Biology 118 11. VASCULATUREWHAT MOVES BLOOD?: Any fluid (whether liquid or gas) will move from an area of higher pressure to lower pressure, or, down a pressure gradient. Resistance tends to slow blood down, opposing movement. •Vascular resistance is the strongest opposing force – this is friction of blood against the inside of blood vessels. This friction increases with decreasing blood vessel diameter. •Viscocity – this can be considered as a fluid’s friction against itself, and will increase as a fluid’s thickness increases. •Turbulence – this is a disorderly movement of fluid; energy is wasted in forming swirls and eddies. CIRCULATORY PRESSURE: Pressure in the circulatory system tends to decrease with distance from the heart. Its initially wide oscillations are also dampened to make blood flow smooth and even. •Arteries – possess elastic tissue in their walls. This allows them to stretch and snap back. This elastic recoil produces pressure that pushes blood forward, even while the heart is in diastole.
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