Understanding the Role of Oestrogen in FSH and LH Regulation

  • Thread starter jsmith613
  • Start date
In summary, Estrogens inhibit FSH and LH in the majority of the estrous cycle, but at ovulation a switch occurs to a positive feedback mechanism. This switch happens as the dominant follicle secretes a lot of estrogens, increasing rather than decreasing GnRH, LH, and FSH secretion. This then triggers ovulation.
  • #1
jsmith613
614
0
It seems (from the book and several websites) that initially, at low conc. oestrogen inhibits FSH and LH. As the follicle matures and oestrogen levels rise FSH and LH are stimulated.

My questions are
1) If low levels of oestrogen inhibit FSH (and LH) how can the follicles mature (they are matured by FSH)

2) Why do we say oestrogen inhibits FSH and stimulates LH if it inhibits and stimulates BOTH pituitary hormones?

Thanks
 
Last edited:
Biology news on Phys.org
  • #2
*I have edited the question so they are more precise
 
  • #3
The problem is that most textbooks oversimplify this topic to the point of being flat out wrong or very confusing.

Estrogens (that's a plural word) normally have negative feedback effects on LH and FSH during most of the estrous cycle (most non-human mammals) and the menstrual cycle (humans and a few non-human primates). So do progestins. However, LH and FSH (along with GnRH that is the hypothalamic neurohormone that regulates LH and FSH) are not just continually secreted. They are secreted in pulses (think "bursts" of secretory activity). And, inhibition by the sex steroids doesn't just suppress overall secretion, but actually alters the pulse pattern. Estrogens suppress LH pulse amplitude, but don't alter frequency (we won't discuss seasonally breeding animals here, because then even this statement needs qualifiers).. Progestins suppress pulse frequency. FSH pulses are a little messier to deal with.

The pattern is what determines how the ovary responds. In the predominantly estrogenic environment of the follicular phase, fast, low amplitude FSH and LH pulses tell the follicles to keep growing. When they get closer to ovulation, there is a short term switch to a positive feedback mechanism. I can't answer why...that's the million dollar question in research in reproductive endocrinology. We know a lot about ways to make it happen, but not fundamentally why. Anyway, that switch happens as the one dominant follicle gets very large and secretes heaploads of estrogens, and that in turn increases instead of decreases GnRH, LH and FSH secretion to the point where we can no longer detect individual pulses, but one big, massive, sustained secretory event that we call a surge. This triggers ovulation. Ovulation is the limiting step that keeps this positive feedback loop from getting out of control...ruptured follicle and no more follicular fluid producing estrogen. The remaining follicle cells undergo a conversion process and become the corpus luteum, which produces progesterone and some estrogens. Now LH and FSH are secreted in very slow pulses during the luteal phase, which doesn't stimulate any more follicle growth and instead allows the corpus luteum to function and produce more progesterone, which helps prep the uterus for implantation if pregnancy occurs. Not all species have luteal phases. Many rodents, for example, only form a functioning corpus luteum if pregnancy occurs and quickly prepare to ovulate again if they don't get pregnant (they have only 4-5 day estrous cycles).
 
  • #4
Moonbear said:
Estrogens (that's a plural word) normally have negative feedback effects on LH and FSH during most of the estrous cycle (most non-human mammals) and the menstrual cycle (humans and a few non-human primates).

So how can the follicle mature if FSH is being inhibited?
 
  • #5
jsmith613 said:
So how can the follicle mature if FSH is being inhibited?

That was the entire context of my post! It's under negative feedback control, that doesn't mean it's totally shut down, just a different PATTERN of secretion. The pattern is what matters, not the absolute amount. Negative feedback, as a general term, is about maintaining a set point, not about shutting down completely.
 
  • #6
Moonbear said:
That was the entire context of my post! It's under negative feedback control, that doesn't mean it's totally shut down, just a different PATTERN of secretion. The pattern is what matters, not the absolute amount. Negative feedback, as a general term, is about maintaining a set point, not about shutting down completely.

oh of course
but another question:
why do we say oestrogen inhibits FSH and stimulates LH if it does both to both hormones?
 

What is oestrogen and FSH?

Oestrogen and FSH (follicle-stimulating hormone) are two hormones that play important roles in the female reproductive system.

What is the function of oestrogen?

Oestrogen is responsible for the development and maintenance of female reproductive organs, such as the uterus, ovaries, and breasts. It also plays a role in regulating the menstrual cycle.

What is the function of FSH?

FSH is responsible for stimulating the growth and development of ovarian follicles, which contain the eggs. It also plays a role in triggering the release of an egg during ovulation.

What happens when oestrogen and FSH levels are imbalanced?

Imbalanced levels of oestrogen and FSH can lead to various reproductive issues, such as irregular menstrual cycles, difficulty conceiving, and menopausal symptoms. It is important to maintain a healthy balance of these hormones for optimal reproductive health.

How can oestrogen and FSH levels be tested?

Oestrogen and FSH levels can be tested through a blood test. This can help diagnose any hormonal imbalances and guide treatment options for reproductive issues.

Similar threads

  • Biology and Medical
Replies
1
Views
2K
  • Biology and Medical
Replies
8
Views
5K
  • Biology and Medical
Replies
4
Views
6K
  • Biology and Chemistry Homework Help
Replies
2
Views
3K
Replies
20
Views
3K
  • Biology and Medical
Replies
29
Views
5K
  • Biology and Medical
Replies
16
Views
48K
Replies
10
Views
651
Replies
4
Views
991
  • Quantum Physics
Replies
15
Views
2K
Back
Top