test 2 copy - The Main Function of Systemic Circulation...

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1 The Main Function of Systemic Circulation deliver adequate O2 and nutrients to systemic tissues remove CO2 & other waste products from systemic tissues conduit for hormone and other substances so they can act at a distant site from their production Functional Parts of Systemic Circulation systemic arteries designed to carry blood under high pressure out to the tissue beds act as control valves to regulate local flow dependent on metabolic demand of tissue capillaries one cell layer thick allows exchange between tissue (cells) & blood venules collects blood from capillaries systemic veins (65% of blood sits here). return blood to heart/dynamic storage Basic theory of circulatory function Blood flow is to metabolic demand (ex. skeletal m. and exercise) Cardiac output is controlled by local tissue flow (blood pumps whatever gets to it) Arterial pressure control is independent of local flow or cardiac output (which is determined by local tissue flow. Local flow and CO certainly influence arterial pressure but is regulated. the main pressure monitor are hormones - determined by S innervation {vasoconstriction}). Vessel Components Endothelium - 1 layer exists in all vessels Elastic tissue (1) Smooth muscle (2) Fibrous tissue (3) Vessel Composition Arteries have 2x the wall thickness of veins Capillary only endothelium Aorta 1>3>2 Typical Artery 2>1>3 Vein 1 = 2 = 3 Hemodynamics (HD) ( = proportional) (I=current flow) Ohm s Law V = IR (Analogous to P = QR) connection btwn ohm s law & HD. V is analogous to P gradient in heart C/1 is analogous to blood flow Flow (Q) The volume of blood that passes a certain point per unit time (ml/min) At given flow, V is inversely to the total csa Q = V * cross sectional area (csa) Flow-directly to P and inversely to resistance (R) Q = P / R (P is kept relatively constant) 10/2=20/4 (flow stays same u don't get anywhere if u P Resistance R= 8 l/ r 4 = viscosity l = length of vessel r = radius If you double radius, you decrease resistence by 16 times slight constriction has the greatest influence. Radius is really the only changeable factor due to sympathetics and nitric oxide (S & NO) Resistance of some liquids / their viscosity Het = hematocrit = packed cell volume. Ex. = polycitemia = RBC = het = viscosity H2O = 1 Whole Blood = 3 (due to RBCs) Plasma = 1.5 Parallel circuit 1/R T = 1/R 1 + 1/R 2 + 1/R 3 + 1/R N R T < smallest individual R Series circuit R T = R 1 + R 2 + R 3 + R N R T = sum of individual R s The systemic circulation is predominantly a parallel circuit Pressure gradient Driving force of blood/difference in P between 2 points to flow At a given Q, the greater the drop in P in a segment or compartment, the greater the resistance to flow. 4 vessels example
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test 2 copy - The Main Function of Systemic Circulation...

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