1. Cardiovascular System Notes: Physiology of the Heart

2. Interesting Heart Fact
Capillaries are so small it takes ten of them to equal the thickness of a human hair.

3. Heart Physiology: Electrical Events
Heart depolarizes and contracts without nervous system stimulation
Rhythm can be altered by autonomic nervous system
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4. Heart Physiology: Setting the Basic Rhythm
Coordinated heartbeat is a function of
Presence of gap junctions
Intrinsic cardiac conduction system
Network of noncontractile (autorhythmic) cells
Initiate and distribute impulses  coordinated depolarization and contraction of heart
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5. PHYSIOLOGY OF THE HEART
The Conducting System (electric)
called an intrinsic conduction or “nodal” system of specialized tissue
1. Sinoatrial Node (SA)
PACEMAKER OF HEART – starts each heartbeat
located in wall of right atrium
made of specialized myocardial cells
sends impulse to both atria, causing them to contract

6. SA Node
AV Node
2. Atrioventricular Node (AV node)
located at base of right atrium – receives impulse from SA node

7. Atrioventricular Bundle
Location: middle of septum
Atrioventricular Bundle
impulse from AV node goes down bundle to base of heart
Direction of Heart Beat
it then travels up the sides of the ventricles through the PURKINJE NETWORK causing the ventricles to contract from the bottom up

8. Superior vena cava Right atrium Internodal pathway Left atrium
Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat.
Slide 1
Superior vena cava
Right atrium
The sinoatrial (SA) node (pacemaker)
generates impulses. 1
Internodal pathway
The impulses
pause (0.1 s) at the
atrioventricular
(AV) node. 2
Left atrium
The atrioventricular
(AV) bundle
connects the atria
to the ventricles. 3
Subendocardial
conducting
network
(Purkinje fibers)
The bundle branches
conduct the impulses
through the
interventricular septum. 4
Inter-
ventricular
septum
The subendocardial
conducting network
depolarizes the contractile
cells of both ventricles. 5
Anatomy of the intrinsic conduction system showing the sequence of
electrical excitation
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9. RATE OF HEART BEAT
Factors affecting heart rate
age, sex, physical activity, temperature, thought processes, chemicals (natural and otherwise)
rate high at birth (100 – 140 bpm) – then declines steadily until average is reached (70 – 80 bpm)
heart rate faster in females – slower in trained athletes

10. Extrinsic Innervation of the Heart
Heartbeat modified by ANS via cardiac centers in medulla oblongata
Sympathetic   rate and force
Parasympathetic   rate
Cardioacceleratory center – sympathetic – affects SA, AV nodes, heart muscle, coronary arteries
Cardioinhibitory center – parasympathetic – inhibits SA and AV nodes via vagus nerves
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11. Homeostatic Imbalances
Defects in intrinsic conduction system may cause
Arrhythmias - irregular heart rhythms
Uncoordinated atrial and ventricular contractions
Fibrillation - rapid, irregular contractions; useless for pumping blood  circulation ceases  brain death
Defibrillation to treat
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12. Figure 18.16 Autonomic innervation of the heart.
The vagus nerve
(parasympathetic)
decreases heart rate.
Dorsal motor nucleus
of vagus
Cardioinhibitory
center
Cardioaccele-
ratory center
Medulla oblongata
Sympathetic
trunk
ganglion
Thoracic spinal cord
Sympathetic trunk
Sympathetic cardiac
nerves increase heart rate
and force of contraction. AV
node SA
node
Parasympathetic fibers
Sympathetic fibers
Interneurons
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13. CARDIAC CYCLE
the events of one complete heartbeat
length of cycle (heartbeat) is about 0.8 sec
atria contract at the same time – as they relax, the ventricles contract
SYSTOLE
contraction of ventricle
DIASTOLE
relaxation of ventricle
amount of blood pumped out of each side of the heart in 1 minute
Cardiac Output
heart rate X stroke volume

14. Heart Sounds
Two sounds (lub-dup) associated with closing of heart valves
First as AV valves close; beginning of systole
Second as SL valves close; beginning of ventricular diastole
Pause indicates heart relaxation
Heart murmurs - abnormal heart sounds; usually indicate incompetent or stenotic valves
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15. heard in 2nd intercostal space at right sternal margin
Figure Areas of the thoracic surface where the sounds of individual valves can best be detected.
Aortic valve sounds
heard in 2nd intercostal
space at right sternal
margin
Pulmonary valve
sounds heard in 2nd
intercostal space at left
sternal margin
Mitral valve sounds
heard over heart apex
(in 5th intercostal space)
in line with middle of
clavicle
Tricuspid valve sounds
typically heard in right
sternal margin of 5th
intercostal space
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16. Mechanical Events: The Cardiac Cycle
Blood flow through heart during one complete heartbeat: atrial systole and diastole followed by ventricular systole and diastole
Systole—contraction
Diastole—relaxation
Series of pressure and blood volume changes
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17. Phases of the Cardiac Cycle
1. Ventricular filling—takes place in mid-to-late diastole
AV valves are open; pressure low
80% of blood passively flows into ventricles
Atrial systole occurs, delivering remaining 20%
End diastolic volume (EDV): volume of blood in each ventricle at end of ventricular diastole
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18. Phases of the Cardiac Cycle
2. Ventricular systole
Atria relax; ventricles begin to contract
Rising ventricular pressure  closing of AV valves
Isovolumetric contraction phase (all valves are closed)
In ejection phase, ventricular pressure exceeds pressure in large arteries, forcing SL valves open
End systolic volume (ESV): volume of blood remaining in each ventricle after systole
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19. Phases of the Cardiac Cycle
3. Isovolumetric relaxation - early diastole
Ventricles relax; atria relaxed and filling
Backflow of blood in aorta and pulmonary trunk closes SL valves
Causes dicrotic notch (brief rise in aortic pressure as blood rebounds off closed valve)
Ventricles totally closed chambers
When atrial pressure exceeds that in ventricles  AV valves open; cycle begins again at step 1
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20. Figure 18.21 Summary of events during the cardiac cycle.
Left heart
QRS P T P
Electrocardiogram
1st
2nd
Heart sounds
Dicrotic notch
120 80
Aorta
Pressure (mm Hg)
Left ventricle 40
Atrial systole
Left atrium
120
EDV
Ventricular
volume (ml) SV 50
ESV
Atrioventricular valves
Open
Closed
Open
Aortic and pulmonary valves
Closed
Open
Closed
Phase 1 2a 2b 3 1
Left atrium
Right atrium
Left ventricle
Right ventricle
Ventricular
filling
Atrial
contraction
Isovolumetric
contraction phase
Ventricular
ejection phase
Isovolumetric
relaxation
Ventricular
filling 1 2a 2b 3
Ventricular filling
(mid-to-late diastole)
Ventricular systole
(atria in diastole)
Early diastole
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21. PULSE & BLOOD PRESSURE
pulse can be found at many sites on the body
Pulse
expansion & contraction of an artery as the left ventricle contracts
normal is 70 – 80 bpm (there are exceptions to this)

22. Blood Pressure
pressure blood exerts on the inner walls of blood vessels
Measuring BP
BP is a measure of the systolic pressure (ventricles contracting) OVER the diastolic pressure (ventricles relaxing)
Example:
110/70 is in normal range
Factors affecting BP
nervous system, blood volume (kidneys), temp, chemicals, diet, exercise

23. The Electrocardiogram (EKG or ECG)
amplifies electric current of heart producing distinct wave patterns

24. QRS Complex
P wave
T wave
P wave
depolarization of atria
QRS Complex
depolarization of ventricles
T wave
repolarization of ventricles

25. Electrocardiography Electrocardiogram (ECG or EKG) Three waves:
Composite of all action potentials generated by nodal and contractile cells at given time
Three waves:
P wave – depolarization SA node  atria
QRS complex - ventricular depolarization and atrial repolarization
T wave - ventricular repolarization
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26. Figure 18.17 An electrocardiogram (ECG) tracing.
Sinoatrial
node
Atrioventricular
node
QRS complex R
Ventricular
depolarization
Ventricular
repolarization
Atrial
depolarization T P Q
S-T
Segment
P-R
Interval S
Q-T
Interval
0.2
0.4
0.6
0.8
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Time (s)

27. Figure The sequence of depolarization and repolarization of the heart related to the deflection waves of an ECG tracing.
Slide 1
SA node R R P T P T Q S Q S
Atrial depolarization, initiated by the SA node, causes the P wave. 1
Ventricular depolarization is complete. 4 R
AV node R T P T P Q Q S S
With atrial depolarization complete, the impulse is delayed at the AV node.
Ventricular repolarization begins at apex, causing the T wave. 2 5 R R P T P T Q Q S S
Ventricular repolarization is complete. 6
Ventricular depolarization begins at apex, causing the QRS complex. Atrial repolarization occurs. 3
Depolarization
Repolarization
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28. Homeostatic Imbalances
Tachycardia - abnormally fast heart rate (>100 beats/min)
If persistent, may lead to fibrillation
Bradycardia - heart rate slower than 60 beats/min
May result in grossly inadequate blood circulation in nonathletes
May be desirable result of endurance training
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29. Homeostatic Imbalance
Congestive heart failure (CHF)
Progressive condition; CO is so low that blood circulation inadequate to meet tissue needs
Reflects weakened myocardium caused by
Coronary atherosclerosis—clogged arteries
Persistent high blood pressure
Multiple myocardial infarcts
Dilated cardiomyopathy (DCM)
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30. Homeostatic Imbalance
Pulmonary congestion
Left side fails  blood backs up in lungs
Peripheral congestion
Right side fails  blood pools in body organs  edema
Failure of either side ultimately weakens other
Treat by removing fluid, reducing afterload, increasing contractility
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31. Developmental Aspects of the Heart
Embryonic heart chambers
Sinus venosus
Atrium
Ventricle
Bulbus cordis
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32. Figure 18.24 Development of the human heart.
Arterial end
Arterial end
Aorta
Ductus
arteriosus
Superior
vena cava 4a
Pulmonary
trunk 4
Tubular
heart
Ventricle
Foramen
ovale 3
Atrium 2
Ventricle 1
Inferior
vena cava
Ventricle
Venous end
Venous end
Day 20:
Endothelial tubes begin to fuse.
Day 22:
Heart starts
pumping.
Day 24: Heart
continues to
elongate and starts to bend.
Day 28: Bending
continues as ventricle
moves caudally and
atrium moves cranially.
Day 35: Bending is
complete.
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33. Developmental Aspects of the Heart
Fetal heart structures that bypass pulmonary circulation
Foramen ovale connects two atria
Remnant is fossa ovalis in adult
Ductus arteriosus connects pulmonary trunk to aorta
Remnant - ligamentum arteriosum in adult
Close at or shortly after birth
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34. Developmental Aspects of the Heart
Congenital heart defects
Most common birth defects; treated with surgery
Most are one of two types:
Mixing of oxygen-poor and oxygen-rich blood, e.g., septal defects, patent ductus arteriosus
Narrowed valves or vessels  increased workload on heart, e.g., coarctation of aorta
Tetralogy of Fallot
Both types of disorders present
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35. Figure 18.25 Three examples of congenital heart defects.
Narrowed
aorta
Occurs in
about 1 in every
500 births
Occurs in
about 1 in every
1500 births
Occurs in
about 1 in every
2000 births
Ventricular septal defect.
The superior part of the
inter-ventricular septum fails
to form, allowing blood to mix
between the two ventricles.
More blood is shunted from
left to right because the left
ventricle is stronger.
Coarctation of the aorta.
A part of the aorta is
narrowed, increasing the
workload of the left ventricle.
Tetralogy of Fallot.
Multiple defects (tetra =
four): (1) Pulmonary trunk
too narrow and pulmonary
valve stenosed, resulting in
(2) hypertrophied right
ventricle; (3) ventricular
septal defect; (4) aorta
opens from both ventricles.
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36. Age-Related Changes Affecting the Heart
Sclerosis and thickening of valve flaps
Decline in cardiac reserve
Fibrosis of cardiac muscle
Atherosclerosis
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