Independent: Ovary Flashcards
(41 cards)
FSH targets what cells?
LH targets what cells?
FSH - granulosa cells
LH - theca & granulosa
Effects of FSH during the early follicular phase?
Acts on the primary follicle (NOT the primordial) to induce..
- Mitosis & cell proliferation
- FSH receptors
- Gap junction formation
- Aromatase to produce estradiol
-
Inhibin B synthesis in granulosa cells
- -> Stimulates androgen production by theca interna
- -> Decrease FSH secretion
Inhibin B is synthesized by ___ to do what?
Synthesized by granulosa cells to
Stimulates androgen production by theca interna
Decrease FSH secretion
FSH in the late follicular phase (high estrogen)
Induces LH receptors on granulosa cells –> low progesterone production
LH in the early vs late follicular phase
Note: the steps are cholesterol > progestins > androgen > estrogen
so in the late follicular phase, they just stop at progesterone
Why does the peak of LH coincide with the drop in estrogen?
LH surge: High occupancy of LH receptor on theca cells blocks androgen precursors needed for estradiol synthesis
When estradiol is high but not at its peak anymore, what does it do to FSH?
When it’s not at its peak anymore, estradiol facilitates the decline of FSH & LH.
So the process is:
- Peak estrogen positive feedbacks FSH & LH
- LH surge turns down estrogen
- Lower lvl estrogen negative feedbacks FSH & LH
Steroidogenesis in the ovary (estradiol)
- Theca interna - LH stimulates androgen synthesis (androstendione & testosterone)
- Granulosa cells - FSH stimulates
- inhibin B to stimulate androgen synthesis
- aromatase expression –> converts androgens to estradiol
Explain estradiol synthesis according to this photo
LH in the theca interna stimulates androgen synthesis
Androgens enter the granulosa cells, where FSH-stimulated aromatase (CYP19) turns it into estradiol
Estradiol can then leave and go out the ovary
How does LH stimulate androgen synthesis?
It stimulates side chain cleavage enzymes:
remember: the steps are cholesterol > progestins > androgen > estrogen
Positive estradiol feedback leads to LH surge through what two ways?
- Increasing the pulse frq of GnRH
- Increases responsiveness of gonadotrophs to GnRH
What does the LH surge do to the follicle?
- Oocyte completes first meiotic division –> secondary oocyte & 1st polar body
- Increase in progesterone production transforms granulosa cells into lutein cells
- Activation of proteolytic enzymes that degrade the follicular wall + formation of stigma (area through which Graafian follicle will burst thru)
- Oocyte with cumulus detaches from the wall of the follicle and floats in the liquor folliculi
- Rapid accumulation of fluid in antrum
What cells make up the corpus luteum?
4 stages of corpus luteum development
Granulosa lutein cells from the granulosa cells
Theca lutein cells from the theca cells
This differentiation was caused by LH
Corpus luteum of cycle; menstruation; albicans; and pregnancy
When does progesterone start rising? What cells are making it? What impact does it have on other hormones?
At the very end of the follicular phase, granulosa cells start producing progesterone
Then, in the luteal phase, they become lutein cells and start producing a ton of progesterone
Progesterone & inhibin A negative feedbacks the other hormones
LH does what to the theca lutein cells and the granulosa lutein cells during the luteal phase?
Stimulates theca lutein cells to produce weak androgens
Stimulates granulosa lutein cells to produce progesterone & estradiol -> prep for fertilization and implantation
NOTE: androgens from theca lutein are still sent to granulosa lutein to become estradiol; but the progesterone is created right in the granulosa lutein cells.
FSH during the luteal phase
Low FSH stimulates granulosa lutein cells to synthesize inhibin A
–> reduce FSH by negative feedback
What is this and what is it producing?
Corpus luteum making lots of steroi dhormones
What kind of cell is the black arrow pointing at in the folds of this corpus luteum?
Theca lutein cells just in the folds; everything else granulosa lutein
Which are larger, theca or granulosa lutein cells?
Granulosa
Why does LH fall in later luteal phase?
What does this do to the corpus luteum?
Negative feedback from progesterone decreasing GnRH pulse frq and downregulating GnRH receptors on gonadotrophs
This kills the corpus luteum –> corpus albicans
What is the key feature to identify corpus albicans histologically?
No nuclei because the cells are dead
Corpus luteum of pregnancy - how does it form and what does it do?
Forms when hCG from the implanting blastocyst rescues the corpus luteum; acts like LH
Continues progesterone & estrogen production to maintain the endometrial lining
Inhibin B vs Inhibin A
Inhibin B: from granulosa cells; suppresses FSH-secreting gonadotrophs; follicular phase
Inhibin A: from granulosa lutein cells; suppresses LH and FSH-secreting gonadotrophs; luteal phase
