Reproductive bio q's

[chiddler]

Artificially high levels of estrogen in a woman would stop ovulation. How does it do that?

A second question: Are fallopian tubes part of the uterus? Book implies answer is yes, but not very explicit.

Thanks!

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[MedPR]

Artificially high levels of estrogen in a woman would stop ovulation. How does it do that?

A second question: Are fallopian tubes part of the uterus? Book implies answer is yes, but not very explicit.

Thanks!

There's typically negative feedback from estrogen on the anterior pituitary (LH) and the hypothalamus (GnRH). If there's no luteal surge, there's no ovulation and I think there needs to be a certain level of estrogen (not too high or too low) for the luteal surge to occur.

The uterus is connected to the fallopian tubes, but I don't think the tubes are considered part of the uterus. Your pancreas is connected to your duodenum, but it isn't considered part of your small intestine.

 

[chiddler]

There's typically negative feedback from estrogen on the anterior pituitary (LH) and the hypothalamus (GnRH). If there's no luteal surge, there's no ovulation and I think there needs to be a certain level of estrogen (not too high or too low) for the luteal surge to occur.

The uterus is connected to the fallopian tubes, but I don't think the tubes are considered part of the uterus. Your pancreas is connected to your duodenum, but it isn't considered part of your small intestine.

That's particularly what I don't understand. Artificially high levels of estrogen suggests that this is above the LH surge threshold, no? Because the LH surge occurs towards the highest peaks of estrogen levels.

FSH levels will remain low so no new follicles are maturing. But what about the already matured oocyte? LH surge itself causes ovulation.

 

[MedPR]

That's particularly what I don't understand. Artificially high levels of estrogen suggests that this is above the LH surge threshold, no? Because the LH surge occurs towards the highest peaks of estrogen levels.

FSH levels will remain low so no new follicles are maturing. But what about the already matured oocyte? LH surge itself causes ovulation.

I don't really know when estrogen inhibits LH vs when you get the positive feedback that leads to the LH surge. I just know there is negative feedback unless levels of estrogen rise rapidly, which is when you get positive feedback and LH surge.

I'm guessing the sudden increase in estrogen is the key; the fact that for those few days before ovulation estrogen isn't being maintained steadily. So, estrogen levels could be artificially high; so high in fact that the "estrogen surge" that normally causes the LH surge cannot occur because estrogen levels are already much higher than the level that estrogen "surges" to pre-ovulation. Does that make sense?

So once there is an implanted zygote, estrogen levels are higher than normal because of the corpus luteum (I think..? I don't remember what maintains estrogen before the placenta comes around). So if the normal estrogen level is 5, and a sudden increase to 10 causes the LH surge, then artificially (or naturally) maintaining estrogen at 12 means it won't be able to jump up from 5 to 10 and cause another luteal surge.

 

[chiddler]

yup that makes much sense. thanks.

 

[typicalindian]

Artificially high levels of estrogen in a woman would stop ovulation. How does it do that?

A second question: Are fallopian tubes part of the uterus? Book implies answer is yes, but not very explicit.

Thanks!

Let me just see if I understand this correctly without going back to the books...

LH causes the secondary oocyte to get released from the ovary into the fallopian tubes along with the maturation of the remaining follicle into the corpus luteum, right? The purpose of the corpus luteum is to release estrogen and progesterone, which work to nourish the endometrium. Once the levels of estrogen and progesterone build up high enough, the GnRH and LH will be inhibited by negative feedback. Once LH stops being secreted, the corpus luteum decays and this causes the endometrium to "die" (menstruation starts) due to the lack of estrogen and progesterone to support it.

so if estrogen levels are artificially high, and maintained at a high level, then LH will be inhibited from being released which will stop any further release of oocytes into the fallopian tubes (ovulation). Does that sound right?

and for your second question: as far as I know, the fallopian tubes (aka uterine tubes) are connected and continuous with the uterus. Otherwise, how would the oocytes go from ovaries into the uterus?

 

[chiddler]

Let me just see if I understand this correctly without going back to the books...

LH causes the secondary oocyte to get released from the ovary into the fallopian tubes along with the maturation of the remaining follicle into the corpus luteum, right? The purpose of the corpus luteum is to release estrogen and progesterone, which work to nourish the endometrium. Once the levels of estrogen and progesterone build up high enough, the GnRH and LH will be inhibited by negative feedback. Once LH stops being secreted, the corpus luteum decays and this causes the endometrium to "die" (menstruation starts) due to the lack of estrogen and progesterone to support it.

so if estrogen levels are artificially high, and maintained at a high level, then LH will be inhibited from being released which will stop any further release of oocytes into the fallopian tubes (ovulation). Does that sound right?

and for your second question: as far as I know, the fallopian tubes (aka uterine tubes) are connected and continuous with the uterus. Otherwise, how would the oocytes go from ovaries into the uterus?

I think I spot an error: "Once the levels of estrogen and progesterone build up high enough, the GnRH and LH will be inhibited by negative feedback." Is not accurate. Estrogen levels high enough cause positive feedback with LH (i don't know about GnRH; i'd assume so since FSH also increases a bit during this phase) and cause the LH surge. The LH is lulled because estrogen is not increasing anymore (reverts to negative feedback) and progesterone is starting to build up (negative feedback).

"Once LH stops being secreted, the corpus luteum decays and this causes the"
Kinda sorta. Stopping the LH surge gives the corpus luteum a 2 week lifespan.

 

[typicalindian]

I think I spot an error: "Once the levels of estrogen and progesterone build up high enough, the GnRH and LH will be inhibited by negative feedback." Is not accurate. Estrogen levels high enough cause positive feedback with LH (i don't know about GnRH; i'd assume so since FSH also increases a bit during this phase) and cause the LH surge. The LH is lulled because estrogen is not increasing anymore (reverts to negative feedback) and progesterone is starting to build up (negative feedback).

"Once LH stops being secreted, the corpus luteum decays and this causes the"
Kinda sorta. Stopping the LH surge gives the corpus luteum a 2 week lifespan.

OH I see, I can't believe I had it all backwards haha. So FSH causes the primary oocyte to mature into the secondary oocyte, along with causing estrogen levels to increase. Normally estrogen will inhibit LH secretion when it is at a constant level, if it changes to a large extent it will reach a threshold. At the threshold a surge of LH get's released from the anterior pituitary which causes ovulation and development of the corpus luteum. Now that estrogen levels are more or less constant, the inhibitory effects on LH resume and now the corpus luteum sustains estrogen and progesterone levels. Once the lifespan of the corpus luteum is done, a fall in estrogen and progesterone levels occurs and menstruation follows.

Thats why in pregnancy hCG takes the role of LH in that it will keep the corpus luteum around which will keep estrogen and progesterone levels at a relatively constant level thus keeping LH inhibited to prevent further ovulation.

Is that right?

 

[chiddler]

OH I see, I can't believe I had it all backwards haha. So FSH causes the primary oocyte to mature into the secondary oocyte, along with causing estrogen levels to increase. Normally estrogen will inhibit LH secretion when it is at a constant level, if it changes to a large extent it will reach a threshold. At the threshold a surge of LH get's released from the anterior pituitary which causes ovulation and development of the corpus luteum. Now that estrogen levels are more or less constant, the inhibitory effects on LH resume and now the corpus luteum sustains estrogen and progesterone levels. Once the lifespan of the corpus luteum is done, a fall in estrogen and progesterone levels occurs and menstruation follows.

Thats why in pregnancy hCG takes the role of LH in that it will keep the corpus luteum around which will keep estrogen and progesterone levels at a relatively constant level thus keeping LH inhibited to prevent further ovulation.

Is that right?

The reason estrogen increases is because the follicle becomes more mature, not directly because of FSH.

Also, no the estrogen levels continue to vary after corpus luteum formation. They just aren't high enough to cause LH surging.

rest is correct!

 

[typicalindian]

The reason estrogen increases is because the follicle becomes more mature, not directly because of FSH.

Also, no the estrogen levels continue to vary after corpus luteum formation. They just aren't high enough to cause LH surging.

rest is correct!

about FSH: right thats what i meant

and the part about the levels varying: makes sense. thanks

 

[chiddler]

I have a better answer:

Continually high estrogen inhibits FSH and therefore new follicles are never released and ovulation never happens.

yeah. "well duh".

 

[MrNeuro]

im fairly confident you inhibit ovulation with only progesterone or estrogen and progesterone.