200079.vtt
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WEBVTT
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The force of blood on artery walls is called blood pressure.
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Normal pressure is important for the proper flow of blood from the heart to the
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body's organs and tissues.
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Each heart beat forces blood to the rest of the body.
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Near the heart, pressure is higher, and away from it lower.
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Blood pressure depends on many things, including how much blood the
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heart is pumping and the diameter of the arteries the blood is moving through.
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Generally, the more blood that's pumped
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and the narrower the artery the higher the pressure is.
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Blood pressure is measured both as the heart contracts, which is called systole,
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and as it relaxes, which is called diastole.
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Systolic blood pressure is measured when the heart ventricles contract.
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Diastolic blood pressure is measured when the heart ventricles relax.
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A systolic pressure of 115 millimeters of mercury is considered normal,
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as is a diastolic pressure of 70.
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Commonly, this pressure would be stated as 115 over 70.
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Stressful situations can temporarily cause blood pressure to rise.
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If a person has a consistent blood pressure reading of 140 over 90,
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he would be evaluated for high blood pressure.
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Left untreated, high blood pressure can damage important organs,
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such as the brain and kidneys, as well as lead to a stroke.WEBVTT
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Ouch!
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Here's how platelets form clots. This small artery has a cut.
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Blood flowing past the cut includes
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red blood cells that carry oxygen,
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platelets that come from
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white blood cell fragments,
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and clotting factors that help blood clot.
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When a blood vessel is damaged, blood cells
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and plasma ooze into surrounding tissue.
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Platelets immediately stick to the edges of the
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cut and release
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chemicals that attract more platelets.
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Eventually, a platelet plug is formed,
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and the outside bleeding stops.
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On the inside,
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clotting factors cause a cascade of activity
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that includes strands of blood-borne material
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called fibrin
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sticking together to seal the inside of the wound.
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Eventually, the blood vessel heals,
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and several days later, the blood clot dissolves.