I.
Excitability
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I .
Rhythmicity
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I I.Conductivity
IV. Contractility
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Disorders of conduction and spread of impulseWPW (Wolf-Parkinson-White) syndrome
Ectopic pacemakers
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Extrasystole and compensatory pause
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Disorders of conduction and spread of impulseStannius ligatures in amphibian heart
First ligature
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Second ligature
Disorders of conduction and spread of impulse
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A- V blockage
Ventricular escape
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Stoke Adam SyndromeContractility
Action potential
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Increase in intracel ular calcium
Contraction
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Excitation-contraction couplingAtrial and ventricular myocytes can contract while pacemaker and conducting system do not
Action potential and contraction in ventricle myocyte
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Excitation-Contraction CouplingMechanism by which AP causes myofibrils to contract
AP passes over cardiac ms membrane
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AP spread to interior of cardiac ms along T tubules
opening of Ca2+ channels in sarcolema
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Ca2+ diffuses down gradient into cell through T tubulesOpening of Ca2+-release channels in SR
Ca2+ binds to troponin & stimulates contraction
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Excitation-Contraction Coupling
During Repolarization
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At the end of plateau of cardiac APCa2+ is rapidly & actively pumped out
via a Na+- Ca2+- exchanger
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Cessation of the contraction
Excitation-Contraction Coupling and Relaxation of Cardiac
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Muscle
Factors affecting myocardium
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1. Cardiac innervation2. Effect of ions concentration in ECF
3. Physical factors
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4. Blood flow
5. Chemical factors (drugs)
? Chronotropic
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? Ionotropic? Bathmotropic
? Dromotropic
Factors affecting myocardium
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1. Cardiac innervation
2. Effect of ions concentration in ECF
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3. Physical factors4. Blood flow
5. Chemical factors (drugs)
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Factors affecting myocardium6. Mechanical factors:
a. Al or none law
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b. Staircase phenomenonc. Starling's law of the heart
Starling's law of the heart
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"Length-tension relationship"`Within limits, the greater the initial length of the fiber,
the stronger wil be the force of its contraction;
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However, overstretching the fiber as in heart failure its
power of contractility decreases'
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i.e. within limits, the power of contraction is directlyproportional to the initial length of the ms
Cardiac ms accommodates itself (up to certain limit) to
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the changes in venous return
Pressure-volume loop
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