electrical and mechanical events of heart cycle Flashcards
(61 cards)
1
Q
what is the sinoatrial node?
A
- cluster of cells that are the pacemakers of the heart
2
Q
what is the SA node described by?
A
- autorhythmic so creates own action potential without stimulation by external factor
3
Q
what is the intrinsic rate per min? what is this without?
A
- approx. 100 beats per minutes
- without ANS or hormones
4
Q
A
5
Q
what do pacemaker cells have?
A
- sloping resting potential
- threshold reached over time
6
Q
why does SA node initiate an action potential?
A
- due to unstable membrane potential that is continuously drifting towards threshold
7
Q
what allows the gradual depolarisation of pacemaker cells?
A
- sodium channels as allow calcium to enter and an action potential to form
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)
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
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
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
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
13
Q
what happens when the impulse reaches the Bundle of His?
A
- propagated into ventricular side of heart
14
Q
where does signal travel after Bundle of His?
A
- travels down interventricular septum via the two bundle branches
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
16
Q
what is the base of valves?
A
- insulating layer that separates atrium to ventricles
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
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
19
Q
what allows signals to travel in muscle fibres?
A
- pores in intercalated discs connect the different muscle fibres
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
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
22
Q
what is the electrocardiogram?
A
- very accurate way of measuring the heart rate by appreciating contraction in one minute
23
Q
what does atrial excitation result in?
A
- small bump of electrical stimulation
- much weaker
24
Q
what is the P wave?
A
- associated with atrial contraction
- first small wave that you can see
25
what is the T wave?
- associated with ventricular relaxation
- when electrical activity ceases the heart relaxes
25
what does straight line before Q wave show?
- AV node holding back signal to allow filling so ventricles have enough blood meaning when they squeeze blood is ejected
25
what is QRS?
- corresponds to ventricular contraction
-activation in intraventricular septum and upwards on side of ventricles
26
what does wave form measure?
- current as it travels through the heart
27
what happens if SA node doesn't fulfil its role as expected?
- other cells from heart jump in to stimulate the heart
- but it is in an unorganised fashion
28
what is the role of atrioventricular valves?
- prevents blood flowing backwards into atria
29
what is the tricuspid valve?
- separates right atrium and right ventricle
30
when does tricuspid valve open?
- when right atrial pressure is higher than right ventricle pressure
31
when does tricuspid valve close?
- when right ventricle pressure is higher than right atrial pressure
32
what is the mitral valve?
- separates left atrium and left ventricle
33
when is the mitral valve open?
- when left atrial pressure is greater than left ventricle pressure
34
when does the mitral valve close?
- closed when left ventricular pressure is higher than left atrial pressure
35
what is the role of semilunar valves?
- allow blood to exit
36
what is the pulmonary valve?
- separates right ventricle and pulmonary artery
37
when does pulmonary valve open?
- when right ventricular pressure is greater than pulmonary artery pressure
38
when do the pulmonary valves close?
- closed when pulmonary artery pressure is greater than right ventricular pressure
39
what are the aortic valves?
- separated left ventricle and aorta
40
when do the aortic valves open?
- when the left ventricular pressure is greater than aortic pressure
41
when do aortic valves close?
- when aortic pressure is higher than left ventricular pressure
42
what is systole?
- contraction of the heart
43
what is isovolumetric ventricular contraction?
- no change in overall volume as blood isn't ejected at the start
44
45
46
what happens at the start of systole? what are the valves doing?
- begins when ventricles are beginning to contract so they squeeze incompressible fluids that begins to increase pressure
- all four valves shut
47
what happens when ventricles contract?
- generate enough ventricular pressure for semilunar valves to open
- so blood flows through into vessels outside heart so blood ejected
48
what is diastole?
- relaxation of the heart
49
what is isovolumetric ventricular relaxation?
- ventricles relax without changing their blood volume
50
what happens at the beginning of diastole? what happens to the valves?
- 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
what happens at later diastole?
- atrioventricular valves are pushed open
- blood comes into ventricles by means of gravity (passively fills)
52
what completes end phase of tubular filling? is it important?
- atria contraction
- under normal conditions this isn't important because HR is slow so ventricles have enough time to fill
53
what happens if HR increases during exercise?
- ventricles beat very fast so less time to fill so gravity isn't sufficient by itself
54
what does it signify if you can heat the heart?
- atrioventricular valves or semilunar valves closing
55
what is the relationship between wave forms in pressure sides defined by?
- whether the valves are opened or closed
56
what valve is open when atrium and ventricle are relaxed?
- mitral valve
57
what happens to the valves when ventricles begin to relax? what sound does it make?
- aortic valves shut as pressure falls bellow aortic pressure
- dub sound
58
what happens when ventricular pressure exceeds aortic pressure?
- aortic valve opens
59
what valve closes when ventricles begin to contract? what sound does it make?
- mitral valve
- lub
