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Chapter 15
The Cardiovascular
System: The Heart
Copyright 2010, John Wiley & Sons, Inc.
Location of the Heart
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Thoracic cavity between two lungs
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surrounded by pericardium:
Fibrous pericardium 
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~2/3 to left of midline
Inelastic and anchors heart in place
Inside is serous pericardium - double
layer around heart
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Parietal layer fused to fibrous pericardium
Inner visceral layer adheres tightly to heart
Filled with pericardial fluid - reduces friction
during beat.
Copyright 2010, John Wiley & Sons, Inc.
Position of the Heart
Copyright 2010, John Wiley & Sons, Inc.
Position of the Heart
Copyright 2010, John Wiley & Sons, Inc.
Heart Wall
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Epicardium - outer layer
Myocardium - cardiac muscle
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Two separate networks via gap junctions in
intercalated discs - atrial & ventricular
Networks- contract as a unit
Endocardium - Squamous epithelium
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lines inside of myocardium
Copyright 2010, John Wiley & Sons, Inc.
Pericardium
Copyright 2010, John Wiley & Sons, Inc.
Cardiac Muscle Tissue
Copyright 2010, John Wiley & Sons, Inc.
Chambers of the Heart
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4 chambers
2 upper chambers = Atria
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2 lower chambers = ventricles
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Between is interatrial septum
Between is interventricular septum
Wall thickness depends on work load
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Atria thinnest
Right ventricle pumps to lungs & thinner than left
Copyright 2010, John Wiley & Sons, Inc.
Structure of the Heart
Copyright 2010, John Wiley & Sons, Inc.
Structure of the Heart
Copyright 2010, John Wiley & Sons, Inc.
Great Vessels Of Heart-Right
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Superior & inferior Vena Cavae
 Delivers deoxygenated blood to R. atrium
from body
 Coronary sinus drains heart muscle veins
R. Atrium  R. Ventricle
pumps through Pulmonary Trunk
R & L pulmonary arteries
 lungs
Copyright 2010, John Wiley & Sons, Inc.
Great Vessels Of Heart-Left
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Pulmonary Veins from lungs
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oxygenated blood
L. atrium Left ventricle
ascending aorta body
Between pulmonary trunk & aortic arch is
ligamentum arteriosum
fetal ductus arteriosum remnant
Copyright 2010, John Wiley & Sons, Inc.
Anterior View of Frontal Section
Copyright 2010, John Wiley & Sons, Inc.
Valves
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Designed to prevent back flow in response
to pressure changes
Atrioventricular (AV) valves
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Between atria and ventricles
Right = tricuspid valve (3 cusps)
Left = bicuspid or mitral valve
Semilunar valves near origin of aorta &
pulmonary trunk
Aortic & pulmonary valves respectively
Copyright 2010, John Wiley & Sons, Inc.
Atrioventricular Valves: Bicuspid
Valves
Copyright 2010, John Wiley & Sons, Inc.
Atrioventricular Valves: Superior
View
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Blood Flow
Through
Heart
Copyright 2010, John Wiley & Sons, Inc.
Blood Flow
Copyright 2010, John Wiley & Sons, Inc.
Conduction System
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1% of cardiac muscle generate action
potentials= Pacemaker & Conduction
system
Normally begins at sinoatrial (SA) node
Atria & atria contract
AV node - slows
AV bundle (Bundle of His)
bundle branches Purkinje fibers
 apex and up- then ventricles contract
Copyright 2010, John Wiley & Sons, Inc.
Pacemaker
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Depolarize spontaneously
sinoatrial node ~100times /min
also AV node ~40-60 times/min
in ventricle ~20-35 /min
Fastest one run runs the heart = pacemaker
Normally the sinoatrial node
Copyright 2010, John Wiley & Sons, Inc.
Frontal plane
Left atrium
Right
Right atrium
atrium
1 SINOATRIAL (SA) NODE
2 ATRIOVENTRICULAR
(AV) NODE
3 ATRIOVENTRICULAR (AV)
BUNDLE (BUNDLE OF HIS)
Left ventricle
4 RIGHT AND LEFT
BUNDLE BRANCHES
Right
Right ventricle
ventricle
5 PURKINJE FIBERS
Copyright 2010, John Wiley
& Sons,view
Inc. of frontal section
Anterior
Electrocardiogram
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Recording of currents from cardiac
conduction on skin = electrocardiogram
(EKG or ECG)
P wave = atrial depolarization
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QRS complex = Ventricular depolarization
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Contraction begins right after peak
Repolarization is masked in QRS
Contraction of ventricle
T-wave = ventricular repolarization
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Just after ventricles relax
Copyright 2010, John Wiley & Sons, Inc.
ECG
Copyright 2010, John Wiley & Sons, Inc.
Cardiac Cycle
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after T-wave ventricular diastole
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After P-wave atrial systole
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Ventricular pressure drops below atrial & AV
valves open  ventricular filling occurs
Finishes filling ventricle (`25%)
After QRS ventricular systole
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Pressure pushes AV valves closed
Pushes semilunar valves open and ejection
occurs
Ejection until ventricle relaxes enough for
arterial pressure to close semilunar valves
Copyright 2010, John Wiley & Sons, Inc.
Cardiac Cycle
Copyright 2010, John Wiley & Sons, Inc.
Flow Terms
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Cardiac Output (CO) = liters/min
pumped
Heart Rate (HR) = beats/minute (bpm)
Stroke volume (SV) = volume/beat
CO = HR x SV
Copyright 2010, John Wiley & Sons, Inc.
Exercise and the Heart
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Aerobic exercise (longer than 20 min)
strengthens cardiovascular system
Well trained athlete doubles maximum
C.O.
Resting C.O. about the same but resting H.R.
decreased
Copyright 2010, John Wiley & Sons, Inc.