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Cardiovascular > Physiology (Cardiovascular) > Flashcards

Physiology (Cardiovascular) Flashcards

1
Q

Where does excitation normally originate in the heart?

A

In the pacemaker cells in the sino-atrial node.

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2
Q

Where is the SA node located?

A

In the upper right atrium close to where the SVC enters.

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3
Q

What cells have spontaneous pacemaker potential?

A

Cells in the SA node.

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4
Q

What movement of ions causes the slow depolarisation in the spontaneous pacemaker potential?

A

Decrease in K+ efflux. Na+ and K+ influx (funny current). Transient Ca2+ influx (T-type Ca2+ channels).

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5
Q

Once the threshold is reached, what channel causes the rising phase of the action potential?

A

Long lasting L-type calcium channels, resulting in calcium influx.

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6
Q

What is the falling phase of the action potential caused by?

A

Inactivation of L-type Ca2+ channels and activation of K+ channels resulting in K+ efflux.

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7
Q

Describe the path of cardiac excitation.

A

SA node -> AV node -> bundle of His -> left and right bundle branches -> purkinje fibres in the ventricles

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8
Q

How does excitation spread from cell to cell?

A

Current flows through gap junctions.

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9
Q

Where is the AV node located?

A

At the base of the right atrium, just above the junction of atria and ventricles.

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10
Q

How are AV node cells specialised?

A

Small in diameter and slow conduction velocity.

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11
Q

Other than gap junctions, how can excitation spread from the SA to AV node?

A

There are some internodal pathways.

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12
Q

In cardiac myocytes, what movement of ions causes the rising phase of the action potential?

A

Na+ influx.

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13
Q

Describe the 5 phases of the action potential in cardiac myotcytes.

A

0 - fast Na+ influx. 1 - closure of Na+ channels and transient K+ efflux. 2 - Mainly Ca2+ influx. 3 - closure of Ca2+ channels and K+ efflux. 4 - resting membrane potential.

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14
Q

Describe the graph of action potential in cardiac myocytes at each phase.

A

0 - rapid upwards y movement. 1 - slight decline in y. 2 - plateau. 3 - rapid decrease in y. 4 - resting potential.

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15
Q

What ion movement is the plateau phase mainly caused by?

A

Influx of Ca2+ through L-type Ca2+ channels.

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16
Q

What is the influence of the parasympathetic nervous system on the heart rate at rest?

A

Vagus nerve exerts a continuous influence on SA node under resting conditions (vagal tone) which slows down the heart rate.

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17
Q

What is bradycardia and tachycardia defined as?

A

Bradycardia - <60bpm. Tachycardia - >100bpm.

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18
Q

What is the effect of vagal stimulation on the heart?

A

Slows heart rate and increases AV nodal delay.

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19
Q

What is the neurotransmitter involved in the parasympathetics of the heart and what receptor does it bind to?

A

ACh, M2 receptor.

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20
Q

What is the sympathetic receptor in the heart and what do the sympathetic nerves innervate?

A

B1. SA node, AV node and myocardium.

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21
Q

What effect does noradrenaline have on the heart?

A

Increases heart rate and decreases AV nodal delay.

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22
Q

What effect does the sympathetic and parasympathetic nervous system have on the slope of the pacemaker potential?

A

Sympathetic increases slope, parasympathetic decreases slope.

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23
Q

What does the PR interval, ST segment and TP interval represent?

A

PR - AV nodal delay. ST - ventricular systole. TP - diastole.

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24
Q

Are there neuromuscular junctions in the cardiac muscle?

A

No.

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25
Q

What are protein channels which form low resistance electrical communication pathways between neighbouring myocytes?

A

Gap junctions.

26
Q

What are the functions of the desmosomes in the intercalated discs?

A

They provide mechanical adhesion between adjacent cardiac cells which ensures that tension developed by one cells is transmitted to the next.

27
Q

Are myofibrils organelles or muscle cells?

A

Organelles.

28
Q

What is the functional unit of a muscle cell?

A

Sarcomeres.

29
Q

What needs to be present for an energised myosin head to bind to an actin filament?

A

Calcium.

30
Q

Is ATP required for contraction or relaxation?

A

Both.

31
Q

What are the regulatory proteins that block the myosin binding sites on actin?

A

Troponin and tropomyosin (troponin-tropomyosin complex).

32
Q

Which of these proteins does calcium bind to?

A

Troponin.

33
Q

Where is calcium mainly released from in the sarcoplasmic reticulum?

A

The lateral sacs.

34
Q

What does the long refractory period in cardiac myocytes prevent?

A

Generation of tetanic contraction.

35
Q

Why can a new action potential not be produced during the plateau phase?

A

The sodium channels are in the depolarised closed state i.e. not available for opening.

36
Q

Why can a new AP be produced during the descending phase?

A

The potassium channels are open and the membrane cannot be depolarised.

37
Q

What is the equation relating end diastolic volume, end systolic volume and stroke volume.

A

SV = EDV - ESV.

38
Q

What is involved in the intrinsic control of stroke volume?

A

Changes in the diastolic length of myocardial fibres.

39
Q

What is the diastolic length of myocardial fibres determined by?

A

The volume of blood within each ventricle at the end of diastole.

40
Q

What is the end diastolic volume (EDV, preload) determined by?

A

Venous return to the heart.

41
Q

What is the Frank-Starling mechanism (Starling’s law of the heart)?

A

The more the ventricle is filled with blood during diastole (EDV), the greater the volume of ejected blood will be during the resulting systolic contraction (SV).

42
Q

What other effect does stretch have inside cardiac myocytes?

A

The affinity of troponin for calcium.

43
Q

What is the difference between optimal length of muscle fibres in skeletal and cardiac muscle?

A

Skeletal: optimum length is resting muscle length, stretching the muscle will make it worse. Cardiac: more stretch = more force.

44
Q

Does Starling’s law apply to the left ventricle and how?

A

Yes, more blood in right atrium leads to more blood eventually reaching left ventricle so increases SV into aorta.

45
Q

What is the heart’s response to increased afterload in the short term and then long term?

A

Short term: Heart can’t eject full SV so EDV increases so force of contraction increases. Long term: ventricular hypertrophy.

46
Q

What effect does stimulating sympathetic nerves have on force of contraction?

A

It increases force of contraction (positive inotropic effect).

47
Q

How does sympathetic stimulation decrease the rate of systole and diastole?

A

Rate of pressure change during systole increases which reduces duration of systole. Rate of ventricular relaxation increases (increased rate of calcium pumping) so reduced duration of diastole.

48
Q

Does the parasympathetic nervous system have any effect on SV?

A

No.

49
Q

What hormones have a positive inotropic and chronotropic effect and how do these effects compare with the nervous system?

A

Adrenaline and noradrenaline released from adrenal medulla. Minor effects compared to sympathetic stimulation.

50
Q

Are the pressures in the right heart similar to the left heart?

A

They have similar patterns but right pressure is much lower.

51
Q

What are the 5 events of the cardiac cycle?

A
  1. Passive filling. 2. Atrial contraction. 3. Isovolumetric ventricular contraction. 4. Ventricular ejection. 5. Isovolumetric ventricular relaxation.
52
Q

What valves open at the starts of passive filling?

A

AV valves.

53
Q

How full do the ventricles become by passive filling?

A

Around 80% full.

54
Q

What is the end diastolic pressure of the atria (after atrial contraction)?

A

A few mmHg.

55
Q

At what part of the ECG does the atria contract?

A

Between the p-wave and the QRS.

56
Q

When will the AV valve close?

A

When the pressure in the ventricle is greater than the atria.

57
Q

Does any blood enter or leave the ventricle during isovolumetric ventricular contraction?

A

No.

58
Q

Describe the ventricular pressure change during isovolumetric ventricular contraction.

A

Rises very steeply.

59
Q

When will the aortic/pulmonary valves open?

A

When the ventricular pressure exceeds the aortic/pulmonary pressure.

60
Q

What produces the dicrotic notch in the aortic pressure curve?

A

The aortic valve vibration.

61
Q

What are the auscultation areas of the heart valves?

A

Aortic: 2nd intercostal space on right of sternum. Pulmonary: 2nd intercostal space on left of sternum. Tricuspid: 4th intercostal space on left of sternum. Mitral: 5th intercostal space mid-clavicular line.

Cardiovascular (32 decks)

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