Inside the Human Body - Learning Zone


Inside the Human Body - Learning Zone

Using spectacular graphics based on the latest science and stories of remarkable people around the world, Michael Mosley examines the human body.


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Transcript


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You're a member of the most fascinating species on this planet.

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And the secret lies under your skin.

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This is a voyage through the most extraordinary organism on Earth.

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You.

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Your eye is a massive construction project.

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And much of the development only begins after you are born.

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The iris, which controls the amount of light entering your eye is complete,

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but the muscles around the lens in the middle are still learning how to focus on the world.

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At the back of your eye

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lies the vast red plane of your retina.

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Light from above shines down, casting images of the outside world across its surface.

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Underneath, these rays enter a forest of 125 million light sensitive cells.

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Each cell senses just a tiny part of the image but together

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they send their information to the brain, which makes sense of it all.

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Most of these are rod cells which can only see in shades of blue.

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They help you see in the dark.

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To see clearly in daylight you need an entirely different set of cells.

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These are known as cone cells.

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Four and a half million are spread over your retina.

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But in one location, they are much denser.

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Here, they begin to group together and the retina's surface begins to bulge.

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Over the first four years of your life, the cones raise a volcano-like mound at the back of your eye.

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Then, around 20,000 cone cells burst through at the summit.

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This is your fovea.

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The part of your eye where your vision is crystal clear.

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It can sense over a million different colours.

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Muscles in your eye work to focus light onto the retina.

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Muscles in the iris respond to light levels, opening up

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the iris in low light, and narrowing it when things get too bright.

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On the remote Thai island of Ko Surin,

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there are a group of people whose brains have learnt to overrule the muscles in their eyes.

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Goong and his friends belong to the Moken tribe get much of their food from the sea.

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But finding food in water is not easy.

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That's because your eyes have adapted to see clearly in air,

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so underwater they lose more than two-thirds of their power to see.

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To compensate, Goong's brain does something remarkable.

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As he descends, light levels drop quickly.

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Normally, your eye would react

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by opening the iris, making the pupil larger and allowing more light in.

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The image may appear brighter, but it comes at a cost.

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Because underwater, a wider iris makes everything appear more blurred.

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Over time, Goong's brain has learned

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to overrule this reflex of the eye...with an astonishing adaptation

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best seen with the help of an infra-red camera.

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Rather than opening his pupils, he closes them -

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some of the muscles of the iris contract to their limit.

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Which constricts the pupil as far as it will go.

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Goong's view of the salty underwater world becomes much sharper.

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It's so effective that Goong can see fine details twice as well as you can.

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Your brain has an incredible ability to adapt your eyes to suit its needs.

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And, for Goong, that means his dinner.

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It is the incredible flexibility of the human brain

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which enables you to respond to almost anything that happens to you.

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But what you think you're seeing is really what your brain is interpreting.

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It's an image that your brain constructs from the nerve impulses

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it gets when light hits receptors in the retina.

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Your brain makes sense of those signals and assembles a picture of the world around you.

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The actual picture on your retina is upside down,

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but your brain is clever enough to turn this the right way up.

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One man's brain has done something even more spectacular.

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I started going blind about ten years old.

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Erik Weihenmayer's brain is 40 years old.

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It lost contact with the visual world 25 years ago.

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Every week I would wake up with different levels of vision.

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Because my retinas were splitting away from my eyes.

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And over a matter of four or five years I was totally blind.

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Ever since, his brain has got used to being in the dark.

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Today, Erik and his co-climber, Greg Childs, are in Utah.

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They're about to attempt the formidable Castleton Rock.

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It's a hard technical climb.

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It's Erik's first attempt to climb here

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and his brain is about to regain a sense of sight...

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with a new piece of technology.

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This is the brain port device.

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This is the camera...

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on these sunglasses here.

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The camera sends a feed to a computer on Erik's hip...

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..Which translates the images into a low-resolution picture of the world.

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This blocky image is then sent to one of the most sensitive parts of Erik's body...his tongue.

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Via a device he puts in his mouth.

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On the surface are hundreds of tiny electrical stimulators.

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When the camera sees an outline, a corresponding line of stimulators buzz away, tickling Erik's tongue.

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I can feel each dot and together they create lines and shapes

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and ultimately images that my brain then reinterprets as

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the space around me.

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Decades after he lost his sight, the visual part of Erik's brain is reawakening.

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Erik's brain has found a way to connect his mind's eye and his tongue.

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Instead of receiving nerve impulses from his dead retina,

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his brain's learning to build up a picture of the world based on nerve impulses from his tongue.

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Is that sight?

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Well, kind of, you know, because I think seeing is more in your brain than in your eyes.

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In rock climbing, most of the risk is taken by the lead climber.

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Erik is feeling so confident with the brainport device,

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that he makes a dramatic decision to lead the final push.

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You pop over this lip and it's completely flat and the wind just

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gusts in your face and you're up there on this flat tower 1,000 feet above the desert floor.

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That was good, thanks.

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This is totally beautiful up here.

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Erik is living proof of the brain's astonishing ability to remould itself...

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and respond to any challenge you throw at it.

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Deep inside your head is a remarkably beautiful structure.

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A maze of tunnels and caverns submerged in fluid.

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These are the semicircular canals

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and the cochlea, which are part of your inner ear...

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they are crucial for both your balance and hearing.

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When sound hits your ear, it sets off a wonderful chain of events.

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It enters as pressure waves, which push and pull your ear drum, making it vibrate.

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On the other side of the ear drum, slowing time allows us to see

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how these vibrations set a series of bones jiggling.

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They end with the smallest bone in your entire body,

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called the stirrup. It is smaller than a grain of rice.

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These bones transmit the vibrations to a sensitive area called the oval window.

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They also protect your ear.

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If a sound is too loud...

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they pull the stirrup away from the most sensitive parts.

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Temporarily at least, you go a bit deaf, but the rest of your ear is protected.

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Beyond the stirrup is a liquid-filled cavern called your cochlea.

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The sound waves enter the water, tickling clumps of tiny hair-like sensors on the floor,

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which begin to dance to the sound of the world outside.

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Thousands of clusters of hair cells each pick out a different part of the sound.

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Each sends a tiny piece of information to your brain,

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where it's interpreted so you can make sense of the sounds around you.

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The ear has evolved to be most sensitive to the sounds of another voice,

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allowing your brain to tune in to the words of another human.

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But your ear doesn't just allow you to hear.

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It also plays an essential role in allowing you to walk.

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For you to take just one step, your brain has to coordinate the precise

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movement of over 100 different muscles, bones and tendons.

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And there is a place where people learn to walk sooner than anywhere else on Earth.

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This is Koarmba.

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She is mother to a baby girl called Kossini.

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They live in Rhumsiki, a tiny village in the remote northern highlands of Cameroon.

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Here, most mothers believe in actively teaching their babies

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to stand and walk, to get them off their backs as soon as possible.

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And it works. These people have trained their brains to find their feet much earlier than you.

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Ever since Kossini was a month old, her mother has repeated the ancient ritual of katete,

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which means "to make jump".

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Every day, she takes hold under the arms and bounces her.

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This daily encouragement helps the gradual development into mature walking.

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But before you can stand up for any length of time,

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your brain must learn to understand the orientation of your body...

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..and that's why your inner ear is so important.

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The semi-circular canals that form three twisting tunnels inside your ear

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are all orientated in a different direction.

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In each lies a saddle-topped fleshy mountain, known as your crista.

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The mountain's slopes are covered in a thick forest of tiny hair cells.

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For the moment, they lie still, waiting...

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But this inner sea never remains calm for long.

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Because every now and then...

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..there's a tsunami.

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A shockwave races through the tunnel and pummels the mountain.

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On its flanks, the hair cells are thrown about in the turbulent waters.

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The pressure builds until...

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electricity flows...

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creating a powerful electrical current.

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Every time your head moves...

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the hairs cells are thrown about inside one or more of the canals.

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And in a fraction of a second, electrical impulses are fired straight to your brain.

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The feeling that emerges is your sense of balance.

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To walk, your brain

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has to learn to sense when you are over-balancing to one side...

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and then instruct your leg to bring your weight back to the centre.

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All of this happens within a fraction of a second.

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To begin with, it's a real struggle.

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But Kossini's half brother

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is already a master of bipedalism.

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And he is just ten months old.

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From now on, and for the rest of his life, walking will be automatic.

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The amazing construction of your ear allows you to both sense and explore the planet you inhabit.

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For nine months, you were enveloped in the warm, comfortable world of your mother's womb.

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Your every need was taken care of.

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The placenta supplied you with oxygen from your mother's blood,

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so your own lungs were hardly used.

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At this stage of your life, your heart had completely different plumbing...

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a hole through its centre diverted blood away from your lungs almost entirely.

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And then, suddenly, your tranquillity was shattered.

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Relax...

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Relax.

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As you were born,

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you went through the most dramatic minute of your life as your body took over from your mother's.

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Once out into the world, you were bombarded with new stimuli.

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Bright glaring lights...

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Cold air on your skin...

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Strange sounds.

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Scientists now believe it's the shock of these stimuli that triggers your first critical breath.

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But before you can absorb life-giving oxygen, your circulation must be rapidly re-plumbed.

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As you draw your first breath...

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The airways of your lungs open, causing blood to rush into them to pick up oxygen...

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That oxygen-rich blood then flows out of the lungs and into the heart.

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As it does so, pressure builds up, closing a flap over the hole.

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This hole will, in time, seal completely.

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Your circulation is now complete.

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Oxygen-rich blood can flow from your heart to the rest of your body...

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deoxygenated blood flows back to your heart and to the lungs, where you get new oxygen.

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So now you can take another breath...

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and another...

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for the rest of your life...

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Your heart's will to beat, to keep going, is incredibly strong.

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If the heart fails, so does everything else...

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Because it's your heart's job to deliver to every cell, to every nook and cranny of your body,

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the substance which keeps it alive - oxygen.

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But how does the body do this?

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The hard graft of carrying oxygen is done by some of the smallest

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and most peculiar cells in your body.

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These red blood cells are well suited to the job of carrying oxygen around your body.

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Each red blood cell contains millions of haemoglobin proteins.

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They have a structure that oxygen likes to bind to.

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Haemoglobin is bulky, so there's not much space for anything else

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inside the red blood cells, which have to squeeze into tiny blood vessels.

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It means that red blood cells are unique amongst all your cells,

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because to carry oxygen, they don't have a nucleus.

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25 trillion red blood cells are pumped around the body, completing a circuit within a minute.

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Each cell makes a tortuous journey...

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through wide arteries that surge like a river in full flood.

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Then branching off into smaller streams called arterioles.

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It's perfectly shaped to squeeze through tiny, slow-moving capillaries.

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And without a fat nucleus, it just about gets through.

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Here, in the smallest, narrowest vessels, our cell does the job it's built for...

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it releases its payload of oxygen into the tissues.

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The reason that your body goes to such lengths to ensure a steady supply of oxygen

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is because oxygen is an essential ingredient in unlocking the energy you need to survive.

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Oxygen from the red blood cells passes into every other cell of your body.

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Here, there are hundreds of little powerhouses called mitochondria.

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They burn oxygen to release all the energy you need to live your life.

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But to do this, they need another ingredient

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which also comes via the bloodstream...

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food.

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Food is mainly absorbed in the small intestine, which is covered in

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finger-like projections called villi and microvilli.

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They increase the surface area of your gut to that of a tennis court,

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so you can absorb as many nutrients as possible.

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If you eat a packet of crisps, for example, it is here that the crisps will be broken down into smaller

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and smaller particles, until they are reduced to glucose...

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which is small enough to be absorbed into the bloodstream,

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ready to be transported to the mitochondria in your cells.

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Over your lifetime, you will eat more than 50 tons of food, and take over 800 million breaths, which you

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will convert into enough energy to power a house for five years.

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And every mouthful and every breath has finished here, with your

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mitochondria using the energy released to get you through the day.

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Your heart is an exquisitely engineered pump made almost entirely of muscle.

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And you can see the extraordinary engineering in action if we slow your heart to a single beat.

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Inside the cavernous chambers, the muscles work together in perfect harmony.

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These muscles never get tired and never stop working until you die.

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As your heart expands, blood flows from your body into its chambers.

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First the atria,

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then the ventricles.

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The left ventricle has to work particularly hard, because each of its contractions must have

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enough power to push blood all the way through your body's vast network of blood vessels.

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And that's a long way. If they were strung together, these vessels would circle the Earth at least twice.

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Like the plumbing in your house, your heart needs valves

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between its chambers and arteries to stop the blood flowing backwards.

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As the valves slam shut, they make the familiar "lub-dub, lub-dub" sound

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of the heartbeat in your chest.

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Every single minute, your heart does this around 70 times.

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And it's all regulated by some little cells at its core...

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At the start of your life,

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when you were just a three-week-old embryo, something happened

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inside your body which was nothing short of a miracle...

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These tireless cells -

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called pacemakers, which control the beat of your heart - came into being...

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They spontaneously beat out a rhythm...

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sending synchronised signals through your heart.

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Which speed up or slow down, according to what your body's doing.

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And these pacemaker cells will stay with you always...

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..faithfully responding to every demand of your life.

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Katlyn Hagan will be relying on her pacemaker cells to do something extraordinary.

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She needs to have major heart surgery...

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her heart will be stopped for anything up to an hour.

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There is a risk of death with heart surgery. I hate saying it, it's not zero.

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I have a great team and we'll take great care of you tomorrow, I promise you.

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We'll do everything we can for you.

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I'm very scared.

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I want to make sure I'm still living after my operation

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so I can be there for my daughters growing up

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and just live a normal life.

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The operation will be tricky.

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It's the very same pacemaker cells that keep Katlyn alive which are causing her problem.

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But before they can operate, they must transfer the job of

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pumping blood around Katlyn's body to a machine...

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..and then stop her heart.

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See it gradually slowing down.

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As the fluid goes in, the heart gets a little whiter,

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cos there's no blood going into it.

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Without a heartbeat,

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Katlyn is in a hinterland between life and death.

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Now they can begin to remove the faulty pacemaker cells.

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To do this, the surgeons use a cryoprobe,

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which freezes and destroys them.

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They have to be careful

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to remove only the cells which are malfunctioning.

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The main procedure is finished.

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It's time to get Katlyn off the bypass machine

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and reconnect her heart.

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By now, her heart has been stopped for nearly an hour...

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The heart's starting to get blood right now.

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So we're inflating the lungs.

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As blood flows back into Katlyn's heart,

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its warmth and nutrients

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are enough to re-start the pacemaker cells.

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All right. Come on.

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-MACHINE BEEPS

-And the rhythm returns.

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It looks good.

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The operation has been a success.

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Katlyn's heart is now beating correctly.

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Driven by a group of pacemaker cells

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created within weeks of her conception.

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These cells will remain with her

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until her last heartbeat.

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We are all born with a shield

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which protects us from the dangers of the outside world.

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It's our first line of defence -

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our skin.

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Your skin is amazing.

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The largest organ in your body -

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up to two meters squared.

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Each centimetre of skin is built from ten million individual cells.

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This tiny square bristles with over 100 hairs.

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And packs 100 sensors

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that can detect the lightest of touches.

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But it must also act as an impenetrable barrier.

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Because your skin

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is covered in millions of bacteria.

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If they get inside your body,

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your warm, moist tissues

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will provide the perfect environment

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for them to take over.

0:32:080:32:09

What prevents them getting in

0:32:090:32:12

is the clever way your skin is constructed.

0:32:120:32:15

Skin cells lock together like armour plates.

0:32:150:32:18

And it's not just passive protection,

0:32:220:32:24

your skin is constantly pushing outwards.

0:32:240:32:27

New layers grow underneath the old

0:32:290:32:32

and push the surface layers away.

0:32:320:32:35

This constant shedding

0:32:350:32:36

prevents most microbes

0:32:360:32:38

from getting a permanent hold.

0:32:380:32:40

However, it also means you lose 30,000 skin cells every day.

0:32:420:32:47

This time next month,

0:32:490:32:51

you'll have replaced all the skin on your body.

0:32:510:32:54

But your skin doesn't just protect you from living organisms.

0:32:590:33:03

It also needs to keep your internal organs safe from getting dehydrated.

0:33:050:33:10

At the base of every hair on your body is a tiny gland,

0:33:140:33:19

known as a sebaceous gland.

0:33:190:33:22

It protects you by squeezing an oily substance call Sebum

0:33:230:33:28

onto the surface of your skin.

0:33:280:33:31

Sebum is what makes your hair greasy.

0:33:310:33:34

And what gives you spots

0:33:340:33:36

and makes your skin waterproof.

0:33:360:33:39

This oil helps to prevent fluids inside your body

0:33:400:33:44

from evaporating into the air,

0:33:440:33:47

which can cause dehydration.

0:33:470:33:49

Your skin is constantly working in two directions.

0:33:510:33:54

Firstly, to stop bacteria from getting into your body.

0:33:560:34:01

And secondly, to protect the organs inside your body from drying out.

0:34:010:34:06

It's a perfectly-engineered protective layer.

0:34:060:34:10

Every minute of your life

0:34:180:34:20

your body is silently performing a host of small miracles

0:34:200:34:24

to keep you alive.

0:34:240:34:26

But all of them would stop, and you with them,

0:34:260:34:30

if one crucial factor in your body

0:34:300:34:32

were to change dramatically.

0:34:320:34:35

And that's your temperature.

0:34:350:34:37

Your body is designed to function at 37 degrees centigrade.

0:34:370:34:43

When your body overheats,

0:34:480:34:50

it stimulates sweat glands deep within your skin.

0:34:500:34:55

They produce beads of sweat.

0:34:550:34:58

Which work their way out of your body

0:34:580:35:01

and onto your skin's surface.

0:35:010:35:03

And it's here that sweat does it's work.

0:35:060:35:09

It cools your body by evaporating into the air...

0:35:130:35:18

keeping you alive when things hot up.

0:35:200:35:24

Extreme heat can be deadly.

0:35:280:35:31

For these elite firefighters in Texas,

0:35:370:35:40

their body's ability to keep their temperature constant

0:35:400:35:43

is a matter of life and death.

0:35:430:35:45

Their triple-lined fire suits

0:35:450:35:48

do much to protect them from the flames.

0:35:480:35:50

But there's something else -

0:35:520:35:55

their ability to sweat.

0:35:550:35:57

Firefighter Mario Rodriguez

0:36:020:36:05

is getting weighed to see how much sweat he looses

0:36:050:36:08

when fighting a fire.

0:36:080:36:09

To measure any temperature change inside his body,

0:36:110:36:14

Rodriguez takes an electronic pill.

0:36:140:36:17

To keep his heart and brain safe,

0:36:170:36:19

his core temperature must remain close to 37 degrees centigrade.

0:36:190:36:24

Before he goes in, his core temperature is just over 37 degrees.

0:36:320:36:37

If his core temperature rises by just four degrees

0:36:500:36:54

he will become confused and fall unconscious.

0:36:540:36:58

A rise of six degrees could cause death.

0:36:580:37:00

After 45 seconds in the 1,200 degree fire...

0:37:040:37:10

he's poaching in his own juices.

0:37:100:37:14

'It was real hot,

0:37:290:37:30

'my bones and all my joints were burning.'

0:37:300:37:34

The heat... Just got to get out of there and get some cool air.

0:37:340:37:37

His core temperature has risen by a very minimal one degree centigrade.

0:37:370:37:43

You're at 207 now.

0:37:460:37:48

So that looks like you lost three pounds of body weight.

0:37:480:37:51

Three pounds equals over a litre of sweat

0:37:510:37:54

lost in just one minute's exposure to the fire.

0:37:540:37:58

Rodriguez walked into a 1,200 degree fire

0:38:000:38:04

and walked out with his body temperature almost exactly the same.

0:38:040:38:09

This is the story of your creation.

0:38:170:38:21

It began with a sperm,

0:38:270:38:29

the smallest cell in the human body,

0:38:290:38:32

fusing with the biggest cell...

0:38:320:38:34

an egg.

0:38:340:38:35

Everyday, the human male

0:38:400:38:41

produces hundreds of millions of DNA Torpedoes...

0:38:410:38:48

otherwise known as sperm.

0:38:480:38:50

Each ejaculation can contain 250 million of them.

0:38:510:38:56

That's enough, at least in theory,

0:38:580:39:01

to cover every inch of Manhattan with people.

0:39:010:39:05

Fortunately, the human female has other ideas.

0:39:080:39:12

For her, it's quality, not quantity.

0:39:120:39:16

Her ovaries usually produce just one egg every month.

0:39:180:39:23

The process of reproduction is so complex

0:39:270:39:31

it's a wonder it happens at all.

0:39:310:39:34

Most of the time, the sperm die in a pool,

0:39:350:39:39

trapped inside the vagina.

0:39:390:39:41

Because the entrance into the womb, through the cervix,

0:39:420:39:47

is out of reach, blocked shut.

0:39:470:39:50

For the sperm to have a chance of getting in,

0:39:500:39:54

timing is everything.

0:39:540:39:55

There are just a few days in any month

0:40:030:40:06

when the woman's body offers them an opportunity.

0:40:060:40:09

Hormones soften the blockage

0:40:090:40:11

at the entrance to the cervix.

0:40:110:40:15

Transforming it from a barrier into a life line.

0:40:150:40:18

But the sperm have to be strong

0:40:230:40:25

to make the 15cm journey.

0:40:250:40:27

It's a long way

0:40:270:40:29

for the smallest cell in the body.

0:40:290:40:32

The straighter and faster they can swim,

0:40:320:40:35

the better chance they have of making it.

0:40:350:40:37

The deformed, lazy and the dead

0:40:370:40:40

are left behind.

0:40:400:40:42

And, of course,

0:40:440:40:45

the more fit sperm you have,

0:40:450:40:47

the greater the chance of success.

0:40:470:40:49

If 250 million sperm began the journey,

0:40:530:40:57

only 1%, that's two and a half million,

0:40:570:41:00

will make it through to the cervix.

0:41:000:41:03

As they swim out of the vagina,

0:41:050:41:07

they're just at the beginning of a long and perilous journey.

0:41:070:41:11

The woman's body is about to launch an attack.

0:41:170:41:22

They have entered the cervix -

0:41:220:41:26

a labyrinth of dead ends.

0:41:260:41:28

perfect for an ambush.

0:41:280:41:31

The sperm have triggered the body's defence system.

0:41:330:41:36

White blood cells have recognised the sperm as a foreign invader

0:41:380:41:42

and, just as they would if they were fighting an infection,

0:41:420:41:45

they've been mobilised to kill.

0:41:450:41:48

They attack the sperm

0:41:500:41:52

as they swim through the cervix and into the uterus.

0:41:520:41:55

By the time the surviving sperm reach the fallopian tube,

0:42:010:42:04

where they are safe from the white blood cells

0:42:040:42:08

there could be as few as 20 left.

0:42:080:42:10

They will be 20 of the very best on offer.

0:42:120:42:15

Here, scientists have recently discovered

0:42:200:42:23

that the woman's body

0:42:230:42:24

has come up with an amazing trick.

0:42:240:42:26

She takes control of the sperm by holding them, one by one,

0:42:290:42:32

on the walls of her fallopian tube.

0:42:320:42:36

She then powers them down.

0:42:380:42:40

They're alive, safe, but fast asleep.

0:42:420:42:45

The woman now has up to five days

0:42:520:42:54

to release the precious egg growing inside her ovary.

0:42:540:42:58

As soon as it's ripe, the egg is released.

0:43:070:43:10

And it's wafted into the opening of the fallopian tube.

0:43:160:43:20

Once the egg is ready and waiting,

0:43:310:43:33

it's time to wake up the sleeping sperm...

0:43:330:43:36

Sending out a powerful chemical beacon,

0:43:430:43:45

the egg guides the sperm in.

0:43:450:43:48

It's the precursor of every new life.

0:43:540:43:57

The sperm - some male, some female -

0:44:000:44:03

compete to reach the egg.

0:44:030:44:05

But there can be only one winner.

0:44:110:44:14

The competing sperm break off the surrounding cloud of cells.

0:44:190:44:24

Until one finally pushes through

0:44:270:44:29

the soft shell underneath.

0:44:290:44:31

The egg is now in danger.

0:44:390:44:41

If a second sperm gets in,

0:44:440:44:46

the egg will die.

0:44:460:44:49

It must protect itself - and quickly.

0:44:520:44:55

Under the shell,

0:44:580:44:59

tiny granules detonate in a chain reaction.

0:44:590:45:03

Firing out chemicals,

0:45:030:45:05

hardening the shell,

0:45:050:45:07

making the egg impenetrable.

0:45:070:45:09

Fertilised, the egg is now safe.

0:45:110:45:14

This was how we all began.

0:45:160:45:19

You truly are an amazing creation.

0:45:190:45:22

We're made up of around a hundred trillion cells,

0:45:290:45:33

all coming from just one single fertilised egg.

0:45:330:45:37

Within hours of fertilisation,

0:45:390:45:42

this new cell, called a zygote,

0:45:420:45:44

divided into two identical cells.

0:45:440:45:47

Then into four...

0:45:470:45:49

then eight...

0:45:490:45:50

16, and so on...

0:45:500:45:53

before implanting in the lining of the womb

0:45:540:45:57

and becoming an embryo.

0:45:570:45:59

In some cases, on rare occasions,

0:46:050:46:09

a single embryo creates two bodies.

0:46:090:46:12

one in 250 early embryos split.

0:46:160:46:21

If they do,

0:46:210:46:22

they must divide completely

0:46:220:46:24

within the first two weeks,

0:46:240:46:26

or they probably never will.

0:46:260:46:28

Once split, the embryos create near-replicas of themselves.

0:46:310:46:35

Identical twins.

0:46:350:46:38

This quirk of nature

0:46:400:46:41

has given synchronised divers, Helen and Carol Galashan

0:46:410:46:45

a distinct advantage.

0:46:450:46:47

Being an identical twin

0:46:470:46:49

definitely helps with synchronised diving.

0:46:490:46:51

We don't really have to try with the synchronised part,

0:46:510:46:54

that part comes quite naturally to us.

0:46:540:46:56

We actually think we're mirror-image twins.

0:46:560:46:58

-We fold our arms opposite ways. Our hair parts the opposite way.

-Even when we're diving,

0:46:580:47:02

The first foot I put on is my right foot, Carol's is her left foot.

0:47:020:47:06

Identical twins actually come from one egg...

0:47:070:47:11

-That splits.

-That splits into two, and non-identical twins come from two eggs.

0:47:110:47:15

So the way we see it is that we were one person that split in two...

0:47:150:47:18

One person in two bodies.

0:47:180:47:20

-Right...

-Ooh.

0:47:230:47:25

This woman's pregnancy is even more unlikely than identical twins.

0:47:270:47:31

She's beaten odds of 4,500 to 1.

0:47:330:47:37

Diane is carrying non-identical triplets.

0:47:370:47:41

Remarkably, Diane's body

0:47:410:47:43

naturally produced not one, but three eggs in a single go.

0:47:430:47:48

It's an incredibly rare type of pregnancy.

0:47:490:47:52

Not only did Diane produce multiple eggs,

0:47:520:47:55

but all of them were fertilised.

0:47:550:47:57

Entirely independently of each other.

0:47:570:48:00

Apparently, I released three eggs,

0:48:010:48:04

and Mike, he had three separate sperm

0:48:040:48:06

that fertilised all three eggs.

0:48:060:48:08

They've all got their own placentas

0:48:080:48:11

and they're all in separate sacks.

0:48:110:48:13

So they've all got have their own little bedroom.

0:48:130:48:17

Effectively, Diane got pregnant three times in one go.

0:48:180:48:22

But there's a downside to having triplets.

0:48:280:48:32

31 weeks - nine weeks early -

0:48:320:48:34

Diane has gone into labour.

0:48:340:48:37

She is going to need an emergency caesarean.

0:48:370:48:40

I'm just going to bring him round to show you, quickly.

0:48:460:48:50

Here we go, you two. Here he is. He's beautiful.

0:48:500:48:54

So he's a little breach baby.

0:48:560:48:59

There he is.

0:48:590:49:01

-Hello!

-Isn't he lovely?

0:49:010:49:03

This is the skinny Minnie.

0:49:070:49:10

All the babies have now been delivered.

0:49:100:49:12

-She's beautiful.

-Last but not least.

0:49:120:49:15

And against the odds,

0:49:150:49:17

they are all alive and well.

0:49:170:49:19

For your body,

0:49:280:49:30

this world is a dangerous place.

0:49:300:49:32

Threats lurk around every corner.

0:49:350:49:38

And it's not just the obvious dangers that threaten you.

0:49:380:49:42

Even now, as you watch this film,

0:49:440:49:46

there are pathogens waiting to get inside you.

0:49:460:49:49

A pathogen is a foreign invader that causes disease.

0:49:490:49:53

They spread in all sorts of ways,

0:49:550:49:59

commonly through sneezing.

0:49:590:50:02

A simple sneeze

0:50:020:50:04

is often all it takes

0:50:040:50:06

for viruses to jump from one person to another.

0:50:060:50:09

Sneezing is one of the most powerful forces your body produces.

0:50:090:50:13

You expel air at 100 miles an hour,

0:50:130:50:16

ejecting anything that isn't bolted down.

0:50:160:50:19

Once a pathogen invader, like the flu virus,

0:50:210:50:25

gets inside your body,

0:50:250:50:26

you have to respond quickly.

0:50:260:50:28

Time to turn on your immune system

0:50:300:50:33

to destroy them.

0:50:330:50:34

Your first response to infection is fever.

0:50:390:50:43

Raising your temperature by just a few degrees

0:50:430:50:46

is enough to slow them down.

0:50:460:50:48

Meanwhile, deep within your tissues,

0:50:540:50:57

an internal army is on the march.

0:50:570:51:00

On the frontline are phagocytes,

0:51:020:51:04

a form of white blood cell.

0:51:040:51:07

They flood the infection site to fight the viruses.

0:51:070:51:10

But in this case, the viruses are too strong.

0:51:120:51:16

Instead, the soldiers themselves become infected.

0:51:160:51:20

Now the only way these cells can kill the viruses

0:51:200:51:23

is to self-destruct.

0:51:230:51:25

As their bodies pile up,

0:51:290:51:33

they form the sticky basis of your snot.

0:51:330:51:36

But your immune system hasn't given up.

0:51:380:51:40

A second wave of attack is released

0:51:430:51:45

as another kind of white blood cell is unleashed...

0:51:450:51:49

the Killer T-cells.

0:51:490:51:52

Instead of attacking the viruses directly,

0:51:520:51:56

they take aim at your own infected cells.

0:51:560:51:59

They give a kiss of death,

0:51:590:52:02

they make the infected cell implode,

0:52:020:52:06

then self destruct,

0:52:060:52:08

destroying the viruses inside.

0:52:080:52:12

It's one of the reasons you'll get a sore throat.

0:52:120:52:14

Despite these two assaults,

0:52:210:52:23

the viruses haven't yet been defeated.

0:52:230:52:26

But your immune system has another trick.

0:52:260:52:30

Yet more white bloods cells,

0:52:300:52:31

this time called B-cells,

0:52:310:52:33

are able to recognise the specific invading pathogen

0:52:330:52:36

and produce a specialised weapon.

0:52:360:52:39

The Y-shaped antibody.

0:52:420:52:44

These can be produced at a rate of 2,000 per cell per second.

0:52:460:52:53

They coat the viruses...

0:52:530:52:55

slowing them down and making them stick together.

0:52:560:53:00

Now the viruses are easily swept up.

0:53:000:53:03

And you begin to feel better,

0:53:080:53:11

the fever drops and your energy starts to return.

0:53:110:53:14

The cells of your immune system

0:53:160:53:19

have won the day.

0:53:190:53:20

One of the most remarkable defence mechanisms your body has

0:53:290:53:33

is its ability to repair itself.

0:53:330:53:35

Johnny Greaves is 33 years old.

0:53:390:53:42

He is a professional boxer.

0:53:420:53:44

For Johnny, boxing isn't just a sport, it's a livelihood.

0:53:450:53:48

I'm here to pay my bills and keep my kids OK,

0:53:510:53:53

so obviously, that's the first thought in my mind,

0:53:530:53:56

bringing home the bacon and paying the kids' bills.

0:53:560:53:59

Johnny is in a dangerous game.

0:54:010:54:03

If he picks up the slightest injury,

0:54:030:54:06

boxing regulations mean he'll have to cancel his next fight.

0:54:060:54:10

If he show's up with a bruise he'll be disqualified.

0:54:130:54:16

His body is going to do everything in its power to avoid this.

0:54:200:54:24

All of Johnny's biological defence mechanisms

0:54:260:54:29

are clicking into action.

0:54:290:54:30

He ducks and dives

0:54:300:54:32

to avoid the punches.

0:54:320:54:34

But as Johnny tires, his defences begin to fail.

0:54:410:54:44

The full extent of Johnny's injuries have yet to be revealed.

0:54:580:55:03

A black eye is about to form.

0:55:030:55:05

His next fight is in two weeks,

0:55:070:55:09

if he is to collect that pay cheque

0:55:090:55:11

he has to heal.

0:55:110:55:14

Now its time for Johnny's body to really earn his living.

0:55:140:55:17

The delicate blood vessels in the tissue under Johnny's eye

0:55:240:55:27

were destroyed by a single punch.

0:55:270:55:29

As the vessels burst,

0:55:360:55:38

blood cells rush out.

0:55:380:55:39

But despite the catastrophic damage,

0:55:410:55:44

a repair crew is on the way.

0:55:440:55:45

Flowing out with the blood are cell fragments.

0:55:490:55:52

Called Platelets,

0:55:530:55:55

they are built to stop bleeding.

0:55:550:55:57

They gradually form a lattice

0:55:570:55:59

that catches the leaking blood cells like a net.

0:55:590:56:03

Extra support comes from a stringy protein - fibrin.

0:56:040:56:10

Together, they form the clot,

0:56:100:56:12

which plugs the hole

0:56:120:56:13

and the bleeding stops.

0:56:130:56:15

Five hours after the fight,

0:56:180:56:20

the effects of the punch

0:56:200:56:21

are beginning to show on Johnny's face.

0:56:210:56:24

His eye is beginning to swell.

0:56:270:56:29

Fluid is flowing into the tissue around the eye.

0:56:330:56:38

It's coming from tiny holes in the walls of the blood vessel.

0:56:380:56:42

It is a form of defence.

0:56:450:56:46

The force of the flow stops any infection in the wound

0:56:500:56:54

from travelling into the bloodstream,

0:56:540:56:56

trapping it in the tissue instead.

0:56:560:56:59

The results of this inflammation are dramatic.

0:56:590:57:03

Johnny's eye has now turned a striking shade of purple.

0:57:050:57:09

The colour is the product of decaying blood cells

0:57:180:57:22

trapped outside the circulatory system,

0:57:220:57:24

where they can't survive.

0:57:240:57:27

Now Johnny's body starts to clear up the mess.

0:57:310:57:35

Macrophages - giant white blood cells -

0:57:380:57:41

sweep through the tissue and absorb the dying cells.

0:57:410:57:44

Inside the macrophage,

0:57:460:57:47

haemoglobin, the chemical that gives red blood cells their unique redness, breaks down.

0:57:470:57:53

It's this that gives the bruise

0:57:530:57:56

it's familiar cocktail of colours.

0:57:560:57:59

As it breaks apart,

0:57:590:58:00

haemoglobin transforms into different-coloured chemicals.

0:58:000:58:05

Over time, the colour shifts

0:58:060:58:09

from green to yellow and finally to brown.

0:58:090:58:12

As the Macrophages leave,

0:58:230:58:25

they draw the coloured chemicals away from the skin.

0:58:250:58:29

Healing is now complete.

0:58:290:58:32

Johnny's body has repaired the damage,

0:58:350:58:38

just in time for another fight.

0:58:380:58:40

Subtitles by Red Bee Media Ltd

0:58:420:58:46

E-mail [email protected]

0:58:460:58:49

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