Bulk Modulus and blood pressure?

[ilovemedi]

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TBR question: A high systolic blood pressure can cause arteries to expand. This expansion results from the relatively large:

A. Bulk Modulus of blood
B. Young's modulus of blood
C Bulk modululs of arteries
D. Young mod of arteries
Answer (highlight) - A.

I'm having difficulty understanding this. I can cross out B and D because Bulk Modulus has to do with expansion as well, right--not just compression. The answer says "if artery expands, either blood is incompressible or arter is flexible." What does "blood is incompressible" mean, and how does that relate to an expanding artery? I thought answer would be C... bulk modulus (also for expansion) of the arties makes more sense than of the blood.

 

[shaboobly]

is this a discrete?

 

[V5RED]

Modulus=Stress/Strain

A high modulus means that a thing is difficult to cause a given change to.

Blood is a liquid. Liquids are mostly incompressible.

If the blood is under a lot of pressure and it can't be compressed due to its high bulk modulus, the arteries will expand instead to relieve the pressure.

Were it the artery with the high modulus, it would mean the artery did not expand and instead the blood would be compressed.

 

[ilovemedi]

@shaboobly: this is a part of the passage, but the passage doesn't at all mention bulk modulus or anything heart related, so it's kinda like a discrete.

When do we know if a Bulk modulus is related to COMPRESSION or EXPANSION. EK lists Bulk modulus is a "compression/expansion" factor... TBR just lists compression?

ALSO - so if arteries had a greater bulk modulus, they would be more resistant to deformation, thus they would be resistant to some sort of deformation... so the blood must have a higher bulk modulus (resistance to deformation), so the arteries expand as a result? is that a correct reasoining

 

[imbackasd]

V5RED explains this nicely. Basically something has to "give" or expand in other words. Higher bulk modulus means less tendency to "give". It makes sense that arteries can "give" due to the higher pressure rather than the liquid being compressed since liquids are (for the most part) incompressible.

A higher bulk modulus of blood means that it cant "give" and thus implies that the arteries must expand as a consequence of this increased pressure.


B = P/(change in volume)

With blood, it experiences a high pressure due to the systolic pressure but no change in volume.

With the arteries. it experiences a higher pressure due to the systolic pressure but also a change in volume due to the increased wall size ( correct if I am wrong about the volume part, volume can be calculated for an artery and used in this equation right?)

Thus blood ends up with a higher bulk modulus due to a higher denominator in the formula.

 

[ilovemedi]

thanks V5red and imbackasd, got it! 😀

 

[bored]

Out of curiosity, we can also say that it's due to the low modulus of the arteries, correct?

 

[sciencebooks]

Out of curiosity, we can also say that it's due to the low modulus of the arteries, correct?

That's kind of what I thought to myself first. Because the arteries stretched, they weren't resistant to change and thus had a lower modulus.