hEART

Discussion in 'NBDE Exams & Licensure Exams' started by elra, Dec 17, 2008.

  1. elra

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    How will chronotrophy and inotropy be affected when there is sympathetic stimulation to the heart -- Chronotropy:Inotropy?

    1. Negatively:Negatively
    2. Positively:positively
    3. Negatively:positively
    4. Positively:positively
     
  2. morphology

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    answer is 4
     
  3. chipotle

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    can someone please explain this !
    thanks
     
  4. molar9

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    What is the source of this question?

    sympathetic increases contraction,rhythm as 4 is the answer.:)
     
  5. jaskiran

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    answer to this question is negatively-positively.:thumbup:
     
  6. aphistis

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    ...you think sympathetic stimulation will slow someone's heart rate? That's certainly an interesting perspective.
     
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  7. Streetwolf

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    Increases rate of spontaneous depolarization (positive chronotropic).
    Increases contractility by increasing the amount of calcium available (positive inotropic).

    Okay I should have looked and noticed this question was posted half a year ago :). So nice that you opened it back up to post an incorrect answer.
     
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  8. robhmnt

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    sympathetic stimulation results in both positive inotropic and chronotropic effect. Here is more detail for those who would like to know.

    Explanation of the positive inotropic effect of symp. stimulation:

    Norepinephrine released by axon terminals of sympathetic neurons stimulates B1 adrenergic receptros. The G-pro increases cAMP levels in the cell, whirch causes a positive inotropic effects by two pathways. First, The opening time of voltage gated calcium channels increases, you get more calcium in the cell, and a stronger contraction (positive inotropic effect). The second pathway is inhibition of phospholamban by phosphorylation. The inhibition of phospholamban results in a higher Ca2+ ATPase activity, which restores the calcium into the Sarcoplasmic reticulum faster. A faster restoration of calcium means a shorter Ca-troponin binding, which will result in a longer relaxation phase. Longer relaxation leads to a larger EDV, and you get a stronger contraction (positive inotropic effect) based on the Starling curve.

    Explanation of the positive chronotropic effect of symp. stimulation:

    As mentioned above, you get higher opening time of Ca2+ channels by cAMP activity. cAMP also increases the inward funny current of pacemaker cells by phosphorylating HCN channels and increasing their opening time. Therefore, the threshold of Action potential in pacemaker cells is achieved faster--->faster heart rate --> positive chronotropic effect.

    Edit: Jaskiran, you are a Hero (for pulling up an old resolved thread to post a wrong answer:laugh:)!
     
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    #8 robhmnt, May 25, 2009
    Last edited: May 25, 2009
  9. toothfairy482

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    LOL! AND with confidence AND the thumbs up!
     
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  10. jaskiran

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    Thanks guys for making fun and explaining.Yeah i know i made a mistake.But nevermind everybody learns from their mistakes.
     
  11. topaiz

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    Chronotropic effects (from chrono-, meaning time) are those that change the heart rate.
    Chronotropic drugs may change the heart rate by affecting the nerves controlling the heart, or by changing the rhythm produced by the sinoatrial node. Positive chronotropes increase heart rate; however, negative chronotropes decrease heart rate.

    An inotrope (pronounced /ˈaɪnətroʊp/) is an agent that alters the force or energy of muscular contractions. Negatively inotropic agents weaken the force of muscular contractions. Positively inotropic agents increase the strength of muscular contraction

    Sympathetic nerve suplly increases the heart rate and force of muscular contraction so in both ways the effect will be positive.

    ANSWER is Positively:positively
     

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