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Physiology 1 > Cardiac output control > Flashcards

Cardiac output control Flashcards

1
Q

What is cardiac output? [1 mark]

A

The amount of blood ejected from the heart per minute.

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2
Q

What is heart rate? [1 mark]

A

How often the heart beats per minute.

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3
Q

What is stroke volume? [1 mark]

A

How much blood (ml) is ejected per beat.

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4
Q

What is the formula for cardiac output? [3 marks]

A

Cardiac output = heart rate × stroke volume

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5
Q

What is the formula for blood pressure? [3 marks]

A

Blood pressure = cardiac output × total peripheral resistance

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6
Q

What can control heart rate & contractility? [2 marks]

A
  • SA node

- Autonomic control

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7
Q

What can control the strength of contraction? [2 marks]

A
  • Sympathetic nerves

- Adrenaline causing an increase in intracellular calcium

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8
Q

What happens in preload and what does it act in accordance to? [3 marks]

A
  • Stretching of heart at rest
  • Increase of stroke volume
  • Acts according to Starling’s law
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9
Q

What happens in afterload and what does it act in accordance to? [3 marks]

A
  • Opposing ejection
  • Reduces stroke volume
  • Acts according to Laplace’s law
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10
Q

What is the energy of contraction? [1 mark]

A

The amount of work required to generate stroke volume

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11
Q

Where does stroke volume come from? [2 marks]

A
  • Contracts until ventricle pressure > aortic pressure (isovolumetric contraction)
  • Ejection from ventricles
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12
Q

What does Starling’s law state? [2 marks]

A

The energy of contraction of cardiac muscle is relative to the muscle fibre length at rest

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13
Q

What happens if you stretch the heart further? [2 marks]

A
  • There is a higher energy of contraction

- A greater stroke volume is achieved in systole

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14
Q

What is the formula for stroke volume? [3 marks]

A

Stroke volume = end diastolic volume - end systolic volume

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15
Q

What happens when the heart is overstretched? [1 mark]

A

The stroke volume is decreased

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16
Q

What is the molecular basis for Starling’s law? [4 marks]

A
  • In unstretched fibre, actin and myosin overlap and so there’s more mechanical interference
  • Less cross bridges are available for contraction
  • In stretched fibres, there’s less overlapping
  • More cross bridges are available and more sensitivity to calcium
17
Q

What happens in orthostasis (standing for a long time)? [3 marks]

A
  • Myocardium isn’t stretched as much
  • Less blood reaches the brain
  • This can leads to dizziness
18
Q

What is afterload determined by? [1 mark]

A

Wall stress directed through the heart wall

19
Q

What is needed to overcome wall stress? [1 mark]

A

More energy of contraction

20
Q

What does overcoming wall stress do? [2 marks]

A

Produces cell shortening and ejection

21
Q

What is the formula for wall tension (T) [4 marks]

A

Wall stress (T) = (Pressure x radius in a ventricle) / 2

22
Q

Why is (pressure x radius) divided by 2? [1 mark]

A

The chamber has 2 directions of curvature

23
Q

What increases afterload? [2 marks]

A

Increased pressure & radius

24
Q

What decreased afterload and stress? [1 mark]

A

Increased wall thickness

25
Q

What happens to afterload in a ventricle with a small radius? [4 marks]

A
  • Greater wall curvature
  • More wall stress directed towards centre of chamber
  • Less afterload
  • Better ejection
26
Q

What happens to afterload in a ventricle with a large radius? [4 marks]

A
  • Less wall curvature
  • More wall stress directed through heart wall
  • More afterload
  • Less ejection
27
Q

Which law overcomes the other in a healthy heart? [1 marks]

A

Starling’s Law > Laplace’s Law

28
Q

What is an inotrope? [3 marks]

A
  • An agent that alters the force or energy of muscular contractions
  • Negative = weakens force of contraction
  • Positive = strengthens force of contraction
29
Q

What is the Anrep effect? [1 mark]

A

A sudden increase in afterload on the heart causes an increase in ventricular inotropy

30
Q

Why does volume overload occur in heart failure? [2 marks]

A
  • Weaker ejection

- Heart doesn’t fully empty before refilling again

31
Q

What is the benefit of ventricular hypertrophy? [2 marks]

A
  • Decreases wall stress

- Maintains stroke volume and cardiac output

32
Q

What is the disadvantage of ventricular hypertrophy? [2 marks]

A
  • Requires more energy

- Amount of energy needed will increase

33
Q

What does an increased venous return lead to? [2 marks]

A
  • An increase in end diastolic volume

- Increased preload and more stretch

34
Q

What happens in Laplace’s law in terms of pressure and volume? [4 marks]

A
  • Longer time spent in isovolumetric contraction
  • To increase ventricular pressure
  • Uses more energy
  • Lowers force of contraction (reducing SV)

Physiology 1 (13 decks)

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