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Chapter 20
The Heart
I. Organization of the Cardiovascular System
A. The cardiovascular system is divided into two circuits - Fig. 20.1
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Pulmonary circuit
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blood to and from the lungs
Systemic circuit
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blood to and from the rest of the body
Vessels carry the blood through the circuits
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Arteries carry blood away from the heart
Veins carry blood to the heart
Capillaries permit exchange
II. Anatomy of the Heart
A. The pericardia - Fig. 20.2
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Visceral pericardium or epicardium
Parietal pericardium
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Pericardial fluid
B. Superficial Anatomy of the Heart - Fig. 20.3
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The heart consists of four chambers
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Two atria and two ventricles
Major blood vessels of the heart include
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Inferior and superior vena cavae
Aorta and pulmonary trunk
C. The Heart Wall - Fig. 20.4, 20.5
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Components of the heart wall include
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Epicardium
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Myocardium
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Endocardium
D. Internal Anatomy and Organization - Fig. 20.6
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Atria
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Thin walled chambers that receive blood from the vena cavae
Ventricles
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Thick walled chambers separated from the atria by AV valves
Chordae tendineae
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Tendinous fibers attached to the AV valves
Papillary muscle and trabeculae carneae
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Muscular projections on the inner wall of ventricles
E. Blood flow through the heart
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Right atria
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Right ventricle
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Tricuspid valve
Pulmonary valve
Pulmonary circuit
Left atria
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Bicuspid valve
Left ventricle
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Aortic valve
Aorta and systemic circuit
F Heart chambers and valves - Fig. 20.7, 20.8
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Structural Differences in heart chambers
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The left side of the heart is more muscular than the right side
Functions of valves
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AV valves prevent backflow of blood from the ventricles to the atria
Semilunar valves prevent backflow into the ventricles from the pulmonary trunk and aorta
F. Blood Supply to the Heart - Fig. 20.9
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Arteries include the right and left coronary arteries, marginal arteries, anterior and posterior interventricular arteries, and the
circumflex artery
Veins include the great cardiac vein, anterior and posterior cardiac veins, the middle cardiac vein, and the small cardiac
vein
III. The Heartbeat
A. Cardiac Physiology - Fig. 20.11
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Two classes of cardiac muscle cells
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Specialized muscle cells of the conducting system
Contractile cells
B. The Conducting System - Fig. 20.12
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The conducting system includes:
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Sinoatrial (SA) node
Atrioventricular (AV) node
Conducting cells
• Atrial conducting cells are found in internodal pathways
• Ventricular conducting cells consist of the AV bundle, bundle branches, and Purkinje fibers
C. Impulse Conduction through the heart - Fig. 20.13
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SA node begins the action potential
Stimulus spreads to the AV node
Impulse is delayed at AV node
Impulse then travels through ventricular conducting cells
Then distributed by Purkinje fibers
D. The electrocardiogram (ECG) - Fig. 20.14
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A recording of the electrical events occurring during the cardiac cycle
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The P wave accompanies the depolarization of the ventricles
The QRS complex appears as the ventricles depolarize
The T wave indicates ventricular repolarization
F. The cardiac cycle - Fig. 20.16, 20.17
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The period between the start of one heartbeat and the beginning of the next
During a cardiac cycle
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Each heart chamber goes through systole and diastole
Correct pressure relationships are dependent on careful timing of contractions
1) Pressure and volume changes: atrial systole
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rising atrial pressure pushes blood into the ventricle
atrial systole
the end-diastolic volume (EDV) of blood is in the ventricles
2) Pressure and volume changes: ventricular systole
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Isovolumetric contraction of the ventricles: ventricles are contracting but there is no blood flow
Ventricular pressure increases forcing blood through the semilunar valves
3) Pressure and volume changes: ventricular diastole
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The period of isovolumetric relaxation when all heart valves are closed
Atrial pressure forces the AV valves open
G. Heart sounds - Fig. 20.18
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Auscultation – listening to heart sound via stethoscope
Four heart sounds
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S1 – “lubb” caused by the closing of the AV valves
S2 – “dupp” caused by the closing of the semilunar valves
S3 – a faint sound associated with blood flowing into the ventricles
S4 – another faint sound associated with atrial contraction
IV. Cardiodynamics
A. Stroke Volume and Cardiac Output - Fig. 20.19, 20.20
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Cardiac output – the amount of blood pumped by each ventricle in one minute
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Cardiac output equals heart rate times stroke volume
B. Factors Affecting Heart Rate
• Autonomic innervation
• Cardiac reflexes
• Tone
• SA node
• Hormones
• Epinephrine (E), norepinephrine(NE), and thyroid hormone (T 3)
• Venous return
C. Factors Affecting stoke volume - Fig. 20.23
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EDV
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Frank-Starling principle
ESV
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Preload
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Contractility
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Afterload
D. Summary: Regulation of Heart Rate and Stroke Volume
• Sympathetic stimulation increases heart rate
• Parasympathetic stimulation decreases heart rate
• Circulating hormones, specifically E, NE, and T 3, accelerate heart rate
• Increased venous return increases heart rate
• EDV is determined by available filling time and rate of venous return
• ESV is determined by preload, degree of contractility, and afterload