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Control of the cardiovascular system
Reverend Dr. David C.M. TaylorSchool of Medicine
http://www.liv.ac.uk/~dcmt
All physiology textbooks cover this material. Your basic textbook will be sufficient
grounding to start with, but some parts of it might not be in sufficient detail.
Alongside this you might like to look at my video on the cardiac cycle…
http://pcwww.liv.ac.uk/~dcmt/cardic%20cycle.mp4
Resources
By the end of this lecture you should be able to discuss The role of the cardiovascular system The factors that affect stroke volume
Physical factors and inotropic agents. Pacemaker activity The factors that affect heart rate
Chronotropic agents The control of cardiac output
Learning outcomes
What is the role of the cardiovascular system?
Depends upon the amount of blood leaving the heart cardiac output
and the resistance of the vasculature total peripheral resistance
Blood Pressure
Peripheral Resistance
Which will give the greater flow ?
Peripheral resistance 2
Which will give the greater flow ?
Heart rate x stroke volume
Cardiac Output
End diastolic volume - End systolic volume
Stroke volume Heart rate
Cardiac output
Factors affecting stroke volume
Preload Afterload
Contractility
Preload
increased end-diastolic volume stretches the heart
cardiac muscles stretch and contract more forcefully Frank-Starling Law of
the heart 40 60 80 100 120 140 160
Percentage sarcomere length (100% = 2.2 µm)
100
80
60
40
20T
ensi
on d
evel
oped
%
Starling’s Law
40 60 80 100 120 140 160Percentage sarcomere length (100% = 2.2 m)
100
80
60
40
20
Ten
sion
dev
elop
ed %
1.8 m2.2 m
3.8 m
Contractility-”Inotropic effect”
positive inotropic agents
increase available intracellular Ca2+
increase number of actinomyosin binding sites
increase force of contraction
positive inotropic agents are
sympathetic stimulation catecholamines glucagon thyroid hormones increased extracellular
Ca2+
positive inotropic agents are
sympathetic stimulation catecholamines glucagon thyroid hormones increased extracellular
Ca2+
Afterload
Changes the amount of work the heart has to do.
Things affecting afterload are
blood pressure viscosity of blood elasticity of arteries
Things affecting afterload are
blood pressure viscosity of blood elasticity of arteries
Stroke Volume
Heart Rate
Cardiac Output
Nervous system increased sympathetic decreased parasympathetic
Chemicals catecholamines thyroid hormones moderate Ca2+ increase
Heart Rate
Other factors age gender “fitness” body temperature
Heart Rate 2
Pacemaker activity
The rhythm of the pump is provided by the pacemaker activity of some specialized muscle cells in the wall of the right atrium - the sinoatrial node
0
mV
-70
0 mS 300
Chronotropic effect
0
mV
-70
0 mS 300
