Steroidogenesis (Estrogen, progesterone)
Luteinization
Ovulation
What secondary sex characteristics does GnRH pulsatile release result in?
Thelarche (breast development)
Menarche
Adrenarche
How does menarche occur?
Increase in GnRH pulsatility until it results in a sufficient LH surge to initiate the first menstrual cycle
T or F: F HPG axis has variability in how it responds to its end products
T – early in the follicular phase estrogen is (-) feedback, but in the late follicular phase it acts as (+) feedback to initiate LH surge
What time of day is pulsatility most prevalent in puberty?
Night/early hours of REM sleep (constant pulsatility during reproductive years)
What are the levels of FSH and LH in early menopause?
High because the ovaries are not responding with more estrogen production, so the pituitary releases more FSH and LH in an attempt to increase estrogen levels
What decreases the HPG’s sensitivity to sex steroids?
GnRH pulsatility
What are the ovarian peptides?
Inhibins and activins
Which cells produce ovarian peptides?
Granulosa cells
What determines whether granulosa cells make inhibins or activins?
Stage of menstrual cycle
Early follicular phase = negative feedback state –> make activins to promote FSH release and prevent LH surge
Late follicular phase = positive feedback state –> make inhibins to prevent FSH release and activate the LH surge
What do inhibins do?
Act on the anterior pituitary to decrease FSH release (therefore increasing LH release
What do activins do?
Promote FSH release from anterior pituitary and stimulate FSH receptors on granulosa cells
What inhibits inhibin release?
Estradiol/estrogens
What promotes the LH surge?
High estrogen and inhibins
Is the majority of the menstrual cycle under positive or negative feedback
Negative – leads to a decline in both LH AND FSH
Estrogen levels rise in late follicular phase, leading to…
switch of HPG axis to positive feedback, estrogen and high inhibins work together to create LH surge and ovulation (day 14)
Theca cell qualities
Superficial
No aromatase – can’t make estrogen
Only have LH receptors
Able to uptake LDL from blood and make pregnenolone
Granulosa cell qualities
Deeper
Aromatase activity – CAN make estrogens
No 17alpha-hydroxylase acitvity – CANT make androgens
Able to uptake LDL from blood or use de novo synthesis
and make pregnenolone
Both LH and FSH receptors
How do increasing androgen levels affect aromatase activity?
Inhibits aromatase activity bc the androgens promote DHT production
How does decreased aromatase activity affect LH receptor expression?
Decreased LH receptor expression, which decreases estrogen production
