Microcirculation

Microcirculation


Fluid movement (Jv) = Κf [(Pc-Pi)-σ(πc-πi)] 

this applies to GFR in kidneys

Pc

Increased Pc 

• dilation of arterioles
• constriction of veins

Decreased Pc

• constriction of arterioles
• constriction of veins

σ

Reflection coefficient  (0 to 1)  0 = leaky and oncotic pressure doesn't have an effect (multiplied by zero)

*can also be increased under pathophysiological conditions (burns and inflammation)*

should  be "decreased"

Kf  

= hydraulic conductivity (permeability to water)

*can also be increased under pathophysiological conditions (burns and inflammation)*


Edema

• cardiogenic
• increased Pc 
• noncardiogenic
• decreased capillary oncotic pressure
• obstructed lymphatics

Ascites (malnutrition - low protein edema)

Local Control of Blood Flow

Active Hyperemia  -  metabolites dilate arterioles

Reactive hyperemia  -  after reduced flow, flow increases (low O2, metabolites)

Hypoxia vasodilates in peripheral circulation but vasoconstricts in pulmonary circulation

• alveolar hypoxia triggers inhibition of voltage gated K+ channels in arterioles leading to depolarization then activation of voltage gated Ca++ channels = vasoconstriction.

Hemodynamic Forces on Vasculature