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1st Year - Cardiology > Physiology 3 - The Cardiac Cycle > Flashcards

Physiology 3 - The Cardiac Cycle Flashcards

1
Q

What are the events during the cardiac cycle?

A
  1. Passive Filling2. Atrial Contraction3. Isovolumetric ventricular Contraction4. Ventricular Ejection5. Isovolumetric ventricular relaxation
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2
Q

What happens during passive filling?

A

The pressure in the atria and ventricles is close to 0.AV valves open so that venous return flows into the ventricles.

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3
Q

What causes the flow of blood during passive filling?

A

A small pressure gradient.

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4
Q

What is the pressure in the aorta during passive filling?Is the aortic valve open?

A

80mmHgNo

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5
Q

How full, roughly, do the ventricles become during passive filling?

A

About 80% full.

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6
Q

What happens during atrial contraction?

A

The atrias contract completing the end diastolic volume

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7
Q

What does the P wave in the ECG signal?

A

Atrial depolarisation

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8
Q

What happens between the P wave and the QRS complex?

A

Atrial contraction

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9
Q

What is the end diastolic volume in a resting normal adult?

A

approx .130ml

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10
Q

When does ventricular contraction start?

A

After the QRS complex

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11
Q

When do the AV valves shut?What does this produce

A

When ventricular pressure exceeds atrial pressureS1

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12
Q

Why is phase 3 called isovolumetric ventricular contraction?

A

The tension rises around a closed volume

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13
Q

When does the aortic/ pulmonary valves open?

A

When the ventricular pressure exceeds the aortic/ pulmonary pressure

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14
Q

What is ejected during ventricular ejection?

A

Stroke volume

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15
Q

SV=? (equation + values)

A

SV = EDV - ESV = 135 - 65 = 70ml

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16
Q

T wave represents?

A

Ventricular repolarisation

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17
Q

When does the aortic/ pulmonary valves shut?What does the produce?

A

When the ventricular pressure falls below aortic/ pulmonary pressureS2

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18
Q

What signals the start of isovolumetric ventricular relaxation?

A

Closure of the aortic/ and pulmonary valves

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19
Q

Why is stage 5 called isovolumetric ventricular relaxation/

A

The tension falls around a closed box

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20
Q

When does the heart start a new cycle?

A

When the ventricular pressure falls below atrial pressure causing the AV valve to open

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21
Q

What does S1 signal?

A

The start of systole (closure of mitral and tricuspid valves)

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22
Q

What does S2 signal?

A

The end of systole and beginning of diastole (closure of aortic and pulmonary valves)

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23
Q

What is the JVP an indirect measure of?How does this work?

A

The pressure in the right atriumThe jugular vein becomes the SVC which connects to the right atrium meaning any changes in the RA will be reflected in the JVP

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24
Q

What is the SA node made of?

A

Specialised pacemaker cells

25
Q

Sinus rhythm?

A

Heart is controlled by the SA node

26
Q

How is an action potential generated?

A

Cells in the SA node exhibit spontaneous pacemaker potential meaning the membrane potential gradually drifts until it reaches threshold which causes the cell to fire

27
Q

Pacemaker potential?

A

Gradual drift of the membrane potential towards depolarisation

28
Q

What is the ionic basis of the pacemaker potential?

A

There is a decrease in K efflux whilst there is slow Na influx

29
Q

What causes depolarisation of the SA node cells?

A

At threshold, activation of voltage-gated Ca channels occur resulting in Ca influx

30
Q

What is the ionic basis of repolarisation?

A

Activation of K channels results in K efflux

31
Q

Passage of excitation through the heart path?

A

SA node -> cell-to-cell conduction -> AV node -> bundle of his -> left and right branches -> purkinje fibres

32
Q

What does cell-to-cell conduction occur via?

A

Gap junctions

33
Q

What are gap junctions part of?

A

Intercalated disc which are specialised intracellular attachment between cardiac muscle cells - they are made up of gap junctions, ask adherents and desmosomes

34
Q

Location of the AV node?

A

Base of the right atria just above the junction of the atria and ventricles

35
Q

How fast is the AV bode conduction velocity?

A

Fast

36
Q

Resting membrane potential of of contractile muscle cells?

A

-90mV

37
Q

What causes the rising phase (depolarisation) of the action potential in contractile muscle cells?What does this reverse the membrane potential to?What phase is this?

A

Fast Na+ influx+30Phase 0

38
Q

What causes phase 1 of ventricular muscle action potential?

A

Closure of Na+ channels and transient K+ efflux

39
Q

What causes phase 2 of ventricular muscle action potential?what is another name for this phase?

A

Mainly the influx of Ca through voltage-gated Ca channelsPlateau phase

40
Q

What causes phase 3 of ventricular muscle action potential?

A

Closure of Ca channels and K efflux

41
Q

What is phase 4?

A

Resting membrane potential

42
Q

What is the main influence of heart rate/

A

Autonomic nervous system

43
Q

What is the parasympathetic supply to the hear?

A

The vagus nerve

44
Q

What type of nerve supply to the SA node dominates under resting conditions

A

The vagal tone - slows the intrinsic heart rate from approx. 100 to 70bpm

45
Q

Where in the heart does the vagus supply?

A

The AV and SA nodes

46
Q

What does the vagal nerve stimulation do?

A

Increases AV nodal delayDecreases heart rate

47
Q

What neurotransmitter does the vagus nerve use to slow the heart?What is a competitive inhibitor of this and can be therefore used to treat extreme bradycardia?

A

acetlycholine acting through M2 receptorsAtropine

48
Q

How does vagal stimulation affect the pacemaker potential?What happens to the slope of the pacemaker potential?What is the name for this effect

A

The cell hyper polarises meaning it takes longer to reach threshold, frequency of AP decreases Slope decreasesNegative chronotropic effect

49
Q

Where do cardiac sympathetic nerves supply

A

AV nodeSA node Myocardium

50
Q

What effects does sympathetic stimulation of the heart have?

A

Increases heart rateDecreases AV nodal delayIncreases force of contraction

51
Q

Neurotransmitter for sympathetic supply to heart

A

Noradrenaline acting through B1-adrenoceptors

52
Q

What effect does noradrenaline have on the slope of the pacemaker potential?
Speed at which pacemaker potential reaches threshold?Frequency of action potentials?
Effect?

A

Increases slopeIncreasesIncreasesPositive chronotropic effect

53
Q

P wave?

A

Atrial depolarisation

54
Q

QRS complex

A

Ventricular depolarisation

55
Q

T wave

A

Ventricular repolarisation

56
Q

PR interval

A

Largely AV nodal delay

57
Q

ST segment

A

Ventricular systole

58
Q

TP interbal

A

Diastole

1st Year - Cardiology (25 decks)

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