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cardiology: key information > Physiology > Flashcards

Physiology Flashcards

1
Q

define autorhythmicity

A

the heart is capable of beating rhythmically in the absence of external stimuli

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2
Q

define sinus rhythm

A

a heart controlled by the SA node

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3
Q

does the SA node have a stable resting membrane potential?

A

no

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4
Q

what does the SA node generate?

A

regular spontaneous pacemaker potentials (phase 4)

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5
Q

what produces the pacemaker potentials in the SA node?

A
  • decrease in K+ efflux
  • funny current (Na+ and K+ influx through HCN channels)
  • transient Ca2+ influx through T-type channels
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6
Q

what is phase 0 due to in the pacemaker cells?

A

Ca2+ influx through L-type channels

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7
Q

what is phase 3 due to in pacemaker cells?

A

inactivation of L-type channels and activation K+ channels

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8
Q

what cell junction does electrical excitation spread through

A

gap junctions

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9
Q

what does the AV node do to the conduction velocity

A

AV cells have a small diameter so slow conduction velocity

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10
Q

what does slowed conduction in the AV node allow?

A

atrial systole to precede ventricular systole

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11
Q

phase 4 of myocytes?

A

resting potential due to K+ efflux via Na+/K+ ATPase

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12
Q

what is the mV resting membrane potential in myocytes?

A

-90mV

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13
Q

role of ivabradine

A

blocks HCN slowing the HR

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14
Q

role of digoxin

A

inhibits Na+/K+ ATPase causing the membrane to depolarise slightly

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15
Q

phase 0 in myocytes

A

upstroke due to Na+ influx

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16
Q

membrane potential in phase 0

A

+20mV

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17
Q

phase 1 in myocytes

A

early repolarisation due to transient K+ efflux

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18
Q

phase 2 in myocytes

A

plateau due to Ca2+ L-type influx which balances K+ efflux

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19
Q

what does durgs that block the K+ channel cause?

A

increase ventricular action potential (can lead to acquired long QT syndrome)

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20
Q

phase 3 in myocytes

A

final repolarisation due to closure of Ca2+ channels and K+ efflux

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21
Q

difference in atrial myocytes

A

another outward K+ channel (ultra-rapid delayed rectifier) so phase 2 is less evident

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22
Q

sympathetic innervation of the heart

A

sympathetic nerves act on B1-adrenoceptors using NA

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23
Q

parasympathetic innervation of the heart

A

vagus nerve acts on M2 muscarinic receptors using ACh decreasing HR

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24
Q

what dominates control of HR in resting conditions?

A

vagal tone exerts a continuous influence of the SA and AV nodes

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25
Q

define chronotropic

A

change in heart rate

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26
Q

define inotropic

A

force of contraction

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27
Q

define lusitropic

A

rate of myocardial relaxation

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28
Q

define dromotropic

A

conduction speed

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29
Q

define ECG

A

record of depolarisation and repolarisation cycle of cardiac muscle obtained from the skin surface

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30
Q

P wave

A

atrial depolarisation

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31
Q

QRS complex

A

ventricular depolarisation (masks atrial repolarisation)

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32
Q

T wave

A

ventricular repolarisation

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33
Q

PR interval

A

AV node delay

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34
Q

ST segment

A

ventricular systole

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35
Q

TP interval

A

diastole

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36
Q

QT interval

A

ventricular depolarisation and repolarisation

37
Q

role of desmosomes between intercalated discs in cardiac cells

A

ensure tension is transmitted from one cell to the next

38
Q

what must happen for myocardial contraction to happen?

A

Ca2+ must bind with troponin to expose the actin binding site for cross-bridge formation

39
Q

what does the refractory period prevent?

A

tetanic contraction

40
Q

what state are the Na+ channels in during the refractory period

A

inactivated

41
Q

define stroke volume

A

volume of blood ejected from each ventricle per heartbeat

42
Q

define EDV

A

volume of blood in each ventricle at the end of diastole

43
Q

what determines EDV

A

venous return

44
Q

what influences venous return?

A
  • venomotor tone
  • skeletal muscle pump
  • respiratory pump (inspiration causes increased intraabdominal pressure)
  • blood volume
45
Q

Starling’s Law

A

the more the ventricle is filled with blood during diastole the greater the volume of blood ejected

46
Q

define afterload

A

resistance into which the heart is pumping

47
Q

what is after load determined by

A

radius of blood vessel and blood viscosity

48
Q

what does after load increase the risk of?

A

hypertrophy

49
Q

intrinsic control of SV

A

change in diastolic length and stretch of fibres (increases affinity for Ca2+)

50
Q

extrinsic control of SV

A

nerves (parasympathetic has no effect on force of cardiac contraction)

51
Q

75bpm diastole and systolic time

A

systole 0.3sec

diastole 0.5sec

52
Q

five phases of the cardiac cycle

A
  1. passive filling
  2. atrial contraction
  3. isovolumetric ventricular contraction
  4. ventricular ejection
  5. isovolumetric ventricular relaxation
53
Q

describe passive filling

A

blood flows into the ventricles (80%)

54
Q

describe atrial contraction

A

completes EDV

55
Q

describe isovolumetric ventricular contraction

A

AV valves shut causing pressure to rise

56
Q

what does the AV valves shutting indicate?

A

lub- S1

beginning of systole

57
Q

describe ventricular ejection

A

ventricular pressure falls below aortic/pulmonary it causes the valves to shut

58
Q

what does the aortic valve shutting cause?

A

valve vibration produces the dicrotic notch

59
Q

describe isovolumetric ventricular relaxation

A

closure of semi-lunar valves causes tension to fall

60
Q

what does shutting of the aortic/pulmonary valves indicate?

A

dub- S2

beginning of diastole

61
Q

why does arterial pressure not fall to zero during diastole?

A

elastic recoil

62
Q

what does the JVP indicate?

A

central venous pressure

63
Q

define MAP

A

average arterial blood pressure during a single cardiac cycle

64
Q

how to calculate MAP

A

DBP + 1/3 Pulse Pressure

[(2x diastolic pressure) + systolic pressure]/ 3

65
Q

normal range of MAP

A

70-105mmHg

66
Q

is diastole twice as long as systole?

A

yes

67
Q

describe the baroreceptor reflex in postural hypotension

A
  • standing causes venous return to decrease (gravity)
  • MAP decreases
  • reduced firing from baroreceptors causes vagal tone to decrease and sympathetic tone to increase
68
Q

define postural hypotension

A

failure of the baroreceptor reflex to response to gravitational shifts

69
Q

positive result of postural hypotension (by 3 minutes)

A
  • systolic of at least 20mmHg

- diastolic of at least 10mmHg

70
Q

what does extracellular fluid consist of?

A

plasma volume

interstitial volume

71
Q

three systems that affect the extracellular fluid?

A
  1. RAAS
  2. NPs
  3. ADH
72
Q

RAAS

A
  • renin is released from the kidney
  • converts angiotensinogen from the liver into angiotensin I
  • ACE from the lungs converts this to angiotensin II
  • activates the adrenal cortex to form aldosterone
73
Q

NPs

A

cause excretion of salt and water

74
Q

ADH synthesis

A

made in the hypothalamus and stored in the posterior pituitary

75
Q

action of ADH

A

acts on kidney tubules causing reabsorption of water and vasoconstriction

76
Q

extrinsic control of vascular smooth muscle

A

nerves and hormones

77
Q

nervous control of vascular smooth muscle

A

vasomotor tone

no parasympathetic innervation

78
Q

hormones on vascular smooth muscles

A
  • adrenaline on alpha-receptors causes vasoconstriction (skin, gut, kidney)
  • adrenaline on beta2 causes vasodilation (cardiac and skeletal muscle)
  • angiotensin II vasoconstrition
  • ADH vasoconstriction
79
Q

intrinsic control of vascular smooth muscle

A
  • chemical local metabolites
  • chemical local humoral agents
  • temperature
  • myogenic response
  • sheer stress
80
Q

local humoral vasodilators

A
  • histamine
  • bradykinin
  • NO
81
Q

local humoral vasoconstrictors

A
  • serotonin
  • thromboxane A2
  • leukotrienes
  • endothelin
82
Q

describe the myogenic response

A

if MAP rises, vessels constrict

83
Q

describe sheer stress on vascular smooth muscle

A

dilates arteries

84
Q

define shock

A

abnormality of the circulatory system resulting in inadequate tissue perfusion and oxygenation leads to anaerobic metabolism and accumulation of waste products and cellular failure

85
Q

define hypovolaemic shock

A

loss of blood volume

86
Q

define cardiogenic shock

A

decreased cardiac contractility causing sustained hypotension

87
Q

define obstructive shock (tension pneumothorax)

A

increased intrathoracic pressure causes decreased venous return

88
Q

define neurogenic shock

A

loss of sympathetic tone causing decreased HR (unlike other types of shock)

89
Q

define vasoactive shock

A

release of vasoactive mediators

cardiology: key information (42 decks)

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