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Cardiovascular physiology > The cardiac cycle > Flashcards

The cardiac cycle Flashcards

1
Q

What is the function of the atria as a pump?

A

Acts as a priming pump to ensure maximum ventricular volume, increases efficiency of heartbeat

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2
Q

Why does the left ventricle have a thicker muscular wall?

A

Systemic circulation has 6x higher resistance, so to keep pulmonary and systemic flow the same, must generate 6x higher pressure.

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3
Q

Where does the heart tap on the chest wall during systole?

A

5th intercostal space

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4
Q

Why does the heart undergo a twisting motion when it contracts?

A

Alternating orientation of the subendocardial and subepicardial myocytes

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5
Q

What is the role of papillary muscles?

A

Attached to cusps of AV valves via chordae tendinae and contract to prevent inversion of these valves following ventricular systole

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6
Q

What causes valves to open/close?

A

Pressure gradient

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7
Q

Describe the state of both valves in isovolumetric phase, why?

A

Both closed
Ventricular pressure sufficient to close inlet but not enough to open outlet valve so avoid backflow and secure stroke volume.

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8
Q

What happens if you have incompetent valves?

A

Valves don’t close fully so backflow can cancel some forward flow (heart failure)

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9
Q

What happens in stenosis of valves?

A

Excessive calcification/atherosclerotic degranulation

Valves can’t fully open so more pressure overcome narrowing, heart grows and potentially heart failure

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10
Q

What causes 1st and 2nd heart sound?

A

S1 lub = closure of AV valve

S2 dub = closure of aortic and pulmonary valves

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11
Q

Describe course of opening/closing of AV and SL valves

A

AV valve open for ventricular filling, for isovolumetric contraction they SL and AV both closed.
Pressure rises then SL valves open.
Isovolumetric relaxation, AV and SL both closed.

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12
Q

What happens to volume and pressure in isovolumetric phase?

A

Volume constant but changes in pressure due to contracting/relaxing ventricle

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13
Q

What happens in ventricular diastole?

A

1) Chamber isovolumetric
AP has ended and pressure is falling
Pressure: artery>ventricle>atria (no flow into ventricles from atria)

2) Full recoil of ventricles as they’re relaxed
Pressure: Artery>atria>ventricles so blood flow into ventricles via AV valves

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14
Q

What happens in atrial systole?

A

Wave of depolarisation emitted from SAN causes atrial contraction forcing remaining blood into ventricles via AV valves

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15
Q

Why do atrial cells contract simultaneously?

A

Have many GJs which allow depolarisation to pass form one cell to another(cells arranged as syncytium) chemical coupling

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16
Q

Why do atria contract before ventricles, why is this important?

A

Annulus fibrosus insulates atria from ventricle electrically

Ventricles filled before ejecting blood

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17
Q

What happens to depolarisation conduction wave from AVN?

A

Conducted via bundle of His and Purkinje fibres to apex of ventricles where it sweeps from bottom to top to initiate V systole

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18
Q

What happens in ventricular systole?

A

1) Isovolumetric contraction as ventricles not pressurised enough to open SL valves (both SL and AV closed)
Increase in ventricular pressure however
Pressure: Artery>ventricle>atria

2)Pressure in ventricle exceeds pressure in aorta (80mmHg), flow out of SL valves down pressure gradient, ventricular volume falls

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19
Q

What follows wave of contraction, why is it important?

A

Relaxation phase, allows chambers to fill properly before another heart beat

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20
Q

How does most blood pass from atria to ventricles?

A

Passively

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21
Q

What causes dicrotic notch?

A

Closure of aortic valve

22
Q

What is CVP?

A

Pressure that fills the heart

23
Q

What 3 times during the cardiac cycle does central venous pressure increase?

A

Atrium contracts
Atrium collects blood
AV valve shuts

24
Q

What is the jugular venous pressure, why is it important?

A

Reflects right atrial pressure
best estimated from right internal jugular vein
has the most direct channel into the atrium

25
Q

How does Jugular venous pressure change?

A

Atrial systole, JVP and thus CVP increase (A wave)

Then as AV valves close (ventricular systole) blood bulges into atrium so short increase in JVP (C wave)

Atrium relaxes so JVP decreases (X descent)

Then atrial fill gently (JVP increases) ( V wave) until AV valve opens (Y descent)

26
Q

What does area of pressure volume loop represent?

A

Work done

27
Q

Why can’t you measure cardiac output from pressure volume loop?

A

Time is not shown, don’t know heart rate

28
Q

What does heart do for most of cardiac cycle?

A

Diastole/filling

29
Q

Why is synchronisaiton of cardiac myocytes important?

A

Produces stronger response, coordinated and regulated electrical excitation = efficient pumping

30
Q

What is RMP of SAN cells?

A

-55mV, though unstable (from around -50 to -70 to threshold of -40 to -55)

31
Q

How long is excitation delayed for as it reaches AVN?

A

0.1 secs

32
Q

Describe delay from SAN to atria, apex and ventricles

A
  1. 04-0.06
  2. 16
  3. 20-0.22
33
Q

At resting heart rate of 60bpm how much time is spent in systole and diastole, how does this change with increasing heart rate?

A

Systole: 1/3
Diastole: 2/3
More time spent in systole

34
Q

What are the two other heart sounds that can be heard?

A

S3 - mitral valve open blood rushes into ventricles

S4 - after atria contract (pathological)

35
Q

How does diastole and systole change with increased heart rate?

A

Both decrease, systole less so

36
Q

How does length of cardiac cycle change with slower heart beat?

A

Longer

37
Q

When does preload refer to?

A

Stretching load just before systole at end of diastole

38
Q

What is the best estimate for preload, EDV or EDP?

A

EDV

39
Q

Does the afterload include the preload?

A

Yes

40
Q

How does very high heart rate affect stroke volume?

A

Reduces it (less filling time)

41
Q

How does cardiac output change after standing up?

A

Decreases by 25% then compensated by baroreceptor reflex

42
Q

What increases venous return to right heart?

A 
Arterioles dilating
Venules dilating (constrition would cause blood to stay in microcirculation)
43
Q

True or false, cardiac output is a measure of both ventricles together

A

False, output of each ventricle per minute

44
Q

What is intrinsic discharge of SAN?

A

100bpm

45
Q

At what rate does depol spread from SAN?

A

1m/sec

46
Q

What do calcium blockers do to AVN AP?

A

Decrease amplitude and increase duration

47
Q

Most Ca2+ for excitation contraction is from ECF, yes or no

A

No

48
Q

What is the difference in Ca2+ conc in cytoplasm and ECF at rest?

A

10000 more in myoplasm

49
Q

Where does depolarisation spread the fastest?

A

Purkinje fibres

50
Q

What is the Fick principle?

A

VO2 = CO(Ca-Cv)

VO2 = rate of O2 uptake

CO = cardiac output

Ca = Concentration of O2 in arterial blood

Cv = Concentration of O2 in venous blood leaving the organ

51
Q

When is coronory flow maximum?

A

Isovolumetric relaxation (pressure in aorta high, ventricle wall not contracting)

52
Q

When do heart sounds occur in cardiac cycle?

A

In isovolumetric filling phase and isovolumetric relaxation (at the start)

Cardiovascular physiology (11 decks)

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