Control of the cardiovascular system

Reverend Dr. David C.M. TaylorSchool of Medicine

dcmt@liverpool.ac.uk

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