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PSL301H1 (21)


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University of Toronto St. George
Shaun Burns

CARDIOVASCULAR SYSTEM (463-479) • Pressure, Volume, & Resistance o Blood flows down a pressure gradient (ΔP), from region of high pressure(heart) to low (blood vessels)  Highest pressure are aorta and systemic arteries, receiving blood from left ventricle  Lowest pressure is in venae cavae, before emptying into right atrium o Pressure of Fluid in Motion Decreases over Distance  Hydrostatic pressure is exerted equally in all directions  In a moving fluid system, pressure falls over distance as energy is lost due to friction • 2 components o Kinetic energy  Dynamic, flowing o Potential energy (hydrostatic pressure)  Exerted on walls of system  Most fluid in cardiovascular system o Pressure changes in Liquids without a Change in Volume  High pressure created by contracting muscle is transferred to the blood • Flows out of ventricle, into blood vessel • pressure created is driving pressure • When wall of chamber expand, pressure on fluid decreases o Blood flows from Higher Pressure to Lower Pressure  Flow ∝ ΔP • The higher the pressure gradient, the greater the flow o Resistance Opposes Flow PSL301H1|Lecture 6  Tendency of cardiovascular system to oppose blood flow is resistance to flow • Flow ∝ 1/R o Increase in resistance results in decrease in flow • Influenced by radius of the tube (r), length of the tube (L), viscosity of the fluid (η) 4 o R=Lη/r  Resistance to flow increases as length of tube increases • Constant  Resistance increases as viscosity increases • Usually constant (RBC count)  Resistance decreases as tube radius increases • Greatest variable due to vasodilation and vasoconstriction • R=1/r 4 o Assuming length and viscosity are constant o Flow ∝ ΔP/R  Flow of blood in circulatory system is directly proportional to pressure gradient  Flow is inversely proportional to resistance of system to flow o Velocity Depends on the Flow Rate and the Cross-Sectional Area  Velocity of flow • How fast blood flows past a point PSL301H1|Lecture 6  Flow rate • How much blood flows past a point in a given time period (L/min or mL/min)  V=Q/A • Velocity of flow through a tube equal
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