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Pharmacology > Cardiac Physiology > Flashcards

Cardiac Physiology Flashcards

1
Q

What are the main features of the conduction system of the heart?

A 
SAN
AV node
AV bundle
Right t& left bundle fibres 
Purkinje fibres
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2
Q

What does the SAN do?

A

Generate spontaneous A.Ps

Pass them to atrial muscle cells + AV node

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3
Q

What is the structure of SAN?

A

Specialised cardiac cells

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4
Q

What does the AV node do?

A

A.Ps conducted more slowly

= ventricles receive signal to contract after atria contract

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5
Q

What does AV bundle do?

A

Pass through hole in cardiac skeleton to reach interventricular septum

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6
Q

What does the right & left bundle branches do?

A

Extend beneath endocardium to apices of right + left ventricles

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7
Q

What do Purkinje fibres do?

A

Conduct A.Ps to ventricular muscle cells (myocardium)

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8
Q

What is the structure of Purkinje fibres?

A

Large diameter cardiac muscle cells with few myofibrils

Many gap junctions

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9
Q

Describe conduction system of heart

A

Depolarisation from SAN across atria
Conduct to AVN
Conduction slow in AVN
Atrioventricular bundle of His connects to branches
Purkinje fibres = terminal bundle branches
Myocardial fibres

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10
Q

Why is conduction slow in AVN?

A

To allow atria to empty into ventricles before ventricular systole

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11
Q

Describe structure of cardiac muscles

A

Faintly striated
Branched, mono-nucleated cells
Connected by intercalated discs ( gap junctions + desosomes)

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12
Q

Why is there slow propagation in cardiac muscles?

A

Gap junctions + small diameter

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13
Q

Why is propagation faster in skeletal muscles?

A

Larger diameter fibres

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14
Q

Where does A.P occur in cardiac muscles?

A

Cell to cell

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15
Q

Where does A.P occur in skeletal muscles?

A

Along length of single fibre

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16
Q

Describe sliding filament theory

A

Ca2+ binds to TN-C on thin filament
Exposes site on actin = can bind to myosin head
ATP hydrolysis supplies energy for actin-myosin conformational change
“Ratcheting” of actin-myosin + shortening of sacromere occurs
Ca2+ dissociates from TN-C + myosin unbinds with energy from ATP
Cycle ends when ATP binds to myosin + sacromere returns to original length

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17
Q

Describe cardiomyocyte contraction

A 
Ca2+ enters through L-type channel
Ca2+-induced release occurs
Stimulates Ca2+ release from SR
Intracellular [Ca2+] increases 
Ca2+ interacts with troponin-C 
Myosin binding site free on actin
Actin moves over myosin = myocyte contraction
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18
Q

What happens after cardiomyocyte contraction has taken place?

A

Ca2+ reabsorbed into SR via sarco-endoplasmic reticulum Ca-ATPase pump
Removed from cell by Na+/Ca2+ exchanger + Ca2+ pump
ATP required to unbind myosin from action + resent sarcomere

19
Q

What is the charge of the inside of cell?

A

Negative

20
Q

What is charge after A.P?

A

Positive

21
Q

What are the three factors that control charge?

A

Conc of ions in + out cell
Ion conductance
Activity of electrogenic pumps

22
Q

What is value of resting potential?

A

-90mV

23
Q

What is value of depolarisation threshold value?

A

-65mV

24
Q

How many phases is there?

A

5

25
Q

What happens in phase 0?

A

Opens Na+ gates
Membrane potential increases
+40mV
Na+ gated “inactivated” = Na+ permeability falls

26
Q

What happens in phase 1?

A

Ca2+ gates open = inward flow of Ca2+

27
Q

What happens in phase 2?

A

K+ balances Ca2+ flow = plateau
Generates cardiomyocyte contraction
Ca2+ channels inactivated

28
Q

What happens in phase 3?

REPOLARISATION

A

K+ channels reopen

Membrane potential falls

29
Q

What happens in phase 4?

Resting potential

A

Return to -90mV

30
Q

What is pacemaker potential?

A

After A.P, membrane potential drifts up until threshold met

Na+ channels open = AP triggered

31
Q

Where is the SAN?

A

Right atrium

close to vena cava

32
Q

Describe A.P on SAN pacemaker cells

A 
Phase 4: spontaneous depolarisation 
Inward movement of Na+, outward K+
K+ movement decays with time
Pacemaker potential depolarises to -55mV
Ca2+ inward current accelerates threshold to -40mV
Phase 0: depolarisation
Ca2+ increases = L-type Ca2+ channels
Phase 3: repolarisation
K+ channels open + help recognise cell as Ca2+ channel inactive
33
Q

Describe parasympathetic regulation of cardiac cycle

A

Cardiomyocyte centre (vagus nerve)
Nerve branches to SA + AV nodes
Secrete acetylcholine; hyperpolarises heart
Decreases HR

34
Q

Describe sympathetic regulation of cardiac cycle

A

Cardioaccelerator centre activates sympathetic neurons (cardiac nerves)
Secreted norepinephrine
Increases force of contractions = increases HR

35
Q

What is a P-wave?

A

Depolarisation of atrial myocardium

36
Q

What does P-wave show on electrocardiogram?

A

Signals onset of atrial contraction

On ECG = positive, not large or peaked

37
Q

What is QRS complex?

A

Ventricular depolarisation

38
Q

What does QRS complex show on electrocardiogram?

A

Signals onset of ventricular contraction

On ECG = negative deflection

39
Q

What is a T-wave?

A

Repolarisation of ventricles

40
Q

What is the PR interval?

A

Start of atrial depolarisation to start of ventricular depolarisation = contract + reflex

41
Q

What does PR interval indicate?

A

Damage to conducting pathway or AVN

42
Q

What is the QT interval?

A

Time required for ventricles to undergo single cycle of depolarisation + repolarisation

43
Q

What is the QT interval lengthened by?

A

Electrolyte disturbances, conduction problems, ischemia + damage

Pharmacology (40 decks)

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