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