Download Key Revision Points for Cardiac Function Key points about the

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SAN is the heart’s pacemaker – intrinsic
rhythm.
Impulses spread through the atria causing
contraction of both atria.
Impulse picked up by AVN.
Impulse spreads through septum in the
bundle of His.
Impulse then spreads through ventricles in
Purkinje fibres causing ventricular
contraction.
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SAN rate is altered by autonomic nervous
system.
Parasympathetic vagus nerve slows heart
rate.
Sympathetic nerve speeds up heart rate.
Release of adrenaline increases heart rate
prior to exercise.
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During exercise there is an increase in carbon
dioxide levels.
This causes an increase in the acidity of
blood.
This is detected by chemoreceptors.
Impulses sent from medulla in the brain.
Decreases vagus stimulation.
Increases sympathetic impulses.
Results in an increase in activity from SAN
and an increase in heart rate.
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Heart rate increases.
Stroke volume increases.
This is due to Starling’s Law.
Cardiac output increases.
Remember: SV x HR = cardiac output
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Cardiac hypertrophy.
Results in increase in stroke volume.
RESTING heart rate decreases.
RESTING cardiac output remains the same
(no need for resting levels to change).