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BDS1 BAMS: Cardiovascular System > The Cardiac Cycle > Flashcards

The Cardiac Cycle Flashcards

1
Q

What is the cardiovascular system formed of?

A

The heart, blood vessels and blood

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2
Q

Why is the cardiovascular system described as a closed loop?

A

Blood is pumped out of the heart by arteries and returned to the heart by veins

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3
Q

What are the functions of the cardiovascular system?

A
  • Transport of oxygen and nutrients to meet the metabolic demands of the body
  • Transport of metabolic waste products (e.g. CO2) for excretion
  • Transport of hormones
  • Maintains constant body temperature and transfers heat
  • Aids response to infection and injury
  • Assists regulation of fluid and pH in the body
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4
Q

What are the individual cells of the heart called?

A

Cardiomyoytes

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5
Q

What type of muscle tissue is the myocardium?

A

Specialised striated muscle tissue

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6
Q

What does the structure of the myocardium allow?

A

Co-ordinated pumping actions so that the metabolic demands of the tissue organs can be met

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7
Q

How are cardiomyocytes connected to one another?

A

Gap junctions, intercalated discs and desmosomes

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8
Q

Which ventricle has a thicker wall?

A

Left ventricle - responsible for pumping blood through systemic circulation. Needs to overcome aortic resistance so blood can enter systemic circulation

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9
Q

Which ventricle has a larger stroke volume?

A

Generally both ventricles pump the same volume of blood - same stroke volume

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10
Q

What are the 2 AV valves called?

A 
Tricuspid valve (right AV valve) 
Bicuspid/mitral valve (left AV valve)
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11
Q

What are the 2 semilunar valves?

A

Pulmonary valve

Aortic valve

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12
Q

What does the pulmonary valve permit?

A

Permits blood to flow from right ventricle and pulmonary artery

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13
Q

What does the aortic valve permit?

A

Permits blood flow from left ventricle to the aorta

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14
Q

What causes the heart valves to open?

A

Pressure differences across the valves (opening and closing of heart valves is a passive process)

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15
Q

What happens to the AV valves when pressure in the atrium is greater than pressure in the corresponding ventricle?

A

Valve is forced open and blood flows from atrium into ventricle

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16
Q

What happens when the contracting ventricle achieves an internal pressure that is greater than the corresponding atrium?

A

The AV valve is forced closed

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17
Q

What happens during systole (ventricular contraction)?

A

Blood flows from ventricles into aorta (left) and pulmonary artery (right)

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18
Q

What do the semilunar valves prevent?

A

They prevent the back flow of blood from the atria into the ventricles during ventricular relaxation

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19
Q

What are the AV valves fastened to?

A

Papillary muscles

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20
Q

What are papillary muscles?

A

Muscular projections of the ventricular wall

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21
Q

What connects papillary muscles to valve cusps?

A

Chordae tendinae

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22
Q

What is the function of papillary muscles?

A

Prevent the back flow of blood by limiting the valve’s movements

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23
Q

What do the “lub” and “dub” sounds correspond to?

A 
"lub" = closure of the AV valves
"dub" = closure of the semilunar valves
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24
Q

When may an additional heart sound (other than the “lub” “dub” sounds) be heard?

A

Due to oscillation of blood flow into ventricle or various disease states e.g. heart valve defect

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25
Q

What is valve regurgitation?

A

Blood leaks back into chambers, occurs by a valve not closing tightly

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26
Q

What is valve stenosis?

A

Thickening/stiffening of valve cusps

Prevents heart valve from opening fully; not enough blood can flow through

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27
Q

What is the end diastolic volume?

A

The volume of blood in the ventricle prior to contraction

28
Q

What is the end systolic volume?

A

The volume of blood in the ventricle after each ejection

Ventricles not completely emptied during systole

29
Q

How do you calculate the stroke volume?

A

End diastolic volume - end systolic volume = stroke volume

EDV - ESV = Stroke volume

30
Q

What is the stroke volume (SV)?

A

Volume of blood ejected per heart beat

31
Q

What is heart rate (HR) determined by?

A

HR is determined by the rate which the cardiac pacemaker (sino-atrial node) fires action potentials

32
Q

Which range do “normal” resting heart rate values lie within?

A

60-100 bpm

33
Q

What determines the rate of action potential firing by the sino-atrial node?

A

Activity of the autonomic nervous system

34
Q

What do sympathetic nerves release (principally)?

A

Noradrenaline

35
Q

Which receptor does noradrenaline bind to on SA node?

A

Beta-1-adrenoceptors

36
Q

What happens when noradrenaline binds to beta-1-adrenoceptors on the SA node?

A

Activation of a G-protein and production of cyclic AMP

Increases heart rate - positive chronotrophy

37
Q

What do parasympathetic nerves release (principally)?

A

Acetylcholine (ACh)

38
Q

Which receptor does Ach bind to on the SA node?

A

M2 muscarinic receptors on SA node

39
Q

What happens when acetylcholine binds to M2 muscarinic receptors on the SA node?

A

Activates inhibitory G protein, blocking cAMP pathway and allows K+ efflux from cell
Decreases heart rate - negative chronotrophy

40
Q

Which type of adrenoceptor does the heart primarily contain on nodal tissues, the cardiac conduction system and the myocardium?

A

Beta-1

41
Q

Which hormones bind to the beta-1 adrenoceptor?

A

Noradrenaline

Adrenaline

42
Q

Activation of the beta-1 adrenoceptor results in…

A
  • Positive inotrophy (increases strength of myocardial contraction)
  • Positive chromotrophy (increases heart rate)
  • Positive lusitrophy (increases rate of myocardial relaxation)
  • Positive dromotrophy (increases conduction speed in AV node)
43
Q

What is positive inotrophy?

A

Increased strength of myocardial contraction

44
Q

What is positive chronotrophy?

A

Increased heart rate

45
Q

What is positive lusitrophy?

A

Increased rate of myocardial relaxation

46
Q

What is positive dromotrophy?

A

Increased conduction speed in AV node

47
Q

Describe the spread of depolarisation throughout the heart

A
  • Depolarisation spreads from the SA node through myocytes of right atrium and left atrium
  • Spread of depolarisation through right atrium to AV node
  • AP propagates from AV node along interventricular septum via the Bundle of His
  • Bundle of His separates into left and right bundle branches which innervate the walls of the myocardium
  • Rapid propagation of AP along purkinje fibres initiates coordinated contraction of the cardiac myocytes of the left and right ventricles
48
Q

Why is propagation of the AP through the AV node relatively slow compared to propagation from the SA node?

A

To allow for completion of atrial contraction prior to initiation of ventricular excitation and contraction

49
Q

What is the SA node?

A

The autonomic pacemaker of the heart

50
Q

How is the SA node action potential initiated?

A

Due to influx and efflux of ions across the membrane

51
Q

Describe the movement of ions during the SA action potential

A
  • Na+ slowly enters cell through leaky Na+ channels
  • AP is fired once threshold is reached
  • Voltage-gated Ca2+ channels open - Ca2+ enters cell
  • Voltage-gated K+ channels open - K+ leave the cells. Ca2+ channels close. Depolarisation occurs.
  • Voltage-gated K+ channels close
52
Q

How is ventricular systole initiated by the movement of ions into myocytes?

A

Opening of Na+ channels -> influx of Na+ causes rapid depolarisation of cardiac muscle cells and this initiates systole

53
Q

What does excitation-contraction coupling refer to?

A

Couples the electric excitation brought by the action potential to the mechanical contraction of the cardiac myocytes

54
Q

Describe the cardiomyocyte contractile cycle

A
  1. Calcium binds to troponin C, leading to a conformational change that displaces tropomyosin from the actin binding sites
  2. Cross-bridge formation occurs with ATP hydrolyzation into ADP and Pi.
  3. Power stroke moves actin filament toward the centre of the sarcomere. ADP and Pi are released from the myosin heads
  4. Actin released with ATP binding to myosin. Myosin heads cocked back into firing position, ready to make cross bridges further downstream.
55
Q

What is an ECG?

A

Electrocardiogram

  • Measures electrical activity of the heart
  • Detects phasic changes in potential difference between 2 electrodes
56
Q

What is an ECG useful for?

A

Checks how heart is fucntioning

Useful in diagnosis of arrhythmias, post myocardial infarction damage etc.

57
Q

Describe the PQRST wave

A 
P wave = atrial depolarisation 
QRS complex = ventricular depolarisation
T wave = ventricular repolarisation 
P-R interval = delay through AV node 
S-T interval = plateau phase of ventricular action potential
58
Q

What is long QT syndrome?

A

Increased time between Q and T waves

Heart muscle takes longer to recharge between beats

59
Q

What is bradycardia?

A

Slowing heart rate

60
Q

What is tachycardia?

A

Quickening of heart rate

61
Q

What is atrial fibrillation?

A

Atrium flutter - they don’t contract properly

One of the most common types of cardiac arrhythmia

62
Q

What is cardiac output (CO)?

A

Volume of blood pumped by the heart per minute

63
Q

How do you calculate CO?

A

CO = SV x HR

64
Q

What does Starling’s Law state?

A

The force of muscle contraction increases as the muscle is stretched in response to increased filling of the heart’s chambers.
-> The magnitude of the stretch predicts the strength of the contraction

65
Q

What is Cardiac Preload?

A

Initial stretching of cardiac myocytes prior to contraction

Indicated by end-diastolic volume (pressure)

66
Q

What is Cardiac Afterload?

A

The pressure the heart must eject blood against

Left ventricle after load is related to aortic pressure

BDS1 BAMS: Cardiovascular System (4 decks)

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