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  • Armando Hasudungan biology and medicine videos

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  • 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

  • Yes, so the menstrual cycle

  • the Hormones of

  • the female is

  • So much more complicated the Male's

  • but 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 over here, so let's zoom in

  • so here is the ovary and

  • it has blood vessels and

  • This 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 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 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 blood and

  • On the [x-axis] is a 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

  • II is the 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 Follicles stimulating hormone and

  • luteinizing hormone

  • but instead we see a

  • 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'll 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 ten 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 a 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 males equivalent of testosterone, Estrogen

  • Peripheral effects include stimulating bone and muscle Growth it stimulates endometrial growth

  • Maintains female Secondary characteristics and maintains a female the glands the breasts amongst many other things

  • So just to draw this graph up to

  • Ten days of the Menstrual cycle. We see a steady a steady

  • low concentration of luteinizing Hormone due to the inhibitory effects of estrogen remember in the first ten 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

  • or 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 it 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 will were low until after ovulation during the luteal phase

  • so at

  • 21 days of the female reproductive cycle progesterone is increasing inhibin is increasing 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 inhibiting 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 [effect] the release of luteinizing hormone and follicle 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

  • 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 are 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 though

  • And then you see a increase in gonadotropin releasing hormone again and the cycle continues

  • Hope you enjoy this video. Thank you

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C1 US hormone estrogen follicle stimulating menstrual cycle

Female Reproductive System - Menstrual Cycle, Hormones and Regulation

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    JillHuang posted on 2021/04/12
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