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AAMC question on blood pressure

Discussion in 'MCAT Study Question Q&A' started by SephirothXR, Aug 9, 2011.

  1. SephirothXR

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    The question asks that if you have a blood pressure of 120/80, what does the 80 refer to?

    a)atria and ventricles contracting
    b)atria and ventricles relaxing
    c)blood enters aorta from left ventricle
    d)blood entering pulmonary arteries from right ventricle

    From my understanding, systole means ventricles contract and atria relax, and diastole means ventricles relax and atria contract. So obviously I was at a huge contradiction here. The answer is B, so can someone explain this or if my background knowledge is just wrong (or partly wrong)?
     
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  3. colberag

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    Ya i was under the impression that when they say systole and diastole you are technically referring to VENTRICULAR sytole/diastole because the peripheral arterial BP measurements are based on the contraction/relaxing of the part of the heart that actually bumps the blood there (the ventricle).

     
  4. TieuBachHo

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    I might be guessing here but 80 is not an atria pressure. It is a blood pressure during the diastolic phase which is when the aortic valve shuts to cause a back drop in pressure, momentary falling back of blood. I would say out of all choices, C is the best candidate. 80 is the pressure after the blood enters aorta from left ventrical. But you say the answer is B, so I have no idea. To be precise, it can be the right atria pressure after left ventrical contraction, or during left ventrical relaxation.

    ---2 cents---
     
  5. Phlame217

    Phlame217 PGY-1 IM
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    A and C both refer to Systole
    B refers to Diastole
    D has nothing to do with it.

    So when referring to blood pressure, two things influence pressure (in this frame of thought). Those two things are the elasticity of the arteries (i.e. the aorta) and the pressure created by the Left Ventricle. So diastole can be thought of the resting blood pressure when the heart is relaxed. This pressure is created by the arteries having been stretched to a certain point and then contracting which maintains a certain pressure. The ventricles then have to overcome this pressure, usually 80 mmHg, to push the blood out of the heart and into the aorta and therefore it usually gets up to 120 mmHg.

    In sum, diastolic pressure is the resting pressure created by a relaxed heart and contracting arteries.

    Systolic is active pressure created by a contracting ventricle moving blood out of the left ventricle into the aorta.
     
  6. neurodoc

    neurodoc Neurologist
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    Think of it this way. Atria contract and push blood into the ventricles; then the ventricles contract and push blood into the pulmonary arteries and aorta. There is a brief period where neither atria or ventricles are contracting just after the ventricles push blood into the PA and aorta. This is when diastolic atreial BP is measured, so the answer is B.
     
  7. evans2000

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    haha even high school students would know the answer is B..You had better start studying for the MCAT
     
  8. notbobtrustme

    notbobtrustme Crux Terminatus
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    hey, that was, literally, the only question I missed in that entire biology section. The answer stems were worded poorly.
     
  9. gabdolce

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    The most important thing to gather from the stem is that 80 is indeed referring to aortic artery pressure indicative of diastole.

    To explain the answer a little more in depth:

    Yes, it is correct that the ventricles are relaxed and that the atria do indeed contract during diastole.

    However, atria are not contracted for the entire duration, or even a majority of the duration of diastole (at least at resting scenarios which the 120/80 seems to signify).

    Look at Wigger's diagram:
    [​IMG]

    You'll notice that the atrial pressure increases for about 20% of the diastolic period (a region referred to as the "atrial kick"). The ventricles actually fill for the most part, passively. Thus, the atrial pressure never really has much need to significantly increase its pressure throughout diastole. So to reiterate, yes, it's correct to say that diastole is a time where the atria contract, it is NOT INCORRECT to say that they are relaxing as well.

    And additionally, as others have iterated before, the other answers are so irrefutably wrong because any mention of ventricles contracting is absolutely incorrect.
     
    #8 gabdolce, Aug 10, 2011
    Last edited: Aug 10, 2011
  10. kkentm

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    doesnt D and C occur simultaneously during systole?
     
  11. Phlame217

    Phlame217 PGY-1 IM
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    Yes they do, however the right ventricle ejecting blood into the pulmonary artery has nothing to do with the body's blood pressure; so in the frame of this question, it has no role.
     

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