ch14&15 - Chapter 14 Blood Vessels, Flow & Pressure...

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Chapter 14 Blood Vessels, Flow & Pressure Flow Rule Circulatory system = closed system Pressure = force exerted by blood Flow occurs from high pressure to low pressure Flow = ΔP/R (pressure/resistance) Pressure Gradients in the Cardiovascular System Pressure gradients drive flow from high pressure to low pressure Flow due to pressure gradients = bulk flow Heart creates pressure gradient for bulk flow of blood A gradient must exist throughout circulatory system to maintain blood flow (make sure that diameter of vessel gets smaller and smaller but hold the same amount of fluid) Pressure Gradient Across Systemic Circuit Pressure in aorta = mean arterial pressure (MAP) = 90 mmHg Pressure in vena cava = central venous pressure (CVP) = 0 mm Hg (veins have no pressure) [blood gets back to heart by skeletal muscle and valves to prevent backflow] Pressure Gradients in Systemic Circuit 14.2 Pressures and Pressure Drops in the Pulmonary and Systemic Circuits 14.3 Resistance in the Cardiovascular System Pressure gradient in systemic circuit much greater than for pulmonary circuit Flow through both circuits equal Flow = DP/R Resistance through pulmonary circuit much less. Effect of Resistance on Flow Factors Affecting Resistance to Flow Radius of vessel In arterioles (and small arteries) - can regulate radius Length of vessel (longer the vessel greater the resistance) Viscosity of fluid = η Blood viscosity dependent on amount of RBCs and proteins (viscosity is thickness) Regulate Blood Flow by Regulating Radius Regulation of radius of arterioles (and small arteries) Vasoconstriction decrease radius increase resistance Vasodilation increase radius decrease resistance Pulmonary circuit less resistance than systemic
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lower pressure gradient required for blood flow Relating Pressure Gradients and Resistance in the Systemic Circulation Flow = ΔP/R Flow = cardiac output = CO ΔP = mean arterial pressure = MAP R = total peripheral resistance = TPR CO = MAP/TPR Neural Control of MAP Negative feedback loops Detector = baroreceptors (measures in 2 parts sends to IC then C then E) Integration Center = cardiovascular centers in the brainstem Controllers = autonomic nervous system Effectors = heart and blood vessels Arterial Baroreceptors Baroreceptors = stretch receptors Arterial baroreceptors High pressure baroreceptors (primarily in atrium) Sinoaortic baroreceptors (to sinus) Location Carotid sinus Aortic arch Example of the Baroreceptor Reflex in Action: Hemorrhage Hemorrhage decrease in blood volume (bleeding on inside) Decrease in mean arterial pressure Baroreceptor reflex quickly compensates for changes in blood pressure (shuts down or constricts the blood vessels around the hemorrhage) It does not correct problem (shunts the blood around it but still continue to bleed out)
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ch14&15 - Chapter 14 Blood Vessels, Flow & Pressure...

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