Control of the cardiovascular
system
Reverend Dr. David C.M. Taylor
School of Medicine
dcmt@liverpool.ac.uk
http://www.liv.ac.uk/~dcmt
Resources
 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
Learning outcomes
 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
What is the role of the cardiovascular
system?
Blood Pressure
 Depends upon the amount of blood leaving the heart
 cardiac output
 and the resistance of the vasculature
 total peripheral resistance
Peripheral Resistance
Which will give the greater flow ?
Peripheral resistance 2
Which will give the greater flow ?
Cardiac Output
 Heart rate x stroke volume
End diastolic volume - End systolic volume
Stroke volume
Cardiac output
Heart rate
Factors affecting stroke volume
Preload
Contractility
Afterload
 increased enddiastolic volume
stretches the heart
 cardiac muscles
stretch and contract
more forcefully
 Frank-Starling Law of
the heart
Tension developed %
Preload
100
80
60
40
20
40 60 80 100 120 140 160
Percentage sarcomere length
(100% = 2.2 µm)
Tension developed %
Starling’s Law
2.2 m
1.8 m
3.8 m
100
80
60
40
20
40
60
80
100
120
140
160
Percentage sarcomere length (100% = 2.2 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+
Afterload
Things affecting afterload are
 Changes the amount of
work the heart has to do.
 blood pressure
 viscosity of blood
 elasticity of arteries
Stroke Volume
Cardiac Output
Heart Rate
Heart Rate
 Nervous system
 increased sympathetic
 decreased parasympathetic
 Chemicals
 catecholamines
 thyroid hormones
 moderate Ca2+ increase
Heart Rate 2
 Other factors




age
gender
“fitness”
body temperature
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