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.
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Position of the Heart
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Position of the Heart
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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
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Pericardium
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Cardiac Muscle Fibers
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Cardiac Muscle Tissue
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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
Contains fossa ovalis - remnant of foramen ovalis
Between is interventricular septum
Wall thickness depends on work load
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Atria thinnest
Right ventricle pumps to lungs & thinner than left
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Structure of the Heart
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Structure of the Heart
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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
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Posterior View of Heart
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Anterior View of Frontal Section
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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
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Atrioventricular Valves: Bicuspid
Valves
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Atrioventricular Valves: Superior
View
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Blood Flow
Through
Heart
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Blood Flow
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Blood Supply Of Heart
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Blood flow through vessels in myocardium =
coronary circulation
Left & right coronary arteries
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branch from aorta
branch to carry blood throughout muscle
Deoxygenated blood collected by coronary
sinus (posterior)
Empties into right atrium
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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
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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
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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
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& 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
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ECG
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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.
Action Potential
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Review muscle
Heart has addition of External Ca2+
Creates a plateau
Prolonged depolarized period
Can not go into tetanus
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Cardiac Cycle
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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
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Controls - Stroke Volume (S.V.)
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Degree of stretch = Frank-Starling law
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Increase diastolic Volume increases strength of
contraction increased S.V.
Increased venous return  increased S.V.
increased sympathetic activity
High back pressure in artery  decreased
S.V.
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Slows semilunar valve opening
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Controls- Heart Rate
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Pacemaker adjusted by nerves
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parasympathetic- ACh slows
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Cardiovascular center in Medulla
Via vagus nerve
Sympathetic - norepinephrine speeds
Sensory input for control:
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baroreceptors (aortic arch & carotid sinus)B.P.
Chemoreceptors- O2, CO2, pH
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Other Controls
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Hormones:
 Epinephrine & norepinephrine
increase H.R.
 Thyroid hormones stimulate H.R.
 Called tachycardia
Ions
 Increased Na+ or K+ decrease H.R. &
contraction force
 Increased Ca2+ increases H.R. &
contraction force
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Autonomic Nervous System Regulation
of Heart Rate
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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
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End of Chapter 15
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