Question about a concept in TBR Bio section in Reproduction and Development, specifically the diagram on how the hormones are regulated on p. 216 (2010 edition). Why does a low concentration of estrogen yield a negative feedback on FSH production. Doesn't make intuitive sense; I would think that low levels of estrogen would cause there to be increased FSH production, since we would need more estrogen for the development of the follicle.
Bio Question
- Thread starter ajumobim
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Like much of endocrinology, this is actually a really complex question! First of all, one note - most MCAT materials simplify this process into something very close to what you're thinking. Basically, they say that the presence of estrogen *usually* has a negative feedback effect on FSH and LH. During the follicular phase, estrogen levels are low, allowing for increased FSH and LH production, which gradually increases estrogen as well. Once estrogen levels reach a certain threshold, we see the classic switch to positive feedback and the LH surge, which promotes ovulation. The idea that high estrogen generally results in negative feedback ties in to the rest of the cycle, such as during pregnancy (when a combination of high estrogen and high progesterone keep LH and FSH levels low). I'd be curious to hear what others think, but I've never seen an MCAT question where this general idea - imprecise though it may be - would cause you to get a question wrong.
Back to your question, though - I found an interesting explanation here https://www.physicsforums.com/threads/oestrogen-and-fsh.575176/. In short, this guy says that low estrogen does "negatively feed back on" FSH, but not in the simple way that we tend to imagine it. Have you read that FSH is generally released in pulses, not continuously? According to the source above, low estrogen levels don't decrease the NUMBER of pulses of FSH release, just the AMOUNT released per pulse. The follicles actually respond to these small, frequent pulses by growing more than they otherwise would have. But again, this explanation goes far beyond anything the MCAT would ever test.
Thanks for the great question and good luck!
Back to your question, though - I found an interesting explanation here https://www.physicsforums.com/threads/oestrogen-and-fsh.575176/. In short, this guy says that low estrogen does "negatively feed back on" FSH, but not in the simple way that we tend to imagine it. Have you read that FSH is generally released in pulses, not continuously? According to the source above, low estrogen levels don't decrease the NUMBER of pulses of FSH release, just the AMOUNT released per pulse. The follicles actually respond to these small, frequent pulses by growing more than they otherwise would have. But again, this explanation goes far beyond anything the MCAT would ever test.
Thanks for the great question and good luck!
