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Download 8. Cardiac Muscle Physiology
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Transcript
The Heart • Circuits • Chambers • Valves (one-way-flow) • Myocardiocytes Volumes? Pressures? heart –> lungs –> heart heart –> body –> heart Artery = Vein = Trace a RBC! The Heart has 4 Valves To prevent retrograde flow of blood. 2 atrioventricular valves (AV) between the atria and ventricles. 1) Right AV (tricuspid) valve 2) Left AV (bicuspid/mitral) valve 2 semilunar valves between a ventricle and artery. 1) Aortic semilunar valve 2) Pulmonary semilunar valve Two heart sounds: “Lub” and “Dup” 1. Closure of AV valves = “Lub” 2. Closure of Semilunar valves = “Dup” http://www.openheartsurgery.com/heart_murmur.html Disorders of Heart Valves Normal Heart Valves Problem Heart Valves Problems Opening: Stenosis – narrowing of valve, when a valve doesn't open completely. Turbulence = noise = murmur. Problems Closing: Prolapse –overlapping or when valve doesn't close tightly. Also termed valvular insufficiency (regurgitation) Retrograde flow = noise = murmur. Myocardiocytes: 1) Autorhythmic 2) Contractile Action Potentials for Autorhythmic Myocardiocytes Action Potentials for Contractile Myocardiocytes stimulus Myocardiocytes: Calcium induced Calcium release Graded Contraction of Heart Force generated by myocardiocyte contraction is: 1. Proportional to amount of Calcium ions (Ca2+) [Ca2+] => more crossbridges, more force & speed. Graded Contraction of Heart Force generated by myocardiocyte contraction is: 1. Proportional to amount of Calcium ions (Ca2+) [Ca2+] => more crossbridges, more force & speed. 2. Modulated by Autonomic N.S. => Sym HR and Force => Para HR Sympathetic – speeds heart rate by Ca2+ influx. Parasympathetic – slows rate by K+ efflux, Ca2+ influx. Graded Contraction of Heart Force generated by myocardiocyte contraction is: 1. Proportional to amount of Calcium ions (Ca2+) [Ca2+] => more crossbridges, more force & speed. 2. Modulated by Autonomic N.S. => Sym HR and Force => Para HR 3. Stretch-Length-Tension Relationship stretch, => Ca2+ entering => contraction force Factors Influencing Stroke Volume The Cardiac Cycle http://www.youtube.com/watch?v=rguztY8aqpk The Cardiac Cycle: Mechanical Events of the Heart 1. Late Diastole: “Heart at rest” all chambers relaxed filling with blood (passive filling ~ 80% full). 2. Atrial Systole: atria contract, adds the last 20% of blood to ventricles (top off ventricles) Occurs after P-wave on EKG End Diastolic Volume (EDV) = Maximum ventricular volume* 3. Ventricular Systole (part 1): Ventricular contraction begins - Pressure (P). Closure of AV valves = 1st heart sound ("lub") Sealed Compartment – all valves are closed. Isovolumetric ventricular contraction: => pressure builds as volume stays the same. 4. Ventricular Systole (part 2): Ejection phase: P pushes open semilunar valves, blood forced out into artery leaving ventricle. Pulmonary Semilunar => 25 mmHg (minimum pressure) Aortic Semilunar => 80 mmHg (minimum pressure) End Systolic Volume (ESV) = volume remaining in heart after ejection (~½)*. Stroke Volume = EDV - ESV (ml/beat) 5. Ventricular Diastole: Relaxation of ventricles, artery back flow slams semilunar valves shut = 2nd heart sound ("dup"). Sealed Compartment again – all valves are closed. Isovolumetric ventricular relaxation: => pressure as volume stays the same. The AV valves then open, refilling starts – back to start of cycle. Cardiac Output (C.O.) = Heart Rate x Stroke Volume *Heart Rate = beats/min *Stroke Volume = EDV-ESV (vol/beat) e.g. calculation: Electrical Conduction System Sino Atrial (SA) Node Atrial Ventricular (AV) Node AV Bundle (of His) L and R Bundle Branches Purkinje Fibers Trace of an ElectroCardioGram (ECG) The ECG P wave: PR interval: QRS complex: T wave: Ventricular Assist Devices http://www.youtube.com/watch?v=D3ZDJgFDdk0