as cross-sectional area decreases...

[laczlacylaci]

Why is C incorrect according to the continuous eq.?

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[theonlytycrane]

(C): velocity would increase, but flow would not decrease. It would increase.

I think bradykinin is supposed to slow blood flow, is there anything in the passage to hint at that for choice (D)?

 

[laczlacylaci]

(C): velocity would increase, but flow would not decrease. It would increase.

I think bradykinin is supposed to slow blood flow, is there anything in the passage to hint at that for choice (D)?

Ah, that is right! I think im burning out.

The passage it says that bradykinin signals for smooth muscle contraction surrounding the ductus arteriosus. So decreased blood flow, indeed. But I guess that was given in the Q-stem anyways. The key says to look at it more as a circuit (Bio+Phys), thats why resistance came in as a play... :/ But I think its understandable w/o bringing in phys.

 

[victorias]

I get that decreasing area would cause the resistance to increase
Isn't flow rate conserved? A1v1 = A2v2 and from this equation, velocity will increase

What do they mean by flow here?

 

[laczlacylaci]

I get that decreasing area would cause the resistance to increase
Isn't flow rate conserved? A1v1 = A2v2 and from this equation, velocity will increase

What do they mean by flow here?

This is how I thought about it:
Q-stem gives that the ductus arteroisus decreases its cross-sectional area=this is vasoconstriction=blood flow decreases<-eliminate AB
For constriction, you increase resistance of the blood flow, which also decreases blood flow.<-D
C: It is true that velocity would increase as area decreases. But normally as velocity increases, blood flow would increase as well.<-eliminate C, leaving us with D.
As for B, yes an increase in v would result in an increase in BF, but that would be for vasodilation. (If the Q-stem asked in the absence of bradykinin, (or some other drug that stimulates dilation of smooth muscle))

 

[majikarp]

I think the key to this answer the phrase ", and so" which implies a causal effect between velocity increase and blood flow decrease. This is not true. Typically as velocity increases, flow rate should increase or stay the same. D is much more logically sound as far as establishing a causal relationship between increased resistance and decreased blood flow. Like the poster above said, I think they want you to make the connection between blood flow rates and V=IR, which by the way is a common on vascular flow type passages.