Oxygen’s surprisingly complex journey through your body - Enda Butler

譯者: Lilian Chiu 審譯者: Helen Chang

You breathe in about 17,000 times per day.

一天中你會呼吸大約一萬七千次。

It's a process you rarely think about,

這是個你很少會去想的過程，

but behind the scenes, a huge coordinated effort is playing out.

但在這個過程的幕後，要投入 極大的努力去協調才能有此成果。

Your vital organs,

你的重要器官、

the gut,

腸道、

brain,

大腦、

bones,

骨頭、

lungs,

blood,

肺、

血液，

and heart

以及心臟，

work together to sustain your life

要同心協力，才能將氧氣

by delivering oxygen to tissues throughout your body.

送到你全身的組織， 以維持你的生命。

Most of our cells need oxygen

我們大部分的細胞都需要氧氣，

because it's one of the key ingredients of aerobic respiration.

因為氧氣是有氧呼吸的 關鍵成分之一。

That's the process that produces a molecule called ATP,

有氧呼吸是一個過程，會產生 叫做三磷酸腺苷（ATP）的分子，

which our cells use to power their many incredible functions.

我們的細胞用它來提供動力 給許多了不起的功能使用。

But getting oxygen throughout our bodies is a surprisingly difficult task.

然而，將氧氣傳送至全身 是一項異常艱鉅的任務。

Gas enters cells by diffusing in from their surroundings.

氣體進入細胞的方式， 是從細胞周圍擴散進去。

And that only happens efficiently over tiny distances.

這個方式要在 非常近的距離內才有效。

So for oxygen to reach the cells within our bodies,

所以，為了要讓氧氣 抵達我們體內的細胞，

it needs a transportation network.

需要有一個運輸網絡。

This is where our 20 trillion red blood cells come in.

這時就該我們的 二十兆個紅血球出場了。

Each one contains about 270 million oxygen-binding molecules of hemoglobin,

每個紅血球皆帶有 2.7 億個 和氧氣結合的血紅素分子，

which is what gives blood its scarlet hue.

這就是血液呈現鮮紅色的原因。

To make these cells, the body uses raw materials

身體用來製造這些紅血球的原料

that become available from the food we eat.

來自我們吃的食物。

So in some ways, you could say that oxygen's journey through the body

因此，在某種意義上，

氧氣在身體中所進行旅程， 其實是始於腸道。

really begins in the gut.

Here, in an amazing display of mechanical and chemical digestion,

這裡有個很棒方式能說明 機械性及化學性消化，

food gets broken down into its smallest elements,

食物被分解成它最小的單位元素，

like iron, the building block of hemoglobin.

以鐵來說，它是由 血紅素當磚塊所組成的。

Iron is carried through the cardiovascular system

通過心血管系統，

to the body's hematopoietic tissue.

鐵會被帶到身體的造血組織。

This tissue is the birthplace of red blood cells,

此組織就是紅血球的誕生地，

and it can be found enclosed within our bone marrow cavities.

它位在我們的骨髓腔內。

The kidneys regulate our levels of red blood cells

腎臟能釋出紅血球生成素，

through the release of erythropoietin,

來調節我們的紅血球數量，

a hormone which causes marrow to increase production.

紅血球生成素是一種賀爾蒙， 能讓骨髓增加產量。

Our bodies churn out roughly 2.5 million red blood cells per second,

我們身體每秒會大量產出 約 250 萬個紅血球，

a number equivalent to the entire population of Paris,

等同整個巴黎的人口數，

so that oxygen that makes it to the lungs will have ample transportation.

這麼一來，到達肺部的氧氣， 就能有很充足的交通運輸。

But before oxygen can even reach the lungs,

但在氧氣抵達肺部之前，

the brain needs to get involved.

大腦需要先參一腳。

The brainstem initiates breathing

腦幹會利用神經系統來發送訊息，

by sending a message through your nervous system,

以啟動呼吸，

all the way to muscles of the diaphragm and ribs.

訊息會一路被送到 橫隔膜及肋骨的肌肉。

This causes them to contract,

這會造成這些肌肉收縮，

thus increasing the space inside the rib cage,

因而增加肋骨內的空間，

which allows the lungs to expand.

讓肺部得以擴張。

That expansion drops your lungs internal air pressure,

擴張就會讓肺的內部氣壓降低，

making air rush in.

使空氣流入。

It's tempting to think of our lungs as two big balloons,

可以把肺部想成兩個大氣球，

but they're actually a lot more complicated than that.

但事實上肺比氣球複雜許多。

Here's why.

原因如下。

位於肺部血管中的紅血球

The red blood cells in the vessels within your lungs

can only pick up oxygen molecules that are very close to them.

只能取得與它們 非常接近的氧氣分子。

If our lungs were shaped like balloons,

如果我們肺部的形狀像是氣球，

air that was not in direct contact with the balloon's inner surface

無法接觸到氣球內部表層的空氣

couldn't diffuse through.

就無法擴散過去。

Luckily, our lungs' architecture ensures that very little oxygen is wasted.

幸運的是，肺部的構造 能將氧氣的浪費降至非常低。

Their interior is divided into hundreds of millions

肺的內部含有數億個

of miniature balloon-like projections called alveoli

迷你的氣球狀凸出物，稱為肺泡，

that dramatically increase the contact area

能大量增加接觸面積，

to somewhere around 100 square meters.

增加到約一百平方公尺。

The alveolar walls are made of extremely thin flat cells

肺泡壁由極扁平的細胞構成，

that are surrounded by capillaries.

這些細胞被微血管包圍。

Together, the alveolar wall and capillaries make a two-cell thick membrane

肺泡壁和微血管會合力 形成一種雙細胞厚膜，

that brings blood and oxygen close enough for diffusion.

拉近血液和氧氣的距離， 近到足夠進行擴散作用。

These oxygen-enriched cells are then carried from the lungs

這些富含氧的細胞接著

會被從心血管網絡帶離肺部，

through the cardiovascular network,

a massive collection of blood vessels that reaches every cell in the body.

心血管網絡是由大量血管組成， 能通達體內的每一個細胞。

If we laid this system out end to end in a straight line,

如果我們把這系統的 血管拉開，接成一直線，

the vessels would wrap around the Earth several times.

其總長度可以環繞地球好幾圈。

Propelling red blood cells through this extensive network

要能使紅血球通過 這麼巨大的網絡，

requires a pretty powerful pump,

就需要一個非常強大的幫浦，

and that's where your heart comes in.

那就是心臟。

The human heart pumps an average of about 100,000 times per day,

人類心臟一天平均跳動十萬下，

and it's the powerhouse that ultimately gets oxygen where it needs to go,

是讓氧氣能抵達 其目的地的動力源，

completing the body's team effort.

完成整個身體的團隊合作。

Just think - this entire complex system is built around the delivery

想想看——光是為了 運輸微小的氧氣分子，

of tiny molecules of oxygen.

就要打造這一整個複雜的系統。

If just one part malfunctioned, so would we.

只要有一個環節故障， 我們也會故障。

Breathe in.

吸氣。

Your gut, brain, bones, lungs, blood, and heart

你的腸道、大腦、骨頭、 肺、血液，以及心臟

are continuing their incredible act of coordination that keeps you alive.

都持續它們了不起的 協調運作，維持你的生命。

Breathe out.

吐氣。