Download Heart and Circulation 13

CARDIOVASCULAR SYSTEM
PHYSIOLOGY
Pulmonary circulation:

Path of blood from right
ventricle through the
lungs and back to the
heart.

Systemic circulation:

Oxygen-rich blood
pumped to all organ
systems to supply
nutrients.

Rate of blood flow
through systemic
circulation = flow rate
through pulmonary
circulation.

Fig. 13.9
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Fig. 13.10b
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Atrioventricular and Semilunar Valves
• Atria and ventricles are separated by AV (atrioventricular)
valves.
– One way valves.
• At the origin of the pulmonary artery and aorta are semilunar
valves.
– One way valves.
– Open during ventricular contraction.
• Opening and closing of valves occur as a result of pressure
differences.
Fig. 13.10a
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Cardiac Cycle
• Refers to the repeating pattern of
contraction and relaxation of the heart.
– Systole:
• Phase of contraction.
– Diastole:
• Phase of relaxation.
Fig. 13.12
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End-diastolic volume - Amount of blood in the ventricles before they
contract - also known as preload. Ave = 110 - 130 ml.
Stroke volume - Amount of blood ejected from the heart in a single
beat. Ave = 70 - 80 ml.
End-systolic volume - Amount of blood remaining in the ventricles after
they contract. Ave = 40 - 60 ml.
Heart Sounds
Closing of the AV and
semilunar valves.
Lub (first sound):

Produced by closing of
the AV valves during
isovolumetric contraction.

Dub (second sound):

Fig. 13.14
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Produced by closing of
the semilunar valves
when pressure in the
ventricles falls below
pressure in the arteries.

Murmur - Abnormal heart sounds produced by abnormal
patterns of blood flow in the heart.

Fig. 13.13
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Electrical Activity of the Heart
• Autorhythmic cardiac muscle cells:
– Demonstrates automaticity:
• Sinoatrial node functions as the pacemaker.
– Spontaneous depolarization (pacemaker
potential):
• Caused by diffusion of Ca2+ through slow
Ca2+ channels.
– Cells do not maintain a stable RMP.
Fig. 13.17
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Electrical Activity of the Heart
• Myocardial cells:
– have a RMP of –90 mV.
• SA node spreads APs to myocardial
cells.
– When myocardial cell reaches threshold,
these cells depolarize.
Fig. 13.18
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Fig. 13.19
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Electrical Activity of the Heart
• Sinus rhythm - SA node is the pacemaker.
Heart rate of 70 - 80 bpm
• Ectopic focus:
– Pacemaker other than SA node:
• If APs from SA node are prevented from reaching
these areas, these cells will generate pacemaker
potentials.
– Junctional rhythm - AV node is the
pacemaker. Results in heart rate of 40 - 60 bpm.
Fig. 13.20
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Excitation-Contraction Coupling in
Heart Muscle
• Depolarization of myocardial cell stimulates
opening of VG Ca2+ channels in
sarcolemma.
– Ca2+ diffuses down gradient into cell.
• Stimulates opening of Ca2+-release channels in SR.
– Ca2+ binds to troponin and stimulates contraction (same
mechanisms as in skeletal muscle).
• During repolarization Ca2+ actively
transported out of the cell via a Na+-Ca2+exchanger.
Electrocardiogram (ECG/EKG)
• The body is a good conductor of electricity.
– Tissue fluids have a high [ions] that move in
response to potential differences.
• Electrocardiogram:
– Measure of the electrical activity of the heart
per unit time.
• Potential differences generated by heart are
conducted to body surface where they can be
recorded on electrodes on the skin.
Electrocardiogram (ECG/EKG)
• The ECG helps the physician gain insight into:
–
–
–
–
The anatomical orientation of the heart
Relative sizes of its chambers
Disturbances of rhythm and conduction
The extent, location, and progress of ischemic
damage to the myocardium
– The effects of altered electrolyte concentrations
– The influence of certain drugs ( i.e. digitalis, calcium
channel blockers, and antiarrhythmic agents)
Fig. 13.22
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Electrocardiogram (ECG/EKG)
• P wave:
– Atrial
depolarization.
• QRS
complex:
– Ventricular
depolarization.
– Atrial
repolarization.
• T wave:
– Ventricular
repolarization.
Fig. 13.23
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Fig. 13.21
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P-R interval - Length of time between the P wave
and the beginning of the QRS complex. Normal
range = 0.12 - 0.20 sec.
Fig. 13.21
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QRS complex - Normal range = 0.06 - 0.10 sec.
Fig. 13.21
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S-T segment - Length of time during which the
entire ventricular myocardium is depolarized.
About 0.12 sec. Myocardial ischemia may be
detected by changes in this segment.
Fig. 13.31
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Fig. 13.21
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Q-T interval - From the beginning of ventricular
depolarization through their repolarization.
Ave. = 0.36 - 0.40 sec; varies inversely with
heart rate.
SINUS RHYTHM
JUNCTIONAL RHYTHM
SECOND DEGREE HEART BLOCK
Cardiac Rate Imbalances
Tachycardia - Abnormally
fast heart rate (>100 bpm).
Bradycardia - Abnormally
slow heart rate (<60 bpm).
Fig. 13.32
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Fig. 13.33
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Fig. 13.24
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Fig. 13.25
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Fig. 13.26
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Discontinuous
Fig. 13.28
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Atherosclerosis
Fig. 13.30a
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• The narrowing of the blood
vessel lumen.
• Responsible (indirectly) for
half the deaths in the Western
world.
• Often begins with a tear in
the tunica interna - and
progressively builds up fatty
plaque. - It usually ends in
arteriosclerosis: the death of
the tunica media and
deterioration of elastic fibers.
LYMPHATIC SYSTEM
Fig. 13.34
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Fig. 13.35
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Fig. 13.36
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