Name: 呼吸背後的隱藏物理學 (The Hidden Physics Behind Your Breath)
Uploaded: 2021-01-14T10:46:23.000Z
Duration: 9 min 19 s
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Breathing is one of the few things you do continuously, everyday, without thinking about

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Except now — now that I pointed it out, you're definitely thinking about breathing.

Our lives would be completely different if we couldn't breathe air — more technically,

See, our bodies, like other vertebrates, depend on oxygen to run our normal aerobic metabolisms.

Some of our bodily processes happen without oxygen, but to really take advantage of the

food we eat, we need to burn some oxygen.

That means at some point, we need to start plucking oxygen out of the air and shoving

it down our throats and into our red blood cells.

This biological process is really dependent on physics.

Those ideal gas laws you may have learned in high school?

We see a beautiful example of them in the simple act of taking a breath.

So breathe in and breathe out, today we're talking about the respiratory system.

We've been talking a lot about blood in this series so far, and with good reason.

Multiple substances need to get to their target tissues so we can have raw materials to carry

Once those materials are in the bloodstream, the circulatory system delivers them to their

And of course, one of the most important of those materials is oxygen.

It's everywhere around us, so all we have to do is pick it out from the air we breathe.

That's where the respiratory system comes in, all the hardware involved to breathe in

You're already familiar with the big players here, the lungs.

You have two of these spongy pink air sacs that span from your stomach to your breastbone,

and while they're similar to each other, they're not identical.

Your right lung — your right, not the right of your screen — has three lobes, while

That's because your heart rests in between your lungs, ever so slightly askew to the

left in a little nook called the cardiac notch.

And below all that, you'll find a weird shaped, kinda round, kinda dome-shaped muscle

This muscle is a huge deal for breathing.

See, your lungs don't have any muscles of their own.

They just go along for the ride with the rib cage.

So when the diaphragm contracts along with the external intercostal muscles between the

ribs, they expand the space, or volume, inside the chest.

What that does is change the pressure inside the lungs since volume and pressure are inversely

So as the volume of a container increases, the pressure on all those air molecules decreases.

And vice versa — as the volume decreases, pressure increases.

And yes, it may seem scary that physics is coming up in an anatomy video, but the movement

of that vitally important oxygen depends on pressure differences.

That's because our lungs can be thought of as containers for gas.

So when you contract your diaphragm and expand your chest's volume, there's less pressure

on the air inside compared to the air outside your body, the stuff that you're breathing

This is where another physics law comes in.

Whenever there's a difference in pressure between two gases and they're connected

somehow, their pressures will tend to equalize.

That means a gas will move from areas of high pressure to low pressure.

It doesn't matter if we're talking about gas molecules in a weather system or in our

Gases tend to flow from high pressure to low pressure.

So with a reduced pressure inside the chest and constant pressure in the air around us,

Your diaphragm and intercostals relax, which decreases the space in your lungs, and with

more pressure inside the lungs than outside, air flows outwards.

Regular breathing really has nothing to do with sucking air in or squeezing air out.

You're just letting physics do its thing to your lungs.

But all that depends on air actually getting into your lungs, so you have a few organs

in place to get air from outside your body into your lungs.

Despite starring roles in your ability to appreciate tacos, your mouth and nose are

the big external interfaces for your respiratory system.

And they both act as air-treatment centers, keeping the air warm and humid, and trapping

Plus, the airway is lined with mucus membranes full of immune cells to make sure pathogens

Yep, the same mucus membranes that create boogers.

After air comes in, it flows down cartilaginous tubes past the larynx, where we can find your

vocal folds that make your beautiful voice.

From here downward, your airway looks an awful lot like an upside down tree.

In this case, the tree trunk, or trachea, is a thick tube of epithelial tissue surrounded

It traces the path of your sternum, right about here, where it splits.

Then the trachea branches off into two bronchi.

Those branches keep splitting off further and further throughout the lung until they

These twigs are only about a millimeter thick and at this point they're not producing

Each of those tiny bronchial branches have anywhere from two to eleven leaves, or alveoli.

Not to be confused with ravioli which is a delicious pasta dish and has nothing to do

These alveoli leaves interact with gases really similarly to how real leaves interact with

These alveoli, hundreds of millions of them are where air really starts interacting with

See, those alveoli have really thin walls, and they're surrounded by extremely tiny

blood vessels called capillaries which also have really thin walls.

In order for us to get oxygen in and carbon dioxide out, those gas molecules need to cross

Remember, these aren't thick concrete walls, they're squishy, mobile cells that readily

But these are gas molecules, they're not actively swimming through fluid.

It happens thanks to diffusion, a physics concept you're familiar with if you use