Cardiac Conduction System

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Cardiac
Conduction
System
(1) Conduction System of Heart
• Conduction System = Heart Beat & Pumping
• Cardiac Contractions = Unconscious
– Autonomic Nervous System  decrease or
increase heart rate depending on circumstance
(2) Depolarization of the Heart
• Generate Action Potential & Depolarization:
– Atria  Ventricles
• Depolarization Path:
1.
2.
3.
4.
SA Node  AV Node
Atria Contract
(Delay)  AV Bundle
Ventricles Contract
(Blood ejected out of arteries, leaving heart)
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter22/ani
mation__conducting_system_of_the_heart.html
(3) Nodes & Bundles
• Sinoatrial Node (SA Node)
– Right atrium
– Starts each heart beat & sets rate
– “Pacemaker”
• Atrioventricular Node (AV Node) = Left
atrium
• AV Bundle =
– Bundle Branches (along septum)
– Purkinje Fibers (along entire muscular wall of heart)
(4) Cardiac Cycle
•
Diastole = Relax
– Blood passively filling atria
•
Systole = Contract
– Ventricles contract
– Blood Ejected out of heart
(5) Diastole
1. Ventricles relax
2. Semilunar valves closed
3. Ventricular Presure < Atrial Pressure
– AV valves open
– Ventricles fill with blood
4. Atria contract and force blood remaining in
chambers into ventricles
(6) Systole
1. Pressure increases in ventricles
-
Filled with blood
2. AV valves close
3. Pressure in ventricles > Arteries leaving heart
-
Semilunar valves open
Blood rushes out of ventricles
4. Atria are relaxed and begin to fill back up
(7) Heart Beat
• You hear something like “lub” “dup”
– “lub” = closing of AV valves
• During ventricular systole
– “dup” = closing of semilunar valves
• During early diastole
• You should NOT hear blood flow
– You’ll hear it if flow is interrupted by blockage
http://www.csulb.edu/org/college/bme/respiratory
_sounds/heart.wav
(8) Cardiac Output
• Cardiac Output
– Amount of blood pumped out by each ventricle / 1
minute
– Cardiac Output = Heart Rate x Stroke Volume
– CO = (HR)(SV)
• Stroke Volume
– Volume of blood pumped out by ventricle
– Increase of SV = Increase of ventricular force +
contraction
• Average Stroke Volume = 0.2L
• Average Cardiac Output = 15L/min
(9) Starling’s Law
• Starling’s Law of the Heart:
– Degree of cardiac muscle extension before
contraction
– Increase Extension = Stronger Contraction
– Degree of Extension  result of percent filling of
ventricles
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