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In this episode of Body Story,

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we unravel the mysteries of the two most important organs of the human body:

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The brain, and the heart.

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And as we understand how these organs work, we also see how fragile they are,

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and how easily they're affected by the chemicals we drink and eat.

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John Palmer's diet is high in cholesterol, and that means danger for the tiny arteries

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that feed blood to his heart.

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Fatty growths are blocking the passing flow of blood cells,

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Today that is going to lead to disaster.

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The alcohol that Greg Moore drinks floods into the gaps between his brain cells

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it interferes with electrical signals that flash through his brain.

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And this has an instant effect, repressing the rational part of his brain.

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Giving the animal within Greg a chance to enjoy itself.

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Greg's night is only just beginning.

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>>We'll replace the whole lot, just get them off as quick as you can.

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>>What they used is completely useless.

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>>Well that's why they brought us in, do the job properly this time.

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NARRATOR: John Palmer is having a bad day.

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It's going to get much worse.

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>>Be right down.

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You take care of them Marcus.

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NARRATOR: For forty-five years, John's heart hasn't missed a single beat.

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But today, it's going to let him down with dire consequences for his entire body.

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A ball of muscle no bigger than his fist, John's heart pumps enough blood to fill

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forty barrels each day.

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Inside its chambers, red blood cells saturated with oxygen, are sucked in and pumped out

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with amazing force.

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They are propelled to do a network of blood vessels 75,000 miles long

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which supplies oxygen to every organ and muscle in John's body.

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>>Hello then?

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>>Kenny. Yeah a few problems, they're a hopeless lot that let loose on this place, you know?

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NARRATOR: John's heart doesn't just supply oxygen to other organs,

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it also supplies itself.

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Clinging to its surface are narrow blood vessels,

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coronary arteries, which feed the hearts own muscular walls.

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The walls of John's heart consist of 50 million elastic muscle cells,

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all contracting together.

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This is the beat of John's heart.

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>>Yeah, we'll get it done. I'll just have to be getting my hands dirty, that's all.

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Yeah, see you later. Bye.

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>>John! When you've got a moment!

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<i>phone rings</i>

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>>Yes!

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NARRATOR: Unluckily for John, lurking inside one of his vital coronary arteries is a tiny time bomb.

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A growth no bigger than a grain of sand, it has the potential to alter the course of John's life.

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>>Here you go!

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>>Ah, just the job!

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>>Came free with our order. <i>laughs</i>

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Looks a bit like Kenny don't you think?

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NARRATOR: The growth inside John's coronary artery consists mainly of cholesterol.

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Our bodies need cholesterol to function normally, but most of what we require is manufactured in our livers.

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John doesn't need the extra cholesterol in his food.

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The surplus seeps into his blood stream, small amounts can be transported safely,

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but too much and it spills out, polluting his blood with globules of free floating fat.

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>>Yeah well we all have days like that don't we?

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Yeah go on then.

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NARRATOR: Cholesterol globules sink into tiny cracks in John's artery wall.

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Creating a fat filled growth. A plaque.

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Over the years it bulges up and out into the artery.

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Slowly but surely, it begins to reduce the free flow of John's blood.

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All of us have some plaque in our arteries,

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but John has many more than most men his age.

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>>IS IT ON THE LAURY?

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NARRATOR: The inner walls of his coronary arteries are riddled with plaques.

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Blood is being squeezed through the vessels which are half the width they ought to be.

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45 years of cholesterol build up lurks beneath a thin and fragile membrane.

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>>It can't be delivered til when?!

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Go on.

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NARRATOR: John is suffering from advanced heart disease.

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But he doesn't know it yet,

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because so far is heart has been able to compensate for the damage.

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Only a week ago, a patch of his heart muscle became starved of oxygen.

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The grain muscle cells sent a distress signal to nearby coronary arteries.

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New blood vessels began to grow.

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A natural heart bypass, bringing a fresh supply of oxygen to the starving cells.

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But this kind of bypass takes at least two days to grow.

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Too slow to save John if an artery were to block suddenly.

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>>If anything else goes wrong today...

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Hey give us a cigarette, will ya?

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[everyone laughs]

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Give us a light.

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NARRATOR: John's heart is designed to respond to the needs of his body moment by moment.

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While he's sitting still, it needs to beat no more than 70 times a minute.

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To maintain its precision, it uses electricity.

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The heart is the only organ with its own power supply.

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A natural pacemaker buried deep in its walls, generates electrical pulses

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which ensure its regular beat.

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Each pulse surges through the cells which make up the heart's muscular walls,

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forcing them to beat in unison and keep perfect time.

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>>We've got another job to get to after this.

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>>Another ten minutes?

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>>Hey kick the ball against that wall, the whole lot will probably fall down by itself.

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[laughs]

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NARRATOR: As John chases after the ball, 70 heart beats per minute is no longer enough

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to meet his body's demand for oxygen.

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It's a long time since he did any exercise,

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and his leg muscles cry out for extra fuel.

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His brain sends an urgent signal to his heart.

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The pacemaker reacts instantly, stepping up the rate it