5 - Pressure P= Force Area P= Flow x Resistance basic...

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Unformatted text preview: Pressure P= Force Area P= Flow x Resistance basic definition flow through an ideal cylinder P aorta – P venous = CO x Total peripheral vascular resistance Poiseuille (pwa-zwe) ’s Law for an ideal fluid predicts a very steep dependence of vascular resistance on radius Flow = P r4 8ηL (and P = F x R, so R = P / F, therefore) Resistance = 8ηL x 1 P r4 P = “driving pressure” Three kinds of pressure differences in blood vessels 1.  2.  3.  Driving pressure (from heart) Transmural pressure Hydrostatic pressure (from standing) MAP = [(2 x DBP) SBP] / 3 Systolic Blood Pressure (SBP) is determined by: 1) velocity of left ventricular ejection (force) 2) systemic arterial resistance 3) distensibility of the aortic and arterial walls 4) left ventricular preload (end-diastolic volume) Diastolic Blood Pressure (DBP) is determined by: 1) arterial distensibility 2) systemic resistance 3) length of the cardiac cycle NUMBER 1 8000 10 E07 4 E10 AREA (cm2) 4 63 141 2800 (~25% are open) Types of Smooth Muscle Forms muscular walls of hollow organs gut, airways, blood vessels & urogenital system Two types of organization Unitary: sheets of electrically coupled cells which act in unison - often spontaneously active (a ‘syncytium’ e.g. gut and blood vessels) Multiunitary: tissue made of discrete bundles of cells which are densely innervated and contract only in response to its innervation (e.g. vas deferens, iris, piloerectors) A B (A)  Rodlike collagen molecules are triple helices cross-linked together in the extracellular space to form unextendable collagen fibrils. (B) Elastin polypeptide chains are cross-linked to form fibers. Elastin molecules uncoil to an extended conformation and recoil spontaneously as stretching forces are relaxed. ©1998 by Alberts, Bray, Johnson, Lewis, Raff, Roberts, Walter. The aorta stores pulse pressure in the form of transmural energy at every beat to maintain mean Compliance arterial blood pressure Arterioles: the resistance vessels 1.  Responsible for the greatest loss in systolic pressure 2.  Small radius produces very large resistance 3.  Smaller radius coupled with lower aggregate cross-sectional area than capillaries 4.  Resistance is increased by sympathetic nervous system ΔP = F • R TENSION of the vasculature wall 1.  T = ΔP · r 2.  Tension of vessel walls is greatest in larger diameter vessels 3.  Vessel walls are adapted to withstand wall tension, not transmural pressure •  Vessels are stabilized with combo of active elements (SMCs) and elastic components •  Tension is constricting force needed to bring together the edges of an imaginary slit along the length of the vessel Laplace’s Law TENSION T = ΔP ·r NUMBER 1 8000 10 E07 4 E10 AREA (cm2) 4 63 141 2800 (~25% are open) Total volume flow is the same at any level of arborization Flow = F (aorta) = F (arterioles) = F (capillaries) … etc. Flow = [A · v] (aorta) = [A · v] (arterioles) … etc. Blood volumes 85 % of the blood is in the systemic circulation Only 15 % of the blood is under high pressure Most of the blood in the body resides in systemic veins Major actions of drug groups used against angina pectoris Organic Nitrates Decrease CO by decreasing preload Reduce spasm Ca channel blockers Decrease CO by decreasing afterload, contractility, HR Reduce spasm Beta blockers Decrease CO by decreasing afterload,contractility and HR Reduce spasm ...
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