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Heart Muscle
Right Heart
pumps the blood
through the lungs
Left Heart pumps
the blood through
the peripheral
organs
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Basic Anatomy
Interatrial septum
Interventricular septum
Tricuspid valve
Bicuspid valveSemilunar valves
What happens when the
right or left ventricle
weakens?
What causes the
characteristic lub-dub
sound?
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Pulmonary Circuit
involves the rightventricle which pumps
deoxygenated blood to
the lungs
Systemic Circuit
involves the left ventricle
and the remainder of the
arteries, capillaries and
veins of the body
Coronary circulationsupplies blood to the
myocardium (right and
left coronary arteries)
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Embolusclot
Ischemia - blood
deficiency in myocardial
cells
Angina pectoris - chest
pain that accompanies
ischemia
Myocardial infarction
heart attack
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Sinoatrial node or pacemaker
typically depolarizes
spontaneously at the rate of70-80 times per minute,
causing the atria to contract
Impulses from SA Node pass
to the Atrioventricular Node,Atrioventricular bundle and
finally to the conduction
myofibers or Purkinje fibers
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Innervation of the Heart
Sympathetic impulses
accelerate heart action
Parasympathetic
impulses decelerate
heart action
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Cardiac CycleDiastole phase of
relaxation
Systole phase of
contraction
LATE DIASTOLE. Atria and ventricles are relaxed. AV valves are open, and the
semilunar valves are closed. Blood is flowing from the atria to the ventricles,
with 65% to 75% of ventricular filling occurring before the end of this phase.
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Cardiac CycleDiastole phase of
relaxation
Systole phase of
contraction
ATRIAL SYSTOLE. The atria contract and pump the additional 25% to 35% of
the blood into the ventricles.
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Cardiac CycleDiastole phase of
relaxation
Systole phase of
contraction
VENTRICULAR SYSTOLE. At the beginning of the ventricular contraction, the
AV valves close, causing the first lub sound. Semilunar valves open and
ventricular ejection begins. (70-90 mL/beat = stroke volume)
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Cardiac CycleDiastole phase of
relaxation
Systole phase of
contraction
EARLY DIASTOLE. As the ventricles begin to relax, the pressure drops rapidly.
The semilunar valves close, preventing the backflow into the ventricles
causing the second dub sound. Then, AV valves open and blood begins toflow from atria to the ventricles.
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CARDIAC OUTPUT = stroke volume X heart rate
Note:
Normal heart rate is 55 to 90 beats per minute
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SITES OF CARDIAC
AUSCULTATION
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Electrocardiogram (ECG)
Depolarization of the atria
Ventricular repolarization
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P atrial depolarization
QRS ventricular depolarization
T ventricular repolarization
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ARRHYTHMIA refers to deviations from normal heart rate or from
normal electrical activity of the conduction system.
a. Rate Arrhythmia
Bradycardia slow heart rate of fewer than 55 bpm which may
be caused by excessive vagal (parasympathetic) stimulation,
decreased body temperature or certain drug
Tachycardia a rapid heart rate of more than 90 bpm, may be
caused by excessive sympathetic stimulation, increased body
temperature or drugs such as caffeine
b. Conduction Arrhythmia
Abnormal rhythmicity of the SA node
Shift of pacemaking function from the SA node to another part
of the heart (ectopic pacemaker or ectopic focus) may be
caused by ischemia or localized heart damage, dilation of atriadue to hypertension, toxic irritants like nicotine, caffeine,
alcohol; lack of sleep, anxiety, extremes in body temperature,
departures from normal body pH
Abnormal pathway or blockage of impulses in the conduction
system
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Physiology of Cardiac MuscleTHREE TYPES OF CARDIAC MUSCLE
1. Atrial Muscle
2. Ventricular Muscle
3. Specialized excitatory and conductive muscle fibers. Contract only
weakly because they contain few contractile fibers, instead, they
exhibit rhythmicity and varying rates of conduction, providing anexcitatory system for the heart
Contract in much the same way as skeletal
muscle except that the duration of contraction
is much longer
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Physiologic Anatomy of Cardiac Muscle
Figure 1. Structure of the heart and course of blood flow
through the heart chambers
Cardiac Muscles are
striated muscles
Cardiac Muscles have
typical myofibrils that
contain actin and myosin
filaments almost identical
to those found in skeletal
muscles
Filaments in cardiac
muscles interdigitate and
slide along each otherduring contraction in the
same manner as occurs in
skeletal muscle
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Physiologic Anatomy of Cardiac Muscle
Figure 2. (a) micrograph of heart muscle tissue (b) cardiac
muscle tissue showing intercalated disks
CARDIAC MUSCLE AS A SYNCYTIUM
Intercalated discs cell membranethat separate individual cardiac
muscle cells from one another
Cell membranes fuse with one
another in such a way that they form
permeable communicatingjunctions (gap junctions) that allow
relatively free diffusion of ions
ATRIAL SYNCYTIUM
[action potentials can be conductedfrom AS to VS by way of the
atrioventricular (A-V) bundle]
VENTRICULAR SYNCYTIUM
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Action Potential in Cardiac Muscle
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EVENT ASSOCIATED IN ACTION POTENTIALGENERATION
a. Stimulus (chemical-electrical-mechanical) is sufficientto alter the resting membrane potential of a particularregion of the membrane
b. The membranes permeability to sodium ions increasesat the point of stimulation
c. Sodium ions rapidly move into the cell through themembraned. As sodium ions move into the cell, the transmembrane
potential reaches zero (the membrane becomes locallydepolarized)
e. Sodium ions continue to move inward, and the inside ofthe membrane becomes positively charged relative tothe outside (reverse polarization)
f. Reverse polarization at the original site of stimulationresults in a local current that acts as a stimulus to theadjacent region of the membrane.
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EVENT ASSOCIATED IN ACTION POTENTIALGENERATION
g. At the point originally stimulated, the membranespermeability to sodium decreases, and its permeabilityto potassium increases.
h. Potassium ions rapidly move outward, again makingthe outside of the membrane positive in relation to the
inside (repolarization)i. Sodium and potassium pumps transport sodium ionsback out of, and potassium ions back into, the cell.
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EVENT ASSOCIATED IN ACTION POTENTIALGENERATION
g. At the point originally stimulated, the membranespermeability to sodium decreases, and its permeabilityto potassium increases.
h. Potassium ions rapidly move outward, again makingthe outside of the membrane positive in relation to the
inside (repolarization)i. Sodium and potassium pumps transport sodium ionsback out of, and potassium ions back into, the cell.
(RESTING MEMBRANE POTENTIAL)Note: the resting membrane potential of normalcardiac muscle is about -85 to -95 mV and about -90 to -100 mV in the specialized conductive fibers
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