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Lecture

Vascular function

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Department
Physiology
Course
Physiology 3120
Professor
Tom Stavraky
Semester
Winter

Description
Human Physiology Wednesday, January 20, 2010 CV VIII” Vascular Function • Relationship between pressure, flow, and resistance  Pressure gradient makes the blood flow; gradient is the difference between the beginning and end of the blood vessel/systemic circulation  In systemic circulation, the pressure gradient is equal t1 P (pressure at end of vessel is 0mmHg)  Flow = pressure gradient/resistance; flow is proportional to pressure gradient & inversely proportional to resistance  Resistance depends on viscosity (directly), length of vessel (directly) and vessel radius (inversely to the exponent 4)  The relationship between these 4 variables is summarized in the Poiseuille-Hagen equation • Laminar & turbulent flow of blood  Laminar  Streamline flow  Parallel to walls of vessel  Small portion of the blood (closest to the wall) moves very slowly; as you move inward toward the centre, the velocity increases so that the blood in the middle layer will flow with the greatest speed  Silent flow  Turbulent  When flow velocity increases to a certain point, the flow will become turbulent  Irregular motion  Parallel as well as perpendicular flow  Creates sound  Probability of turbulent flow (Reynold’s number) • Ratio of inertial to viscous forces • When it exceeds a critical value, turbulence occurs • Turbulence occurs sometimes in the ascending aorta at the peak of systole; also occurs more commonly in anemia due to decreased blood viscosity • Capillary circulation  Point where arterioles connect to capillaries  precapillary sphincters (made up of smooth muscle cells); therefore, blood flow into capillaries is intermittent (i.e. only flows in when sphincter is open)  known as vasomotion in capillaries  Diffusion  Endothelial cells lini
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