Physiology of the Heart

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Physiology of the Heart
Daniel Hodyc Department of Physiology UK 2.LF
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1. Action potential in myocardium2.
Prapagation of AP, arrythmias 3. Excitation -
contraction coupling
Physiology of the Heart
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Action potential in myocardium significantly
differs from AP in skeletal muscle or nerve
Skeletal muscle,nerve
Myocardium
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The origin of different shape of AP curve is in
voltage gated L-type calcium channels
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Ca ions influx strongly influences the strenght
and duration of myocardial contraction
Katecholamines - beta-receptor on the
cardiomyocyte membrane - adenylalcyclace,
cAMP - activation of L-type Ca channels
Acetylcholine - muscarine receptors -
adenylatcyclase inhibition
Plasmatic concentration of Ca
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Effect of Ca-channel blockers (Verapamil,
nifedipin)
Ca channels
action potential duration
force of contraction
???
treatement of congestive heart failure
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Longer AP prevents the tetanic contraction in
myocardium
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The length of plato phase in influenced by K
channels and differs in various parts of
myocardium
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Greater activity of K channels in atrium causes
shorter plato phase
Atrial myocardium
Ventricular myocardium
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Hypercalemia causes higher excitability and leads
to arrythmias
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AP differs in normal myocardium and conductive
sytem
Ventricular myocardium
Conductive system - SAN
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AP in SAN is caused by different channels
Ca - channels
Na - funny channels
K channels
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Effect of acetylcholine on heart frequncy
Slower depolarization
Hyperpolarization
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Spreading of the AP in the heart
Reentry mechanism
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Excitation-contration coupling -
initiation fo the contraction
Special components of cardiomyocytes - T-tubuls,
gap junctions a SR
Ce infulx from the extracellular space is
necessary fo initiation of the contraction, by
the contraction requires much more ions
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Excitation-contraction coupling - Ca
release from SR
Contraction force is dependent on the
concentration of Ca in SR
Calcium induced Ca release from SR
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Excitation-contraction coupling -
relaxation
Secondary active transport
Energy demanding process
Effect of cardiac glykosides
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Relationship between force and frequency Bowdich
(Treppe) effect
Higher frequency
Intracellular Na
Shorter diastole
Less Ca expelled form the cell
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Effect of catecholamines
Ca channel phosphorylation
Faster contraction
Phospholamban
Faster relaxation
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Thank you for your attention
Pictures and schemes Berne, Levy - Physiology
6th - Arronson, Ward - The CV System at
a Glance - Guyton, Hall -
Textbook of Medical Physiology, 11th