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Systems: Cardiovascualar AB > Regulation of Stroke Volume and Heart Rate > Flashcards

Regulation of Stroke Volume and Heart Rate Flashcards

1
Q

How is heart rate regulated?

A

Neural

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2
Q

How is stroke volume regulated?

A
  • Preload
  • Afterload
  • Neural
  • Pathological
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3
Q

How does the sympathetic nervous system cause tachycardia?

A
  • Sympathetic nerves release noradrenaline
  • Plus circulating adrenaline from adrenal medulla
  • Both act on B1 receptors on sinoatrial node
  • Increases slope of the pacemaker potential
  • Increases heart rate
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4
Q

How does the parasympathetic nervous system cause bradycardia?

A
  • Vagus releases acetylcholine
  • Acts on muscarinic receptors on the sinoatrial node
  • Hyperpolarises cells and decreases slope of pacemaker potential
  • Decreases heart rate
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5
Q

What does Starling’s law state?

A

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

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6
Q

How does tension vary with preload?

A
  • If the muscle is stretched above optimum there there will be a slight decrease in tension as less cross bridges formed
  • If the muscle is not stretched then the actin filaments will start to interfere with each other and there will not be as many successful cross bridges formed so less tension
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7
Q

In vivo, what is preload affected by?

A

End diastolic volume

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8
Q

How does increased venous return lead to increased stroke volume?

A

Increased EDV

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9
Q

How does decreased venous return lead to decreased stroke volume?

A

Decreased EDV

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10
Q

How is self-regulation of stroke volume maintained?

A

Stroke volumes of the left and right ventricles are matched

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11
Q

What is afterload?

A

The load against which the muscle tries to contract

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12
Q

What is aortic pressure affected by?

A
  • How much blood is pushed into the aorta (CO)

- How easy it is for that blood to get out of the aorta (TPR)

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13
Q

Why does SV decrease if TPR increases? Use aorta as an example

A
  • TPR increases
  • Aortic pressure increases
  • The ventricle will have to work harder to push open the aortic valve
  • It will have less energy left to do the useful bit of ejecting blood
  • SV will decrease
  • More energy is wasted building up pressure to open the aortic valve
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14
Q

What will happen to afterload if the arterioles are constricted?

A

Increase

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15
Q

What will happen to afterload if the arterioles are dilated?

A

Decrease

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16
Q

In vivo, what is afterload dependent on?

A
  • Arterial pressure against which the blood is expelled

- This is dependent on TPR

17
Q

What vessels affect preload?

A

Venules/veins= the capacitance vessels

18
Q

What vessels affect afterload?

A

Arterioles= resistance vessels

19
Q

How does the sympathetic nervous system increase strength of contraction?

A
  • Sympathetic nerves release noradrenaline
  • Plus circulating adrenaline from adrenal medulla
  • Both act on B1 receptors on the myocytes
  • Increases contractility
  • Gives stronger but shorter contractions
20
Q

What effect does the parasympathetic system have on strength of contraction?

A
  • Little effect

- Probably because the vagus does not innervate the ventricular muscle

21
Q

How does hypercalcaemia effect the SV against EDV curve?

A

Shifts curve up and left

22
Q

How does hypocalcaemia effect the SV against EDV curve?

A

Shifts curve down and right

23
Q

How does ischaemia effect the SV against EDV curve?

A

Shifts curve down and right

24
Q

How does the heart compensate for reduced pumping ability?

A
  • It works around a bigger EDV.

- This results in lower ejection fraction and reduced exercise capacity

25
Q

How do barbiturates effect the SV against EDV curve?

A

Shifts down and right

26
Q

What is CO equal to?

A

HR x SV

27
Q

Why does increasing HR with an electronic pacemaker cause a small increase in CO but SV decreases?

A
  • Shortened cardiac interval cuts into rapid filling phase
  • Reduced end diastolic volume reduces preload
  • Reduces stroke volume
28
Q

Physiological increases in HR are accompanied by what to offset the effects of Starling’s Law?

A
  • Heart rate increases
  • Contractility increases
  • Venous return increases
  • TPR falls
  • CO in
29
Q

What 2 things contribute to an increase in HR?

A
  • Decreased vagal tone

- Increased sympathetic tone

30
Q

How does contractility increase and what is the result?

A
  • Via increased sympathetic tone

- Alters inotropic state and shortens systole

31
Q

What 3 factors contribute to an increase in venous return?

A
  • Vasoconstriction
  • Skeletal/ respiratory pump
  • Maintenance of preload
32
Q

What causes TPR tod fall and what is the result?

A
  • Due to arteriolar dilatation in muscle, skin and heart

- Reduces afterload

Systems: Cardiovascualar AB (42 decks)

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