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Biology: Hormone Events: Female Reproductive Cycle


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About this Lesson

  • Type: Video Tutorial
  • Length: 12:31
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 135 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: Animal Systems and Homeostasis (63 lessons, $84.15)
Biology: Male and Female Reproductive Systems (6 lessons, $9.90)

Taught by Professor George Wolfe, this lesson was selected from a broader, comprehensive course, Biology. This course and others are available from Thinkwell, Inc. The full course can be found at The full course covers evolution, ecology, inorganic and organic chemistry, cell biology, respiration, molecular genetics, photosynthesis, biotechnology, cell reproduction, Mendelian genetics and mutation, population genetics and mutation, animal systems and homeostasis, evolution of life on earth, and plant systems and homeostasis.

George Wolfe brings 30+ years of teaching and curriculum writing experience to Thinkwell Biology. His teaching career started in Zaire, Africa where he taught Biology, Chemistry, Political Economics, and Physical Education in the Peace Corps. Since then, he's taught in the Western NY region, spending the last 20 years in the Rochester City School District where he is the Director of the Loudoun Academy of Science. Besides his teaching career, Mr. Wolfe has also been an Emmy-winning television host, fielding live questions for the PBS/WXXI production of Homework Hotline as well as writing and performing in "Football Physics" segments for the Buffalo Bills and the Discover Channel. His contributions to education have been extensive, serving on multiple advisory boards including the Cornell Institute of Physics Teachers, the Cornell Institute of Biology Teachers and the Harvard-Smithsonian Center for Astrophysics SportSmarts curriculum project. He has authored several publications including "The Nasonia Project", a lab series built around the genetics and behaviors of a parasitic wasp. He has received numerous awards throughout his teaching career including the NSTA Presidential Excellence Award, The National Association of Biology Teachers Outstanding Biology Teacher Award for New York State, The Shell Award for Outstanding Science Educator, and was recently inducted in the National Teaching Hall of Fame.

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~ jgarcia

He was going to fast, and the way he kept switching the images back and forth was confusing me. I had to play the video several times to understand it.

~ jgarcia

He was going to fast, and the way he kept switching the images back and forth was confusing me. I had to play the video several times to understand it.

What we want to do right now is we want to try to explain the hormonal events that are causing two things. One, the buildup of the endometrium, and two, the swelling of the follicle to produce an egg, ovulation, and eventually converting into a corpus luteum, what those things do, how they relate to each other and what does the brain have to do with all of this.
Well, let's start out on Day zero, and we will come back and forth, so stick with me on this. It starts out in the brain. That link between the brain and the pituitary called the hypothalamus. And the hypothalamus, you remember, is in intimate contact with the pituitary and it's going to produce gonadotrophin releasing hormones, GN releasing hormones. Gonadotrophic releasing hormones are going to be hormones that are going to go to the gonads. Eventually, what they are going to do is allow hormones to be released that are going to go to the gonads. In other words, the ovaries. So, where are these hormones going to be reduced from. They are going to be released from the pituitary. What are these hormones? There are two hormones called FSH and LH. What does FSH and LH stand for? Now you're going to start seeing some results to your knowledge. FSH stands for follicle stimulating hormone. What do you think that does? That's right. LH stands for luteinizing hormone. And you see the word, corpus luteum - luteinizing might have something to do with that. And so now, we're starting to get an inkling as to the beginning of the menstrual cycle.
Now, remember this? This was the developing follicle. And one of the things that this developing follicle has is receptors. And the key is that the immature follicles don't have LH receptors. They only have FSH receptors. So, what is going to happen here is the FSH is going to start to trigger this. And what is it going to trigger? It's going to stimulate the follicle. To do what? To take up water, to swell. And so, what we find is that the follicle begins to grow. Now leg's take at look at that in relationship to the hormones that are being produced by the pituitary. These are the pituitary hormones and I have it arranged here so that it scales Days zero to twenty-eight. And, so while she is having her last menstrual flow, during the three to five days that that occurs, we see that both of these are very low. But interestingly enough, the hormones begin to rise. Now I have an interesting story to tell you here. When these things are in low amounts, well, let's just talk about in general, the follicle. Let's go to the follicle first. The follicle is swelling. The follicle, besides swelling, also starts to produce something else. The follicle starts to produce a hormone called estrogen. So what do we have going on here? We have the follicle stimulating hormone particularly causing the follicle to swell. The follicle is producing estrogen. Let's take a look at estrogen and see what's going on with that. Now here's estrogen. We'll line up the days and we'll see what's going on. So, estrogen is going to be this green line right here. And I will write FSH on this line, the purple. And I will write LH on this line. So we can keep track of them. So, look what's happening. As the follicle swells, what's happening to my estrogen? My estrogen is rising, kind of coincides with the growth of the follicle. Now here's what I was going to tell you a second ago. When there's very little estrogen, even though you're making a little bit of FSH and a little bit of LH, estrogen in small quantities has a very interesting effect. What it does is it actually inhibits FSH and LH. So, estrogen, and the way it does that actually as goes to the hypothalamus and it inhibits the gonadotrophin releasing hormone, but the big lesson there is small concentrations inhibit FSH and LH. But, as estrogen increases, guess what it does? It does just the opposite. What it really is going to do is it's going to really increase once there gets to be a lot of it, FSH and LH, especially LH. So when the estrogen increases, FSH and LH increase, too.
One more thin about estrogen. Look at your endometrium. Estrogen is causing a physical change in your uterus, too. So, what's happening also, if we take a look at this first fourteen days here, and you can see what is going on. As the estrogen goes up, the endometrium increases its size. Are we done? We haven't even ovulated yet.
So, let's take a look. So estrogen is going up, up, up. What did I say is going to happen? You get something like this, the LH surge. Now this first chunk of time right here, when we are in what is called the follicle stage. Over here, we get to a point called ovulation. The LH gets to the point. And the LH surges, and the FSH peaks. Now what we literally have is that the follicle stimulating hormone is going to cause the follicle to get to the point where it is about ready to burst. In addition, the follicle, as it is growing, is getting more and more - what did I say before, it has very few FSH receptors, remember that? Now as the follicle grows, it gets more and more LH receptors. So these two things coupling together cause that follicle to burst at about Day 14. At about Day 14, the follicle bursts and ovulation occurs.
Now, let's at our endometrium. Our endometrium is ready for pregnancy. Just in case. So what happens next? The follicle is rupture. What has happened? Literally the Estrogen amount has caused the positive feedback and the LH is going way up. The follicle is ruptured. What's going to happen next. Now we enter into what is called the luteal phase. Remember luteinizing hormone? That's what LH means. Well, guess what? That follicle now converts. And it becomes something called the corpus luteum. And look at this. Out of nowhere, it seems, this hormone starts getting produced. This blue line and we seem to have a lot of that. And that is called progesterone. Another ovarian hormone because it is made in the corpus luteum which used to be the follicle, which is part of the ovary. And progesterone is going to be made by the corpus luteum. And the corpus luteum is going to last about eight to ten days past ovulation. So, about Day 22, the corpus luteum is going to start breaking down. But until then, the progesterone is building up. The estrogen is holding constant. The egg is coming down and everybody is like holding their breath. Will there be a zygote or will there be an egg. Nobody knows, but meanwhile progesterone and estrogen start to do something else.
Here's what they do. Progesterone and estrogen act in something called a negative feedback. And this is very interesting. Progesterone particularly, and estrogen, go back to the hypothalamus and the pituitary. Remember the pituitary is making LH. What this progesterone and estrogen do is they send off a signal to turn off LH and FSH. The pituitary was making LH. What did LH do? LH, if you remember, affected the corpus luteum to make progesterone. You're turning off LH. If you turn off LH, you turn off the corpus luteum. And you turn off progesterone. Now there's one thing about progesterone helps a woman maintain her endometrium. As soon as the progesterone and estrogen drop right here, guess what happens to her endometrium? Her endometrium sloughs off in the menstrual flow. Because of the drop of the progesterone and estrogen. So, here's the thing, if the progesterone and estrogen get high enough, she loses her endometrium. She has her period. She is not pregnant. But I have one more thing. What's a baby going to do. Well, here's the thing. The progesterone and estrogen are still going to go high but the fetus produces a hormone called HCG, human chorion gonadotrophic hormone.
Guess what this does? This is an LH mimic. Think about it. What did LH do? LH allowed you to maintain the corpus luteum. In maintaining the corpus luteum, what did you make? There's the LH. It allowed you to maintain the corpus luteum. If you maintain the corpus luteum, what did the corpus luteum make? Progesterone. What did progesterone do? Progesterone maintained the uterine lining. So as long as there is a baby in there, I don't care how high your progesterone gets, you're always going to have LH. Why? Because the baby is making the LH. Who cares about your corpus luteum anymore. There it is. An intricate cycle of hormonal interchanges that literally, every twenty-eight days bring a menstrual cycle mammal to the point where she can be pregnant and if she is not, start all over. It's an intricate and beautiful cycle that - there's a whole lot of us running around, so it must work pretty well.
Animal Systems and Homeostasis
The Ovarian and Uterine Cycles
Hormonal Events During the Female Reproductive Cycle Page [1 of 2]

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