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SGUL - Physiology 1 > Cardiac Cycle > Flashcards

Cardiac Cycle Flashcards

1
Q

What allows cardiac contraction to be coordinated?

A
  • Heart has pacemaker potential and so generates its own electrical activity
  • IMPORTANT - there are systems to coordinate this electrical activity
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2
Q

What is the effect of the sinoatrial node?

A
  • Pacemaker activity is generated here
  • Allows depolarisation of the atria
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3
Q

What is the purpose of the atrioventricular node?

A
  • Delays electrical signal to allow ventricles to fill
  • This is before the signal is passed to to apex of ventricles - causing ventricular contraction
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4
Q

The atrioventricular node also has pacemaker potential. Suggest why.

A
  • Allows pumping of blood by ventricles even when there is damage to to conduction system upstream of AVN
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5
Q

RECAP : What is membrane potential?

A

Potential difference across the plasma membrane

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6
Q

Potassium ion concentration is higher inside the cell, and sodium ion concentration is higher outside the cell.

Suggest a reason for this.

A
  • Membranes have sodium-potassium pumps
  • These transport 3 sodium ions outside of the cell and 2 potassium ions inside.
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7
Q

Outline what occurs during phase 4 (first step of the pacemaker potential) PART 1

A
  • Cell is at an unstable resting potential (-40mV to -60mV)
  • Voltage-gated sodium ion channels open - influx of sodium ions
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8
Q

Outline what occurs during phase 4 (first step of the pacemaker potential) PART 2

A
  • Membrane potential becomes more positive and cells depolarise
  • Once a threshold potential is met, VGCCs open
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9
Q

Outline what occurs during phase 0 (second step of pacemaker potential)

A
  • Rapid influx of calcium ions
  • Further depolarisation - membrane potential becomes more positive (around +20mV)
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10
Q

Outline what occurs during phase 3 (final step of pacemaker potential)

A
  • VGCCs close but potassium ion channels open
  • Efflux of potassium ions and cell repolarises
  • Hyperpolarisation will trigger opening of sodium ion channels again. Cycle repeats
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11
Q

What do the pacemaker potentials cause?

A

Action potentials in contractile cells in atria and ventricles

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12
Q

RECAP: What are the cardiac muscle cells known as and how are they connected?

A

CARDIOMYOCYTES
- Connected by intercalated discs containing gap junctions

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13
Q

RECAP: What is the purpose of the gap junctions in cardiomyocytes?

A
  • Allows inducing of action potential events in adjacent cells
  • Allows spread of wave of depolarisation - contraction is coordinated
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14
Q

Outline what occurs during phase 4 (first phase of atrial/ventricular action potential)

A
  • Resting membrane potential
  • Cells don’t generate their own electrical activity - rely on external stimuli e.g depolarisation of adjacent cells
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15
Q

Outline what occurs during phase 0 (second phase of atrial/ventricular action potential)

A
  • Depolarisation from SAN stimulates opening of voltage-gated sodium ion channels
  • Influx of sodium ions. Causes depolarisation of the cell
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16
Q

Outline what occurs during phase 1 (third phase of atrial/ventricular action potential)

A
  • Sodium ion channels close
  • Slight repolarisation due to Na/K exchanger
  • VGCCs open
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17
Q

Outline what occurs during phase 2 (fourth phase of atrial/ventricular action potential)

A
  • Plateau phase
  • Calcium influx - intracellular [Ca2+] rises
  • CICR occurs
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18
Q

Outline what occurs during phase 3 (final phase of atrial/ventricular action potential)

A
  • VGCCs close and potassium ion channels open
  • Efflux of potassium ions - causes repolarisation
  • Membrane potential becomes more negative - falls back to resting potential
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19
Q

What are the two ways spreading of the cardiac action potential is coordinated?

A
  • Passing of action potential to adjacent myocytes
  • Coordinated sequence of contraction and relaxation across WHOLE heart
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20
Q

Outline the first step in electrical conduction throughout the heart.

A
  • Action potential initiated at SAN with pacemaker potentials generated by sodium influx
  • Action potential spreads across atria through gap junctions present in myocytes
  • Atria become depolarised and contract simultaneously.
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21
Q

Outline the second step in electrical conduction throughout the heart.

A
  • Wave of depolarisation reaches AVN
  • AVN delays conduction to ventricles to allow proper filling from atria
  • Important to allow proper stroke volume and cardiac output
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22
Q

Outline the third step in electrical conduction throughout the heart.

A

Depolarisation signal passed to apex of ventricles through the Bundle of His

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23
Q

Outline the final step in electrical conduction throughout the heart.

A
  • Ventricular contraction begins at apex
  • Depolarisation spreads across ventricular walls through the Purkinje fibres
  • Contraction is simultaneous
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24
Q

What does an ECG measure?

A

Electrical activity of the heart

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25
Q

What is on the y- and x-axis of an ECG?

A

X-AXIS is time
Y-AXIS is amplitude of depolarisation

26
Q

What do the following represent on an ECG?

  • P-wave
  • PR segment
A

P-WAVE: Atrial depolarisation
PR-SEGMENT: AVN delay

27
Q

What do the following represent on an ECG?

  • QRS complex
  • ST segment
A

QRS-COMPLEX: Ventricular depolarisation
ST-SEGMENT: Ventricles contracting and emptying

28
Q

What do the following represent on an ECG?

  • T-wave
  • TP segment
A

T-WAVE: Ventricular repolarisation
TP-SEGMENT: Ventricles relaxing and filling

29
Q

How does SAN activity trigger muscle contraction?

A
  • Wave of depolarisation induced
  • Causes opening of VGCCs - causes influx of calcium
  • Calcium ions used for muscle contraction
30
Q

How does contraction of a chamber of the heart affect blood pressure and movement of blood?

A
  • Contraction will increase blood pressure
  • Blood will naturally move from an area of high pressure to an area of low pressure
31
Q

What causes valves to open?

A

Pressure differences

32
Q

Why is blood not able to move into the atria from the ventricles?

A

Valves only open one way

33
Q

Which side of the heart pumps at lower pressure?

A

Right

34
Q

Outline what occurs during cardiac diastole.

A
  • Relaxation of all chambers of heart
  • Blood returns to heart through venae cavae (on right) and pulmonary vein (on left)
  • Ventricular filling occurs
  • Due to low ventricular pressure, mitral and tricuspid valves open
35
Q

Outline what occurs during atrial systole

A
  • Atrial contraction causes filling of ventricles
  • Ventricular pressure rises
  • Mitral and tricuspid valves close
  • Ventricular pressure not high enough to trigger opening of aortic/pulmonary valves
36
Q

Outline what occurs during ventricular systole

A
  • Ventricles contract - ventricular pressure increases
  • Once ventricular pressure > aortic/pulmonary pressure, valves open and blood is ejected
  • Atria refill
  • Ventricles relax
37
Q

VENTRICULAR SYSTOLE - What is isovolumetric contraction?

A

Occurs when aortic pressure>ventricular pressure
- Energy is used for contraction but no blood is ejected out of the heart since pressure not high enough
- Characterised by a rise in pressure but no change in volume

38
Q

VENTRICULAR SYSTOLE - What is isovolumetric relaxation?

A
  • Occurs whilst ventricles are relaxing
  • When the volume of the ventricles don’t change significantly when relaxing
  • Causes a pressure drop - allows mitral and tricuspid valves to open and allows cycle to continue
39
Q

Left ventricular pressure changes can be plotted on a graph with a green line and a red line. What do these lines represent?

A

GREEN LINE - Left ventricular pressure changes
RED LINE - Aorta pressure changes
LABELLED DIAGRAM CAN BE FOUND ON SLIDES

40
Q

Outline what occurs at point 1 on the pressure change graph. (FOUND ON SLIDES)

A
  • Contraction of left atrium
  • Ventricular pressure begins to rise, but still relatively low
  • Ventricular pressure > atrial pressure, so mitral valve closes
41
Q

Outline what occurs at point 2 on the pressure change graph. (FOUND ON SLIDES)

A
  • Ventricular systole
  • Aortic valve won’t open until ventricular pressure>aortic pressure
  • Isovolumetric contraction occurs
42
Q

Outline what occurs at point 3 on the pressure change graph. (FOUND ON SLIDES)

A
  • Ventricular pressure>aortic pressure so aortic valve opens
  • Ejection of blood from ventricles into aorta
  • Ventricular pressure begins to reduce
43
Q

Outline what occurs at point 4 on the pressure change graph. (FOUND ON SLIDES)

A
  • Ventricular pressure < aortic pressure so aortic valve closes
  • Isovolumetric relaxation occurs
44
Q

Left ventricular volume changes can be plotted on a graph. What is on the y-axis of this graph?

A

Y-AXIS: Left ventricular volume

LABELLED DIAGRAM is on the slides

45
Q

Outline what occurs at point 1 on the volume change graph. (FOUND ON SLIDES)

A
  • Atrial contraction so ventricular volume rises
  • Ventricles are still relaxed
  • Volume of blood that enters before ventricular systole known as EDV - end diastolic volume (around 120ml)
46
Q

Outline what occurs at point 2 on the volume change graph. (FOUND ON SLIDES)

A
  • Ventricular pressure increases due to filling
  • Mitral valve closes
  • Ventricles contract but volume stays constant - ISOVOLUMETRIC CONTRACTION
47
Q

Outline what occurs at point 3 on the volume change graph. (FOUND ON SLIDES)

A
  • Ventricular pressure > aortic valve so ejection of blood from ventricles. Ventricular volume increases
  • Ejection is initially rapid but over time rate of ejection decreases
48
Q

Outline what occurs at point 4 on the volume change graph. (FOUND ON SLIDES)

A
  • Ventricular pressure decreases, so aortic valve closes
  • ISOVOLUMETRIC RELAXATION - pressure drops but no change in volume of ventricles
  • Volume of blood remaining in ventricles post-ejection is ESV (end systolic volume) - around 40ml
49
Q

What is the equation linking stroke volume, ESV and EDV.

A

STROKE VOLUME = EDV - ESV

50
Q

Outline the importance of the ventricular pressure-volume loop

A

Provides insight into the amount of energy the heart expends during contraction and relaxation

51
Q

What is on the x-axis and y-axis of the ventricular pressure-volume loop?

A

X-AXIS: Left ventricular volume
Y-AXIS: Left ventricular pressure
LABELLED DIAGRAM CAN BE FOUND ON SLIDES

52
Q

Outline what occurs at point A on the pressure-volume loop. (FOUND ON SLIDES)

A
  • Mitral valve opens
  • Ventricles begin to fill and volume begins to increase
  • Ventricles relaxed - not too much change in pressure
53
Q

Outline what occurs at point B on the pressure-volume loop. (FOUND ON SLIDES)

A
  • Mitral valve closes and ventricles contract
  • Undergoes period of isovolumetric contraction
  • Pressure rises but no volume change(since aortic and mitral valves are closed)
54
Q

Outline what occurs at point C on the pressure-volume loop. (FOUND ON SLIDES)

A
  • Ventricular pressure > aortic pressure so aortic valves open
  • Blood ejected from ventricles
  • Ventricular volume decreases. Pressure slightly rises due to contraction of ventricles
55
Q

Outline what occurs at point D on the pressure-volume loop. (FOUND ON SLIDES)

A
  • Aortic valve closes
  • Ventricles relax so pressure of ventricles decrease
56
Q

What does area inside the pressure-volume loop tell you?

A

Work done to eject volume of blood

57
Q

What are the two characteristic of a healthy heart? How would these characteristic change during heart failure?

A
  • A high stroke volume with low energy consumption
  • In heart failure, low stroke volume with high consumption
58
Q

What causes S1?

A
  • Closure of tricuspid and mitral valves at beginning of ventricular systole/after ventricular filling ends
59
Q

What causes S2?

A
  • Closure of aortic valves when ventricular pressure < aortic pressure
  • Ejection of blood occurs at end of ventricular systole
60
Q

What causes S3?

A

Turbulent blood flow into ventricles

61
Q

What causes S4?

A

Forceful atrial systole against stiff ventricles

SGUL - Physiology 1 (68 decks)

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