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Blood vessels

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University of Toronto St. George
Christopher Perumalla

Lecture 27Blood vessels blood flow and blood pressure1Physical laws governing blood flow and blood pressureVasculature is an elaborate system of pipes that runs through the body so fundamental laws of physics that describe the flow to any liquid through a system of pipes also pertain to the blood flow in the cardiovascular system Whenever there is a difference in pressure between two locations the pressure gradient drives the flow from the region of high pressure to low pressure down the pressure gradient The driving force for the bulk flow is always the pressure gradient the difference in pressureFlow rule The cardiovascular system is a circulatory system you end up where you started Pressure is defined by the force exerted by blood Flow is defined as the pressure gradient resistance in the cardiovascular systemSo flow is directly proportional to the gradient and indirectly proportional to resistance If there is a great pressure gradient the flow will go up while If you have a great resistance the flow will go down Pressure gradients in the Cardiovascular system Pressure gradients drive flow from high pressure to low pressure It is done by the bulk flow and not diffusion It is the job of the heart to create this pressure gradient so that the blood can move by bulk flow The hearts pumping action creates a pressure gradient that is used to drive the blood to the body which eventually returns to the heart So a gradient must exist throughout circulatory system to maintain blood flow Pressure gradient across systemic circuit In the systemic circuit the pressure gradient is the pressure in the aorta minus the pressure in vena cava just before it empties into the right atrium The pressure in the aorta was the highest since it was used to deliver the blood to the body and the pressure in the vena cava is the lowest returns to the heart The pressure in the aorta is taken as a mean arterial pressure MAP of about 90 mm Hg while the pressure in the vena cava is nonexistent CVPThe pressure gradientMAPCVP which is 90 mm HgPressure gradient across pulmonary circuit In the pulmonary circuit the pressure gradient is the pressure in the pulmonary arteries minus the pressure in the pulmonary veinsThe pulmonary arterial pressure in 15 mm Hs while the pulmonary venous pressure is 0 mm HgThe pressure gradient15015 mm HgPressures of the pulmonary and systemic circuits The largest drop in pressure is at the level of the arterioles because although they are small in diameter they are many of them Because they are so numerous when all the arterioles are put together their diameter is bigger than that of the artery The pressure drops in the arteries and the veins are smallThe pressure in the pulmonary circuit is lower than the pressure in the systemic circuit The right ventricle generates less pressure than the left ventricle
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