Download CARDIOVASCULAR SYSTEM.

Heart –Electrical Properties
Prof. K. Sivapalan
Introduction.
• Function of the blood is transport of
substances.
• Function of the heart and vessels are:
– Keeping blood flowing.
– Delivering more blood to needy tissue.
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Electrical Properties
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Design of the circulatory system.
• All blood goes to
lungs in pulmonary
circulation
• The blood flows to all
other organs
[including heart] in
systemic circulation.
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Electrical Properties
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Structure of the heart.
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Components of the pumping
system.
•
•
•
•
•
Collectors- atria.
Pumps- intermittent pump – ventricles.
Regulators of flow - valves.
Rhythm control – conducting system.
Adjustments – by autonomic nerves and
hormones.
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Location of the heart.
• In the mediastinum.
• Hanging on the large
vessels.
• Lying on the
diaphragm.
• Supported by fibrous
pericardium.
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Properties of cardiac muscle.
• Branching cells.
• Separated by
intercalated discs –
tight junctions with
pores permeable to
ions. [electrical
continuity]
• Functional syncytium.
• Striations – similar to
skeletal muscles.
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Sarcomere, filaments and fibrils.
Z lines – centre of actin
filaments.
• M line – centre of
myosin filaments.
• A band – length of
myosin filaments.
• Sarcomere is a unit of
myofibrils between
two Z lines.
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Myofibrils and T tubular system.
• Myofibrils - bundle of
actin + myosin
[Yellow]
• Mitochondria [blue].
• Sarcoplasmic
reticulum + T
tubules [pink] at Z
line.
• Intercalated discs at
Z line [light blue].
• Central nucleus
[purple].
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Excitation contraction coupling.
• Action potential spreads
across intercalated discs.
• Spreads along T tubules
[Z line] to Terminal
cistern.
• Calcium released from
cistern and influx from
ECF.
• Actin myosin binding and
sliding.
• Removal of Calcium
results in relaxation.
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Contraction.
•
•
•
•
Actin and myosin do not overlap in a relaxed muscle.
Calcium binding to Troponin C initiates sliding.
Contraction can not reduce length to zero.
In heart, there will be residual blood after maximal
contraction.
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Electrical properties of cardiac
muscle.
• Resting membrane
potential – 85 – 95 mV.
• Depolarized to +20 mV.
• Rising phase – 2 m sec.
• Plateau – 0.15-0.2 sec
in atrium and 0.3 in
ventricles.
• Refractory period – 0.3
sec.
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Ionic basis of action potential.
Na+.
• Depolarization –
sodium influx.
• Plateau – calcium
influx and potassium
efflux.
• Repolarization –
potassium efflux.
Ca++
K+.
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Origin of
Cardiac
Impulse.
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• Pacemaker – junctional tissue.
• Pacemaker potential – after
each impulse declines to firing
level.
• Rate of action potential depends
on the slope of the prepotential.
• It is due to reduction of K+ efflux
(↑ by Ach) and then increase in
Ca++ influx (↑ by NA).
• Ca++ T (transient) channels
complete prepotential and L
(long lasting) action potentials
[no sodium] in nodal tissues.
• SA node – 120/min, AV node –
45/min, Purkinje system –
35/min.
• First area to reach threshold will
be the pace maker.
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Electrical Properties
Spread of impulse.
• SA node.
• Inter nodal pathways
& atrial musculature.
• AV node.
• Bundle of His.
• Bundle branches –
Purkinje fibers.
• Cardiac muscles
through intercalated
discs.
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Conducting system.
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Conduction of impulse.
Tissue
SA node
Conduction Time takenrate. [M/S]
[Sec.]
0.05
Atrial pathways.
1.0
AV node
0.05
Bundle of His.
1.0
Purkinje system
4.0
Ventricular muscle.
1.0
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0.1
0.08
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Spread of impulse in the heart.
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•
•
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SA node to AV node.
Nodal delay.
Septum – left to right.
Apex and wall – from inside
outwards.
• Towards base.
• Examination – ECG.
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