Download Chapter 16: Anatomy and Physiology of the Cardiovascular System

Chapter 16:
Anatomy and Physiology of the
Cardiovascular System
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Cardiac Muscle Fibers
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Contractile Elements Inside a Sarcomere
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Characteristics of Cardiac Tissue
• Automaticity: Pacemaker cells generate their own action
potential.
• Conductivity: Cardiac cells receive the electrical signal
and pass it from one cell to another.
• Contractility: Cardiac muscle shortens because of
depolarization.
• Excitability: Cardiac tissue responds to a stimulus and
generates an action potential.
• Rhythmicity: Cardiac cells generate an action potential at
a regular rate.
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Question
Which of the following terms describes the cardiac tissue
function of the sinoatrial node?
A. Excitability
B. Automaticity
C. Conductivity
D. Contractility
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Answer
B. Automaticity
Rationale: Automaticity is the ability of pacemaker cells to
spontaneously make an action potential and depolarize.
Excitability is the ability of a cardiac cell to respond to a
stimulus and depolarize. Conductivity is the ability of
cardiac tissue to respond to a stimulus and generate an
action potential. Contractility is the ability of cardiac
muscle cells to respond to depolarization by shortening.
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Electrical Events That Occur in the
Myocardial Cell
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The Resting Membrane Potential of
Myocardial Cell
• Inside of the myocardial cell is more negative (-80 mV)
compared to the outside of the cell because of ionic
pumps.
– Determined by concentration of ions on both sides of
cell membrane
– Ion transport proteins in cell membrane need ATP.
• Resting state is the time the heart is in diastole.
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Cardiac Action Potential
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Electrical Conduction System
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Comparison of Electrical and Mechanical
Events During One Cardiac Cycle
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Measuring Cardiac Function
CO = HR (beats/min)
x SV (L/beat)
Normal adult range: 4
to 8 L/min
CI = CO (L/min)
BSA (m
)
Normal adult range:
2.8 to 4.2 L/min
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Effects of the Autonomic Nervous System
on the Heart and Vascular System
Receptor Type
Effects
Alpha-1
Vasoconstriction of blood vessels,
increased BP, increased
contractility of heart
Alpha-2
Decreased BP (reduced
norepinephrine)
Beta-1
Increased heart rate, increased
heart contraction
Beta-2
Dilation of arteries
Muscarinic receptors
Decreased HR, decreased force of
contraction
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Role of the Aortic Reflex and Bainbridge
Reflex on Heart Rate
Aortic Reflex Effects Adjust HR
to BP
Bainbridge Effects Adjust HR to
Handle Venous Return
Rise in BP causes decrease in HR
Increase in venous return causes
increase in HR
Decrease in BP causes increase in
HR
Decrease in venous return causes
decrease in HR
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Starling’s Law of the Heart
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Coronary Arteries
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Coronary Artery Blood Supply for Cardiac
Muscle and Conduction System
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Question
A client is diagnosed with a 95% occlusion of the right
coronary artery (RCA). Which area of the heart’s
conduction system is most likely to be affected?
A. Bundle branches
B. Sinoatrial (SA) node
C. Atrioventricular (AV) node
D. Purkinje fibers
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Answer
C. Atrioventricular node
Rationale: The RCA supplies the AV node in 90% of hearts.
The left anterior descending (LAD) supplies the bundle
branches. The left circumflex supplies the SA node in
45% of hearts and the AV node in 10% of hearts. The
Purkinje fibers are supplied by all of the coronary
arteries.
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Question
A 19-year-old client with supraventricular tachycardia has a
heart rate in the 160s. The client complains of chest
pain. The chest pain is most likely a result of which of
the following?
A. A decrease in diastolic time
B. A decrease in atrial kick
C. Coronary artery disease
D. Decreased oxygen demand
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Answer
A. A decrease in diastolic time
Rationale: The coronary arteries receive blood flow when
the aortic valve is closed (ventricular diastole).
Tachycardia decreases diastolic time, resulting in
decreased blood flow to the coronary arteries. Chest
pain occurs from the decreased coronary perfusion. It is
unlikely that a 19-year-old patient has coronary artery
disease causing the chest pain. Atrial fibrillation can
lead to a loss in atrial kick that would decrease the
cardiac output. Tachycardia would lead to increased
cardiac workload and increased oxygen demand.
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Central Venous Pressure (CVP)
• Defined as pressure of the blood measured in mm Hg in
the thoracic vena cavae before the entry into the right
atrium
– CVP is increased when there is an increase in the
blood volume; increase due to Valsalva maneuver,
change from standing to supine position, or decrease
in pumping action of heart
– CVP is decreased when there is a decrease in blood
volume
– Normal range is 3 to 6 mm Hg
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Influences on Blood Pressure
• Neuroregulation
– Autonomic nervous system
• Hormonal influences
– Renin-angiotensin system
• Hypercapnia/hypoxia
– Vasomotor center
• Unbound calcium in tunica media
– Calcium channel blockers
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