2 Regulation of cardiac contraction

Question 1

What are the steps in excitation-contraction coupling? (cardiac cell)

Answer 1

AP from adjacent cell travels along sarcolemma then down T-tubule

AP triggers v.g Ca2+ channels open and Ca2+ enters cell

Entry of CA2+ triggers release of Ca2+ from SR

Ca2+ bind troponin to initiate contraction

Question 2

How does relaxation of contracted muscle occur? (cardiac cell)

Answer 2

Ca2+ unbinds from troponin

Ca2+ is pumped back into SR for storage (ATP is needed)

Ca2+ is exchanged with Na+

Na+ gradient is maintained by ATPase pump

Question 3

What gradient does blood move via?

Answer 3

From areas of high pressure to low pressure

Contraction of the heart produces the pressure

Question 4

Outline of the cardiac cycle

Answer 4

Late ventricular diastole

Isovolumetric ventricular contraction

Ventricular ejection

Isovolumetric ventricular *relaxation *

Ventricular diastole

Question 5

How is the ventricle filled?

Answer 5

Up to 70% of blood fills it PASSIVELY

Then the pressure becomes less and less so blood fills slower

Need atrial contraction to FULLY fill ventricle

Question 6

Why is atrial dysfunction not life ending?

Answer 6

Because it only fills the heart 30% more

Question 7

What are the normal volumes of SV, EDV and ESV?

Answer 7

SV ~ 80mL
EDV ~ 130mL
ESV ~ 50mL

Question 8

Define cardiac output

Answer 8

Flow rate out of one side of the heart = Amount of blood the heart pumps each minute

~5L per min at REST

Question 9

Define heart rate

Answer 9

Number of contraction per min

Question 10

Define stroke volume

Answer 10

Volume pumped by a ventricle in one contraction

Question 11

Define venous return

Answer 11

Flow rate INTO heart

Question 12

What components control stroke volume?

Answer 12

Venous return (contractility)

Question 13

What is the Frank-Starlin Law?

Answer 13

Within physiological limit, the heart pumps ALL the blood it receives

Increased venous return stretches ventricles = increases force production until CO matches venous return

Question 14

What is contractility regulated by?

Answer 14

Sympathetic nervous system

Question 15

What is a change in contractility defined as?

Answer 15

Change in the work performed by the heart

That is NOT brought about be a change in initial fibre length (increases the force without stretching it)

Question 16

What is the effect of norepinephrine on cardiac output?

Answer 16

Increases cardiac output without changing venous return

Doesn’t change volume of blood heart receives = just increases force of contraction (contractility)

Question 17

What is the action of sympathetic stimulation?

Answer 17

Sympathetic nerve stimulation increases cardiac contractility

At rest, heart is under sympathetic tone

Question 18

What does parasympathetic stimulation have little effect on?

Answer 18

Contractility

Question 19

What is the difference between contractility and Starling’s Law on regulating the heart?

Answer 19

They both increase stroke volume but differently

Starlings increases the venous return

Contractility decreases the ESV because it forces more blood out in each pump

Question 20

What is intrinsic regulation of cardiac contraction?

Answer 20

The heart’s ability to regulate its contraction strength and rhythm without external neural or hormonal influences

Question 21

What is extrinsic regulation of cardiac contraction?

Answer 21

Extrinsic regulations are not part of the organism’s inherent structure but can impact its functions

Question 22

Give examples of intrinsic regulation of cardiac contraction

Answer 22

Venous return produces intrinsic regulation

Intrinsic regulation gives a constant ejection fraction

Question 23

Give examples of extrinsic regulation of cardiac contraction

Answer 23

Autonomic nerves
Hormones
Drugs

Can alter force of contraction

Question 24

What do inotropic agents do?

Answer 24

Agents that alter contractility

Question 25

What does increased inotropy cause?

Answer 25

Increase in ejection fraction because of more contractility

Question 26

Name an inotropic hormone

Answer 26

Adrenaline

Question 27

What part of the heart do sympathetic nerves innervate?

Answer 27

Whole heart

Question 28

What -topic affects do sympathetic stimulation have on the heart?

Answer 28

POSITIVE chronotropic and inotropic actions

Question 29

What -topic affects do parasympathetic stimulation have on the heart?

Answer 29

Negative chronotropic affect (slows heart)

Little inotropic action = cannot weaken contractility