ard14

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Question 29 of Kaplan's online diagnostic test states the blood pressure drops for two reasons: increased cross-sectional area, which makes sense, and increased friction in blood vessel walls, which does not make sense to me. Why would increasing friction decrease blood pressure, shouldn't it do the opposite, increase BP, as is the case with arteriosclerosis?

Thanks
 

vize

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i'm not sure arteriosclerosis causes high blood pressure, rather, high blood pressure may cause arteriosclerosis. i think friction decreases blood pressure because it's going to make it harder for the blood to flow as fast
 
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artmed12

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ard14 said:
Question 29 of Kaplan's online diagnostic test states the blood pressure drops for two reasons: increased cross-sectional area, which makes sense, and increased friction in blood vessel walls, which does not make sense to me. Why would increasing friction decrease blood pressure, shouldn't it do the opposite, increase BP, as is the case with arteriosclerosis?

Thanks
Hi,
a decrease in the velocity of blood will result in a decrease in blood pressure. The question is not asking the reasons blood pressure drops, but the mechanism for the drop:

1. the increase in cross sectional area is referring to when an artery branches into an arteriole then finally the capillaries, imagine a river flowing into many more little rivers, this decreases blood pressure because there is more total area (the many capillaries vs. 1 artery)

2. the increase in friction is due to millions of blood cells flowing through an artery having an abrupt halt when the blood hits the one-celled thick diameter of the microscopic capillaries, this halts the velocity of blood, hence lowers blood pressure.

these are two ways to reduce that blood pressure drops in the body, not the reasons FOR blood pressure drop, you merely misread the question.
 

artmed12

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1 more thing:

you guys are right that an increase in the friction due to arteriosclerosis will increase b.p. because it shrinks the diameter of the artery

but, the friction that was referred to in the question was the friction that slows blood when it gets forced from an arteriole to a thin capillary. the blood pressure drops when it goes through the capillary at a slow rate.
 
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