APK 2105C Lecture Notes - Lecture 31: Vascular Resistance, Hemorheology, Vasoconstriction

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Chapter 14, Part 2
Vessels & Blood Pressure
Resistance in the CV system
o Resistance of individual vessels depends on
Physical dimensions of tube
Lots of branches in the “tubes” through the body
Properties of the fluid
o Factors impacting resistance
Vessel radius = NUMBER ONE factor in impacting resistance
Vessel length
Longer vessels = far more resistance
Not a factor in the body—vessels don’t just get longer instead in
periods of growth
Blood viscosity
Thicker blood = more resistance
Determined by cell/protein conc
Not normally factor in the body
o Poiseuille’s Law
Fluid flowing through a tube encounters resistance from the walls of the
tube and the fluid itself
Resistance = (8Ln)/(pi r^4)
L = length of tube
n = viscosity of fluid
r = internal radius
o r is to ^4
As r decreases, it impacts resistance to the ^4
very big impact
If radius is decreased by 1/2, resistance increases
16 fold
Biggest impact on resistance
L and n are directly proportional to resistance
o Total peripheral resistance (TPR) = combines resistances of all the vessels in the
Vasoconstriction and dilation ANYWHERE changes the TOTAL
resistance of the network of vessels
Flow = pressure gradient / resistance
CO = MAP (mean arterial pressure) / TPR
May need to be rearranged
Refers to CO to a specific location/organ
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