Guyton 2011 pages 115-120 Berne 2008 pages 302-309.
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Transcript of Guyton 2011 pages 115-120 Berne 2008 pages 302-309.
Natural Excitation of
The Heart
Guyton 2011 pages 115-
120
Berne 2008 pages 302-
309
Excitatory and Conductive System of the Heart
Natural Excitation of The Heart
To cause rhythmical contraction of the heart
muscle
Conducting impulses rapidly through the heart.
Is susceptible to damage by heart disease, especially by ischemia of the heart tissues
SA Node = normal pacemaker
Natural Excitation of The Heart
Have two cell type
RMP is much less negative
Lack the iKl, then the ratio of
gK to gNa during phase 4 is
much less
Pacemaker Cells (Small, round cells having few organelles and myofibril)
Conductor Cells (Slender, elongated cells)
SA Node = normal pacemaker
Natural Excitation of The Heart
Change the slope of Phase 4
Change the RMP
Change threshold Potential
Change the Heart Rate
Normal rhythm = 70 – 80 beats/min
SA Node = normal pacemaker
Depolarization and repolarization is slower in slow responses
Na ,
Ca
Ca
K
Natural Excitation of The Heart
Internodal Pathways
Natural Excitation of The Heart
AV Node
Natural Excitation of The Heart
Regions
AN region (transitional zone)
N region (mid portion)
NH region
Cause of the Slow Conduction
Mainly by diminished numbers of
gap junctions
One-way
conduction
Normal rhythm = 40 – 60 beats/min
Purkinje fibers
Natural Excitation of The Heart
Cause of the Rapid
Conduction
mainly by increased numbers
of gap junctions
Normal rhythm = 15– 40beats/min
Summary of the Spread of the Cardiac Impulse Through the Heart (second)
Natural Excitation of The Heart
Natural Excitation of The Heart
Conduction Rate (m/s)
Tissue
0.05 SA node
1 Internodal Pathways
0.05 AV node
1 Bundle of His
2 Left and Right Bundles
4 Purkinje System
1 Ventricular Muscle
Impulse Velocity in Different Part of the Heart
Natural Excitation of The HeartPoint
s
Overrdrive Suppression
Stokes - Adams SyndromeEctopic Pacemaker
Natural Excitation of The Heart
Effect of ANS of cardiac rhythmicity
Effect of ANS of cardiac rhythmicity
Natural Excitation of The Heart
Parasympathetic division
Sympathetic division
Mainly innervates nodes
Acetylcholine
Increased permeability to K
Increases the overall activity of the heart
Norepinephrine
Increased permeability to Na and Ca
Innervates all areas
Decreases Heart Rate
Reentry Phenomenon
Natural Excitation of The Heart
Reentry Mechanism
s
Natural Excitation of The Heart
Pathway around the circle is too long
Like cardiac dilation
Velocity of conduction becomes decreased
Blockage of the Purkinje system, Ischemia of the muscle, High blood potassium levels
The refractory period of the muscle shortened
in response to various drugs, such as epinephrine or after repetitive
electrical stimulation
Global Reentry
Natural Excitation of The Heart
The End