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Control of the cardiovascular system

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.

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Control of the cardiovascular system

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  1. Control of the cardiovascular system Reverend Dr. David C.M. Taylor School of Medicine dcmt@liverpool.ac.uk http://www.liv.ac.uk/~dcmt

  2. 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

  3. 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

  4. What is the role of the cardiovascular system?

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

  6. Which will give the greater flow ? Peripheral Resistance

  7. Which will give the greater flow ? Peripheral resistance 2

  8. End diastolic volume - End systolic volume Stroke volume Heart rate Cardiac output Cardiac Output Heart rate x stroke volume

  9. Factors affecting stroke volume Preload Afterload Contractility

  10. 100 80 60 40 20 Tension developed % 40 60 80 100 120 140 160 Percentage sarcomere length (100% = 2.2 µm) Preload • increased end-diastolic volume stretches the heart • cardiac muscles stretch and contract more forcefully • Frank-Starling Law of the heart

  11. Starling’s 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)

  12. 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+

  13. Afterload • Changes the amount of work the heart has to do. Things affecting afterload are • blood pressure • viscosity of blood • elasticity of arteries

  14. Stroke Volume Cardiac Output Heart Rate

  15. Heart Rate • Nervous system • increased sympathetic • decreased parasympathetic • Chemicals • catecholamines • thyroid hormones • moderate Ca2+ increase

  16. Heart Rate 2 • Other factors • age • gender • “fitness” • body temperature

  17. 0 mV -70 0 mS 300 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

  18. 0 mV -70 0 mS 300 Chronotropic effect

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