Control of the cardiovascular system

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Control of the cardiovascular system

• Reverend Dr. David C.M. Taylor
• School of Medicine
• dcmt_at_liverpool.ac.uk
• http//www.liv.ac.uk/dcmt

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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.
• You will need to understand things that are in
  chapter 11 of Medical Sciences by Naish so that
  you have something to build on, and can
  understand chapter 13 of Clinical Sciences by
  Kumar and Clarke, by the exams in year 2.
• As usual, your PBL groups, and the lectures,
  should give you some guidance about the precise
  areas you need to cover.

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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

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What is the role of the cardiovascular system?
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Blood Pressure

• Depends upon the amount of blood leaving the
  heart
• cardiac output
• and the resistance of the vasculature
• total peripheral resistance

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Peripheral Resistance
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Peripheral resistance 2
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Cardiac Output

• Heart rate x stroke volume

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Factors affecting stroke volume
Preload
Afterload
Contractility
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Preload

• increased end-diastolic volume stretches the
  heart
• cardiac muscles stretch and contract more
  forcefully
• Frank-Starling Law of the heart

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Starlings Law
2.2 ?m
3.8 ?m
1.8 ?m
100 80 60 40 20
Tension developed
40 60 80 100 120 140 160
Percentage sarcomere length (100 2.2 ?m)
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Contractility-Inotropic effect

• positive inotropic agents are
• sympathetic stimulation
• catecholamines
• glucagon
• thyroid hormones
• increased extracellular Ca2

• positive inotropic agents
• increase available intracellular Ca2
• increase number of actinomyosin binding sites
• increase force of contraction

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Afterload

• Things affecting afterload are
• blood pressure
• viscosity of blood
• elasticity of arteries

• Changes the amount of work the heart has to do.

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Heart Rate

• Nervous system
• increased sympathetic
• decreased parasympathetic
• Chemicals
• catecholamines
• thyroid hormones
• moderate Ca2 increase

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Heart Rate 2

• Other factors
• age
• gender
• fitness
• body temperature

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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

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Chronotropic effect