Physiology 3 - The Cardiac Cycle Flashcards Preview

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Flashcards in Physiology 3 - The Cardiac Cycle Deck (58):
1

What are the events during the cardiac cycle?

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

2

What happens during passive filling?

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

3

What causes the flow of blood during passive filling?

A small pressure gradient.

4

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

80mmHgNo

5

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

About 80% full.

6

What happens during atrial contraction?

The atrias contract completing the end diastolic volume

7

What does the P wave in the ECG signal?

Atrial depolarisation

8

What happens between the P wave and the QRS complex?

Atrial contraction

9

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

approx .130ml

10

When does ventricular contraction start?

After the QRS complex

11

When do the AV valves shut?What does this produce

When ventricular pressure exceeds atrial pressureS1

12

Why is phase 3 called isovolumetric ventricular contraction?

The tension rises around a closed volume

13

When does the aortic/ pulmonary valves open?

When the ventricular pressure exceeds the aortic/ pulmonary pressure

14

What is ejected during ventricular ejection?

Stroke volume

15

SV=? (equation + values)

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

16

T wave represents?

Ventricular repolarisation

17

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

When the ventricular pressure falls below aortic/ pulmonary pressureS2

18

What signals the start of isovolumetric ventricular relaxation?

Closure of the aortic/ and pulmonary valves

19

Why is stage 5 called isovolumetric ventricular relaxation/

The tension falls around a closed box

20

When does the heart start a new cycle?

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

21

What does S1 signal?

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

22

What does S2 signal?

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

23

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

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

24

What is the SA node made of?

Specialised pacemaker cells

25

Sinus rhythm?

Heart is controlled by the SA node

26

How is an action potential generated?

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

Pacemaker potential?

Gradual drift of the membrane potential towards depolarisation

28

What is the ionic basis of the pacemaker potential?

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

29

What causes depolarisation of the SA node cells?

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

30

What is the ionic basis of repolarisation?

Activation of K channels results in K efflux

31

Passage of excitation through the heart path?

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

32

What does cell-to-cell conduction occur via?

Gap junctions

33

What are gap junctions part of?

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

34

Location of the AV node?

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

35

How fast is the AV bode conduction velocity?

Fast

36

Resting membrane potential of of contractile muscle cells?

-90mV

37

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?

Fast Na+ influx+30Phase 0

38

What causes phase 1 of ventricular muscle action potential?

Closure of Na+ channels and transient K+ efflux

39

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

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

40

What causes phase 3 of ventricular muscle action potential?

Closure of Ca channels and K efflux

41

What is phase 4?

Resting membrane potential

42

What is the main influence of heart rate/

Autonomic nervous system

43

What is the parasympathetic supply to the hear?

The vagus nerve

44

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

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

45

Where in the heart does the vagus supply?

The AV and SA nodes

46

What does the vagal nerve stimulation do?

Increases AV nodal delayDecreases heart rate

47

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?

acetlycholine acting through M2 receptorsAtropine

48

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

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

49

Where do cardiac sympathetic nerves supply

AV nodeSA node Myocardium

50

What effects does sympathetic stimulation of the heart have?

Increases heart rateDecreases AV nodal delayIncreases force of contraction

51

Neurotransmitter for sympathetic supply to heart

Noradrenaline acting through B1-adrenoceptors

52

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

Increases slopeIncreasesIncreasesPositive chronotropic effect

53

P wave?

Atrial depolarisation

54

QRS complex

Ventricular depolarisation

55

T wave

Ventricular repolarisation

56

PR interval

Largely AV nodal delay

57

ST segment

Ventricular systole

58

TP interbal

Diastole