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呼吸背后的物理学

The Hidden Physics Behind Your Breath

Breathing is one of the few things you do continuously, everyday,
呼吸是为数不多的你每天一直在做
without thinking about it
而不需要去思考的事情
Except now — now that I pointed it out,
除了现在 既然我提到了
you’re definitely thinking about breathing.
你一定在想着呼吸的事
Our lives would be completely different if we couldn’t breathe air
不呼吸空气 准确来说是不能利用氧气的话
— more technically, if we couldn’t utilize oxygen.
我们的生活会天翻地覆
See, our bodies, like other vertebrates,
像其他脊椎动物一样
depend on oxygen to run our normal aerobic metabolisms.
我们身体的正常有氧代谢需要氧气的推动
Some of our bodily processes happen without oxygen,
尽管一些体内进程不需要氧气的参与
but to really take advantage of the food we eat,
但为了有效利用我们摄入的食物
we need to burn some oxygen.
我们仍需消耗一些氧气
That means at some point,
这意味着在某一时刻
we need to start plucking oxygen out of the air
我们要把氧气从空气中提取出来
and shoving it down our throats
然后沿着咽喉
and into our red blood cells.
一路送到血红细胞中
But here’s what I love about this topic.
接下来才是我喜欢这个主题的原因
This biological process is really dependent on physics.
这个生理过程完全依据物理原理
Those ideal gas laws you may have learned in high school?
你们在高中可能学过那些理想气体定律
Dalton’s law
如道尔顿定律
We see a beautiful example of them
我们通过简单的呼吸行为
in the simple act of taking a breath.
发现了关于那些定律的好例子
So breathe in and breathe out,
那么 吸气 呼气
today we’re talking about the respiratory system.
今天我们让来谈谈呼吸系统
We’ve been talking a lot about blood
目前为止我们在这个系列里已经讨论了
in this series so far,
很多与血液有关的话题
and with good reason.
而且都有很充分的理由
Multiple substances need to get to their target tissues
多种物质需要到达它们的目标组织
so we can have raw materials to carry out some key physiology.
使我们拥有原料来进行一些关键生理活动
Once those materials are in the bloodstream,
一旦这些物质进入血液
the circulatory system delivers them to their destinations.
循环系统便将它们运送到目的地
And of course, one of the most important of those materials is oxygen.
不言而喻 最重要的物质之一就是氧气
It’s everywhere around us
氧气在我们周围无处不在
so all we have to do is pick it out from the air we breathe.
我们只需把它从吸入的空气中提取出来
That’s where the respiratory system comes in,
这是呼吸系统的用处
all the hardware involved to breathe in and breathe out.
呼吸系统所有的器官都参与到吸气和呼气中来
You’re already familiar with the big players here, the lungs.
相信你已经对肺脏这个重要器官很熟悉了
You have two of these spongy pink air sacs that span from your stomach to your breastbone,
它是从胃到胸骨间两个海绵状的粉色气囊
and while they’re similar to each other, they’re not identical.
虽然这两个气囊很像 但并不完全相同
Your right lung — your right, not the right of your screen
右肺 在你的右边 不是屏幕的右边
— has three lobes, while
有三个肺叶
your left lung has two.
而你的左肺只有两个
That’s because your heart rests in between your lungs, ever so slightly askew to the left in a little nook
这是因为心脏位于两肺间稍微偏左的角落
called the cardiac notch.
这个角落叫做心切迹
And below all that, you’ll find a weird shaped, kinda round, kinda dome-shaped muscle
在肺的下面有个形状奇怪的圆拱形肌肉
called the diaphragm.
称为横隔膜
This muscle is a huge deal for breathing.
横隔膜对呼吸来说非常重要
See, your lungs don’t have any muscles of their own.
看 你的肺没有自己的肌肉
They just go along for the ride with the rib cage.
它们只是跟着胸腔来扩大或缩小
So when the diaphragm contracts along with the external intercostal muscles between the ribs,
所以 当横隔膜和肋骨之间的外肋间肌收缩时
they expand the space, or volume, inside the chest.
它们会使胸腔的空间或者说容积扩大
What that does is change the pressure inside the lungs
这就改变了肺部的压力
since volume and pressure are inversely related.
因为体积和气压是成反比的
So as the volume of a container increases,
即随着容器体积的增大
the pressure on all those air molecules decreases.
这里面的空气分子压强会减小
And vice versa — as the volume decreases, pressure increases.
反之亦然 体积减小 压强增大
And yes, it may seem scary that physics is coming up in an anatomy video,
在解剖学视频中出现物理学可能很可怕
but the movement of that vitally important oxygen depends on pressure differences.
但至关重要的氧气的运动的确取决于压差
That’s because our lungs can be thought of as containers for gas.
因为我们的肺可以看成是装气体的容器
So when you contract your diaphragm and expand your chest’s volume,
当你收缩隔膜 胸腔容积扩张
there’s less pressure on the air inside
此时你体内的气压
compared to the air outside your body, the stuff that you’re breathing in.
比体外正在被你吸入的空气气压要低
This is where another physics law comes in.
这又是另一个物理定律了
Whenever there’s a difference in pressure between two gases and they’re connected
当两种不同压强的气体连通时
somehow, their pressures will tend to equalize.
这两种气体的压强总会以某种方式趋于平衡
That means a gas will move from areas of high pressure to low pressure.
这意味着气体将从高压区转移到低压区
It doesn’t matter if we’re talking about gas molecules in a weather system
不管我们讨论的是天气系统中的气体分子
or in our physiology.
还是生理系统中的气体分子
Gases tend to flow from high pressure to low pressure.
气体都是倾向于从高压流到低压
So with a reduced pressure inside the chest
所以当胸腔内压强降低
and constant pressure in the air around us,
而周围空气压强不变时
the lungs fill with air.
肺里被灌满了空气
The opposite happens when you exhale.
当你呼气时 情况相反
Your diaphragm and intercostals relax, which decreases the space in your lungs,
你的横膈膜和肋间肌放松 肺部空间收缩
and with more pressure inside the lungs than outside, air flows outwards.
肺内部的压力比外部大 空气向外流动
Regular breathing really has nothing to do with sucking air in or squeezing air out.
有规律的呼吸真的与吸入或挤出空气无关
You’re just letting physics do its thing to your lungs.
只是物理学在你的肺部起作用
But all that depends on air actually getting into your lungs,
但这一切都取决于空气是否真的进入肺部
so you have a few organs
有些器官
in place to get air from outside your body into your lungs.
可以使空气从体外进入肺部
Despite starring roles in your ability to appreciate tacos,
尽管嘴和鼻在品鉴墨西哥卷饼时不可或缺
your mouth and nose are the big external interfaces for your respiratory system.
但嘴和鼻也是呼吸系统的主要外部接口
And they both act as air-treatment centers,
它们相当于空气处理中心
keeping the air warm and humid,
可以保持空气温暖湿润
and trapping any dust before it gets too far.
并阻止尘埃深入人体内部
Plus, the airway is lined with mucus membranes full of immune cells
此外 呼吸道内覆盖了满是免疫细胞的粘膜
to make sure pathogens don’t creep in.
以确保病原体不会侵入
Yep, the same mucus membranes that create boogers.
没错 就是制造鼻屎的粘膜
After air comes in, it flows down cartilaginous tubes past the larynx,
空气进入后 从软骨管流过喉部
where we can find your vocal folds that make your beautiful voice.
在那里可以找到让你发出美妙声音的声带
From here downward, your airway looks an awful lot like an upside down tree.
从这往下 呼吸道看起来像一个倒挂的树
In this case, the tree trunk, or trachea,
树干 即气管
is a thick tube of epithelial tissue surrounded by C-shaped cartilage rings.
是被C形软骨环包围着的厚管上皮组织
It traces the path of your sternum, right about here, where it splits.
它沿着胸骨的路径 就在这里 它分叉的位置
Then the trachea branches off into two bronchi.
然后气管分叉成两个支气管
Those branches keep splitting off further and further throughout the lung
这些分支在肺里不断地分叉
until they become little twigs, or bronchioles.
直到变成小细枝 即细支气管
These twigs are only about a millimeter thick
这些细枝只有大约一毫米厚
and at this point they’re not producing any mucus.
此时它们不会产生任何粘液
Each of those tiny bronchial branches have anywhere from two to eleven leaves, or alveoli.
每个支气管分支都有2到11片叶 即肺泡
Not to be confused with ravioli which is a delicious pasta dish
别和意式馄饨混淆了 那是种美味的面食
and has nothing to do with breathing.
和呼吸没有任何关系
These alveoli leaves interact with gases
这些肺泡叶与气体的相互作用
really similarly to how real leaves interact with the Carbon Dioxide around them.
跟真的叶子与二氧化碳的相互作用非常像
These alveoli, hundreds of millions of them
这些数以亿计的肺泡
are where air really starts interacting with our physiology.
是空气真正开始参与我们生理活动的地方
See, those alveoli have really thin walls,
看 这些肺泡有非常薄的壁
and they’re surrounded by extremely tiny blood vessels called capillaries
它们被非常小的毛细血管包围
which also have really thin walls.
毛细血管也有非常薄的壁
In order for us to get oxygen in and carbon dioxide out
为了让氧气进来 二氧化碳出去
those gas molecules need to cross this barrier.
这些气体分子需要穿过这个屏障
Remember, these aren’t thick concrete walls,
值得一提 这些屏障不是厚厚的混凝土墙
they’re squishy, mobile cells
它们是柔软可移动的细胞
that readily let certain substances cross.
从而很容易让某些物质通过
But these are gas molecules,
然而这些是气体分子
they’re not actively swimming through fluid.
它们不是在液体中游动
So how do they get across the membrane?
那么它们是如何穿过细胞膜的呢?
It happens thanks to diffusion, a physics concept you’re familiar with
归功于扩散这一为人熟知的物理概念
if you use a perfume or spray deodorant.
比如你使用香水或喷除臭剂
At first, the concentration is greatest around the spray bottle,
一开始 喷瓶周围的气味分子浓度最高
so the smell is the strongest around that area.
所以那个区域的气味最浓
But then, as the odorant molecule spread throughout the room,
但是当气味分子扩散到整个房间时
even people far away from the source can smell it.
即使是远离气味来源的人也能闻到它
And the smell is weaker at the source.
而且源头的气味变淡了
Those molecules spread out evenly throughout the room.
那些分子均匀地散布在整个房间里
In the case of diffusing oxygen, it diffuses through the membrane.
氧气扩散的情形 是通过膜扩散
That same principle of diffusion is at work allowing oxygen into our bloodstream
氧气进入我们的血液也是一样的扩散原理
but of course, that comes with some asterisks.
但当然 也有一些特殊的地方需要注意
One of those is because air is transferring from a gas, the atmosphere,
其中一个原因是空气从气体 大气中
to a liquid, your blood.
转移到了液体 你的血液中
So any given air molecule has to be soluble,
所以任一特定的空气分子要进入血液循环
or able to dissolve in your blood,
就必须是可溶的
if you want it to travel through your circulation.
或能溶解在血液中的
For example, carbon dioxide is very soluble in liquids,
例如 二氧化碳在液体中很容易溶解
while Nitrogen, literally eighty percent of the air we breathe, is not very soluble.
而占我们呼吸的空气80%的氮却不易溶解
Now, oxygen isn’t very soluble either,
氧也不是很容易溶解
but it takes advantage of another reason that gases move — pressure differences.
但它利用了气体移动的另一个原理 压力差
If you had equal levels of oxygen in your alveoli and in the capillaries around them,
如果肺泡和周围毛细血管的氧气浓度相同
oxygen wouldn’t move across the barrier.
氧气不会穿过屏障
But when we study the movement of dissolved particles between a liquid and a gas,
但研究溶解粒子在液体和气体间的运动时
like in this instance,
比如这个例子
we have to compare the pressures of individual gases.
我们必须比较不同气体的压强
I’ll explain.
我来解释一下
Air pressure itself is a thing because a bunch of different gas particles collide
空气压强是由于不同的气体粒子相互碰撞
and bump into the walls of their container.
以及撞到容器壁上而产生的压强
When we measure those forces for a given sample of gas,
当我们测量给定气体样本的力时
we call that pressure.
我们称之为压强
When they collide faster and harder, that’s a greater pressure
粒子碰撞得更快 更猛烈时 压强就更大
when there are less and weaker collisions, that’s less pressure.
当碰撞次数更少 更弱时 压强就会更小
Now, if you were to take some of the gas particles away from a sample,
现在 如果你从样本中拿走一些气体粒子
you would change the overall pressure.
你会改变整体压强
After all, those molecules were contributing to all the bumps and collisions.
毕竟 是这些分子促成了所有的碰撞
And through the beautiful and strange magic of math,
利用美妙而神奇的数学
as long as we know the concentration of the gases in a sample, and the volume doesn’t change,
只要知道样本中气体的浓度且体积不变
we can calculate how much each of those gases contributes to overall pressure.
我们就能计算出每种气体对总压强的贡献
This is called partial pressure, how much pressure each gas exerts by itself.
这叫做分压 指每种气体贡献的压强大小
And in the real world, the air in our alveoli is a mixture of gases
现实中 肺泡里的空气是多种气体混合物
— mostly Nitrogen but also Oxygen, water vapor, and carbon dioxide.
主要是氮气 以及氧气 水蒸气和二氧化碳
The partial pressure of these gases drives gas exchange all over the body.
这些气体的分压推动了全身的气体交换
This is why I spent so much of your time talking about partial pressure.
这就是我花了这么多时间讨论分压的原因
Oxygen isn’t a person, it can’t move across membranes just because it feels like it.
氧气不是人 它不能想穿过膜就可以穿过
It just goes along for the ride.
它只是随波逐流
Speaking of a ride, buckle up,
既然说到旅行 那么请准备好了
we’re about to follow an oxygen molecule around the body.
我们要跟着一个氧分子开启身体之旅
Starting in the alveoli,
从肺泡开始
the partial pressure of oxygen is higher than in the capillaries around it,
肺泡内氧气的分压比周围毛细血管的高
and with that partial pressure difference, oxygen flows into the blood.
有了分压差 氧气就流入了血液
Those oxygen molecules bind to the hemoglobin in red blood cells
这些氧分子与红细胞中的血红蛋白结合
and get transported around the body to oxygen-hungry tissues.
并在被运输到体内需要氧气的组织
Once it gets to the tissues, we see partial pressure differences again!
当氧到达目标组织 分压差再次出现了
Its partial pressure in the tissues is lower than the blood,
氧在组织中的分压比血液低
so it flows into the tissues.
因此氧就从血液进入到了组织
The tissues consume that oxygen as part of their aerobic metabolism
组织消耗氧气成为有氧代谢的一部分
and produce carbon dioxide as a byproduct.
并产生二氧化碳这种副产品
Then to get rid of that CO2, they dump it back into the bloodstream.
为了排出二氧化碳 组织把它释放到血液中
It’s not as crude as it sounds,
这并不像听起来那么简单
but either way
但不管怎样
your body now has carbon dioxide heading back to the lungs via blood.
你体内现在就有二氧化碳经血液回到肺部
When that blood makes its way back to the lungs,
当血液回流到肺部时
the partial pressure of carbon dioxide is higher in the blood than the alveoli,
血液中二氧化碳的分压比肺泡的要高
so it flows out.
所以二氧化碳就会排出去
And just like that,
就这样
oxygen comes in, carbon dioxide goes out and we keep on living.
我们靠吸入氧气呼出二氧化碳而生存着
So at this point in the series
在这期视频中
we know how we get oxygen into our bodies
我们了解了身体是如何获得氧气
and how we deliver it to different tissues.
以及怎样把氧气输送到不同组织
Next time, we’ll take a look at one of my favorite topics,
下期 我们来谈谈我最喜欢的话题之一
hormones and steroids.
荷尔蒙和类固醇
Thanks for watching this episode of Seeker Human.
感谢收看本期《探索新闻台》
I’m Patrick Kelly.
我是Patrick Kelly

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视频概述

我们每时每刻都在呼吸,但是呼吸背后隐藏的物理学我们又知道多少呢?

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收集自网络

翻译译者

blue is not blue

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审核员LJ

视频来源

https://www.youtube.com/watch?v=IiSu0nScX7s

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