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  • For most of history,

  • humans had no idea what purpose the heart served.

  • In fact, the organ so confused Leonardo da Vinci,

  • that he gave up studying it.

  • Although everyone could feel their own heart beating,

  • it wasn't always clear what each thump was achieving.

  • Now we know that the heart pumps blood.

  • But that fact wasn't always obvious,

  • because if a heart was exposed or taken out,

  • the body would perish quickly.

  • It's also impossible to see through the blood vessels,

  • and even if that were possible,

  • the blood itself is opaque,

  • making it difficult to see the heart valves working.

  • Even in the 21st century,

  • only a few people in surgery teams

  • have actually seen a working heart.

  • Internet searches for heart function,

  • point to crude models, diagrams

  • or animations that don't really show how it works.

  • It's as if there has been a centuries old conspiracy

  • amongst teachers and students

  • to accept that heart function cannot be demonstrated.

  • Meaning that the next best thing

  • is simply to cut it open and label the parts.

  • That way students might not fully grasp the way it works,

  • but can superficially understand it,

  • learning such concepts as

  • the heart is a four-chambered organ,

  • or potentially misleading statements like,

  • mammals have a dual-circulation:

  • one with blood going to the lungs and back,

  • and another to the body and back.

  • In reality, mammals have a figure-eight circulation.

  • Blood goes from one heart pump to the lungs,

  • back to the second heart pump, which sends it to the body,

  • and then back to the first pump.

  • That's an important difference

  • because it marks two completely different morphologies.

  • This confusion makes many students

  • wary of the heart in biology lessons,

  • thinking it signals an intimidating subject

  • full of complicated names and diagrams.

  • Only those who end up studying medicine

  • compeltely understand how it all actually works.

  • That's when its functions become apparent

  • as medics get to observe the motion of the heart's valves.

  • So, let's imagine you're a medic for a day.

  • What you'll need to get started is a whole fresh heart,

  • like one from a sheep or pig.

  • Immerse this heart in water

  • and you'll see that it doesn't pump when squeezed by hand.

  • That's because water doesn't enter the heart cleanly enough

  • for the pumping mechanism to work.

  • We can solve this problem in an extraordinarly simple way.

  • Simply identify the two atria and cut them off,

  • trimming them down to the tops of the ventricles.

  • This makes the heart look less complicated

  • because the atria have several incoming veins attached.

  • So without them there, the only vessels remaining

  • are the two major heart arteries:

  • the aorta and pulmonary artery,

  • which rise like white columns from between the ventricles.

  • It looks -- and really is -- very simple.

  • If you run water into the right ventricle from a tap

  • (the left also works, but less spectacularly),

  • you'll see that the ventricular valve

  • tries to close against the incoming stream.

  • And then ventricle inflates with water.

  • Squeeze the ventricle and a stream of water

  • squirts out of the pulmonary artery.

  • The ventricular valves, called the tricuspid in the right ventricle

  • and the mitral in the left,

  • can be seen through the clear water

  • opening and closing like parachutes

  • as the ventricle is rhythmically squeezed.

  • This flow of water mimics the flow of blood in life.

  • The valves are completely efficient.

  • You'll notice they don't leak at all when the ventricles are squeezed.

  • Over time, they also close against each other

  • with very little wear and tear,

  • which explains how this mechanism continues to work seamlessly

  • for more than 2 billion beats a heart gives in its lifetime.

  • Now, anyone studying the heart can hold one in their hands,

  • make it pump for real

  • and watch the action unfold.

  • So place your hand above your own

  • and feel its rhymic beat.

  • Understanding how this dependable inner pump works

  • gives new resonance to the feeling you get

  • when you run a race,

  • drink too much caffeine

  • or catch the eye of the one you love.

For most of history,

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B1 US TED-Ed ventricle pump blood water squeezed

【TED-Ed】How the heart actually pumps blood - Edmond Hui

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    Halu Hsieh posted on 2014/05/28
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