LectCirculation - Blood Circulation or Transport System...

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Unformatted text preview: Blood Circulation or Transport System Kinds: None Open system (vessels open to sinuses) Closed system (confined to vessels) Definition: fluid system to which mechanical forces impart regular movement Blood = fluid that fills such a system Blood = hemolymph if open system Blood water ( 78% by weight) cells RBCs, 40-45% by volume white blood cells protein organic solids inorganic ions plasma = blood cell fraction volume fraction of cells = hematocrit Design of Circulation Central circulation = heart + larger vessels Peripheral circulation = microvasculature Heart is a pump myogenic (intrinsic rhythm; beats on its own) neurogenic (requires pacing by nervous system) Inherent rhythmicity of myogenic heart characteristic of all myocardial cells sinoatrial node (pacemaker; drives others) modulated by sympathetic, parasympathetic nerves = Q = Q (volume/time) Fish mammal pulmon ary syste mic Text, Fig. 8.12 Text, Fig. 8.41 Systemic and pulmonary circulations are in series volume reservoir Determinants of Cardiac Action pacemaker action autonomic innervation temperature ( T rate and strength of contraction) stretch ( rate and strength of contraction) Frank-Starling Effect venous return (blood filling heart) afterload (arterial pressure against which heart ejects blood) systole: contraction diastole: relaxation isometric = isovolumetric Text, Fig. 8.22 Text, Fig. 8.29 Text, Fig. 8.10 windkessel Text, Fig. 8.34 Aorta as a Pressure Reservoir or Windkessel elastic strain energy Structure of microvasculature cross-sectional area and flow velocity in peripheral vessels Text, Fig. 8.33 Putting things together What about volume rate of flow? pressure cardiac output Time systolic P diastolic P mean rigid tube no reservoir P V Microcirculation total capillary volume = 14% of blood volume only 30-50% of capillaries are open (5-7% BV) capillaries a single layer of endothelial cells exchange with interstitial fluid: diffusion filtration Rate of exchange depends on: perfused capillary surface area permeability (number and size of pores; see text) hydraulic and osmotic pressures (Starling forces) Starling Forces Originally formulated by Ernst Starling and called Starlings Hypothesis Hydraulic pressure Hydraulic pressure difference across endothelium = transcapillary pressure = blood pressure interstitial fluid pressure Oncotic Oncotic pressure pressure fraction of total blood osmotic pressure attributable to plasma proteins (small) Difference of forces determines whether capillaries experience filtration or reabsorption Starling Forces Originally formulated by Ernst Starling and called Starlings Hypothesis Hydraulic pressure Hydraulic pressure difference across endothelium...
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This note was uploaded on 08/24/2011 for the course PCB 4723C taught by Professor Julian during the Fall '08 term at University of Florida.

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LectCirculation - Blood Circulation or Transport System...

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