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The Cardiovascular System:
Cardiac Function
Outline
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5/2/2017
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Overview of the Cardiovascular System
The Path of Blood Flow Through the Heart
and Vasculature
Anatomy of the Heart
Electrical Activity of the Heart
The Cardiac Cycle
Cardiac Output and Its Control
Dr. C. Gerin -F16
I. Overview of the Cardiovascular
System
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–
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The Heart
Blood Vessels
Blood
Overview of Cardiovascular System
Functions
Transport of substances
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– Oxygen & nutrients to cells
– Wastes from cells to liver & kidneys
– Hormones, immune cells, clotting proteins
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to specific target cells
The Heart
– Four chambers
• 2 Atria
• 2 Ventricles
– Septum
• Interatrial
• Interventricular
– Base
– Apex
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Blood Vessels
Heart Arteries  Arterioles Capillaries  Venules  Veins
– Vasculature
– Arteries – relatively large, branching vessels that
conduct blood away from the heart
– Arterioles – small branching vessels with high
resistance
– Capillaries – site of exchange between blood
and tissue
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Blood Vessels
– Venules – small converging vessels
– Veins – relatively large converging vessels that conduct
blood to the heart
– Closed system
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Blood
– Erythrocytes – red blood cells
• Transports oxygen and carbon dioxide
– Leukocytes – white blood cells
• Defend body against pathogens
– Platelets – cell fragments
• Important in blood clotting
– Plasma – fluid and solutes
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II. The Path of Blood Flow Through the
Heart
and Vasculature
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Series Flow Through the Cardiovascular
System
Parallel Flow Within the Systemic or
Pulmonary Circuit
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Series Flow Through the
Cardiovascular System
– Pulmonary circuit
• Supplied by right heart
• Blood vessels from heart to lungs and lungs to heart
– Systemic circuit
• Supplied by left heart
• Blood vessels from heart to systemic tissues and
tissues to heart
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Oxygenation of Blood
– Exchange between blood and tissue takes
place in capillaries
– Pulmonary capillaries
• Blood entering lungs = deoxygenated blood
• Oxygen diffuses from tissue to blood
• Blood leaving lungs = oxygenated blood
– Systemic capillaries
• Blood entering tissues = oxygenated blood
• Oxygen diffuses from blood to tissue
• Blood leaving tissues = deoxygenated blood
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Path of Blood Flow
– Cardiovascular system = closed system
– Flow through systemic and pulmonary circuits
are in series
– Left ventricle  aorta  systemic circuit 
vena cavae  right atrium  right ventricle 
pulmonary artery  pulmonary circuit 
pulmonary veins  left atrium  left ventricle
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Path of Blood Flow Through the
Cardiovascular System
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Parallel Blood Flow Within the
Systemic
(or Pulmonary) Circuit
– Aorta  arteries  arterioles  capillaries
– Oxygenated blood enters each capillary bed
– Parallel flow allows independent regulation
of blood flow to organs
– Capillaries  venules  veins
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Parallel Flow Patterns in the
Cardiovascular System
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III. Anatomy of the Heart
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Myocardium and the Heart Wall
Valves and Unidirectional Blood Flow
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Location of the Heart
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The Heart
– Located in thoracic cavity
• Diaphragm separates abdominal cavity
from thoracic cavity
– Size of fist
– Weighs approxinately 250 – 350 grams
Pericardium
– Membranous sac surrounding heart (visceral
and parietal serous membrane)
– Lubricates heart decreasing friction
– Pericarditis = inflammation of pericardium
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Figure 18.3 The pericardial layers and layers of the heart wall.
Pulmonary
trunk
Fibrous pericardium
Pericardium
Parietal layer of serous
pericardium
Myocardium
Pericardial cavity
Epicardium (visceral
layer of serous
pericardium)
Myocardium
Endocardium
Heart chamber
© 2013 Pearson Education, Inc.
Heart
wall
Myocardium and the Heart Wall
Three layers of the heart wall:
– Endocardium (inner)
• layer of endothelial cells
– Myocardium (middle)
• cardiac muscle
– Epicardium (outer)= visceral pericardium
• external membrane
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Cardiac Muscle
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Properties of Cardiac Muscle Cells
CARDIOMYOCYTES:
– Smaller than skeletal
– Branches
– Sarcomeres
• striated
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Properties of Cardiac Muscle
– Intercalated Disks
• Gap junctions (channels between cell cytosol , passage
of ions => depolarization)
– Contract as unit
• Desmosomes
– Resist stretch (fill and contraction)
– Atria & Ventricles ( Atrium singular)
• Separate units
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Properties of Cardiac Muscle
– Aerobic muscle (primary hypoxia versus primary
hypoglycemia)
– No cell division after infancy - growth
by hypertrophy
– 99% contractile cells
– 1% autorhythmic cells
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Walls of the Heart
– Walls of ventricles
thicker than walls of
atria (why?)
– Wall of left ventricle
thicker (why??)than
wall of right ventricle
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Figure 18.5e Gross anatomy of the heart.
Aorta
Superior vena cava
Right pulmonary artery
Pulmonary trunk
Right atrium
Right pulmonary veins
Fossa ovalis
Pectinate muscles
Tricuspid valve
Right ventricle
Chordae tendineae
Trabeculae carneae
Inferior vena cava
Frontal section
© 2013 Pearson Education, Inc.
Left pulmonary artery
Left atrium
Left pulmonary veins
Mitral (bicuspid) valve
Aortic valve
Pulmonary valve
Left ventricle
Papillary muscle
Interventricular septum
Epicardium
Myocardium
Endocardium
Figure 18.5b Gross anatomy of the heart.
Brachiocephalic trunk
Superior vena cava
Right pulmonary artery
Ascending aorta
Pulmonary trunk
Right pulmonary veins
Left common carotid artery
Left subclavian artery
Aortic arch
Ligamentum arteriosum
Left pulmonary artery
Left pulmonary veins
Auricle of
left atrium
Right atrium
Right coronary artery
(in coronary sulcus)
Anterior cardiac vein
Right ventricle
Circumflex artery
Right marginal artery
Great cardiac vein
Anterior interventricular
artery (in anterior
interventricular sulcus)
Apex
Small cardiac vein
Inferior vena cava
Anterior view
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Left coronary artery
(in coronary sulcus)
Left ventricle
Thickness of Ventricle Walls
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Function of Cardiac Muscle
– Rhythmic contraction and relaxation generates
heart pumping action
– Contraction pushes blood out of heart into
vasculature
– Relaxation allows heart to fill with blood
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Heartbeat
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Wave of contraction through cardiac muscle
Atria contract as a unit
Ventricles contract as a unit
Atrial contraction precedes ventricle contraction
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Valves and Unidirectional Blood Flow
– Pressure within chambers of heart vary with
heartbeat cycle
– Pressure difference drives blood flow
• High pressure to low pressure
– Normal direction of flow
• Atria to ventricles
• Ventricles to arteries
– Valves prevent backward flow of blood
– All valves open passively based on pressure gradient
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Action of the AV Valves
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Action of the Semilunar Valves
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Heart Valves
– Atrioventricular valves = AV valves
• Right AV valve = tricuspid valve
• Left AV valve = bicuspid valve = mitral valve
• Papillary muscles and chordae tendinae
– keep AV valves from everting
– Semilunar valves
• Aortic Valve
• Pulmonary Valve
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Figure 18.6d Heart valves.
Pulmonary valve
Aortic valve
Area of cutaway
Mitral valve
Tricuspid valve
Opening of inferior
vena cava
Tricuspid valve
Mitral valve
Chordae
tendineae
Myocardium
of right
ventricle
Interventricular
septum
Papillary
© 2013 Pearson Education,
Inc.
muscles
Myocardium
of left ventricle
Valve Pathology
• Two conditions severely weaken heart:
– Incompetent valve
• Blood backflows so heart repumps same blood
over and over
– Valvular stenosis
• Stiff flaps – constrict opening  heart must
exert more force to pump blood
• Valve replaced with mechanical, animal,
or cadaver valve
© 2013 Pearson Education, Inc.
Pathway of Blood Through the
Heart
• Pulmonary circuit
– Right atrium  tricuspid valve  right
ventricle
– Right ventricle  pulmonary semilunar valve
 pulmonary trunk  pulmonary arteries 
lungs
– Lungs  pulmonary veins  left atrium
© 2013 Pearson Education, Inc.
Pathway of Blood Through the
Heart
• Systemic circuit
– Left atrium  mitral valve  left ventricle
– Left ventricle  aortic semilunar valve  aorta
– Aorta  systemic circulation
PLAY
Animation:
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Rotatable heart (sectioned)
Pathway of Blood Through the
Heart
• Equal volumes of blood pumped to
pulmonary and systemic circuits
• Pulmonary circuit short, low-pressure
circulation
• Systemic circuit long, high-friction
circulation
• Anatomy of ventricles reflects differences
– Left ventricle walls 3X thicker than right
© 2013 Pearson Education, Inc.
• Pumps with greater pressure
Coronary Circulation
• Functional blood supply to heart muscle
itself
– Delivered when heart relaxed
– Left ventricle receives most blood supply
• Arterial supply varies among individuals
• Contains many anastomoses (junctions)
– Provide additional routes for blood delivery
– Cannot compensate for coronary artery
occlusion
© 2013 Pearson Education, Inc.
Figure 18.11a Coronary circulation.
Superior
vena cava
Anastomosis
(junction of
vessels)
Aorta
Pulmonary
trunk
Left atrium
Left
coronary
artery
Right
atrium
Right
coronary
artery
Right
ventricle
Right
marginal
artery
Circumflex
artery
Posterior
interventricular
artery
The major coronary arteries
© 2013 Pearson Education, Inc.
Left
ventricle
Anterior
interventricular
artery
Coronary Circulation: Arteries
• Arteries arise from base of aorta
• Left coronary artery branches  anterior
interventricular artery and circumflex artery
– Supplies interventricular septum, anterior ventricular
walls, left atrium, and posterior wall of left ventricle
• Right coronary artery branches  right
marginal artery and posterior interventricular
artery
– Supplies right atrium and most of right ventricle
© 2013 Pearson Education, Inc.
Coronary Circulation: Veins
• Cardiac veins collect blood from capillary beds
• Coronary sinus empties into right atrium; formed
by merging cardiac veins
– Great cardiac vein of anterior interventricular sulcus
– Middle cardiac vein in posterior interventricular
sulcus
– Small cardiac vein from inferior margin
• Several anterior cardiac veins empty directly
into right atrium anteriorly
© 2013 Pearson Education, Inc.
Figure 18.11b Coronary circulation.
Superior
vena cava
Anterior
cardiac
veins
Great
cardiac
vein
Coronary
sinus
Small
cardiac vein
The major cardiac veins
© 2013 Pearson Education, Inc.
Middle cardiac vein
Pathology
• Angina pectoris
– Thoracic pain caused by fleeting deficiency in
blood delivery to myocardium
– Cells weakened
• Myocardial infarction (heart attack)
– Prolonged coronary blockage
– Areas of cell death repaired with noncontractile
scar tissue
© 2013 Pearson Education, Inc.
IV. Electrical Activity of the Heart
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Autorhythmic Cells
Autorhythmicity is the ability to generate own
rhythm
Conduction System
Autorhythmic cells that provide pathway to
spread excitation through the heart
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Conduction System
– Pacemaker cells
• Spontaneously depolarizing membrane potentials to
generate action potentials
• Coordinate and provide rhythm to heartbeat
– Conduction fibers
• Rapidly conduct action potentials initiated by
pacemaker cells to myocardium
• Conduction velocity = 4 meters/second
• Ordinary muscle fibers, CV = 0.4 meter/second
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Pacemaker Cells of the Myocardium
– Sinoatrial node
• Pacemaker of the heart
– Atrioventricular node
Conduction Fibers of the Myocardium
– Internodal pathways
– Bundle of His
– Purkinje fibers
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Autorhythmic Cells
Location
SA Node (Pacemaker)
AV Node
Bundle of His
Purkinje Fibers
Firing Rate at Rest
70-80 APs/min
40-60 APs/min
20-40 APs/min
20-40 APs/min
Fastest depolarizing cells drive all other cells
(they are linked together by gap junctions) =
pacemaker = sets pace for entire heart
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Spread of Excitation Between Cells
– Atria contract first followed by ventricles
– Coordination due to presence of gap junctions
and conduction pathways
– Intercalated disks
• Junctions between adjacent myocardial cells
• Desmosomes to resist mechanical stress
• Gap junctions for electrical coupling
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Electrical Coupling of Cardiac Muscle
Cells
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Anatomy of the Conduction System
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Spread of Excitation
– Interatrial Pathway
• SA Node  right atrium  left atrium
• Rapid
• Simultaneous contraction right and left atria
– Internodal Pathway
• SA Node  AV Node
– AV Node Transmission
• Only pathway from atria to ventricles
• Slow conduction - AV Nodal Delay = 0.1 sec
• Atria contract before ventricles
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Spread of Excitation
Ventricular Excitation
– Down Bundle of His
– Up Purkinje Fibers
• Purkinje Fibers contact ventricle contractile cells
• Ventricle contracts from apex up
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Spread of Excitation
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Control of Heart Beat by Pacemakers
– Autorhythmic cells have pacemaker potentials
– Spontaneous depolarizations caused by closing
K+ channels and opening 2 types of channels
• Two channels that open:
– If channels: Na+ & K+, net depolarization
– Ca2+ channels: further depolarization
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Control of Heart Beat by Pacemakers
– Depolarize to threshold
• Open fast Ca2+ channels- action potential
– Repolarization
• Open K+ channels
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Electrical Activity in Pacemaker Cells
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Ionic Bases of the Autorhythmic Cell
Action Potential
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Contractile Cell Action Potential
– Five phases
• Phase 0 – increased permeability to sodium
• Phase 1 – decreased permeability to sodium
• Phase 2 – increased permeability to calcium,
decreased permeability to potassium
• Phase 3 – increased permeability to potassium,
decreased permeability to calcium
• Phase 4 – resting membrane potential
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Contractile Cell Action Potential
– Long duration of action potential =
250-300 msec
• (only 1-2 msec in skeletal muscle)
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Contractile Cell Action Potential
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Ionic Bases of the Contractile Cell
Action Potential
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Excitation-Contraction Coupling in
Cardiac Contractile Cells
– Properties similar to skeletal muscle
• T tubules
• Sarcoplasmic reticulum calcium
• Troponin-tropomyosin regulation
– Properties similar to smooth muscle
• Gap junctions
• Extracellular calcium
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•
Steps of Excitation-Contraction
Depolarization Coupling
of cardiac contractile cell to
threshold via gap junction
2. Opening of calcium channels in plasma
membrane
3. AP travels down T tubules
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Steps of Excitation-Contraction
Coupling
•
Calcium is released from sarcoplasmic
reticulum by
-
Calcium-induced calcium release
Action potentials in T tubules
5. Calcium binds to troponin causing shift in
tropomyosin
6. Binding sites for myosin on actin are exposed
7. Crossbridge cycle occurs
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Excitation-Contraction Coupling in
Cardiac Muscle
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Relaxation of Cardiac Muscle
– Remove calcium from cytosol
• Ca2+ ATPase in sarcoplasmic reticulum
• Ca2+ ATPase in plasma membrane
• Na+-Ca2+ exchanger in plasma membrane
– Troponin and tropomyosin return to position
covering myosin binding sites on actin
Recording the Electrical Activity of the
Heart with an Electrocardiogram
– Non-invasive technique
– Used to test for clinical abnormalities in
conduction of electrical activity in the heart
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Electrocardiogram
External measure of electrical activity of the
heart
– Body = conductor
• Currents in body can spread to surface (ECG, EMG,
EEG)
– Distance & amplitude of spread depends on size
of potentials and synchronicity of potentials from
other cells
– Heart electrical activity- synchronized
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Einthoven’s Triangle
Lead I: LA (+) and RA (-)
Lead II: LL (+) and RA (-)
Lead III: LL (+) and LA (-)
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Standard ECG Trace
– P wave
– PQ segment
• atrial depolarization
– QRS complex
• AV nodal delay
– QT segment
• vent. depolarization
– T wave
• ventricular systole
– TQ interval
• vent. repolarization
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• ventricular diastole
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ECG Recording
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ECG and Ventricular Action Potential
Ventricular action potential
recorded from a single
contractile cell in the ventricle.
ECG surface recording
of the summed electrical
activity of all cells
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Abnormal Heart Rates
– “Sinus rhythm” =
rhythm generated by
SA node
– Abnormal Heart
Rates:
• Tachycardia- fast
• Bradycardia- slow
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Heart Block
Slowed/diminished conduction through AV
node occurs in varying degrees
1st degree block = slowed conduction through
AV node
– Increases PQ segment
– Increases delay between atrial and ventricular
contraction
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Heart Block
Slowed/diminished conduction through AV
node occurs in varying degrees
1st degree block = slowed conduction through
AV node
– Increases PQ segment
– Increases delay between atrial and ventricular
contraction
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2nd Degree Heart Block
Slowed, sometimes stopped conduction
through AV node
2nd degree block:
– Lose 1-to-1 relationship between P wave and
QRS complex
– Lose 1-to-1 relationship between atrial and
ventricular contraction
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3rd Degree Heart Block
Loss of conduction
through AV node
3rd degree block:
– P wave independent
of QRS complex
– Atrial and ventricular
contractions are
independent
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Extrasystole
Extra contraction
– PAC = premature
atrial contraction
– PVC = premature
ventricular contraction
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Ventricular Fibrillation
Loss of coordination
of electrical activity
– Atrial fibrillation weakness
– Ventricular fibrillation
- death within minutes
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