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Chapter 15 The Cardiovascular System: The Heart
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Location of the Heart
Thoracic cavity between two lungs
~2/3 to left of midline
surrounded by pericardium:
Fibrous pericardium -
Inelastic and anchors heart in place
Inside is serous pericardium - double layer around heart
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
Epicardium - outer layer
Myocardium - cardiac muscle
Two separate networks via gap junctions in intercalated discs - atrial & ventricular
Networks- contract as a unit
Endocardium - Squamous epithelium
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
4 chambers
2 upper chambers = Atria
Between is interatrial septum
Contains fossa ovalis - remnant of foramen ovalis
2 lower chambers = ventricles
Between is interventricular septum
Wall thickness depends on work load
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
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13. Great Vessels Of Heart-Right
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
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14. Great Vessels Of Heart-Left
Pulmonary Veins from lungs
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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15. Posterior View of Heart
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16. Anterior View of Frontal Section
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Valves
Designed to prevent back flow in response to pressure changes
Atrioventricular (AV) valves
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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18. Atrioventricular Valves: Bicuspid Valves
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19. Atrioventricular Valves: Superior View
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20. Blood Flow Through Heart
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Blood Flow
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Blood Supply Of Heart
Blood flow through vessels in myocardium = coronary circulation
Left & right coronary arteries
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
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
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
Left ventricle
Anterior view of frontal section
SINOATRIAL (SA) NODE
ATRIOVENTRICULAR
(AV) NODE
ATRIOVENTRICULAR (AV)
BUNDLE (BUNDLE OF HIS)
RIGHT AND LEFT
BUNDLE BRANCHES 1 2 3 4
Right atrium
Right ventricle
Frontal plane
SINOATRIAL (SA) NODE
ATRIOVENTRICULAR
(AV) NODE
Left atrium
Left ventricle
Anterior view of frontal section
ATRIOVENTRICULAR (AV)
BUNDLE (BUNDLE OF HIS)
RIGHT AND LEFT
BUNDLE BRANCHES
PURKINJE FIBERS 1 2 3 4 5
Right atrium
Right ventricle
Frontal plane
Left atrium
Left ventricle
Anterior view of frontal section
SINOATRIAL (SA) NODE
ATRIOVENTRICULAR
(AV) NODE
ATRIOVENTRICULAR (AV)
BUNDLE (BUNDLE OF HIS) 1 2 3
Right atrium
Right ventricle
Frontal plane
Left atrium
Left ventricle
Anterior view of frontal section
SINOATRIAL (SA) NODE
ATRIOVENTRICULAR
(AV) NODE 1 2
Right atrium
Right ventricle
Frontal plane
Right atrium
Right ventricle
Left atrium
Left ventricle
Anterior view of frontal section
Frontal plane
Left atrium
Left ventricle
Anterior view of frontal section
SINOATRIAL (SA) NODE 1
Right atrium
Right ventricle
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Electrocardiogram
Recording of currents from cardiac conduction on skin = electrocardiogram (EKG or ECG)
P wave = atrial depolarization
Contraction begins right after peak
Repolarization is masked in QRS
QRS complex = Ventricular depolarization
Contraction of ventricle
T-wave = ventricular repolarization
Just after ventricles relax
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ECG
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Cardiac Cycle
after T-wave ventricular diastole
Ventricular pressure drops below atrial & AV valves open  ventricular filling occurs
After P-wave atrial systole
Finishes filling ventricle (`25%)
After QRS ventricular systole
Pressure pushes AV valves closed
Pushes semilunar valves open and ejection occurs
Ejection until ventricle relaxes enough for arterial pressure to close semilunar valves
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Action Potential
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
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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32. Controls - Stroke Volume (S.V.)
Degree of stretch = Frank-Starling law
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.
Slows semilunar valve opening
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Controls- Heart Rate
Pacemaker adjusted by nerves
Cardiovascular center in Medulla
parasympathetic- ACh slows
Via vagus nerve
Sympathetic - norepinephrine speeds
Sensory input for control:
baroreceptors (aortic arch & carotid sinus)- B.P.
Chemoreceptors- O2, CO2, pH
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Other Controls
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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35. Autonomic Nervous System Regulation of Heart Rate
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Exercise and the Heart
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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