The Heart’s External Anatomy & Conduction System

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The Hearts External Anatomy Conduction System
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• Heart at rest
• Blood flows from large veins into atria
• Passive flow from atria into ventricles
• Atria (R L) contract simultaneously
• Blood forced into ventricles
• Ventricles (R L) contract simultaneously
• Atrioventricular valves close ? lubb sound
• Blood forced into large arteries
• Ventricles relax
• Semilunar valves close ? dub sound
• Heart at rest

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Pericardium

• Membrane sac
• Surrounds the heart
• Protection
• Anchors
• Contains serous fluid

HEART
Pericarditis inflammation of the pericardium
decreases serous fluid causing painful adhesions
interfering with heart movements
Pericardium
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Heart Wall

• Epicardium (outside) visceral layer of the
  serous pericardium.
• Myocardium (muscle) cardiac muscle layer
  forming the bulk of the heart.
• Endocardium (within) endothelial layer of the
  inner myocardial surface.

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Cardiac Muscle

• Specialized muscle cells
• Involuntary
• Striated
• Cushioned by endomysium
• Joined by intercalated discs

• Cardiac cell metabolism
• Areobic
• Large mitochondria
• Organic fuels fatty acids glucose
• Fatigue resistance

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Coronary Arteries Branch off aorta above aortic
semilunar valve

• Left coronary artery
• supplies left atrium and left ventricle
• Anterior interventricular artery
• supplies both ventricles
• Right coronary artery
• supplies right ventricle
• Posterior interventricular artery
• supplies both ventricles

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Coronary Veins

• Collects wastes from cardiac muscle
• Drains into a large sinus on posterior surface of
  heart called the coronary sinus
• Coronary sinus empties into right atrium

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The heart beats because of the spread of
electrical impulses to the heart muscle, causing
it to contract.
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Cardiac Conduction System

• Cardiac muscle tissue exhibits autorhythmicity
  generates its own stimulation.
• This is possible because of an internal cardiac
  conduction system which can initiate and
  distribute electrical impulses.

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Cardiac Conduction System

• Comprised of interconnected structures
• Sinoatrial node
• Atrioventricular node
• Atrioventricular Bundle
• Bundle Branches
• Purkinje Fibres

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Sinoatrial (SA) Node

• Natural Pacemaker
• Upper RA
• Neuromyocardial cells
• Sympathetic parasympathetic
• Sympathetic ?HR
• Parasympathetic ?HR

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Atrioventricular (AV) Node

• Junction of atria and ventricles
• Spread of depolarisation - from atrial myocardium
• Delay 0.15 seconds
• Time atria to expel blood
• Time for ventricular filling
• Protection to ventricles
• Less autonomic nervous control than SA node
• Sympathetic ?conduction time
• Parasympathetic ?conduction time

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Linked to the nervous system
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Depolorization The heart is autorhythmic

• Depolarization begins
• in sinoatrial (SA) node
• Spread through atrial myocardium
• Results in myocardial contration of the atria
• Delay in atrioventricular (AV) node
• To the Bundle of His
• AKA atrioventricular bundle

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Depolorization The heart is autorhythmic

• Separates into 2 main
• branches left right
• Located in the interventricular septum
• Left bundle antero-superior division
• Right bundle postero-inferior division
• Bundle branches divide - small, dense network of
  conduction tissue called the Purkinje Fibers

Entire musculature depolarizes quickly
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Electrocardiogram
Variations in electrical potential radiate from
the heart ECG records electrical events in the
heart.
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P-P one cardiac cycle P-Q time for atrial
depolarization Q-T time for ventricular
depolarization T-P time for relaxation
P wave Depolarization of atria Followed by
contraction QRS complex 3 waves (Q, R,
S) Depolarization of ventricles Followed by
contraction T wave Repolarization of ventricles
P-Q interval Time atria depolarize remain
depolarized Q-T interval Time ventricles
depolarize remain depolarized
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P
T
PR
QRS
SA node Represented on the ECG as P wave
AV node conduction is represented on the ECG as
the PR Interval
The Bundle Branch and purkinje fibre
depolarisation constitutes ventricular
depolarisation Represented on the ECG as the QRS
Atrial repolarisation occurs within the QRS
therefore is masked Ventricular repolarisation is
represented on the ECG as a T wave
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1) atrial depolarization begins 2) atrial
depolarization complete (atria contracted) 3)
ventricles begin to depolarize at apex atria
repolarize (atria relaxed) 4) ventricular
depolarization complete (ventricles
contracted) 5) ventricles begin to repolarize at
apex 6) ventricular repolarization complete
(ventricles relaxed)