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

翻訳: Naomi Mandel 校正: Masaki Yanagishita

You breathe in about 17,000 times per day.

人は１日に1万7千回 呼吸します

It's a process you rarely think about,

あまり気にしない事ですが

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

その裏では 壮大な機能が 組織的に働いているのです

Your vital organs,

重要な臓器である

the gut,

腸

brain,

脳

bones,

骨

lungs,

blood,

肺

血液

and heart

心臓は

work together to sustain your life

酸素を体の隅々の組織まで送り込むことで

by delivering oxygen to tissues throughout your body.

みな 共同で命を維持します

Most of our cells need oxygen

大部分の細胞は酸素を必要とします

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

なぜなら酸素は好気性呼吸に 必須な要素だからです

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

その過程はATPと呼ばれる分子を作り

which our cells use to power their many incredible functions.

これは多くの驚くべき機能の 動力源になります

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

しかし酸素を体の隅々まで送ることは 困難な作業です

Gas enters cells by diffusing in from their surroundings.

気体は拡散することで細胞に入りますが

And that only happens efficiently over tiny distances.

これは距離が短いときだけ 効率的に起こります

So for oxygen to reach the cells within our bodies,

酸素が細胞に運び込まれるには

it needs a transportation network.

運搬網が必要です

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

ここで体内の20兆個の赤血球が使われます

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

１つの赤血球には約２億７千万の 酸素結合分子であるヘモグロビンが含まれます

which is what gives blood its scarlet hue.

血液が赤いのはこの分子のためです

To make these cells, the body uses raw materials

赤血球を作るのに 体は原材料を

that become available from the food we eat.

食物から得ます

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

ですから 酸素の体内の旅は

really begins in the gut.

腸から始まるとも言えるでしょう

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

機械的かつ化学的な消化機能が 驚異的に展開し

food gets broken down into its smallest elements,

食物がヘモグロビンの主成分である鉄分などの

like iron, the building block of hemoglobin.

最小単位まで砕かれます

Iron is carried through the cardiovascular system

鉄分は心血管系を通して

to the body's hematopoietic tissue.

造血組織へ運ばれます

This tissue is the birthplace of red blood cells,

造血組織は赤血球の生まれるところで

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

骨髄腔に位置します

The kidneys regulate our levels of red blood cells

腎臓は

through the release of erythropoietin,

骨髄での赤血球産生を増やすホルモンである

a hormone which causes marrow to increase production.

エリスロポエチンを分泌することで 赤血球数を調節します

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

人は１秒に約250万個の赤血球を生産し

a number equivalent to the entire population of Paris,

その数およそパリの総人口に及びます

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

肺に到達した酸素に 十分な運搬体を届けるためです

But before oxygen can even reach the lungs,

しかし酸素が肺に到達するには

the brain needs to get involved.

脳の関与が必要です

The brainstem initiates breathing

脳幹は呼吸を開始するのに

by sending a message through your nervous system,

神経系を通して

all the way to muscles of the diaphragm and ribs.

横隔膜と肋骨の筋肉まで 信号を送ります

This causes them to contract,

神経刺激は筋肉の収縮を起こし

thus increasing the space inside the rib cage,

これが胸郭内部の容積を増大させ

which allows the lungs to expand.

肺を拡張させます

That expansion drops your lungs internal air pressure,

その拡張は肺内部の空気圧を下げ

making air rush in.

空気が流れ込みます

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

肺は２つの大きな風船のように 考えられがちですが

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

実際はそれよりもっと複雑です

Here's why.

なぜかというと

The red blood cells in the vessels within your lungs

肺内部で 血管内の赤血球は

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

ごく近くの酸素分子だけを掴むことが可能で

If our lungs were shaped like balloons,

肺が風船の形だと

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

風船の内側表面に 直接触れていない酸素は

couldn't diffuse through.

拡散できません

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

幸いに肺の構造は 極微量の酸素も 無駄にしないようにできています

Their interior is divided into hundreds of millions

肺の内部は 何億もの微小な風船のような

of miniature balloon-like projections called alveoli

肺胞に分かれており

that dramatically increase the contact area

それが肺の表面積を劇的に増やし

to somewhere around 100 square meters.

100平方メートルにも及びます

The alveolar walls are made of extremely thin flat cells

肺胞の壁は 極めて薄い平らな細胞でできており

that are surrounded by capillaries.

毛細血管で囲まれています

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

肺胞の壁と毛細血管で 細胞２枚の厚さの膜を形成し

that brings blood and oxygen close enough for diffusion.

血液と酸素を接近させ 拡散を可能にします

These oxygen-enriched cells are then carried from the lungs

このような酸素を多く取り込んだ細胞は肺から

through the cardiovascular network,

膨大な血管の集合である心血管系を通して

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

体の隅々の細胞に運ばれます

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

この心血管系を一直線に伸ばしてみると

the vessels would wrap around the Earth several times.

地球を何回も巻くことができます

Propelling red blood cells through this extensive network

体の隅々まで行きわたる こんな血管系に 赤血球を送り込むには

requires a pretty powerful pump,

大変強力なポンプが必要です

and that's where your heart comes in.

そこで心臓の登場です

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

人の心臓は１日に平均10万回も収縮し

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

酸素を必要な場所まで運びます

completing the body's team effort.

体の共同作業を全うしているのです

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

小分子である酸素を運搬するために

of tiny molecules of oxygen.

このように複雑なシステムが 作られているのです

If just one part malfunctioned, so would we.

１つでも機能しないと 人も機能しません

Breathe in.

「息を吸って」

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

腸、脳、骨、肺、血液、心臓

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

それらが信じられないような共同作業を 続けることで人を生かしています

Breathe out.

「息を吐いて」