Hemodynamics and Vasculature (Lecture 18-19) 5/22/09 • Blood o Component: 55% plasma, 45% cells o Viscosity: higher hematocrit produces higher viscosity • Vascular system o Anatomy of different vessels: diameter and total areas (refer to the Table in page 1) o Physical properties: elasticity, compliance, structural basis (textbook P514 Fig 15-2) • Hydrodynamics o Conservation of matter: all of the blood that entered a segment of tube will also leave it. Æ Flow is the same in different parts of circulatory system. Æ Larger areas results in slower velocity (e.g. capillaries) o Poiseuille’s law: flow = force/resistance Æ ( ) 4 8 , r l R P P P R P Q out in π η = − = Δ Δ = Æ Blood flow is very sensitive to the caliber of vessels. (e.g. when sympathetic nerve stimulates the smooth muscle of vessel to contract, the flow goes down) o Blood is closer to laminar flow • Material transfer between the blood and the tissue o Chemical drive: diffusion driven by concentration gradient
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