Regulation of Stroke Volume and Heart Rate

Question 1

Regulation of heart rate

Answer 1

Neural

Question 2

Regulation of stroke volume

Answer 2

Preload
Afterload
Neural
Pathological

Question 3

Sympathetic nervous system regulation of heart rate

Answer 3

Nerves release noradrenaline, circulating adrenaline from adrenal medulla, act on beta1 receptors on sinoatrial node, increases slope of pacemaker potential, increases heart rate = tachycardia

Question 4

Parasympathetic nervous system regulation of heart rate

Answer 4

Vagus releases ACh, acts of muscarinic receptors on sinoatrial node, hyperpolarises cells and decreases slope of pacemaker potential, decreases heart rate = bradycardia

Question 5

Starling’s law

Answer 5

The energy of contraction is proportional to the initial length of the cardiac muscle fibre

Question 6

Result of more blood entering the heart on cardiac muscle fibre length

Answer 6

Increases length

Question 7

Length of the cardiac muscle fibre is also known as

Answer 7

Preload

Question 8

Preload is affected by the

Answer 8

End-diastolic volume

Question 9

Effect of increased venous return (preload) on EDV and stroke volume

Answer 9

Increase EDV and so increased stroke volume

Question 10

Effect of decrease venous return (preload) on EDV and stroke volume

Answer 10

Decrease EDV and so decrease stroke volume

Question 11

Afterload

Answer 11

Load against which the muscle tries to contract (building up enough pressure to open aortic valve)

Question 12

Aortic pressure is affected by

Answer 12

How easy it is for blood to get out through the arterioles - total peripheral resistance

Question 13

Effect of increased total peripheral resistance on aortic pressure and stroke volume

Answer 13

Increases aortic pressure and so decreases stroke volume as ventricle will have to work harder to push open aortic valve

Question 14

Afterload is set by

Answer 14

The arterial pressure against which the blood is expelled

Question 15

Sympathetic nervous system regulation of stroke volume

Answer 15

Nerve release noradrenaline, adrenaline in blood from adrenal medulla, act on beta1 receptors on the myocytes, increases contractility (inotropic effect), gives stronger but shorter contraction, increases stroke volume

Question 16

Effect of increasing contractility on starling graph

Answer 16

Whole graph moves up and becomes steeper

Question 17

Effect of parasympathetic nervous system on stroke volume

Answer 17

Little effect - vagus nerve does not innervate ventricular muscle

Question 18

Effect of hypercalcemia on stroke volume starling curve

Answer 18

Shifts curve up and left (steeper)

Question 19

Effect of hypocalcemia on stroke volume starling curve

Answer 19

Shifts curve down and right (less steep)

Question 20

Effect of ischaemia on stroke volume starling curve

Answer 20

Shifts curve down and right (less steep)

Question 21

How does the heart compensate for a reduced pumping ability

Answer 21

Works around a bigger EDV to achieve same stroke volume as normal

Question 22

Result of working around a bigger EDV

Answer 22

Lower ejection fraction and reduced exercise capacity

Question 23

Effect of barbiturates (anaesthetic drugs) on stroke volume starling curve

Answer 23

Shifts curve down and right (less steep)

Question 24

Cardiac output is determined by

Answer 24

Heart rate x stroke volume

Question 25

Why does increasing heart rate with an electronic pacemaker decrease stroke volume

Answer 25

Shortens cardiac interval which cuts into the rapid filling time, decreases EDV which decreases preload which decreases stroke volume

Question 26

Control of cardiac output

Answer 26

Heart rate increases
Contractility increases
Venous return increases - preload
Total peripheral resistance fall - afterload
Cardiac output increase 4-6 times

Question 27

Heart rate is increased via

Answer 27

Decreased vagal tone and increased sympathetic tone

Question 28

Contractility is increased via

Answer 28

Increased sympathetic tone

Question 29

Effect of increasing contractility

Answer 29

Alters inotropic state and shortens systole

Question 30

Venous return (preload) is increased via

Answer 30

Vasoconstriction and skeletal/respiratory pumps

Question 31

Total peripheral resistance (afterload) is decreased due to

Answer 31

Arteriolar dilation in muscle, skin and heart

Question 32

Control of cardiac input only works through

Answer 32

Integration - all processes working together to produce a co-ordinated increase in CO