Download Cardiac Output Regulation Cardiac Output Regulation

Cardiac
Cardiac Output
Output
Regulation
Regulation
Stroke Volume x Heart rate
70mL/beat x 70 beats/min = 5 L/min
Regulation
Regulation of
of Heart
Heart Rate
Rate
Autonomic Nervous System
¾ Increase in HR
• Sympathetic nervous system
9 Via cardiac accelerator nerves
• Increases HR by stimulating SA
node
9 Norepinephrine release (accelerates
depolarization of SA node)
¾
Decrease in HR
• Parasympathetic nervous system
9 Via vagus nerves
• Slows HR by inhibiting SA node
9 Acetylcholine release (slow sinus
discharge)
ACh
ACh Effector
organs
Terminal
ganglion
ACh
= Parasympathetic
system
= Preganglionic fiber
= Postganglionic fiber
NE
Sympathetic ganglion chain
Craniosacral
parasympathetic
nerves
Cardiac
muscle
= Sympathetic system
Smooth
muscle
= Acetylcholine
= Norepinephrine
= Epinephrine
Thoracolumbar
sympathetic
nerves
= Cell body
= Cell body
= Axon
Adrenal
medulla
ACh
Collateral
ganglion
ACh
Most
exocrine
glands
and
some
ACh endocrine
glands
Terminal
ganglion
1
Figure 9.24
Figure 9.24
(1)
(1)
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Threshold
potential
Threshold
potential
= Inherent SA node pacemaker activity
= SA node pacemaker activity on parasympathetic stimulation
= SA node pacemaker activity on sympathetic stimulation
Regulation
Regulation of
of SV
SV
Extrinsic
control
Stroke volume
Strength of
cardiac contraction
Intrinsic control
Sympathetic activity
(and epinephrine)
End-diastolic
volume
Intrinsic control
Figure 9.25
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Venous return
Regulation
Regulation of
of Stroke
Stroke Volume
Volume
Strength of Cardiac Contraction
¾
Strength depends upon length-tension relationship
Optimal length
Normal resting length
2
Regulation
Regulation of
of Stroke
Stroke Volume
Volume
End Diastolic Volume
¾ Frank-Starling mechanism
• Greater preload results in stretch of ventricles and in a
more forceful contraction
Frank-Starling curve on
sympathetic stimulation
Normal Frank-Starling
curve
Regulation
Regulation of
of Stroke
Stroke Volume
Volume
Other Factors affecting SV:
¾
Average aortic blood pressure
• Pressure the heart must pump against to eject
blood (“afterload”)
¾
Strength of the ventricular contraction
• Contractility
9 Increased contractility results in higher stroke volume
Regulation
Regulation of
of Stroke
Stroke Volume
Volume
Other Factors affecting SV:
• The Skeletal Muscle Pump
9Rhythmic skeletal muscle
contractions force blood in
the extremities toward the
heart
9One-way valves in veins
prevent backflow of blood
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