Umm, can a sister get some help ?

[SaintJude]

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Heart Force Exertion in Diastole
I posted this over in MCAT Q&A, but we're struggling...can anyone pleeeease help--it'll prob take you like 5 seconds.

Why is diastolic blood pressure much lower than systolic blood pressure ? (Note: A typical systole/diastole reading is mmHg is 120/80)

A. Because the heart exerts more force on the blood during diastole.
B. Because the heart exerts no force on the blood during diastole.
C. Because the radii of the blood vessels increase during diastole, while the force exerted by the heart on the blood remains the same.
D. Because the radii of the blood vessels decrease during diastole, while the force exerted by the heart on the blood remains the same.

So answer is B. Understand that but about Choice C...is the part about radii true? What happens to the radii of blood vessels during diastole?
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Thank you!

 

[turkeyjerky]

Nothing

 

[dragon529]

blood vessels radii should have no (or negligible) change during diastole or systole. Usually some other factors (drugs, pathology) change the radii.

 

[Bernoull]

Heart Force Exertion in Diastole
I posted this over in MCAT Q&A, but we're struggling...can anyone pleeeease help--it'll prob take you like 5 seconds.

Why is diastolic blood pressure much lower than systolic blood pressure ? (Note: A typical systole/diastole reading is mmHg is 120/80)

A. Because the heart exerts more force on the blood during diastole.
B. Because the heart exerts no force on the blood during diastole.
C. Because the radii of the blood vessels increase during diastole, while the force exerted by the heart on the blood remains the same.
D. Because the radii of the blood vessels decrease during diastole, while the force exerted by the heart on the blood remains the same.

So answer is B. Understand that but about Choice C...is the part about radii true? What happens to the radii of blood vessels during diastole?
________________

Thank you!

So in systole, the heart contracts and ejects blood into the aorta followed by closure of the aortic valve. Systolic BP is determined by things like the force of ventricular contraction, cardiac output and compliance of the vessels (aorta and beyond). In diastole the aortic valve is shut of course, therefore the heart/ventricles can't exert force on the blood (in the aorta), hence B is right.

Diastolic blood pressure largely depends on aortic compliance, systemic resistance, and how quickly blood drains out of the aorta (i.e. vasodilation will decrease diastolic BP).

C) This is wrong, bcos the radii of blood vessels INCREASES during systole, bcos the vessels are compliant and they need to receive an increased blood supply (aka CO). The converse happens in diastole, especially in the aorta (look up "double heart pump"), the elastic recoil from the "contracting" aorta actually contributes to diastolic BP.

Anyway, C is wrong. A makes no sense. D's first half correct, but the second half is wrong since the Aortic valve is shut in diastole (same reason why A is wrong).

Good luck

 

[GoSpursGo]

Please don't post the same thread in multiple forums. And please keep MCAT questions in the appropriate forum.