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Vasoconstriction (constricting blood vessel) and flow rate?

  1. Sep 30, 2014 #1
    I was wondering why when the blood vessels constricted the speed of the blood decreased?

    I thought that since the flow rate has to be the same, the volume of blood that reaches a smaller area from a bigger area will increase in speed and hence decrease in pressure?

    Perhaps is this due to the fact that the volume of blood from a bigger area has to go through many smaller areas at once, and therefore the velocity would decrease because the volume of blood has to go through many tunnels at once?
     
  2. jcsd
  3. Sep 30, 2014 #2

    Nugatory

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    Staff: Mentor

    Must the flow rate be the same?
     
  4. Sep 30, 2014 #3
    I guess in my hypothetical human body in which the fluids are incompressible, neglible internal friction(viscocity), for each diastolic and cystolic pressure, the pressure would be the same as well as the flow rate.
     
  5. Oct 1, 2014 #4
    In flow through blood vessels (especially capillaries), the pressure change as a result of vessel constriction is negligible compared to the increased pressure from viscous drag. Also, the heart is not a positive displacement pump, so the blood flow rate can change as a result of constrictions. The tendency would be for the blood flow rate to decrease, and the blood pressure to increase.

    Chet
     
  6. Oct 4, 2014 #5
    Thank you Chet!
     
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