Cardiovascular system-I

Cardiovascular system-I - CARDIOVASCULAR PHYSIOLOGY...

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BMED 3100 CARDIOVASCULAR PHYSIOLOGY Introduction The governing principles of transport through the cardiovascular system. The functions of the heart: direction of blood flow and function of valves cardiac muscle contraction mechanisms The electrical conduction through heart The control of the cardiac cycle Pressure-volume relationships Stroke volume Cardiac output Control of heart rate
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BMED 3100 Duration of Contraction
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BMED 3100
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BMED 3100 Cardiac Muscle Striated with sarcomere Single nucleus, may be branched Shorter than skeletal muscle; T-tubules are larger; sarcoplasmic reticulum is smaller Intercalated disks - mechanical coupling Gap junctions - electrical coupling Sympathetic and parasympathetic control as well as hormonal control Mitochondria occupy 1/3 of cell cardiac muscle: 400X
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BMED 3100 Cardiac Muscle Cells Two types of cardiac muscle cells: 1. Myocardial contractile cells 2. Myocardial autorythmic cells, or pacemakers (1%) – generate spontaneous APs, smaller than contractile cells and contain fewer contractile fibers
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BMED 3100 Na-Ca antiport Many RyR channels open and Ca sparks are summed 90% Ca needed Excitation-Contraction Coupling (cardiac muscle)
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BMED 3100 Cardiac Contraction can be Graded Proportional to the number of crossbridges active – determined by how much Ca ++ bound to troponin Low cytosolic Ca ++ –lowforce Catecholamines (epinephrine, norepinephrine) shorten duration and increase force - are regulatory molecules - increase Ca ++ activate β adrenergic receptors, use cAMP to phosphorylate voltage-gated Ca ++ channels Phosphorylation of phospholamban enhances Ca- ATPase activity in sarcoplamic reticulum - more Ca ++ available shorten time Ca bound to troponin
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BMED 3100 Action Potentials in Myocardial Cells main difference is the lengthening of the AP due to Ca ++ entry AP in myocardial cell: 200msec, skeletal muscle fiber: 1-5 msec longer AP helps prevent tetanus (sustained contraction)
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BMED 3100 Autorhythmic Cells Membrane potential of pacemaker cells never constant – pacemaker potential
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Cardiovascular system-I - CARDIOVASCULAR PHYSIOLOGY...

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