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The Cardiovascular System
 Dr. Tom Lehman
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The Cardiovascular/Circulatory Systems
 Circulatory System
 heart, blood vessels and blood
 Cardiovascular System
 heart, arteries, veins and capillaries;
 2 major divisions
 Pulmonary Circuit - right side of heart
 carries blood to lungs for gas exchange
 Systemic Circuit - left side of heart
 supplies blood to all organs of the body
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Heart Anatomy
 Approximately the size of your fist; Weight ~10 oz.
 Location
 Superior surface of diaphragm
 Left of the midline
 Anterior to the vertebral column
 Posterior to the sternum
 Medial to the Right and Left Lung
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Size, Shape and Position
 Located in mediastinum,
medial to the lungs
 Base - broad superior
portion of heart- take-off
of great vessels
 Apex - inferior end, tilts
to the left, tapers to point,
and rests on diaphragm
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Anatomic Position of the Heart
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Anatomic Position
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Anatomic Position
 Apex – 5th Intercostal Space, Left Midclavicular
Line:
 Point of Maximal Intensity: AV Valve Heart
Sounds
 Base – Level of Second Rib
 Take-off of the Great Vessels: Aorta and Pulmonary
Artery
 Best Place to Hear Heart Sounds for Semilunar
Valves
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Anatomic Position
Figure 18.1
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Coverings of the Heart: Anatomy
 Pericardium – a double-walled sac around the
heart composed of:
 A superficial fibrous pericardium
 A deep two-layer serous pericardium
 The parietal layer lines the internal surface of
the fibrous pericardium
 The visceral layer or epicardium lines the
surface of the heart
 They are separated by the fluid-filled
pericardial cavity
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Coverings of the Heart: Pericardium
The Pericardium:
 Protects and anchors the heart
 Prevents overfilling of the heart with blood
 Allows for the heart to work in a relatively
friction-free environment
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The Pericardium
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Pericardial Layers of the Heart
Figure 18.2
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Heart Wall
 Epicardium – visceral layer of the serous
pericardium
 Myocardium – cardiac muscle layer forming the
bulk of the heart
 Fibrous skeleton of the heart – crisscrossing,
interlacing layer of connective tissue
 Endocardium – endothelial layer of the inner
myocardial surface
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Pericardium & Heart Wall
 Pericardial cavity contains 5-30 ml of pericardial fluid
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Myocardium – muscle fibers and fibrous skeleton
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The Heart Chambers
• 4 chambers
• Right and left atria
– 2 superior, posterior chambers
– receive blood returning to
heart
• Right and left ventricles
– 2 inferior chambers
– pump blood into arteries
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External Anatomy - Anterior
Atrioventricular
sulcus
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External Heart: Major Vessels of the Heart
(Anterior View)
 Vessels returning blood to the heart include:
 Superior and inferior venae cavae
 Right and left pulmonary veins
 Vessels conveying blood away from the heart
include:
 Pulmonary trunk, which splits into right and left
pulmonary arteries
 Ascending aorta (three branches) –
brachiocephalic, left common carotid, and
subclavian arteries
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External Heart: Anterior View
Figure 18.4b
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External Heart: The Coronary Circulation
(Anterior View)
 Arteries – Left Main Coronary Artery, divides into
the Left Anterior Descending and Left Circumflex
Coronary Arteries; Right Coronary Artery
 Veins – small cardiac, anterior cardiac, and great
cardiac veins
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Coronary Arteries (Anterior View)
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External Heart: The Coronary Circulation
(Anterior View)
 Arteries – Left Main Coronary Artery, divides into
the Left Anterior Descending and Left Circumflex
Coronary Arteries; Right Coronary Artery
 Veins – small cardiac, anterior cardiac, and great
cardiac veins
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Coronary Circulation: Venous Supply
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Figure 18.7b
External Heart: Major Vessels of the Heart
(Posterior View)
 Vessels returning blood to the heart include:
 Right and left pulmonary veins
 Superior and inferior venae cavae
 Vessels conveying blood away from the heart
include:
 Aorta
 Right and left pulmonary arteries
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External Anatomy - Posterior
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External Heart: Vessels that Supply/Drain the
Heart (Posterior View)
 Arteries – right coronary artery (in atrioventricular
groove) and the posterior interventricular artery (in
interventricular groove)
 Veins – great cardiac vein, posterior vein to left
ventricle, coronary sinus, and middle cardiac vein
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Coronary Vessels: Posterior View
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External Heart Posterior View
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Gross Anatomy of Heart: Frontal Section
Figure 18.4e
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Atria of the Heart
 Atria are the receiving chambers of the heart
 Each atrium has a protruding auricle
 Interatrial Septum
 Pectinate muscles mark atrial walls
 Blood enters right atria from superior and
inferior venae cavae and coronary sinus
 Blood enters left atria from pulmonary veins
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Atria
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Gross Anatomy of Heart: Frontal Section
Figure 18.4e
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Coronal Section of Heart
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Ventricles of the Heart
 Ventricles are the discharging chambers of the heart
 Papillary muscles and trabeculae carneae muscles
mark ventricular walls
 Right ventricle pumps blood into the pulmonary
trunk
 Left ventricle pumps blood into the aorta
 Interventricular Septum separates
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Gross Anatomy of Heart: Frontal Section
Figure 18.4e
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Heart Internal Anatomy
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Heart Valves
 Ensure one-way blood flow
 Atrioventricular (AV) valves
 right AV valve has 3 cusps (tricuspid valve)
 left AV valve has 2 cusps (mitral, bicuspid valve) lamb
 chordae tendineae - cords connect AV valves to papillary
muscles (on floor of ventricles)
 Semilunar valves - control flow into great arteries
 pulmonary: from right ventricle into pulmonary trunk
 aortic: from left ventricle into aorta
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Heart Valves
 Aortic semilunar valve lies between the left
ventricle and the aorta
 Pulmonary semilunar valve lies between the right
ventricle and pulmonary trunk
 Semilunar valves prevent backflow of blood into
the ventricles
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Heart Valves
Figure 18.8a, b
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Heart Valves
Figure 18.8c, d
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AV Valve Mechanics
 Ventricles relax, pressure drops, semilunar valves
close, AV valves open, blood flows from atria to
ventricles
 Ventricles contract, pressure rises, AV valves close,
(papillary m. contracts and pulls on chordae tendineae to
prevent prolapse) pressure rises and semilunar valves
open, blood flows into arteries
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Atrioventricular Valve Function
Figure 18.9
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Operation of Atrioventricular Valves
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Atrioventricular Valves
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Heart Valves
 Aortic semilunar valve lies between the left
ventricle and the aorta
 Pulmonary semilunar valve lies between the right
ventricle and pulmonary trunk
 Semilunar valves prevent backflow of blood into
the ventricles
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Semilunar Valve Function
Figure 18.10
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Operation of Semilunar Valves
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Semilunar Heart Valves
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Pathway of Blood Through the Heart and
Lungs
 Right atrium  tricuspid valve  right ventricle
 Right ventricle  pulmonary semilunar valve 
pulmonary arteries  lungs
 Lungs  pulmonary veins  left atrium
 Left atrium  bicuspid valve  left ventricle
 Left ventricle  aortic semilunar valve  aorta
 Aorta  systemic circulation
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Blood Flow Through Heart
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Pathway of Blood Through the Heart and
Lungs
Figure 18.5
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Atherosclerosis
 A Systemic Disease
 Number 1 Cause of Death in Women and Men
 Number 1 cause of Disability in the USA
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Risk Factors
 Smoking
 Hypertension
 Diabetes Mellitus
 Hypercholesterolemia
 Obesity
 Sedentary Lifestyle
 Family History
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Atherosclerosis
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Atherosclerosis
 Slowly Progressive Disease
 Gradual Narrowing of artery lumen by plaques
 Plaques unstable and may rupture
 Plaques > 70% cause limitation of blood flow to
organ = Ischemia
 Rupture of plaque causes thrombogenesis
 Thrombosis leads to Infarction
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Atherosclerosis
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Coronary Circulation
 Coronary circulation is the functional blood supply
to the heart muscle itself
 Collateral routes ensure blood delivery to heart
even if major vessels are occluded
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Coronary Flow and the Cardiac Cycle
 Reduced during ventricular contraction (systole)
 arteries compressed
 Increased during ventricular relaxation (diastole)
 Most Coronary Blood Flow Occurs in Diastole
 openings to coronary arteries, just above aortic
semilunar valve, fill as blood surges back to valve
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Coronary Blood Supply
 Blood vessels of heart wall nourish cardiac muscle
 Left Main Coronary Artery - under left auricle, 2 branches
 Left Anterior Descending Artery
 supplies interventricular septum + anterior walls of ventricles
 Left Circumflex Coronary Artery
 passes around left side of heart in coronary sulcus, supplies left
atrium and posterior wall of left ventricle
 Right Coronary Artery - supplies right atrium
 passes under right auricle in coronary sulcus, divides:
 marginal artery - supplies lateral rt. atrium + ventricle
 Posterior Descending Coronary Artery
 supplies posterior walls of ventricles and interventricular septum
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Coronary Circulation: Arterial Supply
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Figure 18.7a
Myocardial Infarction
 Sudden death of heart tissue caused by interruption
of blood flow from vessel narrowing or occlusion
 Anastomoses defend against interruption by
providing alternate blood pathways
 circumflex artery and right coronary artery
combine to form posterior interventricular artery
 anterior and posterior interventricular arteries join
at apex of heart
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Coronary Circulation: Arterial Supply
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Figure 18.7a
Heart Catheterization
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Heart Catheterization
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Coronary Angioplasty and Stenting
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Structure of Cardiac Muscle
 Short, thick, branched cells, 50 to 100 m long and 10 to 20 m wide
with one central nucleus
 Sarcoplasmic reticulum
 T tubules much larger than in skeletal muscle, admit more Ca2+ from
ECF during excitation
 Intercalated discs, join myocytes end to end
 interdigitating folds -  surface area
 mechanical junctions tightly join myocytes
 fascia adherens: actin anchored to plasma membrane
 desmosomes
 electrical junctions - gap junctions form channels allowing ions to
flow directly into next cell
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Structure of Cardiac Muscle Cell
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Cardiac Muscle Contraction
 Due to these characteristics, the heart muscle
contracts like a Functional Syncytium
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Microscopic Anatomy of Heart Muscle
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Figure 18.11
Metabolism of Cardiac Muscle
 Aerobic respiration
 Rich in myoglobin and glycogen
 Large mitochondria
 Organic fuels: fatty acids, glucose, ketones
 Fatigue resistant
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Cardiac Muscle Contraction
 Heart muscle:
 Is stimulated by nerves
 Is self-excitable (Automaticity)
 Contracts as a unit = Functional Syncytium
 Has a long (250 ms) absolute refractory period
 Cardiac muscle contraction is similar to skeletal
muscle contraction
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Cardiac Conduction System
 Myogenic - heartbeat originates within heart
 Autorhythmic - depolarize spontaneously and regularly
 Conduction system
 SA node: pacemaker, initiates heartbeat, sets heart rate
 fibrous skeleton insulates atria from ventricles
 AV node: electrical gateway to ventricles
 AV bundle: pathway for signals from AV node
 Right and left bundle branches: divisions of AV bundle
that enter interventricular septum and descend to apex
 Purkinje fibers: upward from apex spread throughout
ventricular myocardium
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Heart Physiology: Sequence of Excitation
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Figure 18.14a
Heart Physiology: Intrinsic Conduction System
 Autorhythmic cells:
 Initiate action potentials
 Have unstable resting potentials called pacemaker
potentials
 Use calcium influx (rather than sodium) for rising
phase of the action potential
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Pacemaker and Action Potentials of the Heart
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Figure 18.13
Depolarization of the SA Node
 SA node - no stable resting
membrane potential
 Pacemaker potential
 gradual depolarization from -60
mV, slow influx of Na+
 Action potential
 at threshold -40 mV, fast Ca+2
channels open, (Ca+2 in)
 depolarizing phase to 0 mV, K+
channels open, (K+ out)
 repolarizing phase back to -60
mV, K+ channels close
 Each depolarization creates one
heartbeat
 SA node at rest fires at 0.8 sec,
about 75 bpm
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Impulse Conduction in the Myocardium
 SA node signal travels at 1 m/sec through atria
 AV nodes thin myocytes slow signal to 0.05 m/sec
 delays signal 100 msec, allows ventricles to fill
 AV bundle and purkinje fibers
 speeds signal along at 4 m/sec to ventricles
 Papillary muscles - get signal first, contraction stabilizes AV
valves
 Ventricular systole begins at apex, progresses up
 spiral arrangement of myocytes twists ventricles slightly
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Myocardial Contraction and Action Potential
Na+ gates open
2) Positive feedback cycle
3) Na+ gates close
4) Plateau
5) Ca+2 channels close K+
channels open
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Extrinsic Innervation of the Heart
 Heart is stimulated
by the sympathetic
cardioacceleratory
center
 Heart is inhibited
by the
parasympathetic
cardioinhibitory
center
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Figure 18.15
Extrinsic Innervation of the Heart
 Cardioinhibitory Impulses – Slow Spontaneous
Depolarization of the SA Node
 Cardioexcitatory Impulses – Increase Spontaneous
Depolarization of the SA Node
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Artificial Pacemaker
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The Electrocardiogram
 Composite of all action
potentials of nodal and
myocardial cells
detected, amplified and
recorded by electrodes on
arms, legs and chest
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Electrical Activity of Myocardium
1)atria begin to
depolarize
2) atria depolarize
3)ventricles begin to
depolarize at apex;
atria repolarize
4)ventricles depolarize
5) ventricles begin to
repolarize at apex
6) ventricles repolarize
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Electrocardiography
 Electrical activity is recorded by electrocardiogram
(ECG)
 P wave corresponds to depolarization of SA node
 QRS complex corresponds to ventricular
depolarization
 T wave corresponds to ventricular repolarization
 Atrial repolarization record is masked by the larger
QRS complex
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Diagnostic Value of the ECG
 Invaluable for diagnosing
abnormalities in
conduction pathways,
MI, heart enlargement
and electrolyte and
hormone imbalances
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ECGs, Normal & Abnormal
No P waves
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ECGs, Abnormal
Arrhythmia: conduction failure at AV node
No pumping action occurs
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Heart Sounds
 Auscultation - listening to sounds made by body
 First heart sound (S1), louder and longer “lubb”,
occurs with closure of AV valves
 Second heart sound (S2), softer and sharper “dupp”
occurs with closure of semilunar valves
 S3 - rarely heard in people > 30
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Murmurs – Abnormal Heart Sounds
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Cardiac Cycle
 Cardiac Cycle refers to all events associated with
blood flow through the heart
 Systole – contraction of heart muscle
 Diastole – relaxation of heart muscle
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Phases of the Cardiac Cycle
Figure 18.20
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Phases of the Cardiac Cycle
 Ventricular filling – mid-to-late diastole
 Heart blood pressure is low as blood enters atria
and flows into ventricles
 AV valves are open, then atrial systole occurs
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Phases of the Cardiac Cycle
Figure 18.20
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Phases of the Cardiac Cycle
 Ventricular systole
 Atria relax
 Rising ventricular pressure results in closing of AV
valves
 Isovolumetric contraction phase
 Ventricular ejection phase opens semilunar valves
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Phases of the Cardiac Cycle
Figure 18.20
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Phases of the Cardiac Cycle
 Isovolumetric relaxation – early diastole
 Ventricles relax
 Backflow of blood in aorta and pulmonary trunk
closes semilunar valves
 Dicrotic notch – brief rise in aortic pressure caused
by backflow of blood rebounding off semilunar
valves
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Phases of the Cardiac Cycle
Figure 18.20
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Cardiac Output (CO) and Reserve
 CO is the amount of blood pumped by each
ventricle in one minute
 CO is the product of heart rate (HR) and stroke
volume (SV)
 HR is the number of heart beats per minute
 SV is the amount of blood pumped out by a
ventricle with each beat
 Cardiac reserve is the difference between resting
and maximal CO
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Cardiac Output: Example
 CO (ml/min) = HR (75 beats/min) x SV (70
ml/beat)
 CO = 5250 ml/min (5.25 L/min)
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Regulation of Stroke Volume
 SV = end diastolic volume (EDV) minus end
systolic volume (ESV)
 EDV = amount of blood collected in a ventricle
during diastole
 ESV = amount of blood remaining in a ventricle
after contraction
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Factors Affecting Stroke Volume
 Preload – amount ventricles are stretched by
contained blood
 Contractility – cardiac cell contractile force due to
factors other than EDV
 Afterload – back pressure exerted by blood in the
large arteries leaving the heart
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Frank-Starling Law of the Heart
 Preload, or degree of stretch, of cardiac muscle
cells before they contract is the critical factor
controlling stroke volume
 Slow heartbeat and exercise increase venous return
to the heart, increasing SV
 Blood loss and extremely rapid heartbeat decrease
SV
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Preload and Afterload
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Figure 18.21
Extrinsic Factors Influencing Stroke Volume
 Contractility is the increase in contractile strength,
independent of stretch and EDV
 Increase in contractility comes from:
 Increased sympathetic stimuli
 Certain hormones
 Ca2+ and some drugs
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Factors Influencing Contractility
 Neurotransmitters - with cAMP as 2 messenger
 norepinephrine and epinephrine (catecholamines) are potent cardiac
stimulants
 Drugs
 caffeine inhibits cAMP breakdown
 nicotine stimulates catecholamine secretion
 Hormones
 TH  adrenergic receptors in heart,  sensitivity to sympathetic
stimulation,  HR
 Electrolytes - K has greatest chronotropic effects
  K myocardium less excitable, HR slow and irregular
  K cells hyperpolarized, requires  stimulation
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Extrinsic Factors Influencing Stroke Volume
 Agents/factors that decrease contractility include:
 Acidosis
 Increased extracellular K+
 Calcium channel blockers
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Regulation of Heart Rate
 Positive chronotropic factors increase heart rate
 Negative chronotropic factors decrease heart rate
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Regulation of Heart Rate: Autonomic Nervous
System
 Sympathetic nervous system (SNS) stimulation is
activated by stress, anxiety, excitement, or exercise
 Parasympathetic nervous system (PNS) stimulation
is mediated by acetylcholine and opposes the SNS
 PNS dominates the autonomic stimulation, slowing
heart rate and causing vagal tone
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Factors Involved in Regulation of Cardiac
Output
Figure 18.23
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Congestive Heart Failure (CHF)
 Congestive heart failure (CHF) is caused by:
 Coronary atherosclerosis
 Persistent high blood pressure
 Multiple myocardial infarcts
 Dilated cardiomyopathy (DCM)
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Examples of Congenital Heart Defects
Figure 18.25
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