Control of the cardiovascular system Reverend Dr. David C.M. Taylor School of Medicine

 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…  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 Percentage sarcomere length (100% = 2.2 µm) Tension developed %

Starling’s Law Percentage sarcomere length (100% = 2.2  m) Tension developed % 1.8  m 2.2  m 3.8  m

Contractility-”Inotropic effect” positive inotropic agents  increase available intracellular Ca 2+  increase number of actinomyosin binding sites  increase force of contraction positive inotropic agents are  sympathetic stimulation  catecholamines  glucagon  thyroid hormones  increased extracellular Ca 2+ positive inotropic agents are  sympathetic stimulation  catecholamines  glucagon  thyroid hormones  increased extracellular Ca 2+

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 Ca 2+ 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 0mS300

Chronotropic effect 0 mV -70 0mS300