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First Semester: Physiology 1 > Lecture 20: Excitation-Contraction Coupling of the Heart and Cardiac Cycle > Flashcards

Lecture 20: Excitation-Contraction Coupling of the Heart and Cardiac Cycle Flashcards

1
Q

Two parts of the cardiac cycle

A

systole and diastole

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2
Q

Systole

A

Contraction and emptying

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3
Q

Diastole

A

Relaxation and filling

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4
Q

Contraction occurs as a result of

A

excitation across the heart

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5
Q

Relaxation follows

A

the subsequent repolarization of the cardiac muscle

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6
Q

Cardiac cycle is divided into how many stages

A

7

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7
Q

Phase A of cardiac cycle

A
  • Atrial contract
  • Final phase of ventricular filling
  • Increased atrial pressure is reflected back to veins causing venous pressure “a” wave
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8
Q

What is associated with the fourth heart sound

A

Phase A: Atrial systole

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9
Q

Fourth heart sound

A
  • Not heard under normal conditions
  • May be heard when ventricle compliance is decreased and forceful ventricular filling produces a sound
  • Ex. Ventricle hypertrophy
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10
Q

Phase B: Isovolumertric Ventricular Contraction

A
  • Ventricles contract and ventricular pressure increases
  • All valves are closed, and closure of AV valves produces the first heart sound (S1)
  • C wave occurs here
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11
Q

S1 signals the onset of

A

Ventricular systole

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12
Q

“C” wave

A

Increase of ventricular pressure leads to bulging of AV valve into atria, causing a small atrial pressure wave
Occurs during phase B

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13
Q

Two atrioventricular valves

A

Tricuspid valve

Mitral valve

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14
Q

First heart sound

A

Two nearly superimposed components:
-Mitral component slightly precedes triscupid component because the earlier electrical stimulation of left ventricular contraction

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15
Q

Phase C: Rapid Ventricular Ejection

A
  • Ventricles contract
  • Ventricular pressure increases and reaches the maximum
  • Aortic valve opens
  • Ventricles eject blood into arteries
  • Ventricular volume decreases
  • Aortic pressure increases and reaches maximum
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16
Q

Two semilunar valves

A
  1. Pulmonary valve

2. Aortic valve

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17
Q

Afterload

A

The pressure against which the heart pumps blood into the circulation

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18
Q

Phase D: Reduced Ventricular Ejection

A
  • Ventricles eject blood into the aorta at a slower rate
  • Ventricles do not empty completely
  • Aortic pressure begins to fall
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19
Q

End-systolic volume

A

The amount of blood remaining in the ventricle at the end of systole

20
Q

Stroke volume

A

The amount of blood ejected by the ventricle in one beat

21
Q

The proportion of EDV that is ejected

A

(SV/ESV) = Ejection fraction

22
Q

Phase E: Isovolumetric Ventricular Relaxation

A
  • Ventricles relaxed
  • Ventricular pressure decreases
  • Aortic valve closes
  • Second heart sound is heard
  • Ventricular pressure is constant (end-systolic volume)
  • V wave
23
Q

V wave

A

Atrial pressure increases as a result of filling from the veins

24
Q

Dicrotic notch

A

Closure of the aortic valve produces a disturbance on the aortic pressure curve

25
Q

Second heart sound

A
  • Aortic valve closes slightly before the pulmonary valve, leading to this sound
  • Inspiration delays the closure of the pulmonic valve, which causes the splitting of the S2
26
Q

Why does splitting of S2 occur during inspiration?

A
  • Associated decrease of intrathoracic pressure produces an increase in venous return to the right side of the heart
  • Resulting increase in right ventricular EDV causes an increase in right ventricular SV and prolongs right ventricular ejection time
  • Prolongation of ejection time delays the closure of the pulmonic valve relative to the aortic valve
27
Q

Phase F: Rapid Ventricular Filling

A
  • Ventricles relaxed
  • Mitral valve opens
  • Ventricles fill passively with blood from the atria
  • Ventricular volume increases
  • Ventricular pressure low
  • Rapid ventricular filling may produce as a third heart sound
28
Q

Third heart sound

A

Occurs early in diastole following the opening of the AV valves

29
Q

Phase G: Rapid Ventricular Filling

A
  • Ventricles relaxed

- Final phase of ventricular filling

30
Q

Ventricular pressure-volume loop

A

Ventricular pressure plotted against volume

31
Q

Heart murmurs

A

Sounds generated by turbulent flow in the surrounding

32
Q

Five things heart murmurs may result from

A
  1. Flow across a partial obstruction (ex. aortic stenosis)
  2. Regurgitant flows across an incompetent valve (ex. mitral reguritation)
  3. Increase flow through normal structures (ex. Systolic murmurs associated with a high output state, during anemia)
  4. Ejection into dilated chamber (ex. dilated aorta)
  5. Abnormal shunting of blood from one vascular chamber to a lower pressure chamber (ex. ventricular septal defect)
33
Q

Heart murmurs may be described by their (5)

A
  1. Timing
  2. Intensity
  3. Pitch
  4. Shape
  5. Location
34
Q

Timing

A

Whether it occurs during systole, diastole, or is continuous (begins in systole and continues into diastole)

35
Q

Intensity

A
  • Ease in which it is identified/heard

- Murmurs are typically quantified by a grading system

36
Q

Systolic murmur intensity grading

A

1/6 to 6/6 with 1 being barely audible and 6 being audible without stethoscope directly on chest wall

37
Q

Diastolic murmur intensity grading

A

1/4 to 4/4 with 1 being barely audible and 4 being very loud

38
Q

Pitch

A
  • Frequency of the murmur ranging from high to low
  • High frequency murmurs are caused by large pressure gradients between chambers (ex. aortic stenosis)
  • Low frequency murmurs implies less of a pressure gradient between chambers (mitral stenosus)
39
Q

Shape

A

How the murmur changes in intensity from onset to completion

40
Q

Three examples of murmur shape

A
  1. Crescendo-decrescendo - first rises then fall off in intensity
  2. Decrescendo - murmur begins at maximum intensity, then falls
  3. Continuous - heard throughout the cardiac cycle
41
Q

Location

A
  • Region of maximal intensity
  • Murmurs are often heard to radiate from their primary location to other areas of the chest. Such patterns of transmission relate to the direction of the turbulent flow
42
Q

Three defects that cause heart murmurs

A
  1. Ventricular septal defect
  2. Changes in blood pressure in a particular region of the body
  3. Cardiac hypertrophy
43
Q

Ventricular septal defect (murmur consequences)

A
  • Initially, the increased blood return to the left ventricle augments stroke volume (via the Frank-Starling Mechanism)
  • Over time the increased volume load can result in chamber dilation and heart failure
44
Q

Changes in blood pressure in a particular region of the body - mitral stenosis example (murmur consequences)

A
  • Blood dams up in the left atrium which means the left atrial pressure in higher than normal
  • High left atrial pressure is passively transmitted to the pulmonary circulation which leads to…
  • Increased pulmonary venous and capillary pressures leads to….
  • The transduction of plasma into the lung interstitium which leads to…
  • Congestive heart failure
45
Q

Cardiac hypertrophy (murmur consequences)

A

Increase in workload of one or both ventricles

First Semester: Physiology 1 (34 decks)

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