Velocity decrease on pressure atherosclerosis

[Ost3oclast]

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Hey guys,

I was wondering if you could clear something up for me. I read the fluids/solids chapter today from tbr. From the concepts in the chapter i understand that increasing velocity decreases pressure. There is an in text problem that directly asks about the pressure in a vein of somebody with atherosclerosis. I have always thought that people with atherosclerosis suffer from high bp due to vein diameter reduction. However i guess this isn't correct. So if vein diameter decrease doesn't lead to high blood pressure in these people, what is the cause of their pressure being higher than normal? I understand that there could be many reasons but is there a common denominator?

 

[SaintJude]

The comprehensive answer is actually quite complicated and out of scope on the MCAT.

But, the simplified answer should be something to understand. The heart does not supply a continual feed of blood, but rather every heart beat pumps a bolus of highly pressurized blood into the arterial system.

Normally, arteries are elastic (b/c their tunica media is thicker compared to that of veins) Their elasticity is very important in maintaining a healthy level of blood pressure because the arteries are able to stretch (or contract) to absorb the pressure changes accordingly.

When the arteries harden (like in atherosclerosis), they are no longer able to stretch and absorb the pressure wave. So it's the decrease in elasticity that counts.

 

[Ost3oclast]

Awesome thanks. I understand the reasons now.

 

[milski]

The pressure differences are there even if you consider a solid tube with constant flow. In the constricted tube you'll have to increase the pressure differential at which you're pumping to fluid to maintain the same flow. The pressure in the constricted parts of the tube will be lower than the pressure in the wider parts. Both of these will be higher than the pressure in a non-constricted tube.

 

[MedPR]

This question got me too 🙂