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If you lined up all the blood vessels in your body,
如果把你身体内的血管都排成一条，
they'd be 95,000 kilometers long and everyday, they carry the equivalent of over 7,500 liters of blood,
它们有95000千米那么长，每天，它们携带7500升血液，
though that's actually the same four or five liters recycled over and over,
虽然那实际上是四到五升一遍一遍的重新循环，
delivering oxygen, and precious nutrients like glucose and amino acids to the body's tissues.
以传递氧气和珍贵的营养，比如葡萄糖、氨基酸等到身体的组织。
All that blood exerts a force on the muscular walls of the blood vessels.
这些血液加在一起，对血管壁施加了一种强力。
That force is called blood pressure, and it rises and falls with the phases of the heartbeat.
那种力量就叫做血压，血压随着心跳升高或降低。
It's highest during systole, when the heart contracts to force blood through the arteries.
血压在心脏收缩的时候是最高的，当心脏收缩迫使血液通过动脉。
This is your systolic blood pressure.
这就是你的收缩压。
When the heart is at rest between beats, blood pressure falls to its lowest value, the diastolic pressure.
当心脏在跳动间歇期间，血压降到最低的数值，这就是舒张压。
A typical healthy individual produces a systolic pressure between 90 and 120 millimeters of mercury,
典型的健康的个体的收缩压在90到120毫米汞柱之间，
and diastolic pressure between 60 and 80.
舒张压在60到80之间。
Taken together, a normal reading is a bit less than 120 over 80.
两者合在一起，正常的读数是介于80到120。
The blood traverses the landscape of the body through the pipes of the circulatory system.
血液是通过循环系统的血管流过整个身体。
In any plumbing system, several things can increase the force on the walls of the pipes:
在任何液流系统，都会有几项因素使管壁受压增高：
the properties of the fluid, extra fluid, or narrower pipes.
液体的特性，多余的液体或狭窄的管腔。
So if the blood thickens, a higher pressure is needed to push it, so the heart will pump harder.
如果血液变得粘稠，血压需要升高来把它推送出去，那么心脏会跳得更厉害。
A high-salt diet will lead to a similar result.
高盐饮食会导致类似的症状。
The salt promotes water retention, and the extra fluid increases the blood volume and blood pressure,
盐促进水的保留，额外的液体增加了血容量和血压，
and stress, like the fight or flight response,
还有压力，比如搏斗或搏斗似的反应，
releases hormones, like epinephrine and norepinephrine that constrict key vessels,
会释放荷尔蒙，如肾上腺素或去甲肾上腺素，它们能收缩主要的血管，
increasing the resistance to flow and raising the pressure upstream.
增加流动的阻力并且升高血压。
Blood vessels can usually handle these fluctuations easily.
血管通常能够很容易地处理这样的波动。
Elastic fibers embedded in their walls make them resilient,
血管壁里的弹性纤维使得血管富有弹性，
but if your blood pressure regularly rises above about 140 over 90,
但是你的血压增高多于140/90，
what we call hypertension, and stays there, it can cause serious problems.
我们就把它叫做高血压，如果一直持续，可引起严重的问题。
That's because the extra strain on the arterial wall can produce small tears.
那是因为额外的血管壁的压力能引起很小的泪泡。
When the injured tissue swells up,
当受伤的组织肿胀起来，
substances that respond to the inflammation, like white blood cells, collect around the tears.
炎症反应的物质，如白细胞会聚集在泪泡周围。
Fat and cholesterol floating in the blood latch on, too,
脂肪和胆固醇在血液中漂浮，停留，
eventually building up to form a plaque that stiffens and thickens the inner arterial wall.
最终会形成粥样块状物，使得动脉血管内壁僵硬和变厚。
This condition is called atherosclerosis, and it can have dangerous consequences.
这种情况就叫做动脉粥样硬化，这能产生危险的后果。
If the plaque ruptures, a blood clot forms on top of the tear, clogging the already narrowed pipe.
如果粥样块状物破裂，血块在块状物顶部成型，堵住已经狭窄的管腔。
If the clot is big enough, it can completely block the flow of oxygen and nutrients to cells downstream.
如果血块够大，它能够堵住氧分和营养传送到下面的细胞。
In vessels that feed the heart, that will cause a heart attack,
当这发生在心脏血管中，就会引起心肌梗塞，
when oxygen-deprived cardiac muscle cells start to die.
没有氧分的时候心肌细胞开始死亡。
If the clot cuts off blood flow to the brain, it causes a stroke.
如果栓塞堵住了大脑的血流，就引起了中风。
Dangerously clogged blood vessels can be widened by a procedure called an angioplasty.
严重阻塞的血管可经由“血管成形术”打通。
There, doctors thread a wire through the vessel to the obstructed site,
医生将一根导线穿入血管，到达阻塞部位，
and then place a deflated balloon catheter over the wire.
然后在导线上穿一支未充气的气球导管。
When the balloon is inflated, it forces the passageway open again.
当气球充气时，血管便能再度打通。
Sometimes a rigid tube called a stent is placed in a vessel to held hold it open,
有时医生会将称为“支架”的硬管植入血管以保持其畅通，
letting the blood flow freely to replenish the oxygen-starved cells downstream.
使血流通行无阻，使下游缺氧的细胞得到补充。
Staying flexible under pressure is a tough job for arteries.
动脉在压力下保持弹性是件不容易的事。
The fluid they pump is composed of substances that can get sticky and clog them,
自心脏泵出的液体含有能变黏稠而使之阻塞的物质，
and your typical healthy heart beats about 70 times a minute,
一个健康的心脏大约每分钟跳70次，
and at least 2.5 billion times during an average lifetime.
平均一生心脏跳动最少25亿次。
That may sound like an insurmountable amount of pressure,
听起来这似乎是一种大到难以承受的压力，
but don't worry, your arteries are well suited for the challenge.
但不要担心，你的动脉生来就是为了应付这种挑战。
