Blood pressure clarification

[Jonass00]

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My college gen physics book gives the example of arteriosclerosis in blood vessel. Because of the constriction the blood must travel with a faster velocity in order to keep a constant flow. As a result the increased velocity causes a decreased pressure which ultimately causes a vessel to collapse.

A1V1=A2V2 does this not apply to this example? decreased area from the constriction causing increased V and ultimately lowered pressure.

Now the confusing part comes from EK 1001 biology #268

Which of the following statements correctly describes the outcome of rapid dilation of arteries an arterioles?

Answer is C. peripheral resistance will decrease and cardiac function may decrease.

Explanation states that when arteries undergo vasodilation the resistance is decreased, which also reduces the pressure at which blood flows. Summary: Blood pressure drops when arteries or arterioles dilate.


From my understanding EK bio tells you to use A1V1=A2V2 and apply bernoulli. This was one of "salty's brown text paragraphs". Clarification please on effects of vasodilation and vasoconstriction on blood pressure. Thank you in advance

 

[Temperature101]

My college gen physics book gives the example of arteriosclerosis in blood vessel. Because of the constriction the blood must travel with a faster velocity in order to keep a constant flow. As a result the increased velocity causes a decreased pressure which ultimately causes a vessel to collapse.

A1V1=A2V2 does this not apply to this example? decreased area from the constriction causing increased V and ultimately lowered pressure.

Now the confusing part comes from EK 1001 biology #268

Which of the following statements correctly describes the outcome of rapid dilation of arteries an arterioles?

Answer is C. peripheral resistance will decrease and cardiac function may decrease.

Explanation states that when arteries undergo vasodilation the resistance is decreased, which also reduces the pressure at which blood flows. Summary: Blood pressure drops when arteries or arterioles dilate.


From my understanding EK bio tells you to use A1V1=A2V2 and apply bernoulli. This was one of "salty's brown text paragraphs". Clarification please on effects of vasodilation and vasoconstriction on blood pressure. Thank you in advance

Blood pressure is pressure the blood exerts against the wall of arteries...Vasoconstriction increases BP and Vasodilation decreases BP. From a pressure perspective: P= F/A...When arteries dilate, their cross sectional areas increase. I am not sure why Bernoulli's equation will not apply in this case because dilation should decrease the blood flow velocity if we refer to the continuity equation (A1V1=A2V2). Then if we follow that logic, BP has to increase, but that does not really happen....May be blood flow is not laminar and/or frictionless (not sure). Can someone else clarify?

 

[milski]

Because the flow changes when you change the diameter of the blood vessels. Bernoulli's law is about the relation between velocity and pressure for a given flow, you cannot use it to predict what will happen if the flow changes.

The flow is determined by the Poiseuille's law, which tells you that if the vessel diameter decreases, either the flow will decrease or the pressure difference between the two ends needs to increase to maintain the same flow.

 

[Temperature101]

Because the flow changes when you change the diameter of the blood vessels. Bernoulli's law is about the relation between velocity and pressure for a given flow, you cannot use it to predict what will happen if the flow changes.

The flow is determined by the Poiseuille's law, which tells you that if the vessel diameter decreases, either the flow will decrease or the pressure difference between the two ends needs to increase to maintain the same flow.

But according to OP, EK use Bernoulli's principle to explain the answer...Why?

 

[milski]

But according to OP, EK use Bernoulli's principle to explain the answer...Why?

That's just his understanding - I'm not sure from where he got that. The explanation that he quoted is talking about decreased resistance, which is Poiseuille's law, not Bernoulli's.

 

[Temperature101]

That's just his understanding - I'm not sure from where he got that. The explanation that he quoted is talking about decreased resistance, which is Poiseuille's law, not Bernoulli's.

Oh ok....

 

[Jonass00]

Ok so with regard to blood pressure concepts I should use poiseuille's law. However,back to my gen physics college book concept. The constriction from the arteriosclerosis causes increased velocity to maintain constant flow. How do i apply poiseuille's to answer the resultant pressure?

 

[milski]

You can use what your college book says to compare a part of the artery which has some sclerosis to another part of it which does not - the one with the sclerosis will be narrower and the blood in it will flow faster.

The cumulative sclerosis over all of the arteries will increase their resistance and according to Poiseuille's law will increase to increase in the blood pressure and/or decrease in the blood flow.