Allied Science Physiology 09-10. Cardiovascular System. Lecture 3.
Allied Science Physiology. Cardiovascular System. Lecture 2.
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Allied Science Physiology. Cardiovascular System. Lecture 2.
•  Cardiac muscle doesn’t require commands from the CNS
to contract
•  Contractile activity of cardiac muscle: myogenic
•  Autorhythmicity is the ability to generate its own rhythm
•  Autorhythmic cells that provide rhythm to the heartbeat. 2
types
–  Pacemaker cell: initiate AP’s
–  Conduction fibers: transmit AP’s
Allied Science Physiology. Cardiovascular System. Lecture 2.
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•  Pacemaker cells
–  Spontaneously depolarizing membrane potentials
to generate action potentials
–  Coordinate and provide rhythm to heartbeat
•  Conduction fibers
–  Rapidly conduct action potentials initiated by
pacemaker cells to myocardium
–  Conduction velocity = 4 meters/second
–  Ordinary muscle fibers, CV = 0.4 meter/second
Allied Science Physiology. Cardiovascular System. Lecture 2.
•  Sinoatrial node (SA node): 70-80 APs/min
–  Pacemaker of the heart
•  Atrioventricular node (AV node): 40-60 APs/min
•  Internodal pathways
•  Bundle of His: 20-40 APs/min
•  Purkinje fibers: 20-40 APs/min
Allied Science Physiology. Cardiovascular System. Lecture 2.
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•
Atria contract first followed by ventricles (fibrous skeleton)
•
Coordination due to presence of gap junctions and conduction
pathways
Figure 13.9
Allied Science Physiology. Cardiovascular System. Lecture 2.
Figure 13.10
Allied Science Physiology. Cardiovascular System. Lecture 2.
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•  Interatrial Pathway
–  SA Node  right atrium  left atrium
–  Simultaneous contraction right and left atria
•  Internodal Pathway: SA Node  AV Node
–  Slow conduction - AV Nodal Delay = 0.1 sec
–  Atria contract before ventricles
•  Ventricular Excitation (fast conduction)
–  Down Bundle of His
–  Up Purkinje Fibers
•  Purkinje Fibers contact ventricle contractile cells
•  Ventricle contracts from apex up
Allied Science Physiology. Cardiovascular System. Lecture 2.
Figure 13.11
Allied Science Physiology. Cardiovascular System. Lecture 2.
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•  ECG is used to look at some aspects of cardiac
electrical activity
•  Non-invasive technique
•  Used to test for clinical abnormalities in
conduction of electrical activity in the heart
•  Body fluids are conductors
•  Currents in the body can spread to surface
Allied Science Physiology. Cardiovascular System. Lecture 2.
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P wave: atrial depolarization
•
QRS complex: vent. depolarization
•
T wave: vent. repolarization
•
P-R: AV node conduction time
•
R-T: vent. contraction (systole)
•
T-Q: vent. relaxation (diastole)
•
R-R: time between heart beats
Figure 13.16b
Allied Science Physiology. Cardiovascular System. Lecture 2.
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Allied Science Physiology. Cardiovascular System. Lecture 2.
All the events associated with the flow of blood
through the heart during a single complete heartbeat
(approx 0.8sec if heart rate is 75bpm)
2 Main periods of cardiac cycle (72 beats/min)
•  Systole (0.3 s)
–  Ventricle contraction
•  Diastole (0.5 s)
–  Ventricle relaxation
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•  Valves open passively due to pressure
gradients
–  AV valves open when
•  P atria > P ventricles
–  Semilunar valves open when
•  P ventricles > P arteries
Allied Science Physiology. Cardiovascular System. Lecture 2.
Phase 1: Ventricular filling (Venous return and atrial contraction)
–  Blood returns to the heart via systemic and pulmonary veins
–  AV valves open (Pressure atria > Pressure ventricles)
–  Passive phase - no atria or ventricular contraction
–  Sharp volume increase; levels off as pressure gradient
decreases
–  Active phase - atria contract
–  Pressure in ventricle increases because extra blood is forced in
–  Volume in ventricle increases
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Phase 2: Isovolumetric ventricular contraction
–  Ventricle contracts - increases pressure
–  AV valve shut (pressure in ventricle > pressure in atria)
–  Semilunar valve still closed
–  No blood entering or exiting ventricle (isovolumetric)
Allied Science Physiology. Cardiovascular System. Lecture 2.
Phase 3: Ventricular ejection
–  Ventricles continue to contract
–  Semilunar valves open (Pressure ventricles > Pressure
aorta)
–  Pressure continues to increase in ventricles: peaks then
declines
–  Aortic pressure increases: peaks then declines
–  Blood volume decreases as ejection occurs
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Phase 4: Isovolumetric Ventricular Relaxation
–  Ventricle relaxes - decreases pressure
–  Ventricular pressure drops as ventricle relaxes
–  Aortic pressure decreases as pressure dissipates
through arterial system
–  Semilunar valve closes
–  Semilunar and AV valves are closed – no blood
movement – no volume change
Allied Science Physiology. Cardiovascular System. Lecture 2.
Figure 13.18
Allied Science Physiology. Cardiovascular System. Lecture 2.
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•  Isovolumetric Ventricular Contraction
–  AV & aortic valves closed
–  Ventricular pressure increases until it exceeds
atrial pressure
•  Ventricular Ejection
–  Aortic valve opens
–  Blood moves from ventricle to aorta
Allied Science Physiology. Cardiovascular System. Lecture 2.
•  Isovolumetric Ventricular Relaxation
–  Ventricle muscle relaxes so that pressure is less
than aorta
–  Aortic valve closes
–  Pressure in ventricle continues dropping until it is less
than atrial pressure
•  Ventricular Filling
–  AV valve opens
–  Blood moves from atria to ventricle
–  Passive until atrium contracts
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Figure 13.18
Allied Science Physiology. Cardiovascular System. Lecture 2.
Figure 13.19
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• Rises and falls with each heartbeat: blood flow is pulsatile
• Normal value for systolic pressure is approx. 120mmHg
• Normal value for diastolic pressure is approx. 80mmHg
• Pulse pressure = Systolic – diastolic = approx. 40mmHg
• Average aortic pressure throughout the cardiac cycle is called mean
arterial pressure – very important (later lecture)
Figure 13.20
Allied Science Physiology. Cardiovascular System. Lecture 2.
•  Aorta (and large arteries) – elastic
–  Pressure reservoir
•  Store energy during systole as walls expand
•  Release energy during diastole as walls
recoil inward
•  Maintains blood flow through entire
cardiac cycle
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•
EDV = end diastolic volume = volume of blood in ventricle at end of
diastole
•
ESV = end systolic volume = volume of blood in ventricle at end of systole
•
SV = stroke volume = volume of blood ejected from heart each cycle = SV
= EDV - ESV (130 mL – 60 mL = 70 mL)
•
Ejection fraction: Fraction of end-diastolic volume ejected during a
heartbeat. Ejection fraction = stroke volume / end diastolic volume = 70
mL / 130 mL = 0.54
Figure 13.21
Allied Science Physiology. Cardiovascular System. Lecture 2.
Sounds occur due to:
First sound = soft lubb
AV valves close
Second sound = louder dubb
Semilunar valves close
Sounds also referred to as ‘lup’ and ‘dup’
Figure 13.22
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•
ECG = measure of electrical
events
•
Electrical events cause
mechanical events,
so precede mechanical events
–  P wave precedes atrial
contraction
–  QRS complex precedes
ventricular contraction
–  T wave precedes
ventricular relaxation
Figure 13.18
Allied Science Physiology. Cardiovascular System. Lecture 2.
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