3/13/14 kin 470 class notes- End-diastolic volumeo Frank-Starling mechanism Greater EDV results in a more forceful contraction Due to stretch of ventricleso Dependent on venous returno Venous return increased by Venoconstriction- Via SNS Respiratory pump- Changes in thoracic pressure pull blood toward heart Skeletal muscle pump- Skeletal muscle pumpo Skeletal muscle pump Rhythmic skeletal muscle contractions force blood in the extremities back toward the hart One-way valves in veins prevent backflow of blood- Average aortic pressureo Aortic pressure is inversely related to stroke volume Represents afterloado High afterload results in decreased stroke volumeo Requires greater force- Ventricular contractilityo Increased contractility, increase SV Circulating epinephrine and norepinephrine- Increase force of contraction in heart- Increases the amount of Ca++ in the heart muscle- Physical characterisitics of bloodo Plasmao Hematocrit- Relationships among pressure, resistance, and flowo Blood flow Directly proportional to the pressure difference between the two ends of the systemo Inversely proportional to resistanceo Blood flow = change in pressure/resistance- Hemodynamicso Resistanceo Depends upon Length of vessel Viscosity of blood Radius of the vessel (most important)- Regulation of local blood flow during exerciseo Skeletal muscle vasodilation Autoregulation Blood flow increased to meet metabolic demands- oxygen delivery during exerciseo oxygen demand by muscles during exercise is 15-25x greater than at rest increased- changes in cardiac output during exerciseo cardiac output increases due to: increased HR linear increase to mac Max HR = 220 – age (years)o Increased SV Increases at different rates No plateau in highly trained
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