Female reproductive cycle hormone regulation as explained by Cliffs Bio

[PocketRocket]

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"1. The hypothalamus and anterior pituitary initiate the reproductive cycle. The hypothalamus monitors the
levels of estrogen and progesterone in the blood. In a negative feedback fashion, low levels of these hormones stimulate the hypothalamus to secrete GnRH, which, in turn, stimulates the anterior pituitary to secrete FSH
and LH."

Wouldn't it be positive feedback because the low levels of estrogen and progesterone stimulate the production of GnRH ?

 

[baronen26]

positive feedback causes more and more of the stimulus and response (they build on each other) - think uterine contractions

negative feedback is caused when the absence of the stimulus causes a response and the response then hinders the stimulus - think most biochemical processes

 

[PocketRocket]

So whats "an increase of stimulus that causes a response that then hinders the stimulus", I thought that was negative feedback

 

[baronen26]

low FSH and LH (response) cause GnRH (stimulus).

GnRH cause release of FSH and LH, which then hinder the release of GnRH. This

 

[FeralisExtremum]

Positive feedback in endocrinology would be, as baronen26 said, when the hormone's effect causes more of it to be produced. Oxytocin during labor is a good example - oxytocin causes the uterus to contract, which makes the cervix stretch, which sends a signal to the brain that causes more oxytocin to be released, and the loop keeps on building up.

What you described is a part of a negative feedback loop. In a negative feedback loop, when the levels of something are high, the sensor basically says "whoa, too much, make less", the sort of corollary to this (but technically not what we think of when we specifically say negative feedback) is that when the levels are low the sensor lifts its inhibition and production resumes.

 

[DAT Destroyer]

"1. The hypothalamus and anterior pituitary initiate the reproductive cycle. The hypothalamus monitors the
levels of estrogen and progesterone in the blood. In a negative feedback fashion, low levels of these hormones stimulate the hypothalamus to secrete GnRH, which, in turn, stimulates the anterior pituitary to secrete FSH
and LH."

Wouldn't it be positive feedback because the low levels of estrogen and progesterone stimulate the production of GnRH ?

It is just a poorly written statement. The negative feedback mechanism controls GnRh activity. Low levels of estrogen and progesterone can stimulate the synthesis of GnRh. However, that does not explain the negative feedback. The negative feedback mechanism occurs when high levels of estrogens suppress the release of GnRH providing a negative-feedback control of hormone levels.

Hope this helps

 

[PocketRocket]

Thank you for the clarification gentlemen. I was thrown off by the wording in Cliffs, but to summarize:

Negative feedback could be both
1) An increase in stimulus that inhibits a response or
2) A decrease in stimulus that promotes a response.
Or is the latter not an example of negative feedback, as stated by orgoman?

Ive always learned negative feedback in the following fashion: A---(enzyme 1)--->B----(enzyme 2)--> C---(high[C] inhibit enzyme 1 or 2)---> decrease in [C]

 

[FeralisExtremum]

The latter (#2) isn't technically negative feedback itself. It's more like the counterbalance for the negative feedback.

 

[enamel88]

this was what I was confused about too. So can you correct me if I'm wrong?

During menstrual cycle:

1. Estrogen causes a positive feedback on the Hypothal so that it Ant Pit can surge LH causing ovulation.
2. Once the corpus luteum forms, the high progesterone and Estrogen levels ALWAYS cause a negative feedback (lets not make any more of GnRh) on the system UNLESS an embryo is implanted producing HCG from the blastocyst (trophoblast) to maintain the corpus luteum so it can maintain the endometrium.

I had to spend some time trying to figure out the neg/pos feedback bc I was confused like Pocketrocket.

 

[PocketRocket]

Now that I think about it, cliffs did say "in a negative feedback fashion"..., meaning that it is not technically neg feedback. But, yes what you have described makes sense to me