they'd be 95,000 kilometers long

它們將會有 95,000 公里這麼長

and everyday, they carry the equivalent of over 7,500 liters of blood,

每一天，它們都裝載了相當於 7,500 公升的血液

though that's actually the same four or five liters recycled over and over,

不過真正只有五到六公升在不斷循環

delivering oxygen, and precious nutrients

藉以運輸氧氣和其他珍貴的養份

like glucose and amino acids to the body's tissues.

，像是葡萄糖和胺基酸，到身體的組織

All that blood exerts a force on the muscular walls of the blood vessels.

血液會對血管壁上的肌肉施加一力量

That force is called blood pressure,

這力量就稱為「血壓」

and it rises and falls with the phases of the heartbeat.

它會隨著心跳的收張而升降

It's highest during systole,

在收縮時達到最高點

when the heart contracts to force blood through the arteries.

當心臟壓縮推動血液進入動脈

This is your systolic blood pressure.

這就是你的收縮壓

When the heart is at rest between beats,

當心臟處於兩次跳動中間靜止狀態時

blood pressure falls to its lowest value, the diastolic pressure.

血壓會降到一個最低值，這就是舒張壓

A typical healthy individual produces a systolic pressure

一個標準健康的人，收縮壓

between 90 and 120 millimeters of mercury,

會在 90 到120 公厘水銀柱

and diastolic pressure between 60 and 80.

而舒張壓則會是 60 到 80

Taken together, a normal reading is a bit less than 120 over 80.

綜合起來，正常的血壓讀值應該稍微低於 120 以及 80

The blood traverses the landscape of the body

血液會經由循環系統的輸送管

through the pipes of the circulatory system.

穿越整個壯闊的身體

In any plumbing system,

在任何管道系統中

several things can increase the force on the walls of the pipes:

許多東西都可能增加管壁的壓力

the properties of the fluid,

液體的特性

extra fluid,

額外的液體

or narrower pipes.

或是較細的管道

So if the blood thickens,

所以，假如血液較濃稠

a higher pressure is needed to push it, so the heart will pump harder.

就需要用更大的壓力去推送，所以心臟會打得更用力

A high-salt diet will lead to a similar result.

高鹽的飲食也會導致同樣的結果

The salt promotes water retention,

鹽份會促進水份的保留

and the extra fluid increases the blood volume and blood pressure,

然後這額外的液體就會增加血液量和血壓

and stress, like the fight or flight response,

再來是壓力，像是戰鬥或是逃跑反應

releases hormones, like epinephrine and norepinephrine

這會釋放荷爾蒙，像是腎上腺素和去甲腎上腺素

that constrict key vessels,

這會壓縮關鍵的血管

increasing the resistance to flow and raising the pressure upstream.

增加流動的阻力，然後提高上游的壓力

Blood vessels can usually handle these fluctuations easily.

血管能夠輕易地經常處理這些變動

Elastic fibers embedded in their walls make them resilient,

裡頭嵌有彈性纖維，這讓血管壁富有彈性

but if your blood pressure regularly rises above about 140 over 90,

但假如你的血壓經常性地超過 140 與 90

what we call hypertension, and stays there,

我們所謂的高血壓，並且停留在這種高壓

it can cause serious problems.

可能會導致嚴重的問題

That's because the extra strain on the arterial wall

這是因為過度的張力施加在動脈管壁上

can produce small tears.

可能造成小裂縫

When the injured tissue swells up,

當受傷的組織腫大

substances that respond to the inflammation,

對發炎有反應的物質

like white blood cells, collect around the tears.

，像是白血球，會聚集在裂縫附近

Fat and cholesterol floating in the blood latch on, too,

漂浮在血管內的脂肪跟膽固醇也會占據此處

eventually building up to form a plaque

最終組合起來成為血小板

that stiffens and thickens the inner arterial wall.

這動使得動脈管壁變得堅硬厚實

This condition is called atherosclerosis,

這狀況稱為「動脈硬化症」

and it can have dangerous consequences.

而這會造成可怕的後果

If the plaque ruptures, a blood clot forms on top of the tear,

假如血小板斷裂，在裂縫處上方會產生血塊

clogging the already narrowed pipe.

阻礙原本已經很窄的管道

If the clot is big enough,

如果血塊夠大

it can completely block the flow of oxygen and nutrients to cells downstream.

會使得要輸送到身體末梢的氧氣以及養份完全被擋住

In vessels that feed the heart,

如是在要送回心臟的血管上

that will cause a heart attack,

當氧氣無法送達，心肌細胞會逐漸死去

when oxygen-deprived cardiac muscle cells start to die.

就會導致心臟病

If the clot cuts off blood flow to the brain,

假如血塊切斷到大腦的血流

it causes a stroke.

就會導致中風

Dangerously clogged blood vessels can be widened

藉由一種名為「血管成型術」的手術，

by a procedure called an angioplasty.

危險地阻塞的血管可以被加寬

There, doctors thread a wire through the vessel

醫生穿過一跟線到血管裡

to the obstructed site,

直到阻塞的地方

and then place a deflated balloon catheter over the wire.

然後經由線導入一個癟氣球

When the balloon is inflated, it forces the passageway open again.

當汽球充氣後，會強迫通道再度打開

Sometimes a rigid tube called a stent

有時，則會放入一種堅硬的管子，稱為支架

is placed in a vessel to held hold it open,

來讓血管保持撐開的狀態

letting the blood flow freely

讓血流可以順暢

to replenish the oxygen-starved cells downstream.

然後肢體末梢的缺氧細胞就能夠再度補充到氧氣

Staying flexible under pressure is a tough job for arteries.

在壓力下保持彈性對動脈來說是個艱困的工作

The fluid they pump is composed of substances

它們抽送的液體裡包含很多物質

that can get sticky and clog them,

這些物質會讓液體變黏並把它們阻塞

and your typical healthy heart beats about 70 times a minute,

你的標準心跳數約是每分鐘 70 下

and at least 2.5 billion times during an average lifetime.

平均一生會至少跳動 25 億下

That may sound like an insurmountable amount of pressure,

這聽起來像是會有難以想像的壓力施加在上面

but don't worry, your arteries are well suited for the challenge.

但別擔心，你的動脈是非常能夠適應這種挑戰的