15 16 Heart and Circulation III and IV

Accumulation of metabolites that induce arteriolar

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accumulation of metabolites that induce arteriolar vasodilation - which increases blood flow to the organ, thus restoring the balance between oxygen consumption and supply. Imbalance
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Vasodilator System Endothelium-Derived Relaxing Factor (EDRF) 1. Endothelial cells covers the luminal wall of all blood vessels. 2. Endothelial cells release both relaxing and contracting factors. 3. Nitric oxide (NO) is a major EDRF 4. NO Mediates Flow-Induced Vasodilation : High flow velocity causes mechanical rubbing of endothelial cells, and elicit the release of NO from endothelial cells to induce vasodilation.
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Mechanism of NO-Induced Vascular Smooth Muscle Relaxation Endothelial Cell Vascular Smooth Muscle Cell Receptor [Ca2+] Nitric Oxide Synthase NO Guanylate Cyclase cGMP GMP (Inactive) Phosphodiesterase Relaxation  NO
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Targeting the NO System for the Treatment of Erectile Dysfunction (From: CMAJ 170: 1429-1437, 2004) Concept : Normal erectile function is dependent on nitric oxide-mediated vasodilation. Inhibition of PDE-5 leads to accumulation of cGMP, prolonged vasodilation and erection.
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Effects of Sympathetic Nerves and Plasma Epinephrine on Arterioles
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Vasoconstrictor System Renin-Angiotensin-Aldolsterone System BP Kidney Renin Angiotensinogen (In plasma) Angiotensin I Angiotensin II Converting Enzyme (Lung) Vasoconstriction Aldosterone-Mediated Fluid and Salt Retention Blood Volume TPR (-) Concept : Angiotensin II is an potent cause of hypertension due to its role in both total peripheral resistance and blood volume.
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Summary of Major Controls of Arteriolar Smooth Muscle Contraction
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Capillaries - for Diffusional Transport
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Structure of a Capillary Endotheial Cell Erythrocyte
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Capillary Recruitment Arteriole Precapillary Sphincter #2 Precapillary Sphincter #1 Capillaries Venule Opening of precapillary sphincters recruits capillaries and enhances diffusional transport by decreasing diffusion distance. Both Sphincters #1 and #2 are open Shorter Intercapillary Distance Only sphincter #1 is open Longer Intercapillary Distance
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Flow Velocities in the Circulation Flow (ml/min) = Cardiac Output = Flow Velocity x Total Cross-Sectional (cm/min) Area (cm2) Velocity α 1/(Total Cross-Sectional Area) Total Cross-Sectional Area = Total Number of Vessels x (Radius)2 Note : Slow flow velocity in capillaries allows long transit time for oxygen exchange.
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