Surface tension
The ambient temperature of the body directly affects blood flow through microvasculature. Changes in temperature affect the viscosity of blood and the surface tension. Surface tension decreases with increasing temperature, decreasing the minimum flow rate (see Surface Tension). The decrease in minimum flow rate by higher temperatures allows more blood to flow and dissipate heat throughout the body. Temperature greatly affects blood flow by influencing the diameter of flow. Decreases and increases in temperature trigger vasoconstriction and vasodilation respectively.