Pages 363-370

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Pages 363-370
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Cardiac muscle cells contract:
 Spontaneously
 Independently
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Two systems regulate heart rhythm:
 Intrinsic Conduction System
 Uses the specialized cardiac muscle cells (nodal tissue)
 75 beats per minute
 Autonomic nervous system
 Speed up or slow down

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
Sinoatrial (SA) node
Atrioventricular (AV) node
Atrioventricular (AV) bundle (bundle of His)
 Discovered by Wilhelm His in 1893


Bundle branches
Purkinje fibers
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Superior
vena cava
Sinoatrial (SA)
node (pacemaker)
Left atrium
Atrioventricular
(AV) node
Right atrium
Bundle branches
Atrioventricular
(AV) bundle
(bundle of His)
Purkinje fibers
Purkinje fibers
Interventricular
septum

Sinoatrial Node = the heart’s natural pacemaker

From the SA node the impulse spreads:
 The “SA Node”
 Located in the right atrium
 Starts each heartbeat; sets the pace
 To the AV node – atria contract …
 Then the impulse travels to the:
 AV bundle > Bundle branches > Purkinje fibers
 Ventricles contract toward atria, ejecting blood

http://highered.mheducation.com/sites/0072495855/stu
dent_view0/chapter22/animation__conducting_system_of_
the_heart.html


Ischemia —lack of adequate oxygen supply to
heart muscle results in fibrillation
Fibrillation—a rapid, uncoordinated
the heart muscle
shuddering of
 Major cause of death from heart attacks
 Use of defibrillator can save life by restoring natural
rhythm using electrical current

Tachycardia —rapid heart rate over 100 bpm
 Prolonged can progress to fibrillation

Bradycardia —slow heart rate less than 60 bpm
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
Cardiac cycle refers to one complete heartbeat

Refers to the sounds of the ventricles
 Systole  contraction
 Diastole  relaxation


beats about 75 times per minute
length of beat is about 0.8 seconds
© 2015 Pearson Education, Inc.

Two distinct sounds
 “Lub” – closing of the AV valves ventricular systole (systolic blood pressure)
 “Dup” – closing of the semilunar valves
 Ventricular diastole (diastolic blood pressure)

Faulty valves reduce efficiency of the heart
 Can lead to abnormal heart sounds (murmurs)
 Sounds like a whooshing or swishing
1.
Autonomic Nervous System
 Sympathetic nervous system
 Parasympathetic nervous system
2.
Hormones and ions via Endocrine System

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3.
Epinephrine and thyroxine increase heart rate
Imbalances of Ca⁺⁺ or K⁺ can depress, stop, or
increase heart rhythms
Physical factors

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Age : faster in young
Gender : faster in females
Exercise
Body temperature
© 2015 Pearson Education, Inc.
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