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The Heart
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Heart Anatomy
Approximately the size of your fist Location
Superior surface of diaphragmLeft of the midlineAnterior to the vertebral column, posterior to
the sternum
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Heart Anatomy
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Coverings of the Heart: Anatomy Pericardium – a double-walled sac around the
heart composed of:A superficial fibrous pericardiumA 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: Physiology
The pericardium:Protects and anchors the heartPrevents overfilling of the heart with bloodAllows for the heart to work in a relatively
friction-free environment
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Pericardial Layers of the Heart
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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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Cardiac Muscle Bundles
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External Heart: Major Vessels of the Heart (Anterior View)
Vessels returning blood to the heart include:Superior and inferior vena cavaRight and left pulmonary veins
Vessels conveying blood away from the heart:Pulmonary trunk, which splits into right and
left pulmonary arteriesAscending aorta (three branches) –
brachiocephalic, left common carotid, and subclavian arteries
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(b)
BrachiocephalictrunkSuperiorvena cava
Rightpulmonary artery
AscendingaortaPulmonary trunk
Rightpulmonary veinsRight atriumRight coronaryartery (in coronarysulcus)Anteriorcardiac veinRight ventricleMarginal arterySmall cardiac veinInferiorvena cava
Left commoncarotid arteryLeftsubclavian arteryAortic arch
Ligamentumarteriosum
Left pulmonary artery
Left atrium
Auricle
CircumflexarteryLeft coronaryartery (in coronarysulcus)
Anteriorinterventricular artery(in anteriorinterventricular sulcus)
Great cardiac vein
Apex
Left pulmonary veins
Left ventricle
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External Heart: Arteries that Supply the Heart 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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External Heart: Arteries that Supply the Heart
Right coronary artery (in atrioventricular groove) Supplies
Right atriumPortions of both ventriclesSA and AV nodes
BranchesMarginal arteryPosterior interventricular artery
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External Heart: Arteries that Supply the Heart Left coronary artery
SupplyLeft atriumPortions of both ventricles
BranchesCircumflex Anterior interventricular
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Arterial Coronary Circulation
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External Heart: Veins that Drain the Heart
Veins that empty in the coronary sinusGreat cardiac veinPosterior cardiac veinMiddle cardiac veinSmall cardiac vein
Vein that empty into the right atriumAnterior cardiac vein
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Venous Coronary Circulation
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External Heart: Major Vessels of the Heart (Posterior View)
Vessels returning blood to the heart include:Right and left pulmonary veinsSuperior and inferior vena cava
Vessels conveying blood away from the heart include:AortaRight and left pulmonary arteries
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(d)
Superiorvena cavaRightpulmonary artery
Rightpulmonary veins
Right atrium
Right coronaryartery (in coronarysulcus)
Right ventricle
Coronary sinus
Middle cardiac vein
Left pulmonary artery
Left atrium
Auricleof left atrium
Left ventricle
Posterior veinof left ventricle
Posteriorinterventricular artery(in posteriorinterventricular sulcus)
Great cardiac vein
Apex
Leftpulmonary veins
Inferiorvena cava
Aorta
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(e)
Superior vena cava
Rightpulmonary arteryPulmonary trunk
Right atriumRightpulmonary veinsFossaovalisPectinatemuscles
TricuspidvalveRight ventricle
ChordaetendineaeTrabeculaecarneaeInferiorvena cava
Aorta
Leftpulmonary arteryLeft atriumLeftpulmonary veins
Pulmonaryvalve
Aorticvalve
Mitral (bicuspid) valve
Left ventricle
PapillarymuscleInterventricularseptumMyocardium
VisceralpericardiumEndocardium
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Atria of the Heart
Atria are the receiving chambers of the heart Each atrium has a protruding auricle Pectinate muscles mark atrial walls
In the left atrium only in the wall of the auricle
Blood enters right atria from superior and inferior venae cavae and coronary sinus
Blood enters left atria from pulmonary veins
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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
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Right and Left Ventricles
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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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Heart Valves
Heart valves ensure unidirectional blood flow through the heart
Atrioventricular (AV) valves lie between the atria and the ventricles
AV valves prevent backflow into the atria when ventricles contract
Chordae tendineae anchor AV valves to papillary muscles
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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
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Heart Valves
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Atrioventricular Valve Function
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Semilunar Valve Function
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Microscopic Anatomy of Heart Muscle Cardiac muscle is striated, short, fat,
branched, and interconnected The connective tissue endomysium acts as
both tendon and insertion Intercalated discs anchor cardiac cells together
and allow free passage of ions Heart muscle behaves as a functional
syncytium
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Microscopic Anatomy of Heart Muscle Heart is resistant to fatigue
Many mitochondria Z discs, I band, A band, Fewer and wider T tubules Simpler sarcoplasmic reticulum
No triads
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Microscopic Anatomy of Cardiac Muscle
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Cardiac Muscle Contraction
Heart muscle:Is stimulated by nerves and is self-excitable
(automaticity)Contracts as a unit or does not contract at
allHas a long absolute refractory period that
prevents tetany Cardiac muscle contraction is similar to
skeletal muscle contraction
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Heart Physiology: Intrinsic Conduction System
Autorhythmic cells:Initiate action potentials Have unstable resting potentials called
pacemaker potentialsUse calcium influx (rather than sodium) for
rising phase of the action potential
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The intrinsic conducting system Hyperpolarization leads to:
Loss of KOpening of Na channels
Membrane becomes less and less negative Threshold is reached Ca channels opens Influx of Ca causes the rising phase of the
action potential
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Pacemaker and Action Potentials
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Mechanisms of contraction
1) Rapid depolarization Threshold Opening of the voltage-regulated Na channels
Fast channels Massive influx of Na
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Mechanisms of contraction
2) Plateau Transmembrane potential approaches +30mV Na channels close and remain inactivated Na is actively pumped out of the cell Voltage-regulated Ca channels opens (slow
channels) Ca enters the cytoplasma
It stimulates more Ca release from the SR
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Mechanisms of contraction
This influx of Ca balances out the efflux of Na Transmembrane potential is kept near 0mV
plateau
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Mechanisms of contraction
3) Repolarization Slow Ca channels start to close Ca is reabsorbed by the SR or pumped out of
the cell Slow K channels begin to open
Efflux of K causes the repolarization
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Mechanisms of contraction
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Heart Physiology: Sequence of Excitation Sinoatrial (SA) node generates impulses about
75 times/minute Atrioventricular (AV) node delays the impulse
It generates impulses about 40-60 times/minSmaller diameter of the fibersFewer gap junctions
Impulse passes from atria to ventricles via the atrioventricular bundle (bundle of His)Bundle of His is the only electrical
connection between atria and ventricle
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Heart Physiology: Sequence of Excitation AV bundle splits into two pathways in the
interventricular septum (bundle branches)Bundle branches carry the impulse toward
the apex of the heartPurkinje fibers carry the impulse to the heart
apex and ventricular wallsDepolarize spontaneously at the rate of
20-40 beats/minThey supply the papillary muscles
Contract before the rest of the ventricles
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Cardiac Intrinsic Conduction
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SA node generates impulse;atrial excitation begins
Impulse delayedat AV node
Impulse passes toheart apex; ventricular
excitation begins
Ventricular excitationcomplete
SA node AV node Purkinjefibers
Bundlebranches
Heart Excitation Related to ECG
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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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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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Electrocardiography
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Electrocardiography PR interval
Atrial depolarization and contraction QT interval
Ventricular depolarization, contraction and repolarization
PR segmentAtrial contraction
ST segmentVentricular contraction
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ECG Tracings
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Heart Sounds
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Heart Sounds
Heart sounds (lub-dup) are associated with closing of heart valvesFirst sound (S1)occurs as AV valves close
and signifies beginning of systoleSecond sound (S2) occurs as SL valves
close at the beginning of ventricular diastole
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Cardiac Cycle
Cardiac cycle refers to all events associated with blood flow through the heartSystole – contraction of heart muscleDiastole – relaxation of heart muscle
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Phases of the Cardiac Cycle
Ventricular filling – mid-to-late diastoleHeart blood pressure is low as blood enters
atria and flows into ventriclesAV valves are open, then atrial systole
occurs
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Phases of the Cardiac Cycle
Ventricular systoleAtria relax Rising ventricular pressure results in closing
of AV valvesIsovolumetric contraction phaseVentricular ejection phase opens semilunar
valves
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Phases of the Cardiac Cycle
Isovolumetric relaxation – early diastoleVentricles relaxBackflow of blood in aorta and pulmonary
trunk closes semilunar valves Dicrotic notch – brief rise in aortic pressure
caused by backflow of blood. This backflow causes the valve to close and creates a slight pressure rebound
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Phases of the Cardiac Cycle
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Cardiodynamics
End-diastolic volume (EDV) Maximum amount of blood held in the
ventricles during diastole End-systolic volume (ESV)
Amount of blood that remains in the ventricles after the contraction and closing of the semilunar valves
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Cardiodynamics
Venous return- amount of blood returning to the heart or blood flow during filling time
Heart rate – number of heart beats in a minute Filling time- duration of ventricular diastole Stroke volume (SV) – amount of blood
ejected from the ventricles with each beatSV = EDV – ESV
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Cardiac output (CO) – the amount of blood pumped by each ventricle in one minute
Cardiodynamics
COCardiac output
(ml/min)=
HRHeart rate
(beats/min)X
SVStroke volume
(ml/beat)
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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)
Cardiac reserve is the difference between resting and maximal CO
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EDV (end diastolic volume) is affected by:Venous return High venous return= high EDV Exercise → ↑Venous return → ↑EDV→ ↑SV↓Blood volume →↓Venous return→↓EDV→↓SV
Factors Affecting stroke volume(EDV-ESV)
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Factors Affecting stroke volume(EDV-ESV)
Filling time Depends on the heart rate↑ HR → ↓Filling time→ ↓EDV→ ↓SV
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Factors Affecting stroke volume(EDV-ESV)
PreloadStretchiness of the ventricles during diastoleDirectly proportional to the EDV
Frank-Starling principle (“more in = more out”) or increased EDV=increased SV
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Factors Affecting stroke volume(EDV-ESV)
ESV (end systolic volume) is affected by:ContractilityForce produced during a contractionPositive inotropic (increases contractility)
Increased sympathetic stimuliCertain hormones, some drugs↑Contractility → ↓ESV→ ↑SV
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Factors Affecting stroke volume(EDV-ESV)
Negative inotropic (decreases contractility) Increased extracellular K+
Calcium channel blockers↓Contractility → ↑ESV→ ↓SV
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GTP GDP
Inactive protein kinase A
Active protein kinase A
ATP cAMP
GTP
SR Ca2+
channel
Ca2+
Ca2+
bindsto
TroponinEnhancedactin-myosininteraction
Extracellular fluid
Cytoplasm
Adenylate cyclase
Ca2+
channel
Ca2+b1-Adrenergicreceptor
Norepinephrine
Ca2+
uptakepump
Sarcoplasmicreticulum (SR)
Cardiac muscleforce and velocity
1
3
2
Heart Contractilityand Norepinephrine
Sympathetic stimulation releases norepinephrine and initiates a cyclic AMP second-messenger system
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Factors Affecting stroke volume(EDV-ESV)
AfterloadThe pressure that must be overcome for the
ventricles to eject blood (back pressure exerted by blood in the large arteries leaving the heart)
Increased by factors that restricts arterial blood flow
↑Afterload→↑ESV →↓SV
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Preload and Afterload
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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
Regulation of Heart Rate: Autonomic Nervous System
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Atrial (Bainbridge) Reflex
Atrial reflex (Bainbridge Reflex) – a sympathetic reflex initiated by increased blood in the atria↑Venous return→ Stimulates baroreceptors
in the atria→ ↑Sympathetic stimulation→ ↑Stimulation of SA node→ ↑HR
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Chemical Regulation of Heart Rate
The hormones epinephrine and thyroxine increase heart rate
Intra- and extracellular ion concentrations must be maintained for normal heart functionHypocalcemia depresses the heart and
hypercalcemia stimulates the heartHyperkalemia causes heart block and
hypokalemia causes weak and irregular contractions
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Other factors influencing heart rate
Age Exercise Body temperature
Tachycardia Bradycardia
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Figure 20-23 Factors Affecting Stroke Volume
Preload
Factors Affecting Stroke Volume (SV)
Venous return (VR)VR = EDV FT = EDV
Filling time (FT) Increased bysympatheticstimulation
Decreased byparasympathetic
stimulation
Increased by E, NE,glucagon,
thyroid hormones
Contractility (Cont)of muscle cellsCont = ESV Increased by
vasoconstrictionDecreased byvasodilation
Afterload (AL)AL = ESVEnd-systolic
volume (ESV)End-diastolicvolume (EDV)
STROKE VOLUME (SV)ESV = SV
VR = EDV FT = EDV
Cont = ESV
AL = ESV
ESV = SVEDV = SVEDV = SV
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Congestive Heart Failure (CHF)
Congestive heart failure (CHF) is caused by:Coronary atherosclerosisPersistent high blood pressureMultiple myocardial infarctsDilated cardiomyopathy (DCM)
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Developmental Aspects of the Heart
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Developmental Aspects of the Heart Fetal heart structures that bypass pulmonary
circulationForamen ovale connects the two atria Ductus arteriosus connects pulmonary trunk
and the aorta
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Examples of Congenital Heart Defects
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Age-Related Changes Affecting the Heart Sclerosis and thickening of valve flaps Decline in cardiac reserve Fibrosis of cardiac muscle Atherosclerosis