The Cardiac Cycle Flashcards

1
Q

describe the left atria

A

receives blood from the pulmonary vein
has a thicker myocardial wall compared to the right atrium
when it contracts, the blood is pumped through the mitral valve into the left ventricle

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2
Q

describe the right atria

A

receives blood from the superior and inferior vena cava
contraction of the atria pumps blood through the tricuspid valve into the right ventricle

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3
Q

what separates the left and right atria

A

the fibromuscular wall called the atrial septum

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4
Q

what is the interatrial septum

A

the fibromuscular wall separating the left and right atria

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5
Q

how are each atria separated from the corresponding ventricle

A

the atrioventricular septum

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6
Q

what must contract at the same time to pump blood from the heart

A

the left and right ventricles

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7
Q

which ventricle pumps more blood

A

they both pump a similar volume of blood

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8
Q

describe the left ventricle

A

thick muscular wall because it generates high pressure with every contraction
high pressure is required to eject the blood from the left ventricle through the aortic valve into the aorta

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9
Q

where does the left ventricle pump blood

A

the aorta

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10
Q

what does the left ventricle pump

A

oxygenated blood into the systemic circulation to supply tissues

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11
Q

describe the right ventricle

A

thinner muscular wall than the left ventricle and the contraction of the right ventricle generates pressure to eject blood through the pulmonary valve into the pulmonary artery

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12
Q

what does the right ventricle pump

A

deoxygenated blood to the pulmonary system

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13
Q

what is the cardiac afterload

A

the pressure that the heart must eject blood against

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14
Q

what is the left ventricle afterload related to

A

aortic pressure

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15
Q

what is the right ventricle afterload related to

A

pulmonary artery pressure

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16
Q

describing the process of opening and closing the heart valves

A

a passive process that occurs due to pressure differences across the valves
when open the heart valves offer very little resistance to blood flow

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17
Q

what are the atrioventricular valves

A

the tricuspid valve and the mitral valve

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18
Q

describe the tricuspid valve function

A

permit blood to flow between the right atria and right ventricle

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19
Q

describe the function of the mitral valve

A

otherwise known as the bicuspid valve, this permits blood to flow between the left atrium and the left ventricle

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20
Q

how do the atrioventricular valves open

A

when atria contract, the pressure in the atrium is greater than in the corresponding ventricle, which forces the valve open and blood flows from this atrium into the ventricle

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21
Q

how do the atrioventricular valves close

A

when the ventricles contract, blood does not flow back into the atria, and the ventricle internal pressure is greater than in the atrium, forcing the atrioventricular valve closed

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22
Q

what are papillary muscles

A

muscular projections of the ventricular walls that are connected to the valve cusps by chordae tendineae

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23
Q

what are chordae tedineae

A

fibrous tissue that connects the papillary muscles to the valve cusps

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24
Q

do the papillary muscles function to open and close the heart valves

A

no

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25
Q

what is the function of papillary muscles

A

prevent the backflow of blood and limit valve cusp movements

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26
Q

what are the semilunar valves

A

pulmonary valve and aortic valve

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27
Q

what is the function of the pulmonary valve

A

permit blood to flow between the right ventricle and the pulmonary artery

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28
Q

what is the function of the aortic valve

A

permit blood to flow between the left ventricle and the aorta

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29
Q

describe what the semilunar valves do when the ventricles contract

A

they allow blood to flow from the ventricles into arteries

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30
Q

describe what semilunar valves do when the ventricles relax

A

close in order to prevent the backflow of blood from arteries into the ventricles

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31
Q

do contracting cardiac muscles generate heart sounds

A

no

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32
Q

what is the lub sound of the heart caused by

A

AV valves closing

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33
Q

what is the dub sound of the heart caused by

A

semilunar valves closing

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34
Q

why may a third heart sound be heard

A

oscillation of blood flow into ventricle or various disease states like a heart valve defect

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35
Q

describe valve regurgitation

A

this is when the blood leaks back into chambers, by a valve that does not close tightly

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36
Q

what is valve stenosis

A

this is thickening or stiffening of the valve cusps, and prevents the heart valve from opening fully - this means not enough blood can flow through

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37
Q

what are congenital heart defects

A

often the pulmonary or aortic valves do not form properly during development

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38
Q

describe the cycle of blood

A
  • lungs oxygenate blood
  • goes through pulmonary veins
  • into the left atrium
  • through the mitral valve
  • into the left ventricle
  • through the aortic valve
  • goes into aorta
  • takes blood to tissues of body systems except for the lungs
  • superior and inferior vena cava bring blood back
  • goes into right atrium
  • through the tricuspid valve
  • into the right ventricle
  • through the pulmonary valve
  • into the pulmonary artery
  • into the lungs
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39
Q

which valve does the blood go through when going from the left atrium to the left ventricle

A

mitral valve

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40
Q

which valve does the blood go through when going from the left ventricle to the aorta

A

aortic valve

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41
Q

which valve does the blood go through to go from the right atrium to the right ventricle

A

tricuspid valve

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42
Q

which valve does the blood go through to go from the right ventricle to the pulmonary artery

A

the pulmonary valve

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43
Q

what are the two basic phases of the cardiac cycle

A

systole and diastole

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44
Q

describe the systole phase of the cardiac cycle

A

this is contraction of the myocardium.
there is atrial systole and ventricular systole.

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45
Q

describe atrial systole

A

atrial contraction to eject blood into ventricles

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46
Q

describe ventricular systole

A

ventricular contraction to eject blood into the aorta and pulmonary artery

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47
Q

describe the diastole phase of the cardiac cycle

A

relaxation of the myocardium which can be both atrial and ventricular

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48
Q

describe atrial diastole

A

relaxation of the atrial muscle to allow refilling and is often masked on an ecg by the ventricular systole

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49
Q

describe ventricular diastole

A

ventricular relaxation which facilitates the refilling of ventricles between contractions

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50
Q

what allows blood flow from the atria to the ventricles

A

opening of the atrioventricular valves

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51
Q

how do ventricles receive blood throughout diastole

A

via passive flow and atrial contraction

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52
Q

describe the process of ventricular filling

A

the atrioventricular valves open allowing blood to flow from the atria to the ventricles
the ventricles receive the blood throughout diastole via passive flow and atrial contraction
this is mid late diastole

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53
Q

what is an isovolumetric contraction

A

a contraction that causes no change in volume

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54
Q

describe early systole

A

ventricles are contracting however all the heart valves are remaining closed
the ventricular myocardium is developing tension and pressure on the blood volume within ventricles is increasing

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55
Q

when does rapid ventricular ejection occur

A

when the pressure in the ventricles exceeds pressure in the aorta and the pulmonary artery

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56
Q

describe rapid ventricular ejection

A

the pressure in the ventricles exceeds pressure in the aorta and the pulmonary artery. the semilunar valves open and the blood is ejected from the left ventricle into the aorta and from the right ventricle into the pulmonary artery

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57
Q

what is the stroke volume

A

the volume of blood ejected from the ventricle during systole

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58
Q

describe early diastole

A

the ventricles begin to relax, the semi lunar valves are closed
as the atrioventricular valves are also closed, there is no blood entering or leaving the ventricles, meaning there is an isovolumetric ventricular relaxation

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59
Q

describe the stages of the cardiac cycle

A

ventricular filling
early systole
rapid ventricular ejection
early diastole
ventricular filling

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60
Q

what is the end diastolic volume

A

the volume of blood in the ventricle prior to contraction ie the volume of blood at the end of the ventricular diastolic phase

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61
Q

what is the end systolic volume

A

the volume of blood remaining in the ventricle after each ejection, meaning the ventricles are not fully emptied during systole

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62
Q

what is the SV

A

the volume of blood ejected by the ventricle per contraction

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63
Q

what is the ejection fraction

A

the volume of blood ejected by the ventricle with each contraction, as percentage of end diastolic volume. it is a measure of the left ventricles efficiency

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64
Q

what is the cardiac output

A

the volume of blood ejected in one minute

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65
Q

how do you calculate the cardiac output

A

using stroke volume times heart rate

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66
Q

which two components of information do you need to calculate the cardiac output

A

the stroke volume and the heart rate

67
Q

what is the heart rate

A

number of contractions per minute

68
Q

what is a normal ejection fraction

A

greater than 55% of the end diastolic volume

69
Q

what is borderline low left ventricle ejection fraction

A

between 50-54% of the end diastolic volume

70
Q

what is the impaired left ventricle ejection fraction

A

between 36-49% of the end diastolic volume

71
Q

what is severely impared left ventricle ejection fraction

A

less than 35%

72
Q

how is heart rate determined

A

by the rate which the sino atrial node fires action potentials to stimulate contraction of the cardiac muscle

73
Q

what is the range for resting heart rate

A

60-100 beats per minute

74
Q

what determines the rate of action potential firing and heart rate

A

the autonomic nervous system

75
Q

how is the sympathetic nervous system involved in control of heart rate

A

has alpha and beta adrenoreceptors, and the heart predominantly contains beta 1 adrenoreceptors on the cardiac conduction system and the myocardium

76
Q

how is the parasympathetic nervous system involved in the control of heart rate

A

involved in the rest and digest mechanism and is mediated by the muscarinic receptors which bind acetylcholine, a neurotransmitter

77
Q

describe the process of how the beta 1 cells of the sympathetic nervous system affect heart rate

A

the noradrenaline binds to the beta 1 adrenoreceptors on the sinoatrial node.
this activates g proteins
this activates adenyl cyclase
this increase cAMP
this activates protein kinase A
protein kinase A phosphorylates and activates receptors and calcium ion channels in cardiomyocytes

78
Q

what are the cardiac effects of the sympathetic nervous system

A

positive chronotropy
positive intropy
positive lusitropy
positive dromotropy

79
Q

what is positive chronotropy

A

increased heart rate

80
Q

what is positive inotropy

A

increased strength of the myocardial contraction

81
Q

what is positive lusitropy

A

increased rate of myocardial relaxation

82
Q

what is positive demotropy

A

increased conduction speed in the atrioventricular node

83
Q

from which cranial nerve are cholinergic nerves derived from

A

the vagus nerve

84
Q

describe the process of how the parasympathetic nervous system brings about a change in heart rate

A

cholinergic nerves derived from the vagus nerve releases neurotransmitter acetylcholine
this binds to m2 muscarinic receptors in the cardiac muscle, particularly at the sinoatrial and atrioventricular nodes which activates inhibitory g protein and blocks the cAMP pathway, allowing the potassium efflux from the cell

85
Q

what are the effects of the parasympathetic nervous system on the control of heart rate

A

negative chonotropy
negative inotropy
negative lusitropy in the atria
negative dromotropy

86
Q

what is negative chonotropy

A

decreasing heart rate

87
Q

what is negative inotropy

A

decreasing force of myocardial contraction

88
Q

what is negative lusitropy

A

decreasing rate of myocardial relaxation

89
Q

what is negative dromotropy

A

decreasing conduction speed in the atrioventricular node

90
Q

how does the cardiac conduction system work in relation to the sinoatrial node

A

a wave of depolarisation is intitiated at the SA node and travels through the cardiac conduction system innervating the myocardium and travelling to cells within the myocardium

91
Q

describe cardiac muscle

A

specialised striated muscle which contracts in coordinated rhythms to pump blood around the body to meet metabolic demands

92
Q

what are cardiomyocytes

A

the heart muscle cells

93
Q

how can the potential o fthe sarcolemma of living cells be described in the heart

A

electrically polarised

94
Q

what is membrane potential

A

potential difference between intracellular and extracellular sides of the cell membrane
generated by ion gradients across the cell membrane
dependent on ionic gradients across the membrane and ionic permeability

95
Q

what transports ions across the sarcolemmal membrane

A

ion channel proteins and transporters

96
Q

what are channels and transporters selective for

A

various ions

97
Q

what are some cell types that have an electrically excitable membrane

A

myocytes and neurons

98
Q

what is depolarisation

A

potential electrical difference across the cell membrane becomes less negative

99
Q

what is repolarisation

A

potential difference across the sarcolemma returns to resting membrane potential following depolarisation and becomes more negative

100
Q

what is action potential

A

the rise and fall in membrane potential which has a characteristic pattern for specific cell types
action potential shape changes in different cardiac regions

101
Q

describe intercalated discs

A

these are located at longitudinal ends of the cardiomyocytes and are involved in cell to cell coupling by desmosomes connected by a gap junction
they facilitate the electrical conduction from cell to cell

102
Q

what is excitation contraction coupling

A

coupling of the electrical activity of the cardiac conduction system to the mechanical contraction of the myocardium

103
Q

describe the process of excitation contraction coupling

A
  • wave of electrical excitation travels from SA node to the myocytes of the right atrium and left atrium to initiate the atrial contraction
  • propagation of depolarisation by action potential through the right atrium to the atrioventricular node
  • the atrioventricular node acts as a delay point allowing for the atria to completely empty blood into the ventricles
  • stimulation of the atrioventricular node facilitates the propagation of action potential depolarisation along the interventricular septum via the bundle of his
  • the bundle of his separates into the left and right bundle branches which innervate the ventricular walls of the myocardium
  • rapid propagation of action potential along the purkinje fibres initiates coordinated simultaneous contraction of the cardiac myocytes of the left and right ventricles
104
Q

what does the atrioventricular node act as in the process of excitation contraction coupling

A

a delay point to allow the atria to completely empty blood into the ventricles

105
Q

what initiates coordinated simultaneous contraction of cardiac myocytes of the left and right ventricles

A

rapid propagation of action potential along the purkinje fibres

106
Q

what are the phases of ventricle action potential

A

phase 0, 1 2 3 and 4

107
Q

what is phase four of the ventricle action potential

A

resting membrane potential

108
Q

what is phase zero of the ventricle action potential

A

rapid depolarisation

109
Q

what is phase one of ventricle action potential

A

early repolarisation

110
Q

what is phase two of ventricle action potential

A

plateau

111
Q

what is phase three of the ventricle action potential

A

repolarisation

112
Q

what are the phases of sinoantrial node action potential

A

phase 0, 3 and 4

113
Q

what is phase four of diastolic depolarisation

A

slow depolarisation of the sino atrial node membrane potential due to slow entry of sodium into the sinoatrial node cells acros the sarcolemma via funny channels

114
Q

what is phase zero of sinoatrial node action potential

A

the threshold potential is reached and calcium channels open to trigger action potential upstroke

115
Q

what must be reduced for relaxation to occur

A

calcium concentrations in the cell

116
Q

what is a possible route for calcium to follow in order to leave the cell

A

via an ATPase

117
Q

describe the cardiomyocyte contractile cycle

A
  • calcium binds to troponin C, leading to a conformational change that displaces tropomyosin from the actin binding sites
  • crossbridge formation occurs with ATP hydrolysation into ADP and Pi
  • power stroke moves the actin filament toward the centre of the sarcomere, and ADP and P are released from the myosin heads
  • actin is released with ATP binding to myosin. myosin heads cocked back into firing position, ready to make the cross bridges further downstream
  • cycle continues until cellular calcium levels decrease, allowing calcium to disassociate from troponin. tropomyosin returns to its original conformation that block actin binding site
118
Q

what is related to the strength of the myocardiacl contraction

A

the size of the systolic transient ie the increase of calcium within the cardiac myocyte cytosol due to the excitation contraction coupling

119
Q

how can the force of cardiac contraction be influenced

A

the length of the heart muscle cell

120
Q

what is starling’s law

A

the more the heart chambers fill, the stronger the ventricular contraction and the greater the stroke volume

121
Q

what is the cardiac preload

A

the initial stretching of cardiac myocytes prior to the contraction, which is indicated by the ventricular end. as stretching of cardiac myocytes cannot be determined in an intact heart

122
Q

what does starling’s law determine about the magnitude of stretch

A

that it predicts the strength of the contraction

123
Q

what is an ecg

A

echocardiogram

124
Q

what is an echocardiogram

A

type of ultrasound scan that is used to assess structure and function of the heart. leads to high temperol resolution

125
Q

describe doppler echocardiogram

A

red blood cells reflect ultrasound waves, and the sound waves are used to measure blood flow through the heart

126
Q

what are erythrocytes

A

red blood cells

127
Q

what can echocardiograms aid in the detection of

A
  • impaired cardiac contractility
  • congentinal heart disease
  • cardiomyopathy
  • endocarditis
  • heart failure
128
Q

what can result in impaired cardiac contractility

A

myocardial infarction like a heart attack

129
Q

what is congenital heart disease

A

birth defects that can impact cardiac function

130
Q

what is cardiomyopathy

A

enlargement of the ventricular walls

131
Q

what is endocarditis

A

infection of the endocardium that damages the heart valves

132
Q

what is heart failure

A

when the heart is unable to adequately pump blood to meet the metabolic demands of the body

133
Q

how does an ecg work

A

it detects phasic change in potential difference between the two electrodes.
the electrodes are placed on limbs and on the surface of the chest
this is recorded on a computer, or paper or an oscilloscope
clinically useful in diagnosis of arrhythmias

134
Q

what is bradycardia

A

slow heart rate

135
Q

what is tachycardia

A

fast heart rate

136
Q

how many stages are there to the cardiac cycle

A

4

137
Q

what is the cardiac cycle

A

the mechanical events where the heart

138
Q

how long does it take for completion of one cardiac cycle

A

0.8 seconds

139
Q

what is the first stage of the cardiac cycle

A

mid to late ventricular diastole

140
Q

describe mid to late ventricular diastole, ie stage two of the cardiac cycle.

A

this is the stage where blood returns to the heart.
blood from the system, pulmonary and coronary veins come into the atria
blood accumulates
this increases the pressure of the atria to be greater than the ventricular pressure
av valves open
70-80% of the blood flows down passively due to gravity
sa nodes fire and produce depolarisation of the atria, making it contract
this pushes the remaining 20% of blood into the ventricles

141
Q

how much blood flows passively into the ventricles in the mid to late diastole stage

A

70-80%

142
Q

which veins bring blood to the atria in the first stage of the cardiac cycle

A

pulmonary
coronary
systemic

143
Q

are the ventricles contracting in mid to late diastole

A

no

144
Q

how does the mid to late diastole period appear on ECG

A

as a P wave

145
Q

what occurs in the mid to late ventricular diastole stage

A

blood returns to the heart in the period of ventricular filling

146
Q

what allows for the final 20% of atrial blood to get into the ventricles

A

the sinoatrial node fires and produces depolarisation of the atria making it contract and push the remaining blood

147
Q

what is the second part of the cardiac cycle

A

the isovolumetric contraction

148
Q

describe the events in the isovolumatric contraction stage of the cardiac cycle

A
  • starts with the blood sitting in the ventricles
  • ventricles slowly start to depolarise, squeeze and contract via the myocardium
  • blood rises toward the pulmonary trunk and aorta
  • pressure in the aorta is naturally 80mmhg so the ventricular pressure at this point is still less
  • this means the semilunar valves remain closed
149
Q

what produces the first heart sound, and what is it called

A

at the isovolumetric contraction phase of the cardiac cycle, the av valves snap shut, producing the first sound referred to as lub

150
Q

what is the end diastolic volume

A

this is the volume of blood in the ventricles at the beginning of the isovolumetric contraction stage

151
Q

what is the pressure of the pulmonary trunk

A

7-10 mmhg

152
Q

which system is more pressurised, the aorta or the pulmonary trunk

A

the aorta

153
Q

at what stage do the av valves close

A

isovolumetric contraction

154
Q

why do the semilunar valves not open in the isovolumetric contraction phase

A

the arterial pressure is greater than the ventricular pressure

155
Q

what is the third stage of the cardiac cycle

A

mid to late ventricular systole

156
Q

what is the mid to late ventricular systole stage

A

the third stage of the cardiac cycle where there is ventricular ejection of blood

157
Q

describe the events that occur in the mid to late ventricular systole stage of the cardiac cycle

A
  • the pressure in the left ventricle rises to about 120mmhg as the myocardium contracts the ventricles and pushes blood upward
  • semilunar valves open and blood moves out
  • av valves remain closed
  • ventricular pressure is greater than arterial pressure in the pulmonary trunk and the aorta
  • blood is pushed up by the ventricles and is ejected
158
Q

how does mid to late ventricular systole appear on the ECG

A

QRS complex

159
Q

which phase of the cardiac cycle involves ventricular ejection

A

mid to late ventricular systole

160
Q

does the right ventricle ever have high pressure

A

no it should not be a high pressure system in healthy individuals, and should only ever get as high as 24-27mmhg during the systole phase

161
Q

are the av valves open in the mid to late systole phase

A

no

162
Q

which valves open during mid to late ventricular systole

A

semilunar

163
Q

which valves are open during mid to late ventricular diastole

A

av valves

164
Q
A