Regulation of Stroke Volume and Heart Rate Flashcards

1
Q

What is the control mechanism of heart rate?

A

Neural

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2
Q

What is the regulation mechanism for stroke volume?

A

Preload

Afterload

Neural

Pathological

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3
Q

How does the sympathetic nervous system regulate heart rate?

A

Releases noradrenaline from nerves and adrenal medulla.

Act on Beta 1 receptors on sinoatrial node

Increases slope of pace maker potential between heart beats

Increases heart rate

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4
Q

What is the effect of the parasympathetic nervous system on heart rate?

A

Vagus nerve releases acetycholine

Acts on muscarinic receptors on sinoatrial node

Hyperpolarises cells and decreases the slope of pacemaker potential

Decreases heart rate = bradycardia

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5
Q

What does starlings law state?

A

Starling’s Law states -
Energy of contraction is proportional to initial length of cardiac muscle fibre

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6
Q

Why is the slope decreasing to the left side of the peak tension?

A

Actin filaments start to interfere with each other

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7
Q

What is the length of the cardiac muscle fibres proportional to?

A

End diastolic volume

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8
Q

What is the stroke volume related to?

A

Tension

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9
Q

What is preload affected by?

A

End diastolic volume

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10
Q

What ensures self regulation of stroke volume of left and right ventricles?

A

Proportional relationship between volume of venous return & stroke volume

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11
Q

What is the afterload?

A

The load against which muscle tries to contract

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12
Q

What is the aortic pressure affected by?

A

How much blood is pushed into aorta (cardia output)
How easy it is for blood to get out of aorta (total peripheral resistance)

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13
Q

Why does an increase in TPR result in a reduction in stroke volume?

TPR- Total Peripheral Resistance

A

Aortic pressure will increase,
Ventricle will have to work harder to push open the aortic valve
It will have less energy left to do useful bit of ejecting blood.

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14
Q

What is responsible for the variable portion of the total peripheral resistance?

A

The arterioles

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15
Q

What is the total peripheral resistance set by?

A

The arterial pressure - what sets the afterload

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16
Q

What affects preload?

A

Venules/veins and capacitance vessels

These all affect the venous return

17
Q

What affects afterload?

A

Arterioles and resistance vessels

18
Q

What does a bigger end diastolic volume mean?

A

Bigger pre-load and therefore more tension and more strength of contraction

19
Q

neural

How does the sympathetic nervous system affect stroke volume?

A

Noradrenaline from nerves & adrenal medulla act on beta 1 receptors of myocytes
Increases contractility - stronger but shorter contraction

20
Q

What does ionotropic refer to?

A

strength of contraction

21
Q

What is the effect of the parasympathetic nervous system on the contractility of the heart?

A

Little effect - vagus nerve does not innervate the ventricular muscle

22
Q

How does the heart compensate for a reduced pumping ability?

A

Works around a bigger end diastolic volume - lower ejection fraction and reduced excersize capacity.

23
Q

What is the effect of barbituates on stroke volume?

A

–shifts curve down and right

24
Q

Why does stroke volume decrease with an increased heart rate?

A

Shortened cardiac cycle cuts into rapid filling stage - smaller EDV (small length of muscle), less tension and therefore less stroke volume

25
Q

What are the combined mechanisms that increase heart rate?

A

Via decreased vagal tone and increased sympathetic tone

26
Q

What shortens systole?

A

Effect of increased sympathetic tone on the contractility - alters ionotropic state

27
Q

How does venous return increase?

A

Via venoconstriction

And skeletal / respiratory pumps

Maintains preload when we expect it to fall with a reduced EDV brought on with a fast heart rate

28
Q

Why does total peripheral resistance fall with a fast heart rate?

A

Arteriolar dilation in muscle, skin & heart

Reduced afterload - makes it easier for heart to pump out blood

29
Q

What are the 4 ways CO increases when workload increases?

A

HR increases

Contractility increases

Venous return increases

Total peripheral resistance falls

30
Q

Summary of regulation of stroke volume

A