0:06
For most of history,
0:08
humans had no idea what purpose the heart served.
0:12
In fact, the organ so confused Leonardo da Vinci,
0:16
that he gave up studying it.
0:18
Although everyone could feel their own heart beating,
0:21
it wasn't always clear what each thump was achieving.
0:25
Now we know that the heart pumps blood.
0:28
But that fact wasn't always obvious,
0:30
because if a heart was exposed or taken out,
0:33
the body would perish quickly.
0:35
It's also impossible to see through the blood vessels,
0:38
and even if that were possible,
0:39
the blood itself is opaque,
0:41
making it difficult to see the heart valves working.
0:44
Even in the 21st century,
0:46
only a few people in surgery teams
0:49
have actually seen a working heart.
0:52
Internet searches for heart function,
0:54
point to crude models, diagrams
0:56
or animations that don't really show how it works.
0:59
It's as if there has been a centuries old conspiracy
1:02
amongst teachers and students
1:04
to accept that heart function cannot be demonstrated.
1:07
Meaning that the next best thing
1:09
is simply to cut it open and label the parts.
1:12
That way students might not fully grasp the way it works,
1:15
but can superficially understand it,
1:18
learning such concepts as
1:19
the heart is a four-chambered organ,
1:22
or potentially misleading statements like,
1:24
mammals have a dual-circulation:
1:26
one with blood going to the lungs and back,
1:29
and another to the body and back.
1:31
In reality, mammals have a figure-eight circulation.
1:34
Blood goes from one heart pump to the lungs,
1:37
back to the second heart pump, which sends it to the body,
1:40
and then back to the first pump.
1:42
That's an important difference
1:43
because it marks two completely different morphologies.
1:47
This confusion makes many students
1:49
wary of the heart in biology lessons,
1:52
thinking it signals an intimidating subject
1:54
full of complicated names and diagrams.
1:57
Only those who end up studying medicine
2:00
compeltely understand how it all actually works.
2:03
That's when its functions become apparent
2:05
as medics get to observe the motion of the heart's valves.
2:08
So, let's imagine you're a medic for a day.
2:11
What you'll need to get started is a whole fresh heart,
2:15
like one from a sheep or pig.
2:17
Immerse this heart in water
2:19
and you'll see that it doesn't pump when squeezed by hand.
2:22
That's because water doesn't enter the heart cleanly enough
2:25
for the pumping mechanism to work.
2:27
We can solve this problem in an extraordinarly simple way.
2:31
Simply identify the two atria and cut them off,
2:35
trimming them down to the tops of the ventricles.
2:38
This makes the heart look less complicated
2:40
because the atria have several incoming veins attached.
2:43
So without them there, the only vessels remaining
2:46
are the two major heart arteries:
2:48
the aorta and pulmonary artery,
2:51
which rise like white columns from between the ventricles.
2:54
It looks -- and really is -- very simple.
2:57
If you run water into the right ventricle from a tap
3:01
(the left also works, but less spectacularly),
3:04
you'll see that the ventricular valve
3:05
tries to close against the incoming stream.
3:09
And then ventricle inflates with water.
3:11
Squeeze the ventricle and a stream of water
3:13
squirts out of the pulmonary artery.
3:16
The ventricular valves, called the tricuspid in the right ventricle
3:19
and the mitral in the left,
3:21
can be seen through the clear water
3:23
opening and closing like parachutes
3:25
as the ventricle is rhythmically squeezed.
3:28
This flow of water mimics the flow of blood in life.
3:32
The valves are completely efficient.
3:34
You'll notice they don't leak at all when the ventricles are squeezed.
3:38
Over time, they also close against each other
3:40
with very little wear and tear,
3:42
which explains how this mechanism continues to work seamlessly
3:46
for more than 2 billion beats a heart gives in its lifetime.
3:50
Now, anyone studying the heart can hold one in their hands,
3:54
make it pump for real
3:55
and watch the action unfold.
3:57
So place your hand above your own
3:59
and feel its rhymic beat.
4:01
Understanding how this dependable inner pump works
4:04
gives new resonance to the feeling you get
4:06
when you run a race,
4:08
drink too much caffeine
4:09
or catch the eye of the one you love.
