Human: The World Within (2021) s01e02 Episode Script
Pulse
1
- Think about it
when you're sitting still
and not breathing
what is the only thing
in your body
that's palpably moving?
- Every second, your body
gives you a little sign
to prove that it's still there.
A pulse.
- It is billions of cells
beating for billions of times
in a lifetime,
never pausing to rest.
- Behind that beat is an
unbelievably vast system
whose one and only job
is to make sure every cell
in your body stays alive.
- The speed,
the strength,
the frequency,
the rhythm
it tells us so much.
- A heart that thumps
blood that flows through
thousands of miles
of arteries and veins
All so we can attempt
the crazy feats
that make humans
unique.
Human life depends on one
substance above all others
Oxygen.
We can go about three weeks
without food,
three days without water.
But without oxygen, we wouldn't
last three minutes.
But why?
Well, if you think about it,
each of us is just
a huge pile of cells,
somewhere around 37 trillion.
Blood cells, skin cells,
brain cells.
And every single one
of those cells
contains an engine
that runs on oxygen.
Think of it like a fire
that's always burning.
Oxygen is the wood or coal.
And to keep the fire stoked,
all we have to do is breathe in.
But getting a supply of oxygen
is the easy part.
Once it's inside the body,
all that fuel has to somehow
find its way
into those 37 trillion engines.
And that requires a system
that never rests.
- The cardiovascular
and circulatory systems
represent our major engine
in our bodies.
Now, this is to make sure
that all of our cells
have oxygen going in,
carbon dioxide leaving,
plenty of nutrients,
and essentially keeps us going.
- The body itself
is pretty small,
but the network of vessels
is enormous.
The vessels themselves
laid end-to-end would be
about 100,000 miles long,
which would encircle the globe
probably four times.
- This vast network of pumps,
valves, and tunnels
delivers oxygen to cells
in every corner of your body,
without you ever having
to think about it.
And what's more insane than that
is we can train this system
to work even more efficiently.
Especially when oxygen
is harder to come by.
- It would be difficult
to sum me up in one word
because I'm a bit
of a contradiction.
On one hand,
I'm a Southern Belle,
a debutante,
and afraid of heights.
But I'm also an extreme
alpinist, an ice climber,
and a rock climber.
♪
My name is Kitty Calhoun.
Ice climbing is who I am.
- High-altitude ice climbing
is the ultimate test
for the cardiovascular system.
Imagine you're scaling
a vertical slab of ice.
Your body is screaming
for oxygen to feed your muscles
to keep moving upwards.
It's true that any elite athlete
has to have an extremely
efficient cardiovascular system.
But climbing is different.
The air at high altitudes
is depleted of oxygen
and freezing temperatures tax
a system that's already
pushed to the brink.
Then add in one last factor
the heart-pounding knowledge
that at any moment,
you could slip.
Training to climb
means teaching the body
to adapt to an atmosphere that
can barely sustain human life.
And that training begins
in one place the heart.
- The heart is the first organ
to start functioning
and is typically the last one
to stop functioning
in the human lifetime.
- It's only the size of a fist,
but it beats more than
100,000 times a day.
The heart itself
is just two pumps
side-by-side.
On the left, the tricuspid
valve collects blood
from all over the body.
On the right, the pulmonary
valve takes that blood
and shoots it into the organ
that surrounds the heart.
The lungs.
There, the blood picks up oxygen
from tiny air-filled sacs
called alveoli
that expand like balloons
every time we inhale.
Then it goes back to the heart
so that all that oxygen-rich
blood can get pumped
to the rest of the body.
After a minute, it returns,
ready for another trip.
That cycle happens
every second of every day.
But throw a mountain
into the mix,
and things get interesting.
- Ice climbing is an activity
where you have to be
in good cardio shape.
When I'm not ice climbing,
I'm getting a good cardio work
in a short amount of time.
- In order for Kitty's heart
to perform well on the ice,
she needs to train it
to pump blood
as dynamically as possible.
- During exercise,
there are a lot of changes
that occur in our
cardiovascular system.
The heart obviously speeds up.
The more beats per minute,
the more blood flow
out of the heart per minute,
therefore the more oxygen
delivery to the tissues.
The efficiency of oxygen
transfer also increases
so that muscles can use
the oxygen more efficiently.
- Consistently exercising
the heart muscle
trains it to push more blood out
with each beat,
which means it doesn't
need to beat as often.
- The human heart is like
any other part
of our biology
Highly adaptive.
The more demands that are placed
on our heart,
the more the heart responds
in terms of its capacity.
Over time, you'll find
the resting heart rate
of a marathon runner
would be much lower
than that of a person
who is much more sedentary.
- Kitty has trained her heart
to withstand
the physical stresses of a climb
up a solid sheet of ice.
But in this sport, there's more
than just exhaustion at stake.
If you're hanging by an axe
from a cliff,
your heart is also being
challenged by something else
Fear.
- You know, there's risk in life,
right?
If you don't step out the door,
then you won't get hit by a car.
If you don't go ice climbing,
then you won't have
an accident ice climbing.
Risk is something that people
try to shut out in their lives,
and I think to live life fully,
to experience all that
life has to give,
that what you
have to do is minimize the risk
by getting experience
and making good decisions.
I do feel fear,
standing down at the bottom
and looking up at the climb.
I still have a healthy fear
of falling.
So one of the biggest tricks
that I use
to keep it together mentally
is breathing.
- When the system runs amuck
like in a panic attack,
the heart speeds up,
the heart pumps
less efficiently,
and is less able to meet the
metabolic demands of the body.
So an ice climber, for example,
would have to get control
of that response,
to slow down their heartbeat
and enable the heart
to fill properly
and pump blood more efficiently.
- Climbing is as much mental
as it is physical.
As Kitty's heart has transformed
over time
to be able to handle
the extreme conditions,
so has her brain.
- I start climbing,
and I'm focused on breathing
and making sure
that I work my feet up high
and then push up off my legs
like you're doing a squat.
And when you do pull
with your arms,
you really try to use your back
as much as you can.
Everything is a balance.
- It's all a highly
coordinated dance.
The mind keeps everything
in check
while muscles all over the body
reach their limit,
in constant need of more oxygen.
Kitty's well-trained heart
handles all these tasks easily.
The hard part
is getting the supply of oxygen
in the first place.
At high altitudes,
the atmosphere contains
a lot less oxygen.
That means there's less fuel
for red blood cells to extract
from the air entering the lungs.
If you've ever been
up that high,
you know how heavy
your breathing gets.
To try and compensate,
the heart goes into overdrive
to pump the blood
to starving muscles.
The low levels of oxygen
in the blood
can cause headaches and fatigue
as the body tries to function
with less fuel.
It can also affect the mind.
- Every organ depends
on the heart for its function.
The brain cannot function
without a moving heart.
- Without oxygen,
the brain gets foggy.
That's another reason
spending too much time
up in the clouds is dangerous.
Your judgment goes right out
the window.
But once again,
Kitty's body is different.
Her red blood cells
are better at adjusting
to the changing atmosphere,
which gives her the edge
she needs to get to the top.
- Yay! Oh, man.
It feels good.
When I'm at the top, I feel
a sense of relief for sure,
a sense of accomplishment.
Climbing is a form of therapy
for me
because I can just escape,
and I enjoy breathing hard,
I enjoy the strength
aspect of it,
I enjoy just moving
in a different way.
- This frozen ice face melts
when the seasons change
leading streams
into rivers
that snake through the landscape
and bring life.
Humans use these waterways
for transport and trade.
We construct cities around them.
They hold spiritual
meaning for us.
The constant flow of water
through rivers
has supported life
for millennia,
much like
the labyrinth intertwined
right underneath our skin.
- Because our blood
has to be conveyed
to every cell in the body,
the enormity of the blood
vessels in our body
is really mind-boggling.
- A lot of simpler life forms
don't need a circulatory system
because they're just one-cell
beings and they can rely
on the diffusion of molecules
within their one cell
to carry everything around
that they need to.
But we as humans are made up
of many cells,
and we needed to evolve a system
that would allow us
to very efficiently move oxygen
throughout our body.
- Over the course of a day,
blood will travel about
12,000 miles
through arteries and veins.
It's a system defined
by constant motion,
something that's also reflected
in our evolution as a species.
- Humans are absolutely
built to move.
I mean, if you look
at our ancestry
and the way we used
to move around,
our musculoskeletal system
is designed for us to be agile,
to go long periods
of time by moving,
and our hearts can perfectly
accommodate this
by making sure we get the right
amount of blood when we need it.
- But here's the tricky thing
not only does our circulatory
system allow us to move,
it only works properly
if we are moving.
For most of us, modern life
doesn't involve hunting
or crossing continents on foot.
And what we're finding out
is that if we stay still
for too long,
the whole system breaks down.
♪
♪
- Driving a bus, you're just
sitting there driving.
Day in, day out,
eight-hour shift.
Sometimes if you're really busy,
you may spend your
entire shift in the seat
because you're running behind
schedule or something.
You're sitting in traffic,
sometimes you might sit
in the seat
for three hours in traffic.
Again, you're not moving.
The advice I give people
is just you gotta be moving.
If you're going to sit down,
you're going to die.
I'm a prime example.
I'm Steve Dean,
and I drive a city bus.
♪
- I think one of the life lessons
that the cells
I've studied has taught me
is this concept of
if you don't use it,
you lose it.
Cells know what they're doing,
but they need to be challenged.
- One of the biggest obstacles
our circulation is up against
is something that we have
absolutely no control over
Gravity.
Humans are an upright species.
We walk on two legs.
So once our blood has traveled
down the arteries
and unloaded oxygen to all
the cells below the heart,
that same blood then has to move
straight upwards again
through our veins to get back
to where it started,
working against
Earth's gravitational pull
the entire time.
In most cases,
arteries rely on the heart
to pump blood,
but veins have to get their
power from another source
Muscles.
When you tense your leg muscles
they propel blood upwards.
But this ingenious adaptation
only works
if the muscles are active.
Otherwise, the pumps have
no energy to work with.
Think about sitting
for long periods of time.
Your leg muscles
aren't doing anything,
so they can't pump that blood
back to the heart
with any real force.
And that can lead
to major problems.
- A bus driver's heart,
cruising through traffic
with no issue,
is beating at a resting pace.
There is no sense of urgency
to increase a heart rate
and throw more blood
to the body.
- You're very sedentary
when you're driving the coach.
You sit there a lot.
And that's kind of one
of the downfalls
of driving the coach.
Back in 2010,
when I was working a lot,
just sitting there driving,
I was up to about 250,
260 pounds.
I felt sluggish.
- Our jobs have never been
more stationary.
They've moved from farms
to cities,
and now onto the Internet.
And we're constantly
told to exercise,
because the damage
can creep up on you, silently.
- On general inspection,
the heart of a sedentary person
might look normal.
However, if you probe more
deeply and look, for example,
at the arteries that supply
blood to the heart muscle,
it's more likely
that those arteries
would have more signs
of fatty deposits,
in part because of
the sedentary lifestyle.
- Not moving actually makes the
body worse at processing fat.
And probably everyone on earth
will tell you
that fat is the enemy.
And here's why
It's really just
a matter of space.
When we exercise, the arteries
surrounding the heart expand.
When we don't, they get thinner.
And blood needs room to move.
- A river can get blocked
by rocks, for example.
Similarly blood vessels
can develop blockages,
called atherosclerosis,
which are essentially
fatty deposits
that start at the wall
and start to protrude inward
and eventually
impede blood flow.
- These blockages
that build over time
can get us into real trouble.
- I felt this burning
in my chest.
I drove myself to
St. Peter's emergency room.
They did an EKG.
The doctor, she said,
"You've had a heart attack."
- The heart not only pumps blood
to the entire body,
but it also pumps blood
to itself.
It's self-sustaining.
No other organ does that.
The heart is so hard-working
that it needs a constant supply
of oxygen and nutrients
to remain functional.
When those arteries get
clogged up with fatty deposits,
that can result in
stoppage of blood flow
to the heart muscle.
And when that heart muscle dies,
that's called a heart attack.
- And unlike other muscles,
heart cells barely regenerate.
When they die, scar tissue
grows in their place,
and scar tissue can't pump.
- It was the very tip
of an artery that was blocked.
They said, "If you'd have
went to sleep,
you might not have woke up."
You know, it's an eye-opening
experience.
I just realized my time
on this earth now has a limit
and made me realize
that I need to do things
in my life different.
Gosh, we're just about here.
Well, I drive Dial-A-Lift now.
Good morning.
- Good morning.
- How are you today?
Dial-A-Lift
is a door-to-door service
for passengers with disabilities
or elderly,
something that prevents them
from riding the normal bus.
- Marianne is my first
rider today.
I take her to
the Sacred Heart Church.
- Is this an express?
- Yup, you're going
straight there today.
- Oh, good.
That works for me.
- I probably added another 3,000
to 4,000 steps a day
by driving Dial-A-Lift.
Good morning. It's Dial-A-Lift.
You're out of the seat,
and then you escort them out
to the van.
After you.
I'll have you go on board there.
You get them on the lift
on the van.
Okay, up we go.
And this step's a little higher.
Sometimes you have your arm out
for them to hold on
so they're steady.
It's things like that
that keep you healthy.
- Well, here we are.
- Yeah, get to go work out.
- Yay!
Hey, that's good for you.
Well, you have
a wonderful day today.
- Do you feel like a celebrity?
- I feel like Steve, as always.
- If you don't need
a strong heart,
your body won't give you one.
If you don't need
strong muscles,
why would your body make one?
So it's in a way like if
you don't use it, you lose it.
But if you use it, you get it.
It's been really exciting for me
to see this in practice,
you know, with people who are
experiencing the increase
in strength
that can come about so quickly
just by exercising
and giving ourselves
a little bit of a challenge.
To me, it's just
very life affirming
to think that at any age,
we always have the opportunity
to adapt and to do better.
♪
- The heart and vessels are
a mind-bendingly vast system.
But to operate, they need blood.
- I mean it's not
for nothing that we refer
to the metaphorical life blood
because the blood is literally
the life giving fluid.
What is blood?
Blood is essentially composed
of two substances.
One is the plasma,
which is basically salts,
water, and proteins.
And the other part is the cells.
- Red blood cells account
for more than 80%
of all of our cells,
and the other 20%
rely on them to survive.
1 million times every minute,
red blood cells absorb
the oxygen we need to live.
- It's an extraordinary piece
of our physiology.
Our heart pumps out five
to six liters of blood a minute,
and that blood is constantly
being circulated around the body
with new oxygen that's
breathed in every few seconds
with waste products
that are being cleaned out
on that same time scale.
It powers our every moment
of our day-to-day lives.
- Their never-ending job
has given red blood cells
a unique structure.
Unlike other cells,
they don't have a nucleus.
Instead, they're filled
with massive quantities
of a protein called hemoglobin.
It's made of iron,
which is why blood is red.
Hemoglobin grabs on to
the oxygen we breathe in,
then, at the right moment,
it lets go,
and oxygen molecules pass
into the surrounding cells.
What's crazy is that hemoglobin
is toxic to the human body.
If it escaped from even a tiny
fraction of our red blood cells,
it could kill us,
but as long as it stays
within the cells walls,
it can't harm us.
Red blood cells have a margin
error of exactly zero
and they do their job perfectly.
That is, as long as there's
enough blood in the body
to go around.
Because when we lose blood,
everything is then in jeopardy,
and just a few minutes can mean
the difference
between life and death.
♪
♪
The city of Accra is home
to 2 million people.
It's Ghana's capital,
its beating heart.
♪
150 miles away over
rugged terrain
is the tiny town of Asissinwa.
A place so remote that
the word "emergency"
takes on a whole new meaning.
- One plus two is three.
Hello!
- The bond between mother
and her child is profound,
and it starts in the womb.
The first thing they share
is blood.
- The fetus doesn't breathe.
It's floating in amniotic fluid,
and it only receives
oxygen through
the mother's blood supply
through the umbilical cord.
The mother's blood supply also
ferries waste out of the fetus,
which then gets cleared
by the mother's kidneys.
- It's an amazing exchange,
but it also means
that when something
goes wrong with one,
both are in danger.
-
It will not be safe.
- I'm Dr. Phillip
Agyeman-Prempeh.
I'm an obstetrician/gynecologist
at Saint Michael Hospital.
We make over 2,000 deliveries
every year in this facility.
- Akua Nyarko came
into our maternity emergency.
She was at 36 weeks plus
4 weeks in her pregnancy.
The abdomen felt very tense,
and we could not hear
the fetal heart rate,
both with the Doppler
and ultrasound.
- During the birthing process,
the mom and the baby
are going through
huge amounts of changes
that affect the physical aspects
of both infant and mother.
Immediately after
the baby is born,
the uterus will contract
to allow all of those
blood vessels that have been
opened during the pregnancy
so that the woman
actually does not hemorrhage,
meaning she does not continue
to bleed too heavily.
- For Akua, something
had gone very wrong.
- The uterus was not contracting.
She was bleeding profusely,
and we realized
that her blood was not clotting.
- We lose blood all the time
In small doses,
and our bodies can handle it.
But if there's a major bleed
that isn't stopping,
the body can't recover.
The response has to be
lightning fast,
and that means a transfusion.
- We needed blood to stabilize
her and save her life.
But we realized
we didn't have enough blood.
- And getting blood into
a remote area can take hours.
- In cases like this,
we would ask for an ambulance
to bring us the products,
but that takes time.
It was a dilemma
and a tough one.
So we called our
biomedical scientist,
and he made an order
for us to get blood.
- Meanwhile the body starts
its own rescue effort fast
by sending messages.
- We have little brains
all over our body,
and the heart
has a pretty big one.
It's been recently discovered
that there are about
40,000 neurons on the heart.
Nerves that go to the brain
as well as nerves
that come from the brain.
It's very responsive.
It has the capacity to
beat faster or slower
to be able to best serve
the needs of the body
at any given time.
- This group of neurons
reacts immediately
when blood leaves the body.
Pressure sensors on
the heart perceive the loss,
and they tell
the nervous system.
It sends out signals
that start a chain reaction
to keep cells alive.
It's a highly
synchronized effort
that depends on
instant communication.
Much like the technology that
Akua's doctors used to contact
the only people who could
send them blood
in time to save her life.
♪
- Emergency. Okay.
We'll get it to you right away.
♪
♪
♪
♪
- We had to perform
an emergency cesarean section
to stabilize her,
and then to prevent her
from losing more blood.
This is a patient
who was very pale.
If we didn't get the blood,
it was highly likely
that she would bleed to death.
- Very little in the body
can happen without blood.
If you empty the heart of blood
and stopped it, then the brain
and the kidneys
and the vital organs
wouldn't get oxygen and you'd
develop massive organ damage
within a period
of three minutes.
The blood is the conduit for all
these other organs to function.
- If cells go without oxygen
for too long,
the body goes
into irreversible shock.
But the heart-brain knows
when it's in trouble,
and its response is smart.
The heart starts to beat faster.
Breathing becomes
shallow and quick.
There's also
a chemical reaction.
Hormones flood blood vessels
in the skin
causing them to constrict.
Blood moves inward
to keep vital organs alive.
That's why people turn pale
when they lose blood.
Skin is not so important,
but the brain is vital.
It's the body's clever way
of redistributing resources.
If the blood loss
is really extreme,
it might be impossible
to reverse the damage.
Tragically
for Akua's unborn child,
it was already too late.
But Akua was still holding on.
♪
- Within 20 minutes,
Zipline brought us the blood.
We started transfusing her.
And then she was able
to pull through.
- With some support,
the body begins to stabilize.
- Our bodies evolved
the cardiovascular system
to ramp up very, very quickly
and ramp down
because we can't maintain
a degree of stress
for long periods of time
without damaging the system.
- The connection between
the brain and the heart
is complex and not one-sided.
The structures in the brain
regulate the heart
through nerve impulses
and hormones,
and it's in the brain
that emotions
and thoughts are processed,
even though sometimes
it doesn't seem that way.
- Anyone who's ever experienced
a sense of panic
knows that we feel it
immediately in our heart.
So why would it be a surprise
that the heart
would be really smart
at being connected
to our emotional state
when that is our internalized
experience of the outside world.
- So if we feel things
in our heart,
does that mean
it has a mind of its own?
- The idea that the heart
might be telling the brain
how to think or how to feel
is an open question
for me personally
and one that I think is very
hotly debated among scientists.
- If there are neurons
on the heart,
then maybe its power
over our emotions
isn't just poetic,
but also biological.
♪
♪
♪
♪
- My name is Bertha Martinez.
I am a volunteer at the
Lincoln Heights Senior Center.
After we retired,
my husband and I started
helping at the center.
We love to dance, and we have
been attending there
for the past 18 years.
- Hombres!
- We always say that
it's our second family.
- Buenos dias.
- Humans are social animals.
-
- That's something that we share
with primates in general.
We live in groups,
and a lot of the way
that we navigate
the world around us,
has to do with
social relationships.
This is something that
is reflected in our biology.
- The brain and the heart
are connected
by the most powerful
neural network in the body,
the vagus nerve.
It passes millions of messages
back and forth every day.
The vast majority
come not from the brain
but from the heart.
And this network is responsible
for communicating emotions
Positive social interactions
light up the vagus nerve
and the heart.
In other words,
our relationships
are constantly shaping
our internal worlds.
- This is my husband Ricardo.
This picture was taken
on our 25th wedding anniversary.
I lost my husband last year.
This chair, my husband used it
all the time to watch TV.
Someone told me why
don't I take everything down
so that way I cannot
feel so bad?
But to me,
it's just the opposite.
- We know that people
who experience intense
emotional disturbance like grief
after the death of a loved one
or the breakup of
a romantic relationship
can develop severe effects
on their hearts.
The heart in these people
tends to acutely weaken
and change shape
into the shape of a takotsubo,
which is a Japanese pot with
a narrow neck and a wide base.
It's been variably called
the broken heart syndrome
or takotsubo cardiomyopathy,
and we know
that emotional stress
can accelerate the development
of heart disease
and increase the risk
of cardiac mortality.
- The exact cause is unknown.
Our best guess is that
a super dose of adrenaline
floods the heart,
shocking cardiac cells
and weakening them.
Hormones like adrenaline
are one of the main ways
the brain communicates
with the heart,
and the risk
of developing takotsubo
might have something to do with
the strength
of neural connections and how
they respond to stress.
The same regions in the brain
that regulate your heartbeat
have been linked to emotional
conditions like depression.
But unlike a heart attack,
the cardiac cells
are just shocked, not lost.
- Fortunately for us, a lot of
the injury to the heart
is potentially reversible.
The heart does tend
to self-correct,
so when our emotional states
return to normal,
the heart itself
can also return to normal.
- Okay.
- I think it's very important to
come out, even when you're sad.
- There is a kind of
takotsubo cardiomyopathy,
or broken heart syndrome,
that occurs after
happy events, too, but the heart
shape changes differently.
- In the same way that adrenaline
can damage cardiac cells,
there are other hormones that
can have the opposite effect.
And there's one molecule
that's most associated
with the complex
social behavior of humans
oxytocin, often called
the love hormone.
Think about the feeling you get
when you hug a friend or dance
with a flirty stranger.
That rush comes
as oxytocin spikes
and makes a beeline
for the heart.
Just like fear can make
your heart pound,
the oxytocin released by touch
can put your heart at rest.
Receptors on cardiac cells
detect its presence
and your heart rate slows.
It also helps reduce
inflammation in blood vessels.
So it can actually have
a therapeutic effect
on stressed arteries and veins.
Even short interactions
can stimulate a rush.
So for the heart,
love looks like thousands
of brief encounters
over a lifetime.
Which is really well-suited
to a function like a dance.
♪
- I've been working
here 12 years,
and there hasn't been
one Thursday
that that place hasn't filled up
with at least 150 people.
Latins like to dance.
- Dance is a good exercise.
If you move, it helps a lot,
especially at my age.
- I think we know that a lack
of love can be very damaging.
The corollary to that is can
the presence of love
be beneficial for the heart?
We know that people in
longstanding relationships
tend to live longer.
- Every little movement ♪
Every little thing you do
- The brain-heart connection
is definitely present
and is something
that we as a field
need to investigate more deeply
to really understand its roots.
- Said a black magic spell
you put me under ♪
- After my husband passed away,
it was hard,
but my second family
from the senior center,
it gave me so much strength.
It been easier
as time passes by.
- Is beyond improvement
- Now I'm doing what I love,
and I'll just keep doing it,
whenever I can.
- Every little movement
- How does the body understand
the passage of time?
We as humans have a rhythm
and a cadence to our life
that I believe is in many ways,
tied to the heartbeat.
- The same pulse inside
every one of us,
setting the pace for our lives.
♪
With a tiny thump that we often
forget about that's, in a way,
much bigger than we are.
All life has a rhythm.
You just have to pause
and take a step back to feel it.
- The physical world is made up
of pulses of energy.
So it's fun to play with that
shift of perspective,
to think about our bodies,
more like an ecosystem
composed of trillions of cells
conspiring every moment
to create our thoughts
and keep our heart beating
and keep our breathing going.
♪
- The human heart
is billions of cells
beating billions of times,
never pausing.
- If we didn't get the blood,
she would bleed to death.
- I lost my husband last year.
- Intense emotional disturbance
can accelerate
cardiac mortality.
- Cells need to be challenged.
If you don't use it,
you lose it.
- I felt this burning
in my chest.
He said, "If you'd
have went to sleep,
you might not have woke up.
♪
♪
- To order "Human:
The World Within" on DVD,
visit shopPBS.org
or call 1-800-PLAY-PBS.
♪
- Think about it
when you're sitting still
and not breathing
what is the only thing
in your body
that's palpably moving?
- Every second, your body
gives you a little sign
to prove that it's still there.
A pulse.
- It is billions of cells
beating for billions of times
in a lifetime,
never pausing to rest.
- Behind that beat is an
unbelievably vast system
whose one and only job
is to make sure every cell
in your body stays alive.
- The speed,
the strength,
the frequency,
the rhythm
it tells us so much.
- A heart that thumps
blood that flows through
thousands of miles
of arteries and veins
All so we can attempt
the crazy feats
that make humans
unique.
Human life depends on one
substance above all others
Oxygen.
We can go about three weeks
without food,
three days without water.
But without oxygen, we wouldn't
last three minutes.
But why?
Well, if you think about it,
each of us is just
a huge pile of cells,
somewhere around 37 trillion.
Blood cells, skin cells,
brain cells.
And every single one
of those cells
contains an engine
that runs on oxygen.
Think of it like a fire
that's always burning.
Oxygen is the wood or coal.
And to keep the fire stoked,
all we have to do is breathe in.
But getting a supply of oxygen
is the easy part.
Once it's inside the body,
all that fuel has to somehow
find its way
into those 37 trillion engines.
And that requires a system
that never rests.
- The cardiovascular
and circulatory systems
represent our major engine
in our bodies.
Now, this is to make sure
that all of our cells
have oxygen going in,
carbon dioxide leaving,
plenty of nutrients,
and essentially keeps us going.
- The body itself
is pretty small,
but the network of vessels
is enormous.
The vessels themselves
laid end-to-end would be
about 100,000 miles long,
which would encircle the globe
probably four times.
- This vast network of pumps,
valves, and tunnels
delivers oxygen to cells
in every corner of your body,
without you ever having
to think about it.
And what's more insane than that
is we can train this system
to work even more efficiently.
Especially when oxygen
is harder to come by.
- It would be difficult
to sum me up in one word
because I'm a bit
of a contradiction.
On one hand,
I'm a Southern Belle,
a debutante,
and afraid of heights.
But I'm also an extreme
alpinist, an ice climber,
and a rock climber.
♪
My name is Kitty Calhoun.
Ice climbing is who I am.
- High-altitude ice climbing
is the ultimate test
for the cardiovascular system.
Imagine you're scaling
a vertical slab of ice.
Your body is screaming
for oxygen to feed your muscles
to keep moving upwards.
It's true that any elite athlete
has to have an extremely
efficient cardiovascular system.
But climbing is different.
The air at high altitudes
is depleted of oxygen
and freezing temperatures tax
a system that's already
pushed to the brink.
Then add in one last factor
the heart-pounding knowledge
that at any moment,
you could slip.
Training to climb
means teaching the body
to adapt to an atmosphere that
can barely sustain human life.
And that training begins
in one place the heart.
- The heart is the first organ
to start functioning
and is typically the last one
to stop functioning
in the human lifetime.
- It's only the size of a fist,
but it beats more than
100,000 times a day.
The heart itself
is just two pumps
side-by-side.
On the left, the tricuspid
valve collects blood
from all over the body.
On the right, the pulmonary
valve takes that blood
and shoots it into the organ
that surrounds the heart.
The lungs.
There, the blood picks up oxygen
from tiny air-filled sacs
called alveoli
that expand like balloons
every time we inhale.
Then it goes back to the heart
so that all that oxygen-rich
blood can get pumped
to the rest of the body.
After a minute, it returns,
ready for another trip.
That cycle happens
every second of every day.
But throw a mountain
into the mix,
and things get interesting.
- Ice climbing is an activity
where you have to be
in good cardio shape.
When I'm not ice climbing,
I'm getting a good cardio work
in a short amount of time.
- In order for Kitty's heart
to perform well on the ice,
she needs to train it
to pump blood
as dynamically as possible.
- During exercise,
there are a lot of changes
that occur in our
cardiovascular system.
The heart obviously speeds up.
The more beats per minute,
the more blood flow
out of the heart per minute,
therefore the more oxygen
delivery to the tissues.
The efficiency of oxygen
transfer also increases
so that muscles can use
the oxygen more efficiently.
- Consistently exercising
the heart muscle
trains it to push more blood out
with each beat,
which means it doesn't
need to beat as often.
- The human heart is like
any other part
of our biology
Highly adaptive.
The more demands that are placed
on our heart,
the more the heart responds
in terms of its capacity.
Over time, you'll find
the resting heart rate
of a marathon runner
would be much lower
than that of a person
who is much more sedentary.
- Kitty has trained her heart
to withstand
the physical stresses of a climb
up a solid sheet of ice.
But in this sport, there's more
than just exhaustion at stake.
If you're hanging by an axe
from a cliff,
your heart is also being
challenged by something else
Fear.
- You know, there's risk in life,
right?
If you don't step out the door,
then you won't get hit by a car.
If you don't go ice climbing,
then you won't have
an accident ice climbing.
Risk is something that people
try to shut out in their lives,
and I think to live life fully,
to experience all that
life has to give,
that what you
have to do is minimize the risk
by getting experience
and making good decisions.
I do feel fear,
standing down at the bottom
and looking up at the climb.
I still have a healthy fear
of falling.
So one of the biggest tricks
that I use
to keep it together mentally
is breathing.
- When the system runs amuck
like in a panic attack,
the heart speeds up,
the heart pumps
less efficiently,
and is less able to meet the
metabolic demands of the body.
So an ice climber, for example,
would have to get control
of that response,
to slow down their heartbeat
and enable the heart
to fill properly
and pump blood more efficiently.
- Climbing is as much mental
as it is physical.
As Kitty's heart has transformed
over time
to be able to handle
the extreme conditions,
so has her brain.
- I start climbing,
and I'm focused on breathing
and making sure
that I work my feet up high
and then push up off my legs
like you're doing a squat.
And when you do pull
with your arms,
you really try to use your back
as much as you can.
Everything is a balance.
- It's all a highly
coordinated dance.
The mind keeps everything
in check
while muscles all over the body
reach their limit,
in constant need of more oxygen.
Kitty's well-trained heart
handles all these tasks easily.
The hard part
is getting the supply of oxygen
in the first place.
At high altitudes,
the atmosphere contains
a lot less oxygen.
That means there's less fuel
for red blood cells to extract
from the air entering the lungs.
If you've ever been
up that high,
you know how heavy
your breathing gets.
To try and compensate,
the heart goes into overdrive
to pump the blood
to starving muscles.
The low levels of oxygen
in the blood
can cause headaches and fatigue
as the body tries to function
with less fuel.
It can also affect the mind.
- Every organ depends
on the heart for its function.
The brain cannot function
without a moving heart.
- Without oxygen,
the brain gets foggy.
That's another reason
spending too much time
up in the clouds is dangerous.
Your judgment goes right out
the window.
But once again,
Kitty's body is different.
Her red blood cells
are better at adjusting
to the changing atmosphere,
which gives her the edge
she needs to get to the top.
- Yay! Oh, man.
It feels good.
When I'm at the top, I feel
a sense of relief for sure,
a sense of accomplishment.
Climbing is a form of therapy
for me
because I can just escape,
and I enjoy breathing hard,
I enjoy the strength
aspect of it,
I enjoy just moving
in a different way.
- This frozen ice face melts
when the seasons change
leading streams
into rivers
that snake through the landscape
and bring life.
Humans use these waterways
for transport and trade.
We construct cities around them.
They hold spiritual
meaning for us.
The constant flow of water
through rivers
has supported life
for millennia,
much like
the labyrinth intertwined
right underneath our skin.
- Because our blood
has to be conveyed
to every cell in the body,
the enormity of the blood
vessels in our body
is really mind-boggling.
- A lot of simpler life forms
don't need a circulatory system
because they're just one-cell
beings and they can rely
on the diffusion of molecules
within their one cell
to carry everything around
that they need to.
But we as humans are made up
of many cells,
and we needed to evolve a system
that would allow us
to very efficiently move oxygen
throughout our body.
- Over the course of a day,
blood will travel about
12,000 miles
through arteries and veins.
It's a system defined
by constant motion,
something that's also reflected
in our evolution as a species.
- Humans are absolutely
built to move.
I mean, if you look
at our ancestry
and the way we used
to move around,
our musculoskeletal system
is designed for us to be agile,
to go long periods
of time by moving,
and our hearts can perfectly
accommodate this
by making sure we get the right
amount of blood when we need it.
- But here's the tricky thing
not only does our circulatory
system allow us to move,
it only works properly
if we are moving.
For most of us, modern life
doesn't involve hunting
or crossing continents on foot.
And what we're finding out
is that if we stay still
for too long,
the whole system breaks down.
♪
♪
- Driving a bus, you're just
sitting there driving.
Day in, day out,
eight-hour shift.
Sometimes if you're really busy,
you may spend your
entire shift in the seat
because you're running behind
schedule or something.
You're sitting in traffic,
sometimes you might sit
in the seat
for three hours in traffic.
Again, you're not moving.
The advice I give people
is just you gotta be moving.
If you're going to sit down,
you're going to die.
I'm a prime example.
I'm Steve Dean,
and I drive a city bus.
♪
- I think one of the life lessons
that the cells
I've studied has taught me
is this concept of
if you don't use it,
you lose it.
Cells know what they're doing,
but they need to be challenged.
- One of the biggest obstacles
our circulation is up against
is something that we have
absolutely no control over
Gravity.
Humans are an upright species.
We walk on two legs.
So once our blood has traveled
down the arteries
and unloaded oxygen to all
the cells below the heart,
that same blood then has to move
straight upwards again
through our veins to get back
to where it started,
working against
Earth's gravitational pull
the entire time.
In most cases,
arteries rely on the heart
to pump blood,
but veins have to get their
power from another source
Muscles.
When you tense your leg muscles
they propel blood upwards.
But this ingenious adaptation
only works
if the muscles are active.
Otherwise, the pumps have
no energy to work with.
Think about sitting
for long periods of time.
Your leg muscles
aren't doing anything,
so they can't pump that blood
back to the heart
with any real force.
And that can lead
to major problems.
- A bus driver's heart,
cruising through traffic
with no issue,
is beating at a resting pace.
There is no sense of urgency
to increase a heart rate
and throw more blood
to the body.
- You're very sedentary
when you're driving the coach.
You sit there a lot.
And that's kind of one
of the downfalls
of driving the coach.
Back in 2010,
when I was working a lot,
just sitting there driving,
I was up to about 250,
260 pounds.
I felt sluggish.
- Our jobs have never been
more stationary.
They've moved from farms
to cities,
and now onto the Internet.
And we're constantly
told to exercise,
because the damage
can creep up on you, silently.
- On general inspection,
the heart of a sedentary person
might look normal.
However, if you probe more
deeply and look, for example,
at the arteries that supply
blood to the heart muscle,
it's more likely
that those arteries
would have more signs
of fatty deposits,
in part because of
the sedentary lifestyle.
- Not moving actually makes the
body worse at processing fat.
And probably everyone on earth
will tell you
that fat is the enemy.
And here's why
It's really just
a matter of space.
When we exercise, the arteries
surrounding the heart expand.
When we don't, they get thinner.
And blood needs room to move.
- A river can get blocked
by rocks, for example.
Similarly blood vessels
can develop blockages,
called atherosclerosis,
which are essentially
fatty deposits
that start at the wall
and start to protrude inward
and eventually
impede blood flow.
- These blockages
that build over time
can get us into real trouble.
- I felt this burning
in my chest.
I drove myself to
St. Peter's emergency room.
They did an EKG.
The doctor, she said,
"You've had a heart attack."
- The heart not only pumps blood
to the entire body,
but it also pumps blood
to itself.
It's self-sustaining.
No other organ does that.
The heart is so hard-working
that it needs a constant supply
of oxygen and nutrients
to remain functional.
When those arteries get
clogged up with fatty deposits,
that can result in
stoppage of blood flow
to the heart muscle.
And when that heart muscle dies,
that's called a heart attack.
- And unlike other muscles,
heart cells barely regenerate.
When they die, scar tissue
grows in their place,
and scar tissue can't pump.
- It was the very tip
of an artery that was blocked.
They said, "If you'd have
went to sleep,
you might not have woke up."
You know, it's an eye-opening
experience.
I just realized my time
on this earth now has a limit
and made me realize
that I need to do things
in my life different.
Gosh, we're just about here.
Well, I drive Dial-A-Lift now.
Good morning.
- Good morning.
- How are you today?
Dial-A-Lift
is a door-to-door service
for passengers with disabilities
or elderly,
something that prevents them
from riding the normal bus.
- Marianne is my first
rider today.
I take her to
the Sacred Heart Church.
- Is this an express?
- Yup, you're going
straight there today.
- Oh, good.
That works for me.
- I probably added another 3,000
to 4,000 steps a day
by driving Dial-A-Lift.
Good morning. It's Dial-A-Lift.
You're out of the seat,
and then you escort them out
to the van.
After you.
I'll have you go on board there.
You get them on the lift
on the van.
Okay, up we go.
And this step's a little higher.
Sometimes you have your arm out
for them to hold on
so they're steady.
It's things like that
that keep you healthy.
- Well, here we are.
- Yeah, get to go work out.
- Yay!
Hey, that's good for you.
Well, you have
a wonderful day today.
- Do you feel like a celebrity?
- I feel like Steve, as always.
- If you don't need
a strong heart,
your body won't give you one.
If you don't need
strong muscles,
why would your body make one?
So it's in a way like if
you don't use it, you lose it.
But if you use it, you get it.
It's been really exciting for me
to see this in practice,
you know, with people who are
experiencing the increase
in strength
that can come about so quickly
just by exercising
and giving ourselves
a little bit of a challenge.
To me, it's just
very life affirming
to think that at any age,
we always have the opportunity
to adapt and to do better.
♪
- The heart and vessels are
a mind-bendingly vast system.
But to operate, they need blood.
- I mean it's not
for nothing that we refer
to the metaphorical life blood
because the blood is literally
the life giving fluid.
What is blood?
Blood is essentially composed
of two substances.
One is the plasma,
which is basically salts,
water, and proteins.
And the other part is the cells.
- Red blood cells account
for more than 80%
of all of our cells,
and the other 20%
rely on them to survive.
1 million times every minute,
red blood cells absorb
the oxygen we need to live.
- It's an extraordinary piece
of our physiology.
Our heart pumps out five
to six liters of blood a minute,
and that blood is constantly
being circulated around the body
with new oxygen that's
breathed in every few seconds
with waste products
that are being cleaned out
on that same time scale.
It powers our every moment
of our day-to-day lives.
- Their never-ending job
has given red blood cells
a unique structure.
Unlike other cells,
they don't have a nucleus.
Instead, they're filled
with massive quantities
of a protein called hemoglobin.
It's made of iron,
which is why blood is red.
Hemoglobin grabs on to
the oxygen we breathe in,
then, at the right moment,
it lets go,
and oxygen molecules pass
into the surrounding cells.
What's crazy is that hemoglobin
is toxic to the human body.
If it escaped from even a tiny
fraction of our red blood cells,
it could kill us,
but as long as it stays
within the cells walls,
it can't harm us.
Red blood cells have a margin
error of exactly zero
and they do their job perfectly.
That is, as long as there's
enough blood in the body
to go around.
Because when we lose blood,
everything is then in jeopardy,
and just a few minutes can mean
the difference
between life and death.
♪
♪
The city of Accra is home
to 2 million people.
It's Ghana's capital,
its beating heart.
♪
150 miles away over
rugged terrain
is the tiny town of Asissinwa.
A place so remote that
the word "emergency"
takes on a whole new meaning.
- One plus two is three.
Hello!
- The bond between mother
and her child is profound,
and it starts in the womb.
The first thing they share
is blood.
- The fetus doesn't breathe.
It's floating in amniotic fluid,
and it only receives
oxygen through
the mother's blood supply
through the umbilical cord.
The mother's blood supply also
ferries waste out of the fetus,
which then gets cleared
by the mother's kidneys.
- It's an amazing exchange,
but it also means
that when something
goes wrong with one,
both are in danger.
-
It will not be safe.
- I'm Dr. Phillip
Agyeman-Prempeh.
I'm an obstetrician/gynecologist
at Saint Michael Hospital.
We make over 2,000 deliveries
every year in this facility.
- Akua Nyarko came
into our maternity emergency.
She was at 36 weeks plus
4 weeks in her pregnancy.
The abdomen felt very tense,
and we could not hear
the fetal heart rate,
both with the Doppler
and ultrasound.
- During the birthing process,
the mom and the baby
are going through
huge amounts of changes
that affect the physical aspects
of both infant and mother.
Immediately after
the baby is born,
the uterus will contract
to allow all of those
blood vessels that have been
opened during the pregnancy
so that the woman
actually does not hemorrhage,
meaning she does not continue
to bleed too heavily.
- For Akua, something
had gone very wrong.
- The uterus was not contracting.
She was bleeding profusely,
and we realized
that her blood was not clotting.
- We lose blood all the time
In small doses,
and our bodies can handle it.
But if there's a major bleed
that isn't stopping,
the body can't recover.
The response has to be
lightning fast,
and that means a transfusion.
- We needed blood to stabilize
her and save her life.
But we realized
we didn't have enough blood.
- And getting blood into
a remote area can take hours.
- In cases like this,
we would ask for an ambulance
to bring us the products,
but that takes time.
It was a dilemma
and a tough one.
So we called our
biomedical scientist,
and he made an order
for us to get blood.
- Meanwhile the body starts
its own rescue effort fast
by sending messages.
- We have little brains
all over our body,
and the heart
has a pretty big one.
It's been recently discovered
that there are about
40,000 neurons on the heart.
Nerves that go to the brain
as well as nerves
that come from the brain.
It's very responsive.
It has the capacity to
beat faster or slower
to be able to best serve
the needs of the body
at any given time.
- This group of neurons
reacts immediately
when blood leaves the body.
Pressure sensors on
the heart perceive the loss,
and they tell
the nervous system.
It sends out signals
that start a chain reaction
to keep cells alive.
It's a highly
synchronized effort
that depends on
instant communication.
Much like the technology that
Akua's doctors used to contact
the only people who could
send them blood
in time to save her life.
♪
- Emergency. Okay.
We'll get it to you right away.
♪
♪
♪
♪
- We had to perform
an emergency cesarean section
to stabilize her,
and then to prevent her
from losing more blood.
This is a patient
who was very pale.
If we didn't get the blood,
it was highly likely
that she would bleed to death.
- Very little in the body
can happen without blood.
If you empty the heart of blood
and stopped it, then the brain
and the kidneys
and the vital organs
wouldn't get oxygen and you'd
develop massive organ damage
within a period
of three minutes.
The blood is the conduit for all
these other organs to function.
- If cells go without oxygen
for too long,
the body goes
into irreversible shock.
But the heart-brain knows
when it's in trouble,
and its response is smart.
The heart starts to beat faster.
Breathing becomes
shallow and quick.
There's also
a chemical reaction.
Hormones flood blood vessels
in the skin
causing them to constrict.
Blood moves inward
to keep vital organs alive.
That's why people turn pale
when they lose blood.
Skin is not so important,
but the brain is vital.
It's the body's clever way
of redistributing resources.
If the blood loss
is really extreme,
it might be impossible
to reverse the damage.
Tragically
for Akua's unborn child,
it was already too late.
But Akua was still holding on.
♪
- Within 20 minutes,
Zipline brought us the blood.
We started transfusing her.
And then she was able
to pull through.
- With some support,
the body begins to stabilize.
- Our bodies evolved
the cardiovascular system
to ramp up very, very quickly
and ramp down
because we can't maintain
a degree of stress
for long periods of time
without damaging the system.
- The connection between
the brain and the heart
is complex and not one-sided.
The structures in the brain
regulate the heart
through nerve impulses
and hormones,
and it's in the brain
that emotions
and thoughts are processed,
even though sometimes
it doesn't seem that way.
- Anyone who's ever experienced
a sense of panic
knows that we feel it
immediately in our heart.
So why would it be a surprise
that the heart
would be really smart
at being connected
to our emotional state
when that is our internalized
experience of the outside world.
- So if we feel things
in our heart,
does that mean
it has a mind of its own?
- The idea that the heart
might be telling the brain
how to think or how to feel
is an open question
for me personally
and one that I think is very
hotly debated among scientists.
- If there are neurons
on the heart,
then maybe its power
over our emotions
isn't just poetic,
but also biological.
♪
♪
♪
♪
- My name is Bertha Martinez.
I am a volunteer at the
Lincoln Heights Senior Center.
After we retired,
my husband and I started
helping at the center.
We love to dance, and we have
been attending there
for the past 18 years.
- Hombres!
- We always say that
it's our second family.
- Buenos dias.
- Humans are social animals.
-
- That's something that we share
with primates in general.
We live in groups,
and a lot of the way
that we navigate
the world around us,
has to do with
social relationships.
This is something that
is reflected in our biology.
- The brain and the heart
are connected
by the most powerful
neural network in the body,
the vagus nerve.
It passes millions of messages
back and forth every day.
The vast majority
come not from the brain
but from the heart.
And this network is responsible
for communicating emotions
Positive social interactions
light up the vagus nerve
and the heart.
In other words,
our relationships
are constantly shaping
our internal worlds.
- This is my husband Ricardo.
This picture was taken
on our 25th wedding anniversary.
I lost my husband last year.
This chair, my husband used it
all the time to watch TV.
Someone told me why
don't I take everything down
so that way I cannot
feel so bad?
But to me,
it's just the opposite.
- We know that people
who experience intense
emotional disturbance like grief
after the death of a loved one
or the breakup of
a romantic relationship
can develop severe effects
on their hearts.
The heart in these people
tends to acutely weaken
and change shape
into the shape of a takotsubo,
which is a Japanese pot with
a narrow neck and a wide base.
It's been variably called
the broken heart syndrome
or takotsubo cardiomyopathy,
and we know
that emotional stress
can accelerate the development
of heart disease
and increase the risk
of cardiac mortality.
- The exact cause is unknown.
Our best guess is that
a super dose of adrenaline
floods the heart,
shocking cardiac cells
and weakening them.
Hormones like adrenaline
are one of the main ways
the brain communicates
with the heart,
and the risk
of developing takotsubo
might have something to do with
the strength
of neural connections and how
they respond to stress.
The same regions in the brain
that regulate your heartbeat
have been linked to emotional
conditions like depression.
But unlike a heart attack,
the cardiac cells
are just shocked, not lost.
- Fortunately for us, a lot of
the injury to the heart
is potentially reversible.
The heart does tend
to self-correct,
so when our emotional states
return to normal,
the heart itself
can also return to normal.
- Okay.
- I think it's very important to
come out, even when you're sad.
- There is a kind of
takotsubo cardiomyopathy,
or broken heart syndrome,
that occurs after
happy events, too, but the heart
shape changes differently.
- In the same way that adrenaline
can damage cardiac cells,
there are other hormones that
can have the opposite effect.
And there's one molecule
that's most associated
with the complex
social behavior of humans
oxytocin, often called
the love hormone.
Think about the feeling you get
when you hug a friend or dance
with a flirty stranger.
That rush comes
as oxytocin spikes
and makes a beeline
for the heart.
Just like fear can make
your heart pound,
the oxytocin released by touch
can put your heart at rest.
Receptors on cardiac cells
detect its presence
and your heart rate slows.
It also helps reduce
inflammation in blood vessels.
So it can actually have
a therapeutic effect
on stressed arteries and veins.
Even short interactions
can stimulate a rush.
So for the heart,
love looks like thousands
of brief encounters
over a lifetime.
Which is really well-suited
to a function like a dance.
♪
- I've been working
here 12 years,
and there hasn't been
one Thursday
that that place hasn't filled up
with at least 150 people.
Latins like to dance.
- Dance is a good exercise.
If you move, it helps a lot,
especially at my age.
- I think we know that a lack
of love can be very damaging.
The corollary to that is can
the presence of love
be beneficial for the heart?
We know that people in
longstanding relationships
tend to live longer.
- Every little movement ♪
Every little thing you do
- The brain-heart connection
is definitely present
and is something
that we as a field
need to investigate more deeply
to really understand its roots.
- Said a black magic spell
you put me under ♪
- After my husband passed away,
it was hard,
but my second family
from the senior center,
it gave me so much strength.
It been easier
as time passes by.
- Is beyond improvement
- Now I'm doing what I love,
and I'll just keep doing it,
whenever I can.
- Every little movement
- How does the body understand
the passage of time?
We as humans have a rhythm
and a cadence to our life
that I believe is in many ways,
tied to the heartbeat.
- The same pulse inside
every one of us,
setting the pace for our lives.
♪
With a tiny thump that we often
forget about that's, in a way,
much bigger than we are.
All life has a rhythm.
You just have to pause
and take a step back to feel it.
- The physical world is made up
of pulses of energy.
So it's fun to play with that
shift of perspective,
to think about our bodies,
more like an ecosystem
composed of trillions of cells
conspiring every moment
to create our thoughts
and keep our heart beating
and keep our breathing going.
♪
- The human heart
is billions of cells
beating billions of times,
never pausing.
- If we didn't get the blood,
she would bleed to death.
- I lost my husband last year.
- Intense emotional disturbance
can accelerate
cardiac mortality.
- Cells need to be challenged.
If you don't use it,
you lose it.
- I felt this burning
in my chest.
He said, "If you'd
have went to sleep,
you might not have woke up.
♪
♪
- To order "Human:
The World Within" on DVD,
visit shopPBS.org
or call 1-800-PLAY-PBS.
♪