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What immediate effect should be there after vasoconstriction

  1. Dec 8, 2015 #1
    as we know vascular circuit is analogue to simple resistant circuit of resistance in parallel combination
    and as the voltage in resistance circuit can only be changed by the battery and change in resistance follows change in current ,,,likewise change in resistance in vascular circuit should be followed by change in blood flow and except heart no other factor should change the systemic B.P
    this theory is applicable in most of the cases like change in BP by sympathetic system during exercise AND also the local metabolite theory for vaso-dilation also support this ..
    but i am confused about the vaso-constrictor effect of the angiotensin 2 in which change in peripheral resistance increases blood pressure???
  2. jcsd
  3. Dec 11, 2015 #2


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    The ohms law correspodence is

    Map ~ co x svr

    Map = mean arterial pressure
    Co = cardiac output
    Svr = systemic vascular resistance

    Symphatetic drive works by upregulation the sinoatrial node pacemaker cells -> increase heart rate.

    And co = sv x heartrate
    Sv = stroke volume unless svr or sv change

    Angiotensin increase svr by vasoconstriction and thus increase blood presssure.

    Maybe i didnt understand the question

  4. Dec 12, 2015 #3
    Actually in this formula if we increase the resistance then two factors can change either the cardiac output due to change in venous return or the arterial blood pressure
    But i didnt understand which factor should change
    Why arterial pressure changes in this conditon Why not cardiac output
  5. Dec 14, 2015 #4


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    Ok now i see the concern.

    Yes the complete regulatory network for human are certainly more complex than some "ohms law" analogy and indeed many things can and do happen but one should distinguish between primary responses and secondary responses.

    The purpose of the "Ohms law" analogy for the heart is to be a simple description only of the primary interconnections between co bp and svr.

    The heart volume and rate will not instantly change due to a remote vasoconstriction, thus the primary effect is elevated blood pressure. Heart rate are primarily influenced by the sympathetic and parsymphatetic nervoussystems and hormones in the blood only.

    Otoh, as secondary effects more complex things can happen. For example the elevated bp can trigger the baroreceptor reflex that will drop the heartrate by downregulating sa node, and thus lowering co. But this a secondary effect of sudden vasoconstriction not the primary one.

    Understanding the full dynamic blood regulatory systems requires that one also understand the secondary effects and their interconnections. Which isnt trivial.
  6. Dec 15, 2015 #5
    but according to my view there should be no such elevation of blood pressure as a primary effect of vasoconstriction because in vascular circuit all organs are arranged in parallel and if there is change in vascular resistance there should be change in blood flow only and only by altering the activity of heart can change the blood pressure
  7. Dec 16, 2015 #6
    is there is some relation with impedance of large arteries and total resistance of vascular circuit with reference to answer of my question
    please help me i have read a lot of books for this topic but still i am confused ..some book support my view about this topic like "boron" and "guyton"
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