Hormones in the menstrual cycle

[garytse86]

A few questions on hormones (again ):

What stimulates oestrogen production?
Is it FSH and LH, or just FSH

Does oestrogen inhibit or stimulate LH production?
The material I got says that ostrogen inhibits both FSH and LH but from the Edexcel board in the mark scheme it states that oestrogen actually stimulates LH production.

Please help I am very confused

Gary

 

[Moonbear]

I don't have much time to give a thorough answer, but can give a quick answer. During most of the cycle, estrogens have negative feedback actions on LH and FSH, which means it inhibits. However, around the time of ovulation (in the hours preceding it), there is a switch from negative feedback to positive feedback, whereby increasing concentrations of estrogens trigger increased release of GnRH and LH/FSH that trigger ovulation. Don't bother asking the obvious question of "HOW" does that switch happen. We don't know. That's actually part of the research I do...if I find an answer to that age-old question, I'll point you to the Science article :-)

 

[garytse86]

valuable information there!

thanks a lot again moonbear


Gary

 

[garytse86]

sorry, but does oestrogen have a positive feedback mechanism activated on FSH prior to ovulation as well, or is it just LH?

 

[Moonbear]

Prior to ovulation, estrogens have positive feedback effects on both LH and FSH. The LH surge is usually mentioned in textbooks, but the FSH surge is often glossed over.

Going back to your original question about what stimulate estrogen production, LH and FSH each have their functions in this. FSH, as the name suggests (follicle stimulating hormone), helps promote follicle maturation. Since the follicle is the primary source of estrogens in females, FSH is contributing to estrogen production.

A few side notes. You'll notice I usually refer to estrogens in the plural. This is because there are several hormones that make up a class of steroids known as estrogens, there isn't actually a single hormone called "estrogen". The most predominant of these is estradiol, but there is some evidence there are biological functions of other estrogens even though they are present in much lower concentrations. Textbooks try to keep things simple and just refer to estrogen in the singular. The other thing worth noting is that despite the way textbooks refer to things as "known facts", there are a lot of things we don't know about reproductive endocrinology. (The same could be said for any field actually.) When you find yourself really puzzled about something in a textbook, and if you're really doing a good job thinking and understanding what you're reading you will find yourself puzzled by more than a few things, there's usually a much more complicated explanation behind it that either is very simplified for the basic text or the text is glossing over the fact that there are aspects of the system that really aren't understood well at all. When I teach introductory courses, I tell my students right up front that I'm going to lie to them a LOT while teaching the course. That's because you can't delve into everything all at once, so you have to simplify things and start out with rules before you can learn to break the rules. Sort of like when your grade school teacher tells you that you can never take the square root of a negative number, then in high school they teach you about imaginary numbers that allow you to take the square root of a negative number. My teaching philosophy is that by the time someone gets to college level, we can tell them we are sometimes oversimplifying things, and that really helps get past the confusing parts and allows the students to think for themselves rather than believing they are being told facts they should memorize and not question.

Anyway, given all that, do you mind if I ask why you are asking so many questions about reproductive endocrinology? It will help me know how much detail to go into with my explanations. If you're learning this for a class and are just trying to clarify some points in your textbook, I will try to stick to simple answers so you don't lose points for knowing too much (yes, it happens, if you know more than some people teach, you wind up losing points because you over think the questions on your exam and get confused when none of them is quite right). If you are just curious and want to learn more about the topic, I can get into more detailed answers. Or, if it's a combination of both (you're learning this for a class and have really gotten interested in the topic to learn more), then I can go into more detail but point out the simpler view that will be enough to get by on for an exam. See, it's just very easy for me to give general answers to topics I know only in general myself, but this is an area I know in great detail, so can easily overwhelm someone with too much information. On the other hand, I might make the error of being overly simple in my answers in attempting to not overwhelm you with too much detail. Just let me know if I err in either direction ;-)

 

[garytse86]

hi moonbear again I really appreciate your help! :)

I am learning this for a class (I am doing AS Biology actually) and I am very interested in how the whole cycle works. Is there any reason that FSH level is high around the time of ovulation?

Gary

 

[Moonbear]

Both FSH and LH are required for maturation of the follicle leading up to ovulation, so that's why there's a surge of both just before ovulation. Something interesting about FSH that won't be covered in your text is that there is usually a secondary surge of FSH after ovulation. We don't know why that occurs. Since GnRH is still secreted in very high concentrations at that time, it could be a recovery of FSH production in the cells that secrete FSH to trigger a second surge. We're not sure what the secondary surge does, but may be a signal to tell the GnRH surge to shut off and resume the rest of the cycle. Don't even try confusing your biology teacher by mentioning this ;-)

I'm glad you find the subject very interesting. Obviously, I'm biased and think that it's a fascinating subject as well :-)

 

[garytse86]

thanks again you have helped me a lot (too much)

can I just ask, do you work exactly on the menstrual cycle for your research? This cycle is so interesting (cos it's dynamic)... but wouldn't you get so confused as there are so many hormones involved in the system? So there is no answer to "why" negative and positive feedback mechanisms occur for the same hormones acting on the same target homrones?

 

[Moonbear]

My research is technically on the neuroendocrine regulation of the menstrual/estrous cycle. Basically, I study the circuits in the brain that are responsible for relaying the steroid feedback signals to the GnRH neurons (those are the neurons that release GnRH, or gonadotropin releasing hormone, that tells the pituitary to secrete LH and FSH). There are a lot of hormones and neurotransmitters to keep track of, but when it's what you focus on all day long, every day, it gets easier. Every field has its own complexities, just those who specialize in those systems get more and more familiar with them over time. I remember taking my first endocrinology course in college and thinking how complicated everything was and being so impressed the professor could remember it all and know so much to even answer our sometimes off-the-wall questions, and now I look back and realize how little we actually learned about endocrinology in that class! The complexity and dynamics are what I find so exciting about the field. I like that I can measure hormones in the blood, look at the ovaries and pituitary and then relate that to the changes I see in the brain...I've never been one who is satisfied with studying cells in a dish, I like to see it in the whole animal (nothing wrong with in vitro studies, just not what excites me personally, and sometimes they are necessary for what I do too). But I'm also a very visual person, so I love studying the brain and getting to SEE neurons (using a microscope of course)...it's so much more satisfying than relying on an instrument to give me numbers that represent something I can't see for myself. But that's the cool thing about science and research...there's something out there for everyone!

If your interest in endocrinology/reproductive biology persists, there's an excellent group of researchers at the Babraham Institute in the UK who study these systems (I point that out because I see you are from England from the info that shows up under your name on your posts). I've met several of them at conferences and have worked with some of the folks who have gotten their PhD's there, so I know they do very solid science and train their students well, so keep it in mind for a little ways down the road if you find this something you'd like to keep studying in depth.