00:00
Now, a stress is presented
itself, how are you actually
dealing with that in terms of
how's your body dealing with it.
00:10
So physiologically speaking,
we are going to talk about
what happens to your body.
00:13
So there's two systems that
get activated in parallel.
00:17
I mean they both being
activated at the same time.
00:20
Both have different roles
and both do it at a different pace.
00:23
Sympathetic nervous system which
we had talked about previously.
00:26
And the HPA-axis, we're going
to describe what that actually
means in the next coming slides.
00:31
So the sympathetic nervous system
initiates or moderates
something called the fight
or flight response.
00:37
Again something
we mentioned before
and you'll continue to see.
00:40
And this is when your body is
presented with an acute stressor
and or something that's in
front of you right now,
a lion attacking.
00:46
As you can see here
we have a lion attacking.
00:48
And you're forced to make
a decision.
00:53
Am I going to put on my
gladiator helmet, get oiled up
and fight this tiger.
00:58
Or am I going to turn around
and run away so that the tiger
does not devour me.
01:03
So you are going to fight
or you are going to run away.
01:06
So this is something that's
mediated about this
sympathetic nervous system.
01:09
And it's usually quite fast.
01:10
Very fast-acting.
01:11
You need to think of a situation
that may be happened to you.
01:14
It's not something you mull
over the next few minutes.
01:19
So what's happening here is
your body is responding to this.
01:23
And the sympathetic nervous system
is actually releasing
something called
a "Stress Hormone."
And this comes from the adrenal
glands.
01:29
And the adrenal glands actually
release something called
Adrenaline or Noadrenaline.
01:33
Something that's known as
epinephrine norepinephrine.
01:36
And these will mitigate
and initiate that response.
01:39
And you've heard that before
saying,
I had a rush of adrenaline.
01:42
And I was able to
these wonderful tasks.
01:45
I was able to beat up a tiger.
01:46
I was able to pick up a car.
01:47
All these wonderful things
and that is initiated by this
exact response of flight
or fight and it's mediated
by adrenaline.
01:54
Now the sympathetic nervous
system will do things
that's gets you ready and ready
to fight or flight.
02:02
And that is things like
increase heart rate.
02:04
So you see physiological
changes.
02:06
Increase heart rate,
increase in breathing,
changes in blood flow,
slow in digestion.
02:11
Because it's going to reallocate
those resources to deal
with the impending fight
or flight.
02:18
And it dulls your pain.
02:19
So you're probably wondering
why it's going to dull my pain.
02:22
So if you are about to fight
a tiger, you don't want
high sense of pain, you want
dull to the pain.
02:26
In case that tiger does gives
you a couple of shots
to your face, you'll feel it,
you can keep fighting, okay.
02:31
Now, let's take a look at
the other pathway
that gets initiated.
02:37
And this is the HPA-axis,
or the Hypothalamic Pituitary
Adrenal axis.
02:41
It's a manifold.
02:42
And this is a slower process.
02:44
So we're going to walk through
some of the main components
and then I'm going to subsequently
show you something
called "Negative Feedback."
And how all these pieces
tie together.
02:52
So there's a structure that
we've mentioned before
and we'll come up again
called "Hypothalamus."
And this is a structure deep
in your brain and releases
something called "Corticotropin
Release Hormone or CRH."
CRH then goes on once it gets
released to stimulate
the pituitary gland to release
something called
adrenocorticotropic hormone
or ACTH.
03:13
ACTH then goes on to signal
the adrenal glands to release
something called cortisol
into the blood stream.
03:19
It's lots of stuff to digest
there and put your head around.
03:22
But we're going to break it
down into couple of components.
03:24
And so what's happening here is
this is a bio-chemical cascade
or sequence of things
that's happening.
03:29
So think of it as
a domino effect.
03:31
So quickly again
hypothalamus releases CRH.
03:35
CRH stimulates release of ACTH.
03:37
And ACTH goes on to
release cortisol, okay.
03:40
So we'll walk through
that in just a moment.
03:43
Now what is cortisol.
03:45
Cortisol, let's look at
the definition here,
is a glucocorticoid, a hormone
that shifts the body from sugar
to fat as an energy source.
03:52
So why do we care,
why is that important.
03:53
So cortisol is doing something
very, very important in that is,
it's telling your body,
"I'm going to now use my fat
which is an energy store which
normally you would not use."
So let me back track a bit.
04:08
You're sitting here right now
watching this video and you have
your desk and you got a big
bowl of chips besides you.
04:14
You are eating those chips.
04:16
Now your body is actually
not using that as energy.
04:18
It's taking those chips
and it's converting it into fat.
04:22
Because you have enough energy,
it says, "I'm going to use this
energy and turn it
into fat in case
I need it at some other point."
Now evolutionary speaking,
if we backtrack even
further in cave man days,
food was a scarce resource.
04:35
They were not sure where
actually it was coming from.
04:38
And when they would find food,
they would gobble it up
and that would get stored
as fat.
04:42
And they would use it as it
didn't know when it would get
it's next meal.
04:46
Fast forward it today, it's the
first time in human civilization
we have an over
abundance of food.
04:50
So it's never really a common
situation
where you have zero food.
04:55
I'm generalizing,
obviously some of we don't.
04:57
But generally speaking, we have
unlimited access to food.
05:00
And so we don't really need this
fat which is why all have an
extra piece of love that we
all carry around with us.
05:05
But in this situation when
the HPA-axis is activated,
it's going to say,
"I'm going to go use my fat
stores as energy,
and I'm not going to use
the sugar
which I'm normally eating."
So food now it's converted
into sugar.
05:18
So it's not going to use that.
05:20
Now what that does, is it keeps
our blood sugar levels high.
05:24
And the time we actually need
it in case we our having to do
something like fight.
05:29
Or for a situation of over time
we're going to need this energy.
05:33
It's making that energy
available and it's using
our stores instead right now so
that we have access to that high
blood sugar when we need it.
05:42
Now, is cortisol all good?
Well cortisol is actually quite
useful in this situation
I have mentioned.
05:49
But long term cortisol
is not a good thing.
05:51
So we know that prolonged
release of cortisol due to
chronic stress can
have harmful effects.
05:56
Now in each of these situations
that I'm mentioning to you,
I'm talking to you about
fairly acute stress.
06:01
So a tiger attacking you
or your wife yelling at you.
06:05
Small periods of time, if it's
alright, may be sometimes
it's a little bit longer,
but essentially is short lived
phenomenon.
06:11
As opposed to, you are that
doctor in the ER and you have
this prolong stress.
06:15
You are a lawyer, or you are in
a very stressful job
of all the time you are stress,
stress, stress, stress,
levels of cortisol will go up
because the HPA-axis
is being activated.
06:25
And they are not turning off
which is not a good thing.
06:27
And so it ends up having
long term half effects.
06:31
One of those is it actually
inhibits the activity
of white blood cells.
06:34
And therefore, also impacts
the immune system.
06:37
So once you're impacting
white blood cells
and you're ready to wore off
disease and other things,
that's not good.
06:44
It makes you prone to
susceptible to getting sick.
06:47
So you do not want prolonged
exposure to stress where it
causes increase levels of
cortisol because it leads to
vulnerability to illness.
06:55
Okay, so now let's take a look
at this figure where we can make
sense of all these crazy
parts I just mentioned.
07:03
So like I said, the hypothalamus
is going to release
corticotropin releasing hormone
or CRH, that is done.
07:10
And now we are going to activate
the anterior pituitary
to release ACTH, okay.
07:15
Now that goes on to activate
the adrenal cortex that will
go on to release cortisol.
07:19
Now this is a unique situation
here and a premise that you will
need to understand for the MCAT
and that's something called
Negative feedback.
07:27
Now everything going from
hypothalamus to the adrenal cortex,
this way we're talking
about a positive feedback.
07:35
One initiates the next,
initiates the next.
07:38
Now we need to
somehow turn this off.
07:41
The body needs to say,
"Hey, I just release the CRH
and I activated ACTH."
Is that enough
or do I need more?
ACTH is now initiated to release
cortisol, is that enough?
Or should I stop?
Now what it does is, there is
receptors in the body and brain
that actually detect levels
of ACTH
and detect levels of cortisol.
08:00
And when enough
cortisol is release.
08:03
The levels in the blood are
high enough, it will actually
be detected by the hypothalamus.
08:07
And say "Hey, hypothalamus,
you should stop releasing CRH
because we have enough
cortisol."
And it will also activate
anterior pituitary
to not release anymore ACTH.
08:18
So it's the off sort saying,
"We have enough, hold off."
And that negative feedback
will stop that cascade.
08:25
And they'll put the system
on pause.
08:28
Until it gets reactivated again,
positive feedback continues
and then the negative feedback
comes back
to turn the system off again.
08:35
So we call that whole
process negative feedback.
08:37
And this will apply to more than
more systems than just HPA-axis.
08:41
This is why I was saying you
should probably note this.