This programme contains scenes some viewers may find upsetting.
This diver is able to swim in the depths of the ocean without breathing.
This is "The Iceman".
He can thrive where his flesh should freeze...
..while Gerald is about to make his final journey,
from life to death.
Their stories are part of your story,
the story of what makes YOU human.
Inside you is a wonderful, hidden universe...
..covered with skin, which protects you against the harsh world outside...
..controlled by a brain, which is the most complex on the planet.
Even how you make another human involves unrivalled ingenuity.
This is a fantastic voyage
through the most extraordinary survival machine on Earth...
..you.
Just existing for one minute feels like the simplest thing in the world.
Yet what goes on inside you every 60 seconds is wonderfully complicated.
If you stop and think about it,
it is truly remarkable, the way that your body,
every minute of every hour of every day,
is doing a million different things to keep YOU alive. And you're not even aware of it.
Your heart will beat 70 times, driving 5 litres of blood
around the 96,000 kilometres of your circulation.
Deep inside your bone marrow,
each minute, 150 million red blood cells will be born.
And while you're sitting there, the 250 square metres of your gut
are busy digesting the meal you've just eaten.
What's really impressive is not just that our bodies
do all these things all the time,
but they respond instantly to any change in our environment.
No matter where you go...
..or what you do...
..every minute of your life depends
on your body performing countless small miracles.
And this film will show you how you do it.
Your survival depends on your body working hard
to keep everything inside you balanced and stable, just so.
But to begin with, you need a lot of help.
For the first nine months of your life, you are kept alive and warm
by a life-support machine, which also breathes for you and eats for you,
a machine also known as Mum.
Then, suddenly, you're on your own.
This is Tyriece.
He's just been through a very traumatic minute,
the first minute after his birth.
For nine months, you were enveloped
in the warm, comfortable, watery world of your mother's womb.
Your every need was taken care of.
As you lay immersed in a bath of amniotic fluid,
your temperature was a comfortable 37 degrees.
You didn't have to eat for yourself,
you didn't even have to breathe for yourself.
Your mother's blood supplied you with oxygen,
so your own lungs weren't needed.
And because you didn't need your lungs,
your body didn't bother sending blood to them,
but shunted it through a hole in your heart instead.
Then, suddenly, the tranquillity of the womb was shattered.
SHE GROANS
Well done.
He's coming. There he is.
There he is, we can see his face.
Nice and relaxed. Nice and relaxed.
I can see my grandson!
For April, the hard work of labour is almost over.
He's turning to face this way.
Can you feel him? Yeah.
There he is.
Say hello.
But for baby Tyriece, the struggle for survival is just beginning.
As he emerges into the world,
his body must take over from his mother's.
The shock of cold air and bright lights triggers your first breath.
But before Tyriece can take in oxygen,
his heart has to connect with his lungs.
And to do this, the hole in his heart has to close.
As you draw your first breath, the airways of your lungs open,
and the drop in pressure causes blood to rush into them to pick up oxygen.
That oxygen-rich blood then flows to the heart for the very first time.
The pressure of this flood of blood pushes on a flap, closing the hole.
But sometimes it doesn't seal.
One in four of us has a hole in the heart,
and most will never know.
Your heart and lungs are now fully connected.
Your circulation is complete.
Finally got my boy. Got what I've always wanted. Over the moon.
Yeah.
So you can take another breath and another.
From now on, without thinking,
you will breathe around 16 times every minute.
You only really start thinking about breathing when you stop.
I'm going see how long I can hold my breath for, starting right now.
'Try it yourself.'
Oh!
HE COUGHS
Oh, that was not impressive.
That was...40 seconds.
I reckon I could probably do about another 10 seconds.
It really hurt. So...under a minute.
Not impressive at all.
There are some people who can go...
a hell of a lot longer than that.
This man can hold his breath for a whopping nine minutes.
Herbert Nitsch is a world champion at freediving.
Powered by a single breath,
he can not only stay underwater for longer than seems humanly possible
but glide through the water with the freedom of a fish.
I find it always difficult to explain the sensations I have down there -
the quietness, the peacefulness.
That you are just floating, there is no gravity.
The fish or mammals in the water come right into your face, look at you.
I'm, like, "OK, that's maybe even closer than I would want to, maybe."
But they're just curious, because they think that you are one of them.
Before a dive, Herbert takes in as much air as he can.
But, surprisingly, the key to success is not so much his lungs as his heart.
As Herbert plunges deep into the sea,
the cold water on his face prompts something we all have -
the dive reflex.
This reflex causes your heartbeat to slow
by as much as 25%, so you use less oxygen.
And the dive reflex does something more.
It priorities the brain and the heart's survival,
by switching off the more dispensable parts of the body.
After mere seconds, Herbert's body shuts off blood flow to his extremities.
First, his toes and fingers.
Then his hands and feet.
And, finally, his arms and legs...
until all that remains
is a circuit of blood flowing between his heart and his brain.
And that is what allows him to stay underwater
for an incredible nine minutes.
What this really shows is how good your heart is
at adapting to any environment.
Your heart is an exquisitely engineered pump, made of muscle.
And you can see the true elegance of this engineering
if you slow it to a single beat.
Inside the cavernous chambers,
the muscles work together in perfect harmony.
These muscles never get tired and never stop working.
As your heart expands, blood flows from your body into its chambers.
Then an electrical signal storms through the heart,
causing it to contract...
..forcing blood all the way through your body's vast network of vessels.
And to stop the blood flowing backwards, your heart needs valves.
As they slam shut, these valves make the familiar "lub dub, lub dub".
HEARTBEATS
The soundtrack of your life.
That "lub dub" rhythm changes in step with your needs.
What I love about my heart is it is incredibly sensitive.
It responds immediately to any demands put upon it.
At the moment, it is rattling along at around 64 beats a minute.
Time to give it a bit of a work-out.
Right.
It has now gone up to 84.
Bit faster.
Up to 99.
Jog, jog, jog and now...108. Right, I'm going see how far I can push it,
run up and down the stairs a few times.
My heart matches the workload in my muscles.
As they work harder, my heart responds
by pushing more blood around my body,
keeping my blood oxygen levels balanced.
Right, 120.
And now that I'm at rest, it's already beginning to drop.
That is a truly wonderful piece of machinery.
And what's driving that machinery are a small but vital group of cells -
the pacemaker cells.
These are the cells that control the beat of your heart.
They spontaneously create its rhythm.
And they have been doing this since long before you were born.
When you were just an embryo, merely three weeks old,
they first started beating.
And from that moment, these same pacemaker cells would stay with you
for the rest of your life, never to be replaced.
Most other cells in your body come and go.
Your stomach lining is replaced every three days.
Your skin sheds and regrows every month.
And every ten years, you'll have a new skeleton.
But your pacemaker cells stay with you always,
faithfully speeding up or slowing down,
depending on your body's demands.
Hi. Stephanie Fuller. Nice to meet you. I'm Katlyn.
How are you?
They're so important that when they go wrong,
the consequences can be devastating.
So, tomorrow's the big day.
I don't know if we can call it the big day.
Katlyn Hagan was born with a heart defect,
which is causing some of her pacemakers to misfire,
giving her a dangerously irregular heartbeat.
She's here to meet leading heart surgeon Stephanie Fuller.
There's a risk of death with heart surgery.
I hate saying it, it's not zero, but I have a great team,
and we'll take great care of you tomorrow, I promise you.
We'll do everything we can for you. OK?
Katlyn's biggest problem really stems from the abnormal pacemaker cells.
They are a risk for developing clots in the heart,
developing a stroke
and continuing to have abnormal heart rhythms
that eventually can cause her to have heart failure.
It's not just Katlyn's future
that depends on the outcome of this operation -
she has a one-year-old daughter.
I'm very scared. I want to make sure that I'm still living after my operation
so I can be there for my daughter's growing up,
and just live a normal life.
I don't know where my picture is. OK.
It's right here. Thank you.
Just a little more sleepy medicine.
You're going to feel very warm and comfortable and very relaxed.
I'm scared.
We're going take very, very good care of you.
Everything's going perfectly.
Katlyn's heart is revealed.
In a healthy heart, the rhythm set by the pacemakers
flows through the muscle as an electrical wave.
And this wave follows a precise sequence, which controls the contractions.
But in Katlyn's heart,
some of the pacemaker cells are firing out of sequence,
making the electrical flow chaotic.
First, the surgeons must transfer the job of pumping blood to a machine.
When that's done, they can stop her heart.
Lean back on the cardio, please.
See it gradually slowing down, and as the fluid goes in,
the heart gets a little whiter, because there's no blood going into it.
CONTINUOUS HIGH-PITCHED TONE
Without a heartbeat, Katlyn is in a hinterland between life and death.
Now the surgeons can begin to prune away the faulty pacemaker cells
using a cryoprobe, which freezes them.
They have to be extremely careful only to freeze the cells which are misfiring.
It's very important that we make sure that we haven't destroyed
the pacemaker cells that Katlyn very much needs to keep.
Katlyn has been without a pulse for nearly an hour.
I'm going to be coming off in just a second.
It's time to get her off the bypass machine and to reconnect her heart.
The hope is that when this is done,
her pacemakers will start to beat again all by themselves.
Her heart's starting to get blood right now.
So we're inflating the lungs.
As Katlyn's blood flows back into her heart,
its warmth is enough to restart the pacemakers.
All right. Come off.
Amazingly, this is all it takes to bring the rhythm back.
Looks good.
The operation was a great success.
STEADY HEARTBEAT
Your heart's will to beat is incredibly strong.
SWIFT HEARTBEAT
And that's just as well, because it drives your entire circulation.
SLOWER HEARTBEAT
Right.
Ooh, yes.
I like that. I do like that.
Now, that is magical and ever so slightly spooky.
I can see the blood vessels running underneath my skin.
What's happening is there is a beam of light which is near infrared
and it's being absorbed by the blood
while the fat which is around it is being reflected,
so the blood shows up as these wonderful black lines.
And it looks like the branches of a tree, big vessels turning into little vessels.
It really is extraordinary.
And you can actually empty the vessels there.
If I put my finger there, I can see that vessel empty and then fill again
as the blood being pushed by my heart courses round.
And all of this complexity has a vital purpose -
to carry life-giving oxygen to every nook and cranny of your body.
The hard graft of carrying that oxygen
is done by some of your smallest and most peculiar cells.
Their story begins deep inside the marrow of your bones.
Here, every minute of your life, 150 million red blood cells
are produced by a dedicated factory.
The workers are specialised white blood cells,
affectionately known as nurse cells.
They carefully nurture each red blood cell for five days and then set it free.
As it's swept away in the bloodstream,
it joins 25 trillion others whizzing around your body.
They're on a long journey.
If all the blood vessels in your body were joined, they'd stretch
more than twice the way around the Earth.
Each cell travels through wide arteries...
..spiralling off into smaller arterioles...
..and then squeezing through tiny capillaries.
Here, in the smallest, narrowest vessels,
our cell does the job it's been created for.
It releases its payload of oxygen into your tissues.
It'll do this over and over again for the rest of its life.
But that life is short.
After four months of hard graft,
travelling the length and breadth of your body,
your red blood cell begins to look rather knackered.
As it returns to the bone marrow where it was born,
chemical changes on the aging cell attract the attention of the nurse cells.
But this time their job is not to nurture but to destroy.
Every minute, 150 million red blood cells come to a sticky end.
But as fast as the old cells are destroyed, new cells are created...
..so that you always have enough
to keep up the balance of oxygen in your blood.
And this oxygen is so vital for life because it's a key ingredient
in releasing the thing that keeps us all going - energy.
You need energy for every single thing you do,
no matter how grand or how tiny.
And you get it by combining oxygen
with one of the other essentials of life...
..food.
I try to eat a rich and varied diet with just the occasional big blowout.
Now, I've got a real feast here at the moment -
nice piece of fish, chips underneath.
Lots of protein and fat there,
and a big blow of salad here with lots of colour in it,
oozing with vitamins and other goodies.
But I think you would be surprised at just how meagre a diet
some people can survive on.
This is Debbie Taylor.
And this is what Debbie Taylor eats.
This is all Debbie Taylor eats.
This is lunch.
And this is dinner.
Now aged 31, for over a decade she's barely eaten anything else.
In the fridge, I have sausages.
I haven't had sausages since I was under 11 years old,
but I still cook them for other people.
I've never had a pepper,
so I don't know what it tastes like and I don't want to either.
Not had grapes since I was at primary school, I should think.
There can't be any nice flavour in that, cos it's all rubbery, look.
It's probably really chewy on the outside.
I can imagine that getting stuck in your throat or something
and it just...
No matter the occasion, Debbie's diet doesn't deviate.
On Christmas Day, I won't eat the turkey or anything like that.
I'll leave that to the family.
I'll just eat a bag of crisps.
When we go away on holiday, I usually pack a suitcase, hand luggage,
full of the crisps that I eat, my flavour,
because sometimes you'll find that they don't sell them abroad,
so I have to take them with me.
Debbie's unusual eating habit began as an effort to lose weight.
I mean, I know crisps are carbs, but at the end of the day,
I'm not eating meat with it and gravy and all the...
you know, vegetables.
It petrifies me, the thought of eating a meal.
With such a singular diet,
there's a price to pay from a lack of vitamins and minerals.
The hair is really bad,
nails don't grow, skin's colour is awful.
Sometimes you can't sleep. Teeth, as well, are another thing.
When you brush them, they bleed a lot.
Despite the long-term problems, a diet of just crisps
gets Debbie through her busy working day.
My job is a housekeeper in a hotel.
It is a very energetic job, physical job.
It may seem surprising,
but in terms of energy alone, Debbie's crisp diet is no problem.
And that's because the human digestive system is very efficient
at squeezing all it can out of any food, including crisps.
After chewing, your food drops into an expandable bag of acid,
also known as your stomach.
The pulverised pieces then pass into your small intestine
where they get broken down even further.
Here, there's a carpet of finger-like projections called villi.
And on top, smaller versions called microvilli.
Together, they increase the surface area of your gut to that of a tennis court.
In the small intestine, any carbohydrates you've eaten
are rapidly taken up and converted into a simple sugar - glucose.
This glucose is carried in your blood to your tissues,
which contain a network of tiny power stations called mitochondria.
Here, the glucose is finally combined with oxygen to produce precious energy.
And this is what powers everything you do.
Every minute of your life, your body is working furiously to keep you going.
It ensures that everything is just so.
It generates the right amount of energy it needs to keep moving
by combining food with just the right amount of oxygen
from the air you breathe.
This oxygen is carried by the right number of red cells in your blood.
And that blood, in turn, is driven by your heart
beating at just the right speed.
But that is not the end of the story,
because there is another delicate balancing act
that your body has to perform if you are to stay alive.
For these elite firefighters in Texas, their body's ability
to regulate temperature is a matter of life and death.
And the way they do it is by sweating.
Sweating is a part of the game when it comes to firefighting.
I've seen guys actually pour sweat out of their boots.
They've taken their T-shirts and they wring the sweat out.
If I couldn't sweat, I couldn't go in and do what I need to do.
I couldn't be a firefighter.
When your body starts to overheat,
it stimulates sweat glands deep down within your skin...
..to produce a tiny bead of sweat.
Each bead must then work its way to your skin's surface.
And it's here that sweat performs its magic.
As it evaporates into the air, it takes heat with it.
This is how your body keeps its cool
and keeps you alive when things hot up.
Today, Fire Chief David Herr is running a test to find out
exactly how much a firefighter sweats when doing a high-temperature rescue.
We're bringing the firefighter up these stairs first.
The smoke and the heat will begin to already take a toll on him.
He's going to continue forward on, looking for the victim,
make his way up through this narrow passageway here,
pick him up and then carry him out the Charlie-side door.
Firefighter Mario Rodriguez has the dubious honour
of being the test subject.
First, he's weighed naked.
By comparing his weight before and after the test,
they can calculate how much sweat he has lost.
He swallows an electronic pill containing a thermometer,
which will monitor his core temperature
to see how much it varies from the normal 37 degrees.
The fire is set and its temperature is also measured.
I have a good angle on the fire, a good reading.
Currently getting 1,200 degrees.
At this temperature, aluminium melts.
Before he goes in, Rodriguez kits up.
The suit should protect him from the flames and the worst of the heat.
Firefighter Rodriguez, hold on.
His core temperature is checked.
It's now just over 37 degrees Celsius.
You're starting to warm up already. You know what your task is.
Let's get going. Be safe.
All that stands between Rodriguez and certain death
is his suit and his ability to sweat.
The temperature has just rocketed by 1,200 degrees.
Yet if his temperature were to increase by just a few degrees,
that could have devastating consequences.
An increase of just four degrees would leave him confused and unconscious.
A rise of seven degrees would kill him.
After 45 seconds in the fire, Rodriguez is poaching in his own juices.
It was real hot.
My bones and all my joints starting burning.
Just the heat, just gotta get out of there and get some cool air.
Stand by, let me get your core temperature reading.
Despite everything he's been through,
his core temperature has risen by just one degree Celsius.
Now he's weighed again to see how much sweat he's lost.
You're at 207 now,
so that looks like you lost three pounds of body weight.
Three pounds equals 1.4 litres of sweat.
That's three times more than you would lose in an average day.
Thanks to all that sweating, Rodriguez was able to maintain his core temperature,
despite the extreme heat of the fire.
It's important to keep your body at 37 degrees,
because this is the optimum temperature
for the chemical processes that keep you alive.
Not all animals have the ability to regulate their temperature.
This is Ozzy. He's a bearded dragon and, like all reptiles, he is essentially solar-powered.
At the moment, he's quite active, because it's very warm in here.
But if I were to take him outside where it's around 10 degrees,
he would soon go into shock, curl up and he would die.
But we're different.
We can go where we want, when we want.
One of the reasons why we are such a successful species,
in fact, why we dominate the planet,
is because we keep our bodies at a really constant warm 37 degrees,
no matter how extreme the external environment.
And that applies just as much to the cold.
These are the frozen wastes of Iceland...
..and this is Wim Hof,
also known as "The Iceman".
Cold is a noble force. It ignites beautiful feelings within.
It's so majestic, I feel a king.
I want to show the forgotten language of the cold.
To explore how Wim endures the cold,
he's agreed to spend the afternoon in an industrial fridge.
His friend, Henny, who's not used to the cold, will act as a comparison.
A thermal camera measures their skin temperature
to see whether Wim is better at keeping warm.
Henny starts off well.
But after a while he starts to show signs that his body's defences are struggling.
When you get cold, your skin goes pale
as it redirects blood away from the surface.
Tiny piloerector muscles pull up your hairs,
so they stand erect.
You see this as goose bumps.
The hairs trap a layer of air
that insulates your body like a wafer-thin duvet.
But in reality, goose bumps are pretty useless at keeping you warm.
I'm not comfortable.
I don't stay any much longer in here, I think.
Finally, Henny starts to shiver.
It's his body's attempt to generate heat by making his muscles move.
But shivering, too, is ineffective,
using large amounts of energy to generate precious little heat.
Shivering is a sign that Henny's starting to fade,
but Wim is fine.
One hour in this fridge and still warm.
That counts for something, huh?
A cold beer.
Strangely enough, the thermal camera shows
there's no difference in skin temperature between Wim and Henny.
It must be something going on inside that's keeping Wim warmer.
I quit.
After an hour and four minutes, Henny can't stand it any more.
Wim, however, is still happy.
But sitting naked in a fridge is child's play compared to what Wim does next.
He's about to take a swim in this lake.
The water here is just above freezing,
two degrees Celsius.
Wim intends to stay in for 15 minutes.
That would kill most people.
Yet Wim believes that everyone has the potential to do what he does.
There is a natural ability in everybody to neutralise the cold.
It's about nothing abstract, it's no hocus-pocus, it's the mind.
Anybody can do what I do.
It is trainable.
Water looks clear, good.
Inviting, attractive.
Powerful.
Inviting me to come in and to take part.
The first minute in ice-cold water is the most dangerous.
Your body goes into a panic-like cold shock,
which can trigger a heart attack.
But it has no effect on Wim.
I don't feel the cold. I feel the power, yes.
I don't feel the pain, because I am stronger than the pain at that moment.
Repeated exposure has changed Wim's threshold
for withstanding cold and pain.
He no longer feels the shock.
Instead, he's able to endure it and stay calm,
even to enjoy it.
MUFFLED SINGING
# Is everybody fine? #
It's a privilege to be here.
Look at this.
Diamonds!
Five minutes in,
and he's still going.
Looks like a dinosaur.
Whales.
Monsters.
After ten minutes, there's a new danger.
The cold starts to chill the thinnest parts of your body -
your arms and your legs.
Nerve impulses slow down,
so they no longer trigger your muscles to contract.
Most people come to a grinding halt, which makes them vulnerable to drowning.
But not Wim.
Because he's adapted to the cold, he keeps swimming vigorously,
and this helps him generate heat to keep him going.
I feel charged, actually.
Sort of charged.
I feel like a bit electric.
Yeah, electrified.
After 15 minutes swimming in ice-cold water, he emerges.
Wim has survived an experience that would kill most of us -
a testimony to the body's amazing ability to adapt to almost unimaginable extremes.
From the moment you were born, your body has been engaged in
a minute-by-minute struggle for survival...
..overcoming whatever struggles you have thrown at it.
It has juggled ceaselessly to keep everything in balance.
But as we near the end, a lifetime's work takes its toll.
Finally, you approach the last minute of your life.
CLOCK CHIMES
Gerald is nearing the end.
After 84 years, his body is worn out.
The body's been failing lately, with things like diabetes,
with blood pressure.
My hearing's not what it should be,
lost half me teeth, I've got cataracts.
So, oh, yes, I've not bucked the trend for falling to bits, by any means.
In his 84 years, Gerald has taken over 800 million breaths.
His heart has made over 3,000 million beats.
And all the while, his core temperature has remained within a band
of just a few degrees,
keeping Gerald's body in perfect balance.
Hello, love. I've brought you a drink.
Oh, that's good of you. OK, all right?
Thanks very much. That's all right.
I'm just going to pop your legs up, actually, all right?
Oh, that's one of me in the cathedral choir - looking angelic, more than I was.
That was my mother and father.
I was the only child and I certainly did have naughty spells.
Well, that was me in the Army,
when I was a wireless operator in Siam.
That was Mary and myself cutting the cake.
I can't really think of any partnership where the love was deeper
and more lasting and more secure.
But now Gerald's systems are failing.
A year ago, he was diagnosed with liver and lung cancer,
and severe anaemia.
I don't want to die, but pretty evidently,
unless some miracle happens, I ain't going to be here very long,
and so let's get on with me life as best I can.
Gerald is squarely facing the prospect of his imminent death.
I'm not frightened. I believe that it'll not be just like
cutting off, er, a tape with some scissors. It might be.
But either way, I just have blind trust that I shall not disappear completely.
CLOCK CHIMES
But life doesn't release its grip readily.
Even at this final stage, Gerald's body is trying to keep its critical balance.
Gerald is severely anaemic.
He has only a third of the normal number of red blood cells.
The level of oxygen in his blood is so low, it's surprising he's still alive.
In a last struggle to keep going, Gerald's body tries to compensate.
He takes deeper, more frequent breaths to try and draw in more oxygen...
..while his heart contracts harder and faster
in an attempt to force more blood around his circulation.
One, two, three and...
Yet even this is not enough.
OK. Alan's got your weight.
No-one knows how much longer he can last.
Grateful for each day,
and in the morning I always say thank you for another day,
and fingers crossed and God willing.
Do you want a drink? This one? Thank you.
Gerald's blood count drops even lower.
Soon he can no longer leave his bed, but he's battling on.
Still no pain, and I'm still managing
to eat reasonably and enjoy me crosswords and so on.
But after a further week, Gerald loses his appetite.
He is finding it hard to eat anything at all.
With no food supply, as well as very low oxygen,
the mitochondria inside his body are starved of fuel.
With barely any energy,
his body becomes entirely unable to maintain its precious balance.
Gerald begins slipping in and out of consciousness.
He has kept going far longer than anyone expected.
But without energy, his heart is failing.
His blood no longer circulates.
And so Gerald draws his last breath.
I think he's gone.
The balance is undone.
Now all that's left are the memories.
I would like to be remembered as a good father and as a husband.
As far as the grandchildren are concerned, a good grandfather.
Hopefully, they'll overlook my shortcomings.
Gerald reminds me very powerfully of my own father's death,
except when my father died, it was rather more flamboyant.
For some reason, he decided to start singing,
and he sang and sang for several minutes, and then he stopped and he was gone.
And I have all these lovely memories of him.
I think of him with huge affection every single day.
And this is the true miracle of your everyday existence.
From your first breath to your last,
you become so much more than the sum of your parts.
You become someone with hopes and dreams, likes and loves,
able to touch the lives of others.
Subtitles by Red Bee Media Ltd
E-mail subtitling@bbc.co.uk