Transcript ANPS 020 Black 01-24

Overview of the Cardiovascular System
Topics to be addressed:
Blood
Anatomy of Blood Vessels
Anatomy of the Heart
The Conduction System
The Cardiac Cycle
Cardiodynamics
Blood Flow and its Regulation
Adaptation and Disorders of the Cardiovascular System
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The Cardiac Cycle and the ECG
Pumping Blood:
a mechanical event initiated by electrical events
Normally, the SA node generates an action potential, and passes the
signal down the conductive system
Purkinje fibers distribute the stimulus to the contractile cells, which
make up most of the ventricle wall
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Characteristics of Cardiac Muscle Cells
Small size
Single, central nucleus
Branching interconnections between cells
Intercalated discs
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Structure of Cardiac Muscle Cells:
Intercalated Discs
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Structure of Cardiac Muscle Cells
Intercalated discs contain two types of cell-cell junctions:
• Desmosomes physically tie cells together
• Gap Junctions connect cytoplasm
• allow ion flow directly from one cell into another
• “electrical coupling”
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The Action Potential of a single contractile
cardiac muscle cell
Net gain of +
charge
Net loss
of +
charge
**The resting membrane potential of contractile cells is stable (unlike that of
the conductive cells like those of the SA node)
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The Role of Calcium Ions in Cardiac Contractions
Contraction of a cardiac muscle cell is produced by an increase in calcium ion
concentration around myofibrils
Actin-Myosin crossbridges form
From Silverthorn Human Physiology, 4th ed., Pearson/Benjamin Cummings 2007
Cardiac muscle tissue is very sensitive to extracellular Ca2+ concentrations
Calcium channel blockers are a group of powerful medications for heart patients
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Comparison of the action potential and resulting
contraction between skeletal and cardiac muscle
In skeletal muscle, the action
potential was brief relative to
the contraction. A second
action potential soon after
the first increased
cytoplasmic calcium levels
and increased the
contraction
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Comparison of the action potential and resulting
contraction between skeletal and cardiac muscle
The Absolute Refractory
Period is very long: cardiac
muscle cells cannot be
stimulated again until this
period is over
In cardiac muscle, the action
potential lasts longer than the
contraction. One contraction
is over before another can
begin, preventing summation
of contraction and tetany.
This ensures time for the
heart to fill between
contractions.
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Monitoring Heart Activity: the ECG
The Electrocardiogram (ECG or EKG) is a recording of electrical
events in the heart, representing ALL the action potentials from
ALL the cardiac cells – conducting and contractile
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Features of an ECG
P wave: Atria depolarize
QRS complex: Ventricles depolarize
T wave: Ventricles repolarize
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Common Clinical ECG Measures
P–R interval
Time from start of atrial depolarization
to start of QRS complex
Q–T interval
Time from ventricular depolarization
to ventricular repolarization
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Abnormal ECG Recordings
Normal
P waves absent
SA node nonfunctional
Slower heart rate now driven by AV node
P waves not always followed by QRS wave
A form of “heart block”
Problem within conduction system between
SA node and rest of system
Chaotic deflections
“Ventricular fibrillation”
Bad. Very bad.
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Defibrillators shock the heart back into a
normal rhythm
Portable AEDs (automated external defibrillators) are now common
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The Cardiac Cycle
One cycle = from the start of one heart beat to the start of the next heartbeat
Two Phases:
Systole (contraction)
Diastole (relaxation)
Begins with initiation of action potential at SA node
Produces action potentials in cardiac muscle cells (contractile cardiac cells) of Atria
Both Atria begin contracting = Atrial Systole
Signal is transmitted through conducting system
(conducting cardiac cells of AV node, Bundle branches, Purkinje fibers)
Both Ventricles contract, apex to base, pushing out blood = Ventricular Systole
atria begin relaxing = Atrial Diastole
Ventricles relax, heart refills = Ventricular Diastole
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The Cardiac Cycle
The period between the start of one heartbeat and the beginning of the next
What makes blood
move?
1. A pressure gradient
Blood moves from area of
high pressure to area of
low pressure
2. Open valve
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Steps in the Cardiac Cycle
Initiated by
pacemaker
potential at
SA node
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Steps in the Cardiac Cycle
Ventricles are contracting
and exerting pressure, but
valves are closed so blood
is unable to move out
“Isovolumetric contraction”
phase
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Steps in The Cardiac Cycle
Pressure generated
by ventricle wall
finally great enough
to exceed trunk
pressure; semilunar
valves are pushed
open
“Ejection” phase
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Steps in The Cardiac Cycle
Ventricle wall begins
relaxation, with pressure
falling below trunk
pressure.
Back flow of blood from
trunk toward ventricle
closes semilunar valve
and ends ejection phase
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Steps in The Cardiac Cycle
Ventricle wall relaxed,
with pressure falling
below that in atria; AV
valves open as blood
moves from atria to
ventricles
“Filling” stage
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The Cardiac Cycle
Looking at only the electrical events and resulting contractile events
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The Cardiac Cycle
Plotting pressures generated by atrial and ventricular contraction
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Comparison of Right and Left Heart
Pressures
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The Cardiac Cycle
Changes in blood volume are driven by changes in pressure and state of
the valves
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Heart sounds normally heard during the
Cardiac Cycle
Heart Murmur :
Abnormal sounds produced by
regurgitation through faulty valves
or by damaged valve flaps
“Lub” = S1
Produced by turbulence as AV valves
close and blood pushes against them
“Dub” = S2
Produced by turbulence as semilunar
valves close and blood pushes against
them
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The Cardiac
Cycle
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