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human physiology and exercise > electrical and mechanical events of heart cycle > Flashcards

electrical and mechanical events of heart cycle Flashcards

1
Q

what is the sinoatrial node?

A
  • cluster of cells that are the pacemakers of the heart
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2
Q

what is the SA node described by?

A
  • autorhythmic so creates own action potential without stimulation by external factor
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3
Q

what is the intrinsic rate per min? what is this without?

A
  • approx. 100 beats per minutes
  • without ANS or hormones
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4
Q
A
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5
Q

what do pacemaker cells have?

A
  • sloping resting potential
  • threshold reached over time
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6
Q

why does SA node initiate an action potential?

A
  • due to unstable membrane potential that is continuously drifting towards threshold
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7
Q

what allows the gradual depolarisation of pacemaker cells?

A
  • sodium channels as allow calcium to enter and an action potential to form
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8
Q

what does rate of firing depend on?

A
  • initial value of membrane potential
  • slope of drift towards threshold (steeper= quicker it reaches threshold)
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9
Q

describe sympathetic stimulation of the heart

A
  • norepinephrine released on cells that increases permeability of Na+ channels
  • increase in slope of drift and quicker depolarisation occurs
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10
Q

describe parasympathetic stimulation of heart

A
  • decrease in slope of drift due to overall decrease of inward current
  • hyperpolarisation of membrane due to increased K+ permeability
  • initial value is much further from threshold potential
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11
Q

how does atrial contraction occur?

A
  • SA node initiates the impulse
  • electrical activity spreads through muscle fibres to top part of atrium
    -contraction via gap junctions
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12
Q

where does stimulus spread after atrial contraction?

A
  • spreads via a network of conduits beginning at atrioventricular node and it goes into Bundle of His
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13
Q

what happens when the impulse reaches the Bundle of His?

A
  • propagated into ventricular side of heart
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14
Q

where does signal travel after Bundle of His?

A
  • travels down interventricular septum via the two bundle branches
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15
Q

where does signal terminate and what happens?

A
  • terminates at cardiac muscle fibre via purknje fibres
  • ventricles contract as stimulus spreads upwards depolarising muscle fibres
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16
Q

what is the base of valves?

A
  • insulating layer that separates atrium to ventricles
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17
Q

what do valves stop?

A
  • stop propagation of signal from fibre to fibre
  • stops atrium and ventricle from contracting at same time as blood would never enter the ventricles
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18
Q

what does AV node do and why?

A
  • delays signal to slow down the propagation
  • enough time for ventricles to fill from blood from much weaker atria
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19
Q

what allows signals to travel in muscle fibres?

A
  • pores in intercalated discs connect the different muscle fibres
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20
Q

why is activity measured clinically?

A
  • gives the timing events of the heart cycle and indication of magnitude of stimulation in every part of the heart
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21
Q

what happens to the line when smaller parts are stimulated?

A
  • line becomes bigger when smaller parts (weaker/ damaged) are stimulated then signal is much smaller
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22
Q

what is the electrocardiogram?

A
  • very accurate way of measuring the heart rate by appreciating contraction in one minute
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23
Q

what does atrial excitation result in?

A
  • small bump of electrical stimulation
  • much weaker
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24
Q

what is the P wave?

A
  • associated with atrial contraction
  • first small wave that you can see
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25
Q

what is the T wave?

A
  • associated with ventricular relaxation
  • when electrical activity ceases the heart relaxes
25
Q

what does straight line before Q wave show?

A
  • AV node holding back signal to allow filling so ventricles have enough blood meaning when they squeeze blood is ejected
25
Q

what is QRS?

A
  • corresponds to ventricular contraction
    -activation in intraventricular septum and upwards on side of ventricles
26
Q

what does wave form measure?

A
  • current as it travels through the heart
27
Q

what happens if SA node doesn’t fulfil its role as expected?

A
  • other cells from heart jump in to stimulate the heart
  • but it is in an unorganised fashion
28
Q

what is the role of atrioventricular valves?

A
  • prevents blood flowing backwards into atria
29
Q

what is the tricuspid valve?

A
  • separates right atrium and right ventricle
30
Q

when does tricuspid valve open?

A
  • when right atrial pressure is higher than right ventricle pressure
31
Q

when does tricuspid valve close?

A
  • when right ventricle pressure is higher than right atrial pressure
32
Q

what is the mitral valve?

A
  • separates left atrium and left ventricle
33
Q

when is the mitral valve open?

A
  • when left atrial pressure is greater than left ventricle pressure
34
Q

when does the mitral valve close?

A
  • closed when left ventricular pressure is higher than left atrial pressure
35
Q

what is the role of semilunar valves?

A
  • allow blood to exit
36
Q

what is the pulmonary valve?

A
  • separates right ventricle and pulmonary artery
37
Q

when does pulmonary valve open?

A
  • when right ventricular pressure is greater than pulmonary artery pressure
38
Q

when do the pulmonary valves close?

A
  • closed when pulmonary artery pressure is greater than right ventricular pressure
39
Q

what are the aortic valves?

A
  • separated left ventricle and aorta
40
Q

when do the aortic valves open?

A
  • when the left ventricular pressure is greater than aortic pressure
41
Q

when do aortic valves close?

A
  • when aortic pressure is higher than left ventricular pressure
42
Q

what is systole?

A
  • contraction of the heart
43
Q

what is isovolumetric ventricular contraction?

A
  • no change in overall volume as blood isn’t ejected at the start
46
Q

what happens at the start of systole? what are the valves doing?

A
  • begins when ventricles are beginning to contract so they squeeze incompressible fluids that begins to increase pressure
  • all four valves shut
47
Q

what happens when ventricles contract?

A
  • generate enough ventricular pressure for semilunar valves to open
  • so blood flows through into vessels outside heart so blood ejected
48
Q

what is diastole?

A
  • relaxation of the heart
49
Q

what is isovolumetric ventricular relaxation?

A
  • ventricles relax without changing their blood volume
50
Q

what happens at the beginning of diastole? what happens to the valves?

A
  • begin to relax so drop in pressure closes semilunar valves
  • all four valves closed as pressure inside ventricles hasn’t dropped enough to allow atrium levels to exceed this and open
51
Q

what happens at later diastole?

A
  • atrioventricular valves are pushed open
  • blood comes into ventricles by means of gravity (passively fills)
52
Q

what completes end phase of tubular filling? is it important?

A
  • atria contraction
  • under normal conditions this isn’t important because HR is slow so ventricles have enough time to fill
53
Q

what happens if HR increases during exercise?

A
  • ventricles beat very fast so less time to fill so gravity isn’t sufficient by itself
54
Q

what does it signify if you can heat the heart?

A
  • atrioventricular valves or semilunar valves closing
55
Q

what is the relationship between wave forms in pressure sides defined by?

A
  • whether the valves are opened or closed
56
Q

what valve is open when atrium and ventricle are relaxed?

A
  • mitral valve
57
Q

what happens to the valves when ventricles begin to relax? what sound does it make?

A
  • aortic valves shut as pressure falls bellow aortic pressure
  • dub sound
58
Q

what happens when ventricular pressure exceeds aortic pressure?

A
  • aortic valve opens
59
Q

what valve closes when ventricles begin to contract? what sound does it make?

A
  • mitral valve
  • lub

human physiology and exercise (18 decks)

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