Regulation of Stroke Volume and Heart Rate

Question 1

What is heart rate regulated by?

Answer 1

Autonomic nervous system

Question 2

What are the 2 components of the autonomic nervous system?

Answer 2

Sympathetic

Parasympathetic

Question 3

What does the sympathetic nervous system release?

Answer 3

Noradrenaline

Circulating adrenaline from adrenal medulla

Question 4

What does noradrenaline and circulating adrenaline act on?

Answer 4

B₁ receptors on sinoatrial node

Question 5

What impact does the sympathetic nervous system have on the SA node?

Answer 5

Increase slope of the pacemaker potential

Increases heart rate (tachycardia)

Question 6

What is tachycardia?

Answer 6

Increased heart rate

Question 7

What is increased heart rate called?

Answer 7

Tachycardia

Question 8

What does the parasympathetic system release?

Answer 8

Acetylcholine

Question 9

What nerve from the parasympathetic system acts on the heart?

Answer 9

Vagus

Question 10

What does the parasympathetic system act on?

Answer 10

Muscurinic receptors on sinoatrial node

Question 11

What effect does the parasympathetic system have on the sinoatrial node?

Answer 11

Hyperpolarises cells and decreases slope of pacemaker potential

Decreases heart rate (bradycardia)

Question 12

What is bradycardia?

Answer 12

Decreased heart rate

Question 13

What is decreased heart rate called?

Answer 13

Bradycardia

Question 14

What is regulation of stroke volume done by?

Answer 14

Preload

Afterload

Neural

Pathological

Question 15

What does Starling’s Law state?

Answer 15

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

Question 16

How does tension of cardic muscle fibres change with length (preload)?

Answer 16

Tension increases until it reaches a maximum then it decreases as the length increases

Question 17

What is the relationship between tension and length (preload) due to?

Answer 17

Overlap of myosin in the muscle, impacting the amount of cross bridges that can be made

Question 18

What is the curve of tension against length (preload) essentially the same as?

Answer 18

End diastolic volume against stroke volume

Question 19

What impact does increases venous return have on EDV and stroke volume?

Answer 19

Increases EDV and so increases stroke volume

Question 20

What effect does decreasing venous return have on EDV and stroke volume?

Answer 20

Decreases EDV and so decreases stroke volume

Question 21

What does the relationship between EDV and stroke volume ensure?

Answer 21

Self regulation so the stroke volume of the left and right ventricles are the same

Question 22

What is afterload?

Answer 22

The load against which a muscle tries to contract

Question 23

What is the aortic pressure impacted by?

Answer 23

Total peripheral resistance (TPR)

Question 24

What happens to aortic pressure if total peripheral resistance increases?

Answer 24

Aortic pressure increases

Question 25

What happens to stroke volume if total peripheral resistance increases?

Answer 25

Ventricles need to work harder to push open the AV vale and so it will have less energy left to eject blood, so stroke volume will decrease

Question 26

What is afterload set by?

Answer 26

Arterial pressure against which blood is expelled, which in turn depends on the total peripheral resistance

Question 27

What affects preload?

Answer 27

Venules/veins Capacitance vessels

Question 28

What affects afterload?

Answer 28

Arterioles Resistance vessels

Question 29

What does the sympathetic system act on to impact stroke volume?

Answer 29

B₁ receptors on the myocytes

Question 30

What does the sympathetic system acting on B₁ receptors of myocytes cause?

Answer 30

Increases contractibility (inotropic effect) Gives stronger, but shorter contractions

Question 31

What impact does the parasympathetic system have on stroke volume?

Answer 31

Little effect Due to vagus nerve not innervating the ventricular muscle

Question 32

What is preload?

Answer 32

How full the ventricle is before it starts contracting (EDV)

Question 33

What is afterload?

Answer 33

How difficult it is for the heart to pump out the blood (the TPR)

Question 34

What does TPR stand up for?

Answer 34

Total peripheral resistance

Question 35

What are examples of pathological impacts on stroke volume?

Answer 35

Hypercalcemia Hypocalcemia Ischaemia Barbiturates

Question 36

How does hypercalcemia impact the stroke volume/EDV curve?

Answer 36

Shifts it up and left

Question 37

How does hypocalcemia impact the stroke volume/EDV curve?

Answer 37

Shifts it down and right

Question 38

How does ischaemia impact the stroke volume/EDV curve?

Answer 38

Shifts it down and right

Question 39

How does barbiturates impact the stroke volume/EDV curve?

Answer 39

Shifts it down and right

Question 40

What is ischaemia?

Answer 40

Restriction in blood supply to tissues

Question 41

What is restriction in blood supply to tissues called?

Answer 41

Ischaemia

Question 42

What are barbiturates?

Answer 42

Drug that acts on the CNS as a depressant

Question 43

How does the heart compensate for a reduced pumping ability?

Answer 43

By working around a bigger EDV, resulting in a lower ejection fractiona and reduced exercise capacity

Question 44

What does the heart working around a larger EDV result in?

Answer 44

Lower ejection fraction Reduced exercise capacity

Question 45

What formula describes cardiac output?

Answer 45

Cardiac output = heart rate x stroke volume

Question 46

How does increasing heart rate with an electronic pacemaker impact cardiac output and stroke volume?

Answer 46

Small increase in cardiac output But stroke volume decreases (because shortened cardiac interval cus into the rapid filling phase, reduced EDV reduces preload, in turn reduces stroke volume)

Question 47

Why does increasing heart rate with an electronic pacemaker cause a decrease in stroke volume?

Answer 47

Shortened cardiac interval cuts into rapid filling phase Reduces EDV which reduces preloa This reduces stroke volume by Starling's law

Question 48

What are some things that accompany physiological increases in heart rate to offset the effect of decreased stroke volume?

Answer 48

Heart rate increases (decreased vagal tone and increases sympathetic tone) Contractility increases (increases sympathetic tone, shortens systole) Venous return increases (via vasoconstriction, maintains preload) Total peripheral resistance falls (via arteriolar dilation in muscle, skin and heart reducing afterload) Cardiac output increases 4-6 times