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The Heart
Functions of the Heart
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The heart works in conjunction with
cardiovascular centers and peripheral
blood vessels to achieve this goal
The function of the heart
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Generates blood pressure to produce a
gradient that pushes blood through the
vascular system
Regulates blood supply - changes in
contraction rate & force match blood
delivery to metabolic needs
Routes blood, ensuring one-way blood
flow, separates pulmonary and
systemic circulations
The Heart
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Heart – typically weighs
250–350 grams (healthy
heart)
A muscular double pump
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Pulmonary circuit –
takes blood to and from
the lungs
Systemic circuit –
vessels transport blood
to and from body tissues
Location and Orientation within the Thorax
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Largest organ of the
mediastinum
• Located between
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the lungs
Apex lies to the
left of the midline
Base is the broad
posterior surface
Figure 18.2
Structure of the Heart
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Right and left atria - Superior chambers, receive blood from the pulmonary
and systemic circuits
Right and left ventricles - Inferior chambers, the pumping chambers of the
heart
External markings
• Left/right auricles
• Apex
Internal Structures
• Interventricular septa
• Fossa ovalis
Chambers
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Right Atrium
• Forms right border of heart
• Receives blood from
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systemic circuit
Fossa ovalis - depression in
interatrial septum, remnant
of foramen ovale
Right Ventricle
• Receives blood from right
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atrium through the tricuspid
valve (right atrioventricular
valve)
Pumps blood into pulmonary
circuit via the pulmonary
semilunar valve into
pulmonary trunk
Internal walls of right
ventricle
• Trabeculae carneae
• Papillary muscles
• Chordae tendineae
Chambers
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Left atrium
• Makes up heart’s posterior
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surface
Receives oxygen-rich blood
from lungs
Opens into the left ventricle
through the Mitral valve (left
atrioventricular valve)
Left Ventricle
• Forms apex of the heart
• Internal walls of left
ventricle
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Trabeculae carneae
Papillary muscles
Chordae tendineae
• Pumps blood through
systemic circuit via the
Aortic semilunar valve
(aortic valve)
Heart Valves – Valve Structure
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Each valve composed of endocardium with
connective tissue core
Atrioventricular (AV)
valves between atria and
ventricles
Aortic and pulmonary
valves at junction of
ventricles and great arteries
Function of the Atrioventricular Valves
Figure 18.9a
Function of the Semilunar Valves
Figure 18.10a, b
Structure of the Heart – Coverings
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Pericardium – two primary layers
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Fibrous pericardium - strong layer of dense connective tissue
Serous pericardium -formed from two layers
• Parietal pericardium
• Visceral pericardium
• Pericardial cavity
Structure of the Heart – Layers of the Heart Wall
• Epicardium - Visceral layer of the serous pericardium
• Myocardium
• Consists of cardiac muscle
• Muscle arranged in circular and spiral patterns
• Endocardium
• Endothelium resting on a layer of connective tissue
• Lines the internal walls of the heart
Structure of Heart Wall
• Walls differ in thickness
• Atria – thin walls
• Ventricles – thick walls
• Left ventricle – three times thicker
than right
• Exerts more pumping force
• Flattens right ventricle into a
crescent shape
• Systemic circuit
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Longer than pulmonary circuit
Offers greater resistance to blood
flow
Blood Flow Through the Heart
• Beginning with oxygen-poor blood in the
superior and inferior venae cavae
• Go through pulmonary and systemic
circuits
• A blood drop passes through all
structures sequentially
Figure 18.6
Cardiac Muscle Tissue
• Forms a thick layer called myocardium
• Striated like skeletal muscle
• Contractions pump blood through the heart and into blood vessels
• Contracts by sliding filament mechanism
• Cardiac muscle cells
• Short
• Branching
• Have one or two nuclei
Cardiac Muscle Tissue
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Cells join at intercalated discs
• Complex junctions
• Form cellular networks
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Cells are separated by delicate endomysium
• Binds adjacent cardiac fibers
• Contains blood vessels and nerves
Electrical Activity of Heart
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Heart beats rhythmically as result of action potentials it
generates by itself (autorhythmicity)
Two specialized types of cardiac muscle cells
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Contractile cells
• 99% of cardiac muscle cells
• Do mechanical work of pumping
• Normally do not initiate own action potentials
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Autorhythmic cells
• Do not contract
• Specialized for initiating and conducting action potentials
responsible for contraction of working cells
Cardiac Conduction System
• SA node ~ 75 bpm - sets the pace of the heartbeat
• AV node ~ 50 bpm - delays the transmission of action potentials
• Purkinje fibers ~ 30 bpm - can act as pacemakers under some
conditions
70-80/min
40-60/min
20-40/min