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BVM1 - Cardiovascular system > 3. Origin of the heartbeat and the cardiac cycle > Flashcards

3. Origin of the heartbeat and the cardiac cycle Flashcards

1
Q

Where is the primary pacemaker region?

A

Sinoatrial node (SA)

  • generates an electrical signal that spreads through cellular gap junctions
  • spontaneously depolarises
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2
Q

What are Purkinje fibres?

A

Wiring system

- modified myocytes not nerves

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3
Q

Which ventricle has more bundles?

A

Left as it is thicker

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4
Q

What is the order of conduction in the heart?

A

SA node → Atrial muscle → AV node (small pause) → Bundle of His → Purkinje fibres → ventricular muscle

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5
Q

During pacemaker potential (heart is relaxed) describe the movement of ions

A

K+ leaves cell

Na+ (leaky channels) and Ca2+ enter the cell

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6
Q

During rapid depolarisation describe the movement of ions

A

Ca2+ enters the cell through voltage sensitive Ca2+ channels (T channels)
- at threshold of 2nd set of Ca2+ channels are opened = L type calcium channels

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7
Q

During repolarisation describe the movement of ions

A

K+ leaves the cell

- potassium channels open and the cell is able to repolarise

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8
Q

What other autonomic foci are involved in spontaneous depolarisation?

A
  • atrial foci (60-80 bpm)
  • junctional foci (40-60 bpm)
  • ventricular foci (20-40 bpm)
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9
Q

Why is the SA node faster?

A

80-100 bpm

- essentially overrides the rest of the foci between the muscle

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10
Q

How would you describe cardiac muscle?

A

Functional syncytium - essentially all of the cells are acting as one cell
- electrically and mechanically coupled

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11
Q

What are the principal features of cardiac muscle?

A

Intercalated discs, central nuclei (usually one but sometimes two) with perinuclear space, branched fibres, good blood supply

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12
Q

What is If?

A

Funny or pacemaker current - Na+

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13
Q

What is phase 4 of the action potential?

A

Resting membrane potential

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14
Q

What is phase 0 of the action potential?

A

Rapid depolarisation

- fast Na+ channels open = voltage sensitive

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15
Q

What is phase 1 of the action potential?

A

Notch

- fast Na+ channels close

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16
Q

What is phase 2 of the action potential?

A

Plateau

  • Ca2+ enters (voltage - sensitive gated channels) - L type Ca2+ channels
  • K+ permeability is low
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17
Q

What is phase 3 of the action potential?

A

Repolarisation

- K+ leaves (K+ channels open; calcium channels close)

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18
Q

What makes cardiac muscle contract?

A

Needed for systole

  • calcium moves through the T-tubules
  • some moves into the sarcoplasmic reticulum
  • Calcium induced calcium release
  • Ca2+ + troponin C = contraction
19
Q

What makes cardiac muscle relax?

A

Needed for diastole

  • facilitated transport (Na+/Ca2+ exchanger, 3:1)
  • pumps Ca2+ ATPase
20
Q

Why is a long plateau phase and timing of tension development important?

A
  • Relatively long refractory period (due to plateau phase)
  • Inability to respond to further stimulation
  • Allows the ventricles sufficient time to empty and refill before the next contraction
21
Q

Define Systole/systolic

A

Chambers emptying/contracting

22
Q

Define Diastole/diastolic

A

Chambers filling/relaxing

23
Q

What are the phases of the cardiac cycle?

A
  1. Atrial contraction = diastole
  2. Isovolumetric contraction = systole
  3. Rapid ejection = systole
  4. Reduced ejection = systole
  5. Isovolumetric relaxation = diastole
  6. Rapid filling = diastole
  7. Reduced filling = diastole
24
Q

How are heart sounds produced?

A

Valves closing

25
Q

When are S1 sounds heard?

A

Closure of the AV valves (systole)

26
Q

When are S2 sounds heard?

A

Closure of semilunar valves (diastole)

27
Q

When are S3/S4 sounds heard?

A

Related to the movement of blood

  • species/age variation
  • horses have all four but cats and dogs only have S1-S2
28
Q

What are murmurs? How are they produced?

A

Abnormal sounds
Defective valves
- usually heard during the quiet phase of the cardiac cycle

29
Q

On an ECG, what does the P wave represent?

A

P wave = atrial depolarisation

30
Q

On an ECG, what does the QRS complex represent?

A

QRS complex = depolarisation of the ventricles

31
Q

On an ECG, what does the T wave represent?

A

T wave = re-polarisation of the ventricles

32
Q

On an ECG, what does the PR interval represent?

A

PR interval = AV conduction time

33
Q

On an ECG, what does the ST segment represent?

A

ST segment = isoelectric period - both ventricles are completely depolarised

34
Q

On an ECG, what does the QT interval represent?

A

QT interval = time for both ventricular depolarisation and repolarisation to occur so estimates the duration of an average ventricular action potential

35
Q

What does an ECG tell us?

A
  • heart rate, heart rhythm, origin of excitation
  • anatomical orientation of the heart
  • relative sizes of the heart chambers
  • spread of impulse
  • decay of excitation
36
Q

What is tachycardia?

A

Heart rate in excess of normal

37
Q

What is bradycardia?

A

Heart rate below normal

38
Q

What is sinus arrhythmia?

A

Normal QRS complex, PR and QT intervals but RR interval varies in a set pattern

39
Q

What is sinus tachycardia?

A

Normal response to exercise; also seen in fever, hyperthyroidism and as a reflex to low arterial pressure

40
Q

What is sinus bradycardia?

A

May be abnormal but usually indicative of very fit individuals

41
Q

Describe a first degree AV block

A

Prolonged PR intervals define first degree AV block, contraction delayed due to increased time for AV conduction

42
Q

Describe a second degree AV block

A

AV node fails to transmit all atrial impulses (more p waves than QRS complexes)
Atria beat more than once for each ventricular contraction

43
Q

Describe a third degree AV block

A

Transmission of impulse from atria to ventricles fails. Atria and ventricles beat independently of each other
(P and QRS complexes completely dissociated from each other)

BVM1 - Cardiovascular system (4 decks)

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