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  • If you lined up all the blood vessels in your body,

  • they'd be 95,000 kilometers long

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

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

  • delivering oxygen, and precious nutrients

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

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

  • That force is called blood pressure,

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

  • It's highest during systole,

  • when the heart contracts to force blood through the arteries.

  • This is your systolic blood pressure.

  • When the heart is at rest between beats,

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

  • A typical healthy individual produces a systolic pressure

  • between 90 and 120 millimeters of mercury,

  • and diastolic pressure between 60 and 80.

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

  • The blood traverses the landscape of the body

  • through the pipes of the circulatory system.

  • In any plumbing system,

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

  • the properties of the fluid,

  • extra fluid,

  • or narrower pipes.

  • So if the blood thickens,

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

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

  • The salt promotes water retention,

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

  • and stress, like the fight or flight response,

  • releases hormones, like epinephrine and norepinephrine

  • that constrict key vessels,

  • increasing the resistance to flow and raising the pressure upstream.

  • Blood vessels can usually handle these fluctuations easily.

  • Elastic fibers embedded in their walls make them resilient,

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

  • what we call hypertension, and stays there,

  • it can cause serious problems.

  • That's because the extra strain on the arterial wall

  • can produce small tears.

  • When the injured tissue swells up,

  • substances that respond to the inflammation,

  • like white blood cells, collect around the tears.

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

  • eventually building up to form a plaque

  • that stiffens and thickens the inner arterial wall.

  • This condition is called atherosclerosis,

  • and it can have dangerous consequences.

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

  • clogging the already narrowed pipe.

  • If the clot is big enough,

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

  • In vessels that feed the heart,

  • that will cause a heart attack,

  • when oxygen-deprived cardiac muscle cells start to die.

  • If the clot cuts off blood flow to the brain,

  • it causes a stroke.

  • Dangerously clogged blood vessels can be widened

  • by a procedure called an angioplasty.

  • There, doctors thread a wire through the vessel

  • to the obstructed site,

  • and then place a deflated balloon catheter over the wire.

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

  • Sometimes a rigid tube called a stent

  • is placed in a vessel to held hold it open,

  • letting the blood flow freely

  • to replenish the oxygen-starved cells downstream.

  • Staying flexible under pressure is a tough job for arteries.

  • The fluid they pump is composed of substances

  • that can get sticky and clog them,

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

  • and at least 2.5 billion times during an average lifetime.

  • That may sound like an insurmountable amount of pressure,

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

If you lined up all the blood vessels in your body,

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TED-ED】血圧のしくみ - ウィルフレッド・マンザーノ (【TED-Ed】How blood pressure works - Wilfred Manzano)

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    SylviaQQ に公開 2021 年 01 月 14 日
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