13 14 Heart and Circulation I and II (1)

Contractile proteins in cardiac muscle cells 1

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Contractile Proteins in Cardiac Muscle Cells 1. Cardiac muscle cells are striated – reflecting the ordered organization of actin and myosin filaments. 2. Ca2+ activates cardiac muscle contraction via the troponin-tropomyosin mechanism. 3. Protein Isoforms : Contractile proteins (e.g. actin, myosin, troponin) in cardiac, skeletal and smooth muscle cells are isoforms, because they are highly similar in amino acid sequence and function, but different in enzyme kinetics. 4. Detection of the cardiac isoform of troponin in blood is a useful tool for assessing damage to the heart in heart attack patients.
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Admission Cardiac Troponin T Status is Associated with Survival of Patients (From: Current Opin. Crit. Care 15: 377-383, 2009)
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Cardiac Cycle
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Events of a Cardiac Cycle 1. Electrical event precedes mechanical event. 2. Atrial and ventricular contraction and relaxation lead to changes in pressure and volume in cardiac chambers and circulation. 3. Cardiac valves regulate unidirectional blood flow through the circulation
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Four Phases of Cardiac Cycle
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Four Phases of Cardiac Cycle LA  LV Aorta PLA > PLV < Paorta Filling Phase (T-Q) QRS LA LV Aorta PLA < PLV < Paorta IVC (very brief) LA LV  Aorta PLA < PLV > Paorta Ejection (Q-T) T LA LV Aorta PLA < PLV < Paorta IVR (very brief) Systole = IVC + Ejection Diastole = IVR + Filling
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LV Volume During Cardiac Cycle IVR Filling IVC Ejection EKG T P QRS End- Systolic Volume (ESV) End- Diastolic Volume (EDV) Passive Filling Active Filling EDV – ESV = Stroke Volume
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Ejection Fraction Ejection Fraction = Stroke Volume/End-Diastolic Volume Ejection Fraction measures the ability of the ventricle to eject its content into the circulation. A stronger ventricle ejects a higher proportion of its content into the circulation. Therefore, Ejection Fraction is an index of cardiac contractility
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Left Ventricular Pressure During Cardiac Cycle IVR Filling IVC Ejection T P QRS 0 mmHg 120 Atrial Contraction Aortic Valve Opens at 80 mmHg Closes at 100 mmHg LV Pressure: Diastolic Pressure ~ 0; Systolic Pressure ~120 mmHg
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Aortic Pressure During Cardiac Cycle IVR Filling IVC Ejection T P QRS Diastolic (Aortic Valve Opens) Aortic Valve Closes 120 0 mmHg 80 Aortic Pressure : Diastolic ~ 80 mmHg; Systolic ~ 120 mmHg. Systolic
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Aortic Pressure During a Cardiac Cycle Ventricular Ejection (Aortic Valve Opens) Ventricular Relaxation (Aortic Valve Closes)
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Left Atrial Pressure During Cardiac Cycle IVR Filling IVC Ejection T P QRS a wave (atrial Contraction) 120 0 mmHg C wave (ventricular contraction) V wave (venous return)
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Regulation of Cardiac Output
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Cardiac Output Regulation Cardiac Output = Heart Rate x Stroke Volume Preload Afterload Contractility Four Determinants of Cardiac Output 1. Heart rate 2. Preload 3. Afterload 4. Contractility
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Heart Rate Heart rate is regulated by the sympathetic and parasympathetic nervous system Maximum Increase in Heart Rate ~ 300% Maximum Increase in Stroke Volume ~ 50% Therefore, the capability of increasing heart rate is extremely important for increasing cardiac output during exercise Resting athletes have low heart rate and high stroke volume Resting non-athletes have High heart rate and low stroke volume
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Major Factors Influencing Heart Rate
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Heart Rate Responses of Sprint-Trained Runners
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