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Cardiovascular > Physiology 1 > Flashcards

Physiology 1 Flashcards

1
Q

What is the heart?

A

An electrically controlled muscular pump

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2
Q

Where are the electrical signals that control the heart generated?

A

Within the heart itself

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3
Q

What is autorhythmicity?

A

Heart capable of beating rhythmically in absence of external stimuli

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4
Q

Where in the heart does excitation normally originate?

A

Pacemaker cells in sino-atrial node

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5
Q

What in the heart initiates the heart beat?

A

Pacemaker cells in sino-atrial node

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6
Q

Where is SA node located?

A

Upper right atrium

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7
Q

What is the function of the SA node?

A

Sets pace for entire heart

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8
Q

What is a heart controlled by SA node said to be?

A

In sinus rhythm

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9
Q

How does cardiac excitation normally originate?

A

* Cells in SA node do not have stable resting membrane potential
* Exhibit spontaneous pacemaker potential
* Spontaneous pacemaker potential take membrane potential above threshold to generate an action potential

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10
Q

What is the pacemaker potential?

A

Slow depolarisation of membrane potential to threshold

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11
Q

What is the ionic basis for spontaneous pacemaker potential? (3)

A

* Decrease in K+ efflux
* Na+ and K+ influx (funny current)
* Transient Ca++ influx

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12
Q

What channel type causes transient Ca++ influx?

A

T-type Ca++ channels

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13
Q

What is the ionic basis for pacemaker action potential?

A

Once threshold is reached:
* Depolarisation caused by activation of long lasting L-type Ca++ channels
* Results in Ca++ influx

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14
Q

What is repolarisation caused by? (2)

A

* Inactivation of L-type Ca++ channels
* Activation of K+ channels causing K efflux

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15
Q

Understand diagram

A

…

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16
Q

How does cardiac excitation normally spread across the heart?

A
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17
Q

What allows the cell-to-cell current flow in the heart?

A

Gap junctions

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18
Q

What exists between cardiac myocytes?

A

Intercalated disc

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19
Q

What is the atrioventricular node?

A

Small bundle of specialised cardiac cells

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20
Q

Where is AV node located?

A

Base of right atrium

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21
Q

What is the only point of electrical contact between atria and ventricles?

A

AV node

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22
Q

Why is conduction delayed in AV node?

A

To allow atrial systole to precede ventricular systole

23
Q

What is the function of the Bundle of His and Purkinje fibres?

A

Allow rapid spread of action potential to ventricles

24
Q

How does AP spread through ventricular muscle?

A

Cell-to-cell conduction via gap junctions

25
Q

Is the action potential in cardiac muscle cells the same as the action potential is pacemaker cells?

A

No, different

26
Q

Do cardiac myocytes have an unstable resting potential like pacemaker cells?

A

No, resting membrane potential remains at -90 mV until cell is excited

27
Q

What is phase 0 of action potential in atrial and ventricular myocytes?

A

Fast Na+ influx reverses membrane potential to +20 mV (depolarisation) (NOT calcium influx like in pacemaker cells)

28
Q

What is phase 1, 2, 3 and 4 of action potential in atrial and ventricular myocytes?

A

* Phase 1 - closure of Na+ channels and transient K+ efflux
* Phase 2 - mainly Ca++ influx
* Phase 3 - repolarisation, closure of Ca++ channels and K+ efflux
* Phase 4 - resting membrane potential

29
Q

What is plateau phase of action potential?

A

Unique to cardiac muscle cells - membrane potential is maintained near the peak of action potential for a few hundred milliseconds

30
Q

What causes plateau phase of action potential?

A

Influx of Ca++ through L-type Ca++ channels (phase 2)

31
Q

What causes repolarisation in cardiac muscle action potential?

A

Inactivation of Ca++ channels and activation of K+ channels resulting in K+ efflux

32
Q

What is heart rate mainly influenced by?

A

Autonomic NS

33
Q

What is the effect of sympathetic stimulation of the heart?

A

Increases HR

34
Q

What is the effect of parasympathetic stimulation of the heart?

A

Decreases HR

35
Q

Explain autonomic NS influence on normal resting heart rate

A

* Vagus nerve (parasympathetic) exerts continuous influence on SA node under resting conditions
* Vagal tone dominates under resting conditions
* Vagal tone slows intrinsic HR from 100 ppm to a normal resting HR of 70 ppm

36
Q

Which group of people tend to have increased vagal tone?

A

Athletes

37
Q

What is normal resting heart rate?

A

60 - 100 bpm

38
Q

What is a resting heart rate less than 60? More than 100?

A 
\<60 = bradycardia
\>100 = tachycardia
39
Q

What does vagus nerve supply in the heart?

A

SA and AV node

40
Q

What is the effect of vagal stimulation of the heart? (2)

A

* Slows heart rate
* Increases AV nodal delay

41
Q

What neurotransmitter is responsible for vagal parasympathetic stimulation of the heart?

A

Acetylcholine acting on muscarinic M2 receptors

42
Q

What drug is given to patients with extreme bradycardia to speed up the heart?

A

Atropine - a competitive inhibitor of acetylcholine

43
Q

What is the effect of vagal stimulation on pacemaker potentials? (4)

A

* Cell hyperpolarises
* Takes longer to reach threshold
* Slope of pacemaker potential decreases
* Frequency of AP decreases

44
Q

What is the effect of vagal stimulation on pacemaker potentials, or anything that slows down heart rate known as?

A

Negative chronotropic effect

45
Q

What do cardiac sympathetic nerves supply?

A

SA, AV node and myocardium

46
Q

What is the effect of sympathetic stimulation on the heart?

A

* Increases HR
* Decreases AV nodal delay
* Increases force of contraction

47
Q

What neurotransmitter is responsible for sympathetic stimulation of the heart?

A

Noradrenaline acting through B1 adrenoceptors

48
Q

What is the effect of noradrenaline on pacemaker cells? (3)

A

* Slope of pacemaker potential increases
* Pacemaker potential reaches threshold quicker
* Frequency of action potential increases

49
Q

What is the effect of noradrenaline on pacemaker potentials, or anything that speeds up heart rate known as?

A

Positive chronotropic effect

50
Q

What is an ECG?

A

Depolarisation and repolarisation cycle of cardiac muscle obtained from skin surface

51
Q

What are standard limb leads of ECG? (3)

A

* Lead I: right arm - left arm
* Lead II: right arm - left leg
* Lead III: left arm - left leg

52
Q

What are the ECG waves?

A

* P - atrial depolarisation
* QRS complex - ventricular depolarisation/arial repolarisation * T - ventricular repolarisation

53
Q

What are the ECG intervals?

A

* PR interval: AV node delay
* ST segment: ventricular systole
* TP interval: diastole

Cardiovascular (28 decks)

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