The Heart - Collin College

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The Heart
Heart Anatomy

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Approximately the size of your fist
Location
 Superior surface of diaphragm
 Left of the midline
 Anterior to the vertebral column, posterior to
the sternum
Heart Anatomy
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
Coverings of the Heart: Physiology

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
Pericardial Layers of the Heart
Heart Wall
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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
Cardiac Muscle Bundles
External Heart: Major Vessels of
the Heart (Anterior View)
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Vessels returning blood to the heart include:
 Superior and inferior vena cava
 Right and left pulmonary veins
Vessels conveying blood away from the heart:
 Pulmonary trunk, which splits into right and
left pulmonary arteries
 Ascending aorta (three branches) –
brachiocephalic, left common carotid, and
subclavian arteries
Brachiocephalic
trunk
Superior
vena cava
Left common
carotid artery
Left
subclavian artery
Aortic arch
Right
pulmonary artery
Ligamentum
arteriosum
Left pulmonary artery
Ascending
aorta
Pulmonary trunk
Right
pulmonary veins
Right atrium
Right coronary
artery (in coronary
sulcus)
Anterior
cardiac vein
Right ventricle
Marginal artery
Small cardiac vein
Inferior
vena cava
(b)
Left pulmonary veins
Left atrium
Auricle
Circumflex
artery
Left coronary
artery (in coronary
sulcus)
Left ventricle
Great cardiac vein
Anterior
interventricular artery
(in anterior
interventricular sulcus)
Apex
External Heart: Arteries that Supply
the Heart
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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
External Heart: Arteries that Supply the
Heart

Right coronary artery (in atrioventricular groove)
 Supplies
 Right atrium
 Portions of both ventricles
 SA and AV nodes
 Branches
 Marginal artery
 Posterior interventricular artery
External Heart: Arteries that Supply
the Heart

Left coronary artery
 Supply
 Left atrium
 Portions of both ventricles
 Branches
 Circumflex
 Anterior interventricular
Arterial Coronary Circulation
External Heart: Veins that Drain the
Heart


Veins that empty in the coronary sinus
 Great cardiac vein
 Posterior cardiac vein
 Middle cardiac vein
 Small cardiac vein
Vein that empty into the right atrium
 Anterior cardiac vein
Venous Coronary Circulation
External Heart: Major Vessels of
the Heart (Posterior View)
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Vessels returning blood to the heart include:
 Right and left pulmonary veins
 Superior and inferior vena cava
Vessels conveying blood away from the heart
include:
 Aorta
 Right and left pulmonary arteries
Aorta
Left
pulmonary artery
Left
pulmonary veins
Auricle
of left atrium
Left atrium
Superior
vena cava
Right
pulmonary artery
Right
pulmonary veins
Right atrium
Great cardiac vein
Inferior
vena cava
Posterior vein
of left ventricle
Right coronary
artery (in coronary
sulcus)
Coronary sinus
Apex
Posterior
interventricular artery
(in posterior
interventricular sulcus)
Middle cardiac vein
(d)
Right ventricle
Left ventricle
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
(e)
Left
pulmonary artery
Left atrium
Left
pulmonary veins
Mitral
(bicuspid) valve
Aortic
valve
Pulmonary
valve
Left ventricle
Papillary
muscle
Interventricular
septum
Myocardium
Visceral
pericardium
Endocardium
Atria of the Heart
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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
Ventricles of the Heart
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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
Right and Left Ventricles
Pathway of Blood Through the
Heart and Lungs
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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
Heart Valves

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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
Heart Valves
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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
Heart Valves
Heart Valves
Atrioventricular Valve Function
Semilunar Valve Function
Microscopic Anatomy of Heart
Muscle
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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
Microscopic Anatomy of Heart
Muscle
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Heart is resistant to fatigue
 Many mitochondria
Z discs, I band, A band,
Fewer and wider T tubules
Simpler sarcoplasmic reticulum
 No triads
Microscopic Anatomy of Cardiac
Muscle
Cardiac Muscle Contraction
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Heart muscle:
 Is stimulated by nerves and is self-excitable
(automaticity)
 Contracts as a unit or does not contract at all
 Has a long absolute refractory period that
prevents tetany
Cardiac muscle contraction is similar to
skeletal muscle contraction
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
The intrinsic conducting system
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Hyperpolarization leads to:
 Loss of K
 Opening 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
Pacemaker and Action Potentials
Mechanisms of contraction
1) Rapid depolarization
 Threshold
 Opening of the voltage-regulated Na channels
 Fast channels
 Massive influx of Na
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
Mechanisms of contraction
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This influx of Ca balances out the efflux of Na
Transmembrane potential is kept near 0mV
 plateau
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
Mechanisms of contraction
Heart Physiology: Sequence of
Excitation
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Sinoatrial (SA) node generates impulses about
75 times/minute
Atrioventricular (AV) node delays the impulse
 It generates impulses about 40-60 times/min
 Smaller diameter of the fibers
 Fewer 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
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 heart
 Purkinje fibers carry the impulse to the heart
apex and ventricular walls
 Depolarize spontaneously at the rate of
20-40 beats/min
 They supply the papillary muscles
Contract before the rest of the
ventricles
Cardiac Intrinsic Conduction
Heart Excitation Related to ECG
SA node generates impulse;
atrial excitation begins
SA node
Impulse delayed
at AV node
AV node
Impulse passes to
heart apex; ventricular
excitation begins
Bundle
branches
Ventricular excitation
complete
Purkinje
fibers
Extrinsic Innervation of the Heart
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Heart is stimulated
by the sympathetic
cardioacceleratory
center
Heart is inhibited by
the parasympathetic
cardioinhibitory
center
Electrocardiography
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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
Electrocardiography
Electrocardiography
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PR interval
 Atrial depolarization and contraction
QT interval
 Ventricular depolarization, contraction and
repolarization
PR segment
 Atrial contraction
ST segment
 Ventricular contraction
ECG Tracings
Heart
Sounds
Heart Sounds

Heart sounds (lub-dup) are associated with
closing of heart valves
 First sound (S1)occurs as AV valves close
and signifies beginning of systole
 Second sound (S2) occurs as SL valves
close at the beginning of ventricular diastole
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
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
Phases of the Cardiac Cycle
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Ventricular systole
 Atria relax
 Rising ventricular pressure results in closing
of AV valves
 Isovolumetric contraction phase
 Ventricular ejection phase opens semilunar
valves
Phases of the Cardiac Cycle
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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. This backflow
causes the valve to close and creates a slight
pressure rebound
Phases of the Cardiac Cycle
Cardiodynamics
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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
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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 beat
 SV = EDV – ESV
60
Cardiodynamics

Cardiac output (CO) – the amount of blood
pumped by each ventricle in one minute
CO
Cardiac output
(ml/min)
=
HR
Heart rate
(beats/min)
X
SV
Stroke
volume
(ml/beat)
Cardiac Output: Example
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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
62
Factors Affecting stroke volume
(EDV-ESV)
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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
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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)
 Preload
 Stretchiness
of the ventricles during diastole
 Directly proportional to the EDV

Frank-Starling principle (“more in = more out”)
or increased EDV=increased SV
65
Factors Affecting stroke volume
(EDV-ESV)
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ESV (end systolic volume) is affected by:
 Contractility
 Force produced during a contraction
 Positive inotropic (increases contractility)
 Increased sympathetic stimuli
 Certain 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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Heart Contractility
and Norepinephrine
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Sympathetic
stimulation releases
norepinephrine and
initiates a cyclic
AMP secondmessenger system
Extracellular fluid
Norepinephrine
b 1-Adrenergic
receptor
Adenylate cyclase Ca2+
Ca2+
channel
Cytoplasm
GTP
GTP
1
GDP
ATP
cAMP
Active
protein
kinase A
Ca2+
Inactive
protein
kinase A
3
Ca2+
2
Enhanced
actin-myosin
interaction
Troponin
uptake
pump
binds
to
Ca2+
SR Ca2+
channel
Cardiac muscle
force and
velocity
Sarcoplasmic
reticulum (SR)
Factors Affecting stroke volume
(EDV-ESV)
 Afterload
 The
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
69
Preload and Afterload
Regulation of Heart Rate:
Autonomic Nervous System
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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
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
72
Chemical Regulation of Heart Rate
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The hormones epinephrine and thyroxine
increase heart rate
Intra- and extracellular ion concentrations must
be maintained for normal heart function
 Hypocalcemia depresses the heart and
hypercalcemia stimulates the heart
 Hyperkalemia causes heart block and
hypokalemia causes weak and irregular
contractions
Other factors influencing heart rate
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Age
Exercise
Body temperature
Tachycardia
Bradycardia
Figure 20-23 Factors Affecting Stroke Volume
Factors Affecting Stroke Volume (SV)
Venous return (VR)
VR =
VR =
EDV
EDV
Filling time (FT)
FT = EDV
FT = EDV
Increased by
sympathetic
stimulation
Decreased by
parasympathetic
stimulation
Increased by E, NE,
glucagon,
thyroid hormones
Contractility (Cont)
of muscle cells
Cont =
Cont =
Preload
End-diastolic
volume (EDV)
ESV
ESV
End-systolic
volume (ESV)
STROKE VOLUME (SV)
EDV =
EDV =
SV
SV
ESV =
ESV =
SV
SV
Increased by
vasoconstriction
Decreased by
vasodilation
Afterload (AL)
AL = ESV
AL = ESV
Congestive Heart Failure (CHF)

Congestive heart failure (CHF) is caused by:
 Coronary atherosclerosis
 Persistent high blood pressure
 Multiple myocardial infarcts
 Dilated cardiomyopathy (DCM)
Developmental Aspects of the
Heart
Developmental Aspects of the
Heart

Fetal heart structures that bypass pulmonary
circulation
 Foramen ovale connects the two atria
 Ductus arteriosus connects pulmonary trunk
and the aorta
Examples of Congenital Heart
Defects
Age-Related Changes Affecting the
Heart
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Sclerosis and thickening of valve flaps
Decline in cardiac reserve
Fibrosis of cardiac muscle
Atherosclerosis

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