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