Independent: Ovary Flashcards
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
In the follicular phase, LH causes cholesterol > progesterone>androgens in the theca cell, then the androgens go to the granulosa cell where FSH activates aromatase to turn it into estradiol (pictured).
What happens in the luteal phase?
Same thing happens in the theca lutein cell (LH turns cholesterol>androstenedione), and the granulosa lutein cells still turn that androstenedione into estradiol to release, but now the granulosa lutein cells can also respond to LH:
Take up LDL > cholesterol > progesterone, but dont have the enzymes to turn that progesterone into androgens, so they send progesterone directly into the blood.
Ovarian cyst
Non-neoplastic fluid-filled cavities that originate from unruptured Graafian follicles
Polycystic ovary syndrome
High androgens & LH but low FSH
–> bilateral ovarian enlargement with multiple follicular cysts
Ovarian tumors can originate from
surface epithelium, oocytes, follicular cells, or stromal cells
Menopause (~50yo)
Cessation of menses; follicles dont develop in response to FSH/LH
- > reduced estradiol, progesterone, and inhibin B –> loss of negative feedback on hypothalamus/pituitary
- > high FSH & LH
Most menopausal symptoms (bone loss, hot flashes, increased coronary artery disease) are the result of what?
Estrogen deficiency.
Only low estrogen levels are produced in adipose tissues from androgen precursors
Function of the oviduct
What are its regions?
- It’s where the ovum discharges into
- Provides proper environment for fertilization and development of preimplantation embryo
- Conducts preimplantation emrbyo to the uterus
intramural part, isthmus, ampulla, infundibulum, fimbria
Components of the oviduct wall
Mucosa
- Simple columnar epithelium - cilitated cells & secretory cells
- Lamina propria - highly cellular & vascular
Muscularis - Inner circular, outer longitudinal smooth muscle
Serosa/adventitia - blood vessels & loose ct
Estrogen has what impact on the serosa and muscularis of the ampulla?
What do the ciliated simple columnar cell do?
What do the secretory / peg cells do?
Name these cells in the blue vs the black brackets
Black= ciliated
Blue = peg
As you go from infundibulum to isthmus, what histological changes do u see?
Smaller lumen
Less folds in the mucosa
Thicker muscularis
Estradiol on the epithelium, lamina propria, and muscularis of the oviduct
Progesterone on the oviduct
Fertilization occurs in what region of the oviduct?
Ampulla
What happens during fertilization of the secondary oocyte?
- Zona pellucida has sperm receptors and will initiate the acrosome reaction: acrosomal enzymes digest a path thru the zona pellucida
- Cortical reaction: egg releases granules to ZP inpenetrable to sperm (prevents polyspermia)
- Entry of sperm nucleus triggers completion of second meiotic division –> mature ovum & second polar body
- Nuclei of ovum and sperm fuse to form a zygote
