Download Heart Physiology

Cardiovascular System Notes:
Physiology of the Heart
Interesting Heart Fact
Capillaries are so small it
takes ten of them to equal
the thickness of a human
hair.
Heart Physiology: Electrical
Events

Heart depolarizes and contracts without
nervous system stimulation
 Rhythm can be altered by autonomic
nervous system
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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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• 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
SA Node
AV Node
2. Atrioventricular
Node (AV node)
• located at base of right atrium –
receives impulse from SA node
• Atrioventricular
Bundle
• Location: middle of septum
Atrioventricular
Bundle
• Direction of Heart
Beat
• impulse from AV node goes down
bundle to base of heart
• it then travels up the sides of the
ventricles through the PURKINJE
NETWORK causing the ventricles to
contract from the bottom up
Figure 18.15a Intrinsic cardiac conduction system and action potential succession during one heartbeat.
Superior vena cava
Slide 1
Right atrium
1 The sinoatrial (SA)
node (pacemaker)
generates impulses.
Internodal pathway
2 The impulses
pause (0.1 s) at the
atrioventricular
(AV) node.
3 The
atrioventricular
(AV) bundle
connects the atria
to the ventricles.
4 The bundle branches
conduct the impulses
through the
interventricular septum.
Left atrium
Subendocardial
conducting
network
(Purkinje fibers)
Interventricular
septum
5 The subendocardial
conducting network
depolarizes the contractile
cells of both ventricles.
Anatomy of the intrinsic conduction system showing the sequence of
electrical excitation
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• 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
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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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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Figure 18.16 Autonomic innervation of the heart.
The vagus nerve
(parasympathetic)
decreases heart rate.
Dorsal motor nucleus
of vagus
Cardioinhibitory
center
Cardioacceleratory 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
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Parasympathetic fibers
Sympathetic fibers
Interneurons
• 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
• Cardiac Output
• amount of blood pumped out of each
side of the heart in 1 minute
• heart rate X stroke volume
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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Figure 18.20 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
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Tricuspid valve sounds
typically heard in right
sternal margin of 5th
intercostal space
Mechanical Events: The Cardiac Cycle
• 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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Phases of the Cardiac Cycle
• 1. Ventricular filling—takes place in mid-tolate 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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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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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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Figure 18.21 Summary of events during the cardiac cycle.
Left heart
QRS
P
Electrocardiogram
T
1st
Heart sounds
Dicrotic notch
120
Pressure (mm Hg)
P
2nd
80
Aorta
Left ventricle
40
Atrial systole
Left atrium
0
Ventricular
volume (ml)
120
EDV
SV
50
ESV
Atrioventricular valves
Aortic and pulmonary valves
Phase
Open
Closed
Open
Closed
Open
Closed
1
2a
2b
3
1
Left atrium
Right atrium
Left ventricle
Right ventricle
Atrial
contraction
Ventricular
filling
1
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Ventricular filling
(mid-to-late diastole)
Ventricular
Isovolumetric
contraction phase ejection phase
2a
2b
Ventricular systole
(atria in diastole)
Isovolumetric
relaxation
3
Early diastole
Ventricular
filling
• PULSE & BLOOD
PRESSURE
• Pulse
• pulse can be found at
many sites on the body
• expansion & contraction
of an artery as the left
ventricle contracts
• normal is 70 – 80 bpm
(there are exceptions to
this)
• 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
• The Electrocardiogram • amplifies electric current of heart
(EKG or ECG)
producing distinct wave patterns
P wave
QRS Complex
T wave
• P wave
• depolarization of atria
• QRS Complex
• depolarization of ventricles
• T wave
• repolarization of ventricles
Electrocardiography

Electrocardiogram (ECG or EKG)
 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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Figure 18.17 An electrocardiogram (ECG) tracing.
Sinoatrial
node
Atrioventricular
node
QRS complex
R
Ventricular
depolarization
Ventricular
repolarization
Atrial
depolarization
T
P
Q
P-R
Interval
0
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S
0.2
S-T
Segment
Q-T
Interval
0.4
Time (s)
0.6
0.8
Figure 18.18 The sequence of depolarization and repolarization of the heart related to the deflection waves of an ECG
tracing.
SA node
R
R
T
P
Q
Q
S
S
4 Ventricular depolarization is
complete.
R
R
Q
Q
S
5 Ventricular repolarization begins
at apex, causing the T wave.
S
2 With atrial depolarization
complete, the impulse is delayed at
the AV node.
R
T
P
Q
S
3 Ventricular depolarization begins at
apex, causing the QRS complex. Atrial
repolarization occurs.
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R
T
P
Q
T
P
T
P
T
P
1 Atrial depolarization, initiated by
the SA node, causes the P wave.
AV node
Slide 1
6
Depolarization
S
Ventricular repolarization is complete.
Repolarization
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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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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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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Developmental Aspects of the
Heart

Embryonic heart chambers
 Sinus venosus
 Atrium
 Ventricle
 Bulbus cordis
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Figure 18.24 Development of the human heart.
Arterial end
Arterial end
Superior
vena cava
4a
4
Tubular
heart
Ventricle
2
Ductus
arteriosus
Pulmonary
trunk
Foramen
ovale
Atrium
3
Ventricle
1
Venous end
Day 20:
Endothelial
tubes begin
to fuse.
Aorta
Day 22:
Heart starts
pumping.
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Day 24: Heart
continues to
elongate and
starts to bend.
Venous end
Day 28: Bending
continues as ventricle
moves caudally and
atrium moves cranially.
Inferior
vena cava
Day 35: Bending is
complete.
Ventricle
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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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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Figure 18.25 Three examples of congenital heart defects.
Narrowed
aorta
Occurs in
about 1 in every
500 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.
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Occurs in
about 1 in every
1500 births
Coarctation of the aorta.
A part of the aorta is
narrowed, increasing the
workload of the left ventricle.
Occurs in
about 1 in every
2000 births
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.
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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