00:01
Now, let's talk about
the ovarian cycle.
00:04
There are actually three phases
within the ovarian cycle.
00:08
And they are follicular,
ovulatory, and secretory.
00:13
What's really great
about these phases,
if you think about the words,
it actually tells you
what's going on.
00:20
So now let's talk about
what's going on in the ovary
very specifically,
because it's a very
intricate process.
00:28
Now the whole goal of the ovary
is to release a mature egg.
00:32
That's how we get a baby.
00:34
But we need to think about,
what happens
to make that process go?
Okay, let's break down what's going
on in the ovarian cycle.
00:43
Do you see that word
follicular phase?
We want to focus on
the follicle,
and what's going on
inside the follicle.
00:51
Now the follicle is actually
a collection of fluid
and it's a space.
00:55
And inside that space,
the ovum or the egg
is going to reconstitute,
or grow, or mature.
01:02
And inside that follicle is where we
have the production of estrogen.
01:07
Remember that feedback loop
with the anterior pituitary
and also with the hypothalamus?
That happens because of what is
going on inside the follicle.
01:17
Now, FSH is going to predominate
in the follicular phase
because we have to make sure
the follicle is ready
and we have to make sure
the ovum is matured.
01:27
But about 24 to 36 hours
prior to ovulation,
then we need a message to say,
"Pop, the egg is ready."
And that's the role of
LH or luteinizing hormone,
which is also produced
by the anterior pituitary.
01:43
So remember that 24 to 36 hours
prior to ovulation,
we're going to experience a surge
in luteinizing hormone,
which is going to be
the trigger for ovulation.
01:55
So now let's talk about
the last half of the ovarian cycle.
01:59
The luteal phase.
02:01
Luteal comes from the word lutein,
which means yellow.
02:05
So guess what color it is.
02:07
It is yellow.
02:08
And it makes a small mass of cells
that are left over
after the egg erupts
from the follicle.
02:16
So as the cells collapse,
the corpus luteum is formed.
02:20
And its major function
is to produce progesterone.
02:23
And progesterone
has an incredible responsibility,
because it is the hormone
that stabilizes the endometrium.
02:30
Estrogen makes
the lining of the uterus fluffy...
02:34
for a baby.
02:35
And progesterone helps to keep
the lining in place.
02:38
And it will do that
all the way up until about
8 to 10 weeks in pregnancy
when the placenta takes over the
function of producing progesterone.
02:48
So that's the role of the luteum,
the corpus luteum, the yellow body.
02:54
Now, if there's a pregnancy,
there is going to be
the production of hCG
Human chorionic gonadotropin.
03:01
And that hCG will send a message
to the corpus luteum that,
"Hey, I need you to keep
producing progesterone
until the placenta
is ready to take over."
However,
in 12 to 14 days,
if there's no production of HCG,
and no baby,
then the corpus luteum
will degenerate
and the progesterone levels
will drop.
03:20
And that drop in progesterone sends
a message back to the hypothalamus
that I need you
to start producing GnRH
and then begin this cycle
all over again.
03:32
That is the ovarian cycle.
03:34
Now, let's look again, at those two
specific neurotransmitter hormones,
LH and FSH.
03:41
And I want you to really see
how those levels change
over the course
of the menstrual cycle.
03:46
So on this graphic,
you'll see days
1 through 28
of a menstrual cycle.
03:51
And you'll see that at
the beginning of the cycle,
the LH and the FSH levels
are low.
03:57
But as the ovum
and the follicle mature,
you start to see
those levels go up.
04:03
Now remember, what happens
24 to 36 hours prior to ovulation?
We get a surge of...?
LH. Exactly.
So now you see it.
04:15
That's a trigger for ovulation.
04:17
And after ovulation.
04:19
Well, we don't need any more LH
and we certainly don't need
to stimulate the ovary anymore.
04:24
So those levels
are going to drop.
04:26
And they continue to drop until
we get to the end of the cycle.
04:29
And if you can see sort
of at the end,
the FSH level is starting
to go back up again,
that comes from the drop
in progesterone.
04:37
So this is how that fits together
in the ovarian cycle.
04:41
Now, let's take a look
at progesterone.
04:43
So, you can see again,
in the follicular phase,
the progesterone levels are low,
because who is responsible for
producing progesterone?
The corpus luteum.
04:54
And it's not there
until after ovulation.
04:57
So you see around day
12 to 14 ovulation occurs,
and then progesterone levels
begin to rise.
05:04
And if there's no pregnancy,
and there's no message
from the conceptus
back to the corpus luteum,
those progesterone
levels will then begin to fall.
05:13
And you can actually see it
in this graphic.
05:16
And that decrease in progesterone is
the signal back to the hypothalamus
that it's time to release
GnRH again.
05:25
Let's look at the final hormone,
estradiol.
05:28
And it's not the least important
because we talked about it last.
05:31
So don't get it confused.
05:33
So, estradiol, again,
is a type of estrogen.
05:36
And I want you to look at
where it is on the graph
and how it changes over the course
of the cycle.
05:42
So, at the beginning
of the follicular phase,
then we see that estradiol levels
are low.
05:48
As we get towards ovulation,
we want to make sure that the
endometrium is nice and fluffy.
05:54
Estrogen and estradiol
make things fluffy,
so the levels are
going to begin to go up.
06:00
And then after ovulation, they're
going to drop down a little bit,
and that's because
of that feedback loop.
06:05
We don't want to produce any
more mature eggs.
06:08
So that level is going to drop.
06:10
And then we're going to find
that estrogen levels begin to go up
and then drop again.
06:15
So, if we have to think about
the hormones that predominate
in which part of the cycle,
what do you think predominates
in the first half
when we talk about
estrogen and progesterone?
Estrogen, exactly.
06:32
What about the second half,
which hormone is the highest?
Progesterone.
06:40
Perfect.