Hormonal Dynamics in the Menstrual Cycle

Armando Hasurungan, biology and medicine videos. Please make sure to subscribe, join the forum and group for the latest videos. Please visit Facebook Armando Hasurungan. In this video we will look at the hormonal regulation of the female reproductive cycle. So we will be looking at the menstrual cycle basically. And yeah, so the menstrual cycle. The hormones of the female is so much more complicated than the males. Hopefully we'll be able to understand it by the end of this video. So we begin with the hypothalamus and the pituitary glands, which are made up of the anterior and posterior pituitary glands. We'll be focusing on the anterior pituitary gland. The hypothalamus regulates hormones released by the anterior pituitary through the portal blood here. In the female reproductive system, the hypothalamus produces a hormone called gonadotropin-releasing hormone, which will travel... here to the anterior pituitary via the portal blood. And it will cause the cells in the anterior pituitary gland to produce two important hormones, known as FSH, follicle-stimulating hormone, and LH, luteinizing hormone. Please note that in males, this same process also occurs. Males also produce gonadotropin-releasing hormone, which will... cause the anterior pituitary to release luteinizing hormone and follicle stimulating hormone. So what will these hormones do in the female body? Well these hormones will travel to the female ovaries where the female eggs are produced. So let's just recap quickly what the ovary is and where it is. So here we have the uterus and the ovaries which connects to the uterus via the fallopian tube, essentially. But it's now known as a uterine tube. So we will focus on this ovary here. So let's zoom in. So here is the ovary, and it has blood vessels. And it's through these capillaries, these blood vessels, that the hormones can enter. Now, in each ovary, there are follicles. Women have many, many follicles in the ovaries. And... each month only some will begin to mature but only one will ovulate and become essentially will ovulate and produce an egg. Now let's just say it's the beginning of the menstrual cycle so just after a female has shed her uterine wall just had the period. Now within the ovaries females have many many many primordial follicles and each month only some of these primordial follicles will mature into primary follicles, and they will keep maturing, but only one will ovulate. So here, I'm drawing one primary follicle, and it's the beginning of the menstrual cycle. Before we continue on, let's look at the changes of the hormone concentrations. that come from the brain by looking at a graph. So here we have a y-axis, which shows the concentration of the hormones in the blood. And on the x-axis is the duration of the female menstrual cycle, which normally goes for about 28 days. So the dotted line in the middle is 14 days, which is halfway. Now just to simplify things even more, the menstrual cycle can be divided into... two phases. The first 14 days is known as the follicular phase and the last 14 days is known as the luteal phase and this is important to keep in mind. So the first is the follicular phase, the second is luteal phase. Now initially in the beginning of the menstrual cycle there is an increase in gonadotropin releasing hormone secreted by the hypothalamus because it's the start of the menstrual cycle. And this should cause a steady increase in follicle stimulating hormone and luteinizing hormone. But instead we see an increase and then a slow dropping level of follicle stimulating hormone and we have a steady level of luteinizing hormone. Why is this? Well the reason is actually quite complicated but just hold on to that thought and hopefully it will make sense. So let's go back to the ovary. So follicle stimulating hormone. will initially rises, remember, because the follicular phase is the first phase of the menstrual cycle. Follicle stimulating hormone will enter the ovaries and what they will essentially do is stimulate. It will stimulate follicle maturation of these primary follicles. And so some of these primary follicles will mature into a secondary follicle. I'm only drawing one secondary follicle for simplicity. While these follicles are maturing, they produce another hormone called estrogen. Now, estrogen has many effects. In the first 10 days of the menstrual cycle, so in the beginning, estrogen has a negative feedback on the pituitary gland, inhibiting the release of luteinizing hormone. To put it simply, at low concentrations, estrogen inhibits luteinizing hormone secretion from the anterior pituitary. And that is why we only see a steady level of luteinizing hormone in the blood. Because even though gonadotropin-releasing hormone from the hypothalamus is stimulating the release of luteinizing hormone, at low concentrations, estrogen will inhibit luteinizing hormone release. Another fact is that follicle-stimulating hormone is secreted primarily in response to low estrogen concentrations. So when estrogen levels rise, follicle stimulating hormone levels will fall. And that is why we see in the graph a steady drop in follicle stimulating hormone because there's an increase in estrogen levels from the follicles. So let's draw another graph and see the concentrations of the hormones produced by the ovaries during the menstrual cycle, which goes on for 28 days. So as the follicle matures, they will produce more estrogen. Which as I mentioned, at low concentrations, estrogen will inhibit the secretion of luteinizing hormone. And also, the increase in estrogen concentrations will cause a decrease in follicle stimulating hormone secretion. Estrogen is an important hormone, especially for females. Because estrogen is basically male's equivalent of testosterone. Estrogen... Peripheral effects include stimulating bone and muscle growth, it stimulates endometrial growth, maintains female secondary characteristics, and maintains the glands, the breasts, amongst many other things. So just to draw this graph, up to 10 days of the menstrual cycle, we see a steady low concentration of... luteinizing hormone due to the inhibitory effects of estrogen, remember, in the first 10 days. And we also see a steady drop of follicle stimulating hormone due to the increase in estrogen levels as well, which has a negative feedback. So what happens after 10 days? Well, after 10 days, estrogen levels will continue to rise as the follicles mature in the ovaries. And after 10 days, as estrogen levels rise, it will have a positive feedback and it will stimulate the release of luteinizing hormone. So at low concentrations, estrogen will inhibit luteinizing hormone secretion. However, at high concentrations, estrogen will stimulate luteinizing hormone secretion. Now things are changing. The increase in gonadotropin-releasing hormone and estrogen will stimulate then luteinizing hormone secretion and you see this massive spike in luteinizing hormone concentration. It's this massive luteinizing hormone concentration that will trigger ovulation of the most mature follicle in the ovary. The ovulation of the follicle will release what we know as the female egg, the oocyte. After ovulation, the luteinizing hormone levels will drop back down. Gonadotropin-releasing hormone will slowly drop as well. Follicle-stimulating hormone also had a small spike as a side effect of the surge of luteinizing hormone release. So luteinizing hormone triggers ovulation and oocyte is released. After the follicle ovulates, the follicle will turn into a corpus luteum, which is a dead follicle basically. Now, that is why the first 14 days of the menstrual cycle is called the follicular phase, because it all has to do with the follicles and its maturation. And the last 14 days is known as the luteal phase, because we have the formation of the corpus luteum. The corpus luteum will... essentially slowly degrade. However, it also has a purpose in that it secretes hormones. It secretes three hormones, estrogen again, inhibin, and progesterone. So what we see in the concentration levels of these ovarian hormones, estrogen will increase until ovulation and then drop slightly. Inhibin was not present until after ovulation, then it begins to increase thanks to the corpus luteum. Progesterone levels were low until after ovulation during the luteal phase. So at 21 days of the female reproductive cycle, progesterone is increasing, inhibin is increased, and estrogen is still detectable. And all these hormones are all produced thanks to the corpus luteum. So what do these hormones do? Well, inhibin has a negative feedback, and it will essentially inhibit the secretion of follicle-stimulating hormone. Because we are at the luteal phase, we don't need any more follicles to mature just yet. So that is why inhibin is preventing follicle-stimulating hormone release, to prevent follicle maturation. So here I wrote, as the secondary corpus luteum develops, inhibin secretion will suppress follicle stimulating hormone release. Progesterone is the most important hormone in the luteal phase and has many functions. One of which is having a negative effect on the hypothalamus, inhibiting the secretion of gonadotropin-releasing hormone. Now, after ovulation, during the luteal phase, the progesterone levels will increase slowly and the estrogen levels will decrease slowly, kind of. And this will suppress gonadotropin-releasing hormone release. And so progesterone will inhibit gonadotropin-releasing hormone release, which will also affect the release of luteinizing hormone and follicular stimulating hormone. So during the luteal phase, as progesterone and inhibin increase, this will essentially cause a decrease in gonadotropin-releasing hormone, luteinizing hormone, and follicular stimulating hormone. But the main effect of progesterone is that it will stimulate endometrial growth. The endometrial lining is the lining of the uterus, which will shed each month, or the endometrium is where the egg will implant if it's fertilized by sperm. Okay, let's just say there was no fertilization, because this is just a normal menstrual cycle. And of course, all good things have to come to an end. The corpus luteum in the ovary will degenerate. allowing a new set of follicles to mature. So as the corpus luteum degenerates, all these hormones that were produced by the corpus luteum, the estrogen, inhibin, and progesterone, they will decrease like so. So when the corpus luteum degenerates, progesterone will decrease. And this will mean that progesterone cannot inhibit gonadotropin-releasing hormone release. And so gonadotropin-releasing hormone levels will increase, and this will allow a new menstrual cycle to occur. Also, because of the decrease in progesterone and estrogen in part, means that these hormones cannot maintain the endometrium, the endometrial lining in the uterus. And so the endometrium will shed, and this is known as the period. And after the endometrial lining sheds, This allows a new cycle to occur, and then you see an increase in gonadotropin-releasing hormone again, and the cycle continues. Hope you enjoyed this video. Thank you.

So we will be looking at the menstrual cycle basically. And yeah, so the menstrual cycle. The hormones of the female is so much more complicated than the males.

Hopefully we'll be able to understand it by the end of this video. So we begin with the hypothalamus and the pituitary glands, which are made up of the anterior and posterior pituitary glands. We'll be focusing on the anterior pituitary gland.

The hypothalamus regulates hormones released by the anterior pituitary through the portal blood here. In the female reproductive system, the hypothalamus produces a hormone called gonadotropin-releasing hormone, which will travel... here to the anterior pituitary via the portal blood. And it will cause the cells in the anterior pituitary gland to produce two important hormones, known as FSH, follicle-stimulating hormone, and LH, luteinizing hormone. Please note that in males, this same process also occurs.

Males also produce gonadotropin-releasing hormone, which will... cause the anterior pituitary to release luteinizing hormone and follicle stimulating hormone. So what will these hormones do in the female body? Well these hormones will travel to the female ovaries where the female eggs are produced. So let's just recap quickly what the ovary is and where it is.

So here we have the uterus and the ovaries which connects to the uterus via the fallopian tube, essentially. But it's now known as a uterine tube. So we will focus on this ovary here.

So let's zoom in. So here is the ovary, and it has blood vessels. And it's through these capillaries, these blood vessels, that the hormones can enter.

Now, in each ovary, there are follicles. Women have many, many follicles in the ovaries. And...

each month only some will begin to mature but only one will ovulate and become essentially will ovulate and produce an egg. Now let's just say it's the beginning of the menstrual cycle so just after a female has shed her uterine wall just had the period. Now within the ovaries females have many many many primordial follicles and each month only some of these primordial follicles will mature into primary follicles, and they will keep maturing, but only one will ovulate.

So here, I'm drawing one primary follicle, and it's the beginning of the menstrual cycle. Before we continue on, let's look at the changes of the hormone concentrations. that come from the brain by looking at a graph. So here we have a y-axis, which shows the concentration of the hormones in the blood. And on the x-axis is the duration of the female menstrual cycle, which normally goes for about 28 days.

So the dotted line in the middle is 14 days, which is halfway. Now just to simplify things even more, the menstrual cycle can be divided into... two phases. The first 14 days is known as the follicular phase and the last 14 days is known as the luteal phase and this is important to keep in mind. So the first is the follicular phase, the second is luteal phase.

Now initially in the beginning of the menstrual cycle there is an increase in gonadotropin releasing hormone secreted by the hypothalamus because it's the start of the menstrual cycle. And this should cause a steady increase in follicle stimulating hormone and luteinizing hormone. But instead we see an increase and then a slow dropping level of follicle stimulating hormone and we have a steady level of luteinizing hormone. Why is this? Well the reason is actually quite complicated but just hold on to that thought and hopefully it will make sense.

So let's go back to the ovary. So follicle stimulating hormone. will initially rises, remember, because the follicular phase is the first phase of the menstrual cycle. Follicle stimulating hormone will enter the ovaries and what they will essentially do is stimulate. It will stimulate follicle maturation of these primary follicles.

And so some of these primary follicles will mature into a secondary follicle. I'm only drawing one secondary follicle for simplicity. While these follicles are maturing, they produce another hormone called estrogen. Now, estrogen has many effects.

In the first 10 days of the menstrual cycle, so in the beginning, estrogen has a negative feedback on the pituitary gland, inhibiting the release of luteinizing hormone. To put it simply, at low concentrations, estrogen inhibits luteinizing hormone secretion from the anterior pituitary. And that is why we only see a steady level of luteinizing hormone in the blood. Because even though gonadotropin-releasing hormone from the hypothalamus is stimulating the release of luteinizing hormone, at low concentrations, estrogen will inhibit luteinizing hormone release. Another fact is that follicle-stimulating hormone is secreted primarily in response to low estrogen concentrations.

So when estrogen levels rise, follicle stimulating hormone levels will fall. And that is why we see in the graph a steady drop in follicle stimulating hormone because there's an increase in estrogen levels from the follicles. So let's draw another graph and see the concentrations of the hormones produced by the ovaries during the menstrual cycle, which goes on for 28 days.

So as the follicle matures, they will produce more estrogen. Which as I mentioned, at low concentrations, estrogen will inhibit the secretion of luteinizing hormone. And also, the increase in estrogen concentrations will cause a decrease in follicle stimulating hormone secretion.

Estrogen is an important hormone, especially for females. Because estrogen is basically male's equivalent of testosterone. Estrogen... Peripheral effects include stimulating bone and muscle growth, it stimulates endometrial growth, maintains female secondary characteristics, and maintains the glands, the breasts, amongst many other things. So just to draw this graph, up to 10 days of the menstrual cycle, we see a steady low concentration of...

luteinizing hormone due to the inhibitory effects of estrogen, remember, in the first 10 days. And we also see a steady drop of follicle stimulating hormone due to the increase in estrogen levels as well, which has a negative feedback. So what happens after 10 days? Well, after 10 days, estrogen levels will continue to rise as the follicles mature in the ovaries. And after 10 days, as estrogen levels rise, it will have a positive feedback and it will stimulate the release of luteinizing hormone.

So at low concentrations, estrogen will inhibit luteinizing hormone secretion. However, at high concentrations, estrogen will stimulate luteinizing hormone secretion. Now things are changing. The increase in gonadotropin-releasing hormone and estrogen will stimulate then luteinizing hormone secretion and you see this massive spike in luteinizing hormone concentration. It's this massive luteinizing hormone concentration that will trigger ovulation of the most mature follicle in the ovary.

The ovulation of the follicle will release what we know as the female egg, the oocyte. After ovulation, the luteinizing hormone levels will drop back down. Gonadotropin-releasing hormone will slowly drop as well. Follicle-stimulating hormone also had a small spike as a side effect of the surge of luteinizing hormone release. So luteinizing hormone triggers ovulation and oocyte is released.

After the follicle ovulates, the follicle will turn into a corpus luteum, which is a dead follicle basically. Now, that is why the first 14 days of the menstrual cycle is called the follicular phase, because it all has to do with the follicles and its maturation. And the last 14 days is known as the luteal phase, because we have the formation of the corpus luteum. The corpus luteum will...

essentially slowly degrade. However, it also has a purpose in that it secretes hormones. It secretes three hormones, estrogen again, inhibin, and progesterone. So what we see in the concentration levels of these ovarian hormones, estrogen will increase until ovulation and then drop slightly. Inhibin was not present until after ovulation, then it begins to increase thanks to the corpus luteum.

Progesterone levels were low until after ovulation during the luteal phase. So at 21 days of the female reproductive cycle, progesterone is increasing, inhibin is increased, and estrogen is still detectable. And all these hormones are all produced thanks to the corpus luteum. So what do these hormones do? Well, inhibin has a negative feedback, and it will essentially inhibit the secretion of follicle-stimulating hormone.

Because we are at the luteal phase, we don't need any more follicles to mature just yet. So that is why inhibin is preventing follicle-stimulating hormone release, to prevent follicle maturation. So here I wrote, as the secondary corpus luteum develops, inhibin secretion will suppress follicle stimulating hormone release. Progesterone is the most important hormone in the luteal phase and has many functions. One of which is having a negative effect on the hypothalamus, inhibiting the secretion of gonadotropin-releasing hormone.

Now, after ovulation, during the luteal phase, the progesterone levels will increase slowly and the estrogen levels will decrease slowly, kind of. And this will suppress gonadotropin-releasing hormone release. And so progesterone will inhibit gonadotropin-releasing hormone release, which will also affect the release of luteinizing hormone and follicular stimulating hormone.

So during the luteal phase, as progesterone and inhibin increase, this will essentially cause a decrease in gonadotropin-releasing hormone, luteinizing hormone, and follicular stimulating hormone. But the main effect of progesterone is that it will stimulate endometrial growth. The endometrial lining is the lining of the uterus, which will shed each month, or the endometrium is where the egg will implant if it's fertilized by sperm. Okay, let's just say there was no fertilization, because this is just a normal menstrual cycle.

And of course, all good things have to come to an end. The corpus luteum in the ovary will degenerate. allowing a new set of follicles to mature.

So as the corpus luteum degenerates, all these hormones that were produced by the corpus luteum, the estrogen, inhibin, and progesterone, they will decrease like so. So when the corpus luteum degenerates, progesterone will decrease. And this will mean that progesterone cannot inhibit gonadotropin-releasing hormone release. And so gonadotropin-releasing hormone levels will increase, and this will allow a new menstrual cycle to occur. Also, because of the decrease in progesterone and estrogen in part, means that these hormones cannot maintain the endometrium, the endometrial lining in the uterus.

And so the endometrium will shed, and this is known as the period. And after the endometrial lining sheds, This allows a new cycle to occur, and then you see an increase in gonadotropin-releasing hormone again, and the cycle continues. Hope you enjoyed this video.

Thank you.

Transcript for:Hormonal Dynamics in the Menstrual Cycle

Transcript for:
Hormonal Dynamics in the Menstrual Cycle