12 vasculature 118 - Biology 118 11. VASCULATURE WHAT MOVES...

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Biology 118 11. VASCULATURE WHAT 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. Capillaries –
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