Incredible Human Machine Page #5

Just the idea of food

can get our mouths to water.

We salivate roughly a pint every day.

And in that saliva are enzymes that,

along with our teeth,

begin to break down the food that we eat.

But not before we get to savour it first.

Some 1 0,000 taste buds line our tongues,

each one home to about 50 taste receptor cells

that tell the brain what we're eating.

And if some of those precious receptors

are scorched off,

it will only take a week to 1 0 days

to grow back a brand-new set.

Once the muscular tongue manoeuvres food

into our oesophagus, we're on autopilot.

When we eat, a flap of skin called the epiglottis

seals off our windpipes.

Except when it doesn't.

l'm OK.

Then it's back to the beginning.

A typical journey down the oesophagus

takes about five seconds.

From here it's squeezed, like toothpaste.

Once it passes into the stomach as it's doing

here it's time to slow down a bit and digest.

Normally this stretchy, J-shaped bag

isn't much bigger than a fist.

(Groan)

But after a big meal,

it can expand to more than 20 times that size.

For the next several hours highly acidic gastric

juices spew from the stomach's walls,

breaking down proteins in our food while muscle

contractions knead and churn it into a pulp.

The acid here is so strong the stomach must

continuously secrete a layer of protective mucus

so that it doesn't digest itself.

lt absorbs very few nutrients, though.

For that we pass into the 20-foot

''dis-assembly'' line of the small intestine

with the help of a specialised camera pill.

For about five hours, food's building blocks

are pushed, prodded,

sprayed with digestive juices

and wrung like a rag here,

until its vital elements

are forced through the intestinal wall

and into the bloodstream.

From here, most of our meal's nutrients

will flow directly to the liver,

the body's largest internal organ.

The liver breaks down, repackages and delivers

nutrients to our cells for growth and power.

Our bodies ultimately try to balance

energy intake.

But sometimes more goes in than out.

The result.. fat.

This is how fat looks on the inside...

and on the outside.

lt doesn't take a lot of excess calories

to make you gain weight.

Just 1 5 more a day than you need -

about the amount in four pistachio nuts -

will add a pound and a half of fat over a year.

Once the small intestine

has taken in everything worth ingesting,

the rest is pushed along to the large intestine.

For another 20 hours or so,

the last of the water is absorbed,

and billions of bacteria work to break down

the remaining contents.

ln the end,

anything we can't digest gets flushed...

(Toilet flushing)

..out of our bodies.

Food's complicated journey

has a larger purpose.

Once we've extracted what we need

to feed the incredible machine

and gotten our cellular engines humming,

it's nothing short of astounding

what we can do with them,

thanks to amazing contraptions called muscle.

The incredible human machine in action.

Just about every body part,

from our skin receptors

to the balance centre in our inner ears,

help to make these amazing complexities of

movement seem almost effortless,

automatic even.

But if we peer beneath our skin,

we see that one tissue above all

propels us into a thousand different positions.

From the soles of our feet

to the tips of our fingers some 650 muscles,

about 40% of our body mass,

power every move we make.

As our day pushes on,

these skeletal muscles lift us through it

usually without our thinking about it.

Without them we couldn't run or blink,

smile or speak for that matter.

Hello?

Just muttering a single word...

Hello?

(Prolonged) Hello?

..involves muscles in the face, lips, tongue, jaw,

larynx - as many as 1 00 muscles.

Many of the same muscles let us form a frown.

Turn them upside down and all 34 muscles

in the face let us deliver a kiss.

Walking,. a highly coordinated series of falls

that we've taken for granted

since we were toddlers

requires no fewer than 200 skeletal muscles.

Back muscles to keep you from falling forward,

abdominal muscles

to keep you from falling back.

lt takes 40 or so musclesjust to raise one leg

and move it forward.

Now, add into that running,

swimming,

shooting, riding,

and fencing,

and you get an idea of how many different

muscles are at work inside Eli Bremer,

top-seeded US Olympic pentathlete.

l think what l do is very normal and someone

will ask what a typical training day is.

And l'll tell them, ''Swim about four miles

and run about ten miles.''

You know, it's not that big of a deal.

l mean, l think anybody could do it.

And then l get this weird look like,

''You must be crazy.''

So, what propels him?

lf we zoom in on one of these muscles in motion

and closer still at the hundreds of muscle fibres

that run its length,

we find two proteins, actin and myosin.

And their actions couldn't be simpler.

They link up,

squeezing together like cogs on a wheel.

And then they relax,

releasing their grip and going back to normal.

lf during a fencing bout

Eli wants to strike an opponent

the actin and myosin in his tricep bind,

while in his biceps they release.

When he winds up for another blow

the opposite happens.

Now his biceps bind and his triceps release.

By binding and releasing

all our skeletal muscles

we get our every motion.

And 3, 2, 1 ...go!

The more we work our muscles

the more actin and myosin we make,

the bulkier our skeletal muscles become,

as Olympic hopeful Doreen Fullhart

demonstrates.

To lift, her brain sends electrical impulses down

nerves to muscle fibres

telling the actin and myosin to bind...

..and release.

But for our muscles to work,

that signal from the brain must get through.

That requires an intricate but delicate

wiring system.

(Monitor beeps)

- Have you met Dr Redett?

- Good to see you again.

Good to see you.

34-year-old Jason Keck severed some nerves

in a logging accident three months ago

and he hasn't moved his left arm since.

Just a few years ago, doctors could do virtually

nothing to fix this kind of damage.

Today Doctor Dr Allan Belzberg and his team

at Johns Hopkins School of Medicine

will try to get Jason's wiring system

working again.

The nerve is just an electric cable,

when all is said and done.

A very sophisticated one,

but nonetheless an electrical cable.

We have a nerve that's been broken,

that's been stretched and snapped.

We can bring the ends together and fix it.

lf we can't get the ends together we can fill

the gap in and splice in some material.

And if we can't do that

then again we go to this nerve transfer concept

of robbing Peter to pay Paul.

Anything? Nothing?

Paul in this case is Jason's arm.

To find a suitable Peter to rob,

Belzberg zaps various nerves with electricity

to see where current is being lost.

Not unlike an electrician checking wires

in a house.

What makes this interesting

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