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
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
3
Q
what separates the left and right atria
A
the fibromuscular wall called the atrial septum
4
Q
what is the interatrial septum
A
the fibromuscular wall separating the left and right atria
5
Q
how are each atria separated from the corresponding ventricle
A
the atrioventricular septum
6
Q
what must contract at the same time to pump blood from the heart
A
the left and right ventricles
7
Q
which ventricle pumps more blood
A
they both pump a similar volume of blood
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
9
Q
where does the left ventricle pump blood
A
the aorta
10
Q
what does the left ventricle pump
A
oxygenated blood into the systemic circulation to supply tissues
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
12
Q
what does the right ventricle pump
A
deoxygenated blood to the pulmonary system
13
Q
what is the cardiac afterload
A
the pressure that the heart must eject blood against
14
Q
what is the left ventricle afterload related to
A
aortic pressure
15
Q
what is the right ventricle afterload related to
A
pulmonary artery pressure
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
17
Q
what are the atrioventricular valves
A
the tricuspid valve and the mitral valve
18
Q
describe the tricuspid valve function
A
permit blood to flow between the right atria and right ventricle
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
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
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
22
Q
what are papillary muscles
A
muscular projections of the ventricular walls that are connected to the valve cusps by chordae tendineae
23
Q
what are chordae tedineae
A
fibrous tissue that connects the papillary muscles to the valve cusps
24
Q
do the papillary muscles function to open and close the heart valves
A
no
25
what is the function of papillary muscles
prevent the backflow of blood and limit valve cusp movements
26
what are the semilunar valves
pulmonary valve and aortic valve
27
what is the function of the pulmonary valve
permit blood to flow between the right ventricle and the pulmonary artery
28
what is the function of the aortic valve
permit blood to flow between the left ventricle and the aorta
29
describe what the semilunar valves do when the ventricles contract
they allow blood to flow from the ventricles into arteries
30
describe what semilunar valves do when the ventricles relax
close in order to prevent the backflow of blood from arteries into the ventricles
31
do contracting cardiac muscles generate heart sounds
no
32
what is the lub sound of the heart caused by
AV valves closing
33
what is the dub sound of the heart caused by
semilunar valves closing
34
why may a third heart sound be heard
oscillation of blood flow into ventricle or various disease states like a heart valve defect
35
describe valve regurgitation
this is when the blood leaks back into chambers, by a valve that does not close tightly
36
what is valve stenosis
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
37
what are congenital heart defects
often the pulmonary or aortic valves do not form properly during development
38
describe the cycle of blood
- 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
39
which valve does the blood go through when going from the left atrium to the left ventricle
mitral valve
40
which valve does the blood go through when going from the left ventricle to the aorta
aortic valve
41
which valve does the blood go through to go from the right atrium to the right ventricle
tricuspid valve
42
which valve does the blood go through to go from the right ventricle to the pulmonary artery
the pulmonary valve
43
what are the two basic phases of the cardiac cycle
systole and diastole
44
describe the systole phase of the cardiac cycle
this is contraction of the myocardium.
there is atrial systole and ventricular systole.
45
describe atrial systole
atrial contraction to eject blood into ventricles
46
describe ventricular systole
ventricular contraction to eject blood into the aorta and pulmonary artery
47
describe the diastole phase of the cardiac cycle
relaxation of the myocardium which can be both atrial and ventricular
48
describe atrial diastole
relaxation of the atrial muscle to allow refilling and is often masked on an ecg by the ventricular systole
49
describe ventricular diastole
ventricular relaxation which facilitates the refilling of ventricles between contractions
50
what allows blood flow from the atria to the ventricles
opening of the atrioventricular valves
51
how do ventricles receive blood throughout diastole
via passive flow and atrial contraction
52
describe the process of ventricular filling
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
53
what is an isovolumetric contraction
a contraction that causes no change in volume
54
describe early systole
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
55
when does rapid ventricular ejection occur
when the pressure in the ventricles exceeds pressure in the aorta and the pulmonary artery
56
describe rapid ventricular ejection
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
57
what is the stroke volume
the volume of blood ejected from the ventricle during systole
58
describe early diastole
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
59
describe the stages of the cardiac cycle
ventricular filling
early systole
rapid ventricular ejection
early diastole
ventricular filling
60
what is the end diastolic volume
the volume of blood in the ventricle prior to contraction ie the volume of blood at the end of the ventricular diastolic phase
61
what is the end systolic volume
the volume of blood remaining in the ventricle after each ejection, meaning the ventricles are not fully emptied during systole
62
what is the SV
the volume of blood ejected by the ventricle per contraction
63
what is the ejection fraction
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
64
what is the cardiac output
the volume of blood ejected in one minute
65
how do you calculate the cardiac output
using stroke volume times heart rate
66
which two components of information do you need to calculate the cardiac output
the stroke volume and the heart rate
67
what is the heart rate
number of contractions per minute
68
what is a normal ejection fraction
greater than 55% of the end diastolic volume
69
what is borderline low left ventricle ejection fraction
between 50-54% of the end diastolic volume
70
what is the impaired left ventricle ejection fraction
between 36-49% of the end diastolic volume
71
what is severely impared left ventricle ejection fraction
less than 35%
72
how is heart rate determined
by the rate which the sino atrial node fires action potentials to stimulate contraction of the cardiac muscle
73
what is the range for resting heart rate
60-100 beats per minute
74
what determines the rate of action potential firing and heart rate
the autonomic nervous system
75
how is the sympathetic nervous system involved in control of heart rate
has alpha and beta adrenoreceptors, and the heart predominantly contains beta 1 adrenoreceptors on the cardiac conduction system and the myocardium
76
how is the parasympathetic nervous system involved in the control of heart rate
involved in the rest and digest mechanism and is mediated by the muscarinic receptors which bind acetylcholine, a neurotransmitter
77
describe the process of how the beta 1 cells of the sympathetic nervous system affect heart rate
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
what are the cardiac effects of the sympathetic nervous system
positive chronotropy
positive intropy
positive lusitropy
positive dromotropy
79
what is positive chronotropy
increased heart rate
80
what is positive inotropy
increased strength of the myocardial contraction
81
what is positive lusitropy
increased rate of myocardial relaxation
82
what is positive demotropy
increased conduction speed in the atrioventricular node
83
from which cranial nerve are cholinergic nerves derived from
the vagus nerve
84
describe the process of how the parasympathetic nervous system brings about a change in heart rate
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
what are the effects of the parasympathetic nervous system on the control of heart rate
negative chonotropy
negative inotropy
negative lusitropy in the atria
negative dromotropy
86
what is negative chonotropy
decreasing heart rate
87
what is negative inotropy
decreasing force of myocardial contraction
88
what is negative lusitropy
decreasing rate of myocardial relaxation
89
what is negative dromotropy
decreasing conduction speed in the atrioventricular node
90
how does the cardiac conduction system work in relation to the sinoatrial node
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
describe cardiac muscle
specialised striated muscle which contracts in coordinated rhythms to pump blood around the body to meet metabolic demands
92
what are cardiomyocytes
the heart muscle cells
93
how can the potential o fthe sarcolemma of living cells be described in the heart
electrically polarised
94
what is membrane potential
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
what transports ions across the sarcolemmal membrane
ion channel proteins and transporters
96
what are channels and transporters selective for
various ions
97
what are some cell types that have an electrically excitable membrane
myocytes and neurons
98
what is depolarisation
potential electrical difference across the cell membrane becomes less negative
99
what is repolarisation
potential difference across the sarcolemma returns to resting membrane potential following depolarisation and becomes more negative
100
what is action potential
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
describe intercalated discs
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
what is excitation contraction coupling
coupling of the electrical activity of the cardiac conduction system to the mechanical contraction of the myocardium
103
describe the process of excitation contraction coupling
- 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
what does the atrioventricular node act as in the process of excitation contraction coupling
a delay point to allow the atria to completely empty blood into the ventricles
105
what initiates coordinated simultaneous contraction of cardiac myocytes of the left and right ventricles
rapid propagation of action potential along the purkinje fibres
106
what are the phases of ventricle action potential
phase 0, 1 2 3 and 4
107
what is phase four of the ventricle action potential
resting membrane potential
108
what is phase zero of the ventricle action potential
rapid depolarisation
109
what is phase one of ventricle action potential
early repolarisation
110
what is phase two of ventricle action potential
plateau
111
what is phase three of the ventricle action potential
repolarisation
112
what are the phases of sinoantrial node action potential
phase 0, 3 and 4
113
what is phase four of diastolic depolarisation
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
what is phase zero of sinoatrial node action potential
the threshold potential is reached and calcium channels open to trigger action potential upstroke
115
what must be reduced for relaxation to occur
calcium concentrations in the cell
116
what is a possible route for calcium to follow in order to leave the cell
via an ATPase
117
describe the cardiomyocyte contractile cycle
- 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
what is related to the strength of the myocardiacl contraction
the size of the systolic transient ie the increase of calcium within the cardiac myocyte cytosol due to the excitation contraction coupling
119
how can the force of cardiac contraction be influenced
the length of the heart muscle cell
120
what is starling's law
the more the heart chambers fill, the stronger the ventricular contraction and the greater the stroke volume
121
what is the cardiac preload
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
what does starling's law determine about the magnitude of stretch
that it predicts the strength of the contraction
123
what is an ecg
echocardiogram
124
what is an echocardiogram
type of ultrasound scan that is used to assess structure and function of the heart. leads to high temperol resolution
125
describe doppler echocardiogram
red blood cells reflect ultrasound waves, and the sound waves are used to measure blood flow through the heart
126
what are erythrocytes
red blood cells
127
what can echocardiograms aid in the detection of
- impaired cardiac contractility
- congentinal heart disease
- cardiomyopathy
- endocarditis
- heart failure
128
what can result in impaired cardiac contractility
myocardial infarction like a heart attack
129
what is congenital heart disease
birth defects that can impact cardiac function
130
what is cardiomyopathy
enlargement of the ventricular walls
131
what is endocarditis
infection of the endocardium that damages the heart valves
132
what is heart failure
when the heart is unable to adequately pump blood to meet the metabolic demands of the body
133
how does an ecg work
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
what is bradycardia
slow heart rate
135
what is tachycardia
fast heart rate
136
how many stages are there to the cardiac cycle
4
137
what is the cardiac cycle
the mechanical events where the heart
138
how long does it take for completion of one cardiac cycle
0.8 seconds
139
what is the first stage of the cardiac cycle
mid to late ventricular diastole
140
describe mid to late ventricular diastole, ie stage two of the cardiac cycle.
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
how much blood flows passively into the ventricles in the mid to late diastole stage
70-80%
142
which veins bring blood to the atria in the first stage of the cardiac cycle
pulmonary
coronary
systemic
143
are the ventricles contracting in mid to late diastole
no
144
how does the mid to late diastole period appear on ECG
as a P wave
145
what occurs in the mid to late ventricular diastole stage
blood returns to the heart in the period of ventricular filling
146
what allows for the final 20% of atrial blood to get into the ventricles
the sinoatrial node fires and produces depolarisation of the atria making it contract and push the remaining blood
147
what is the second part of the cardiac cycle
the isovolumetric contraction
148
describe the events in the isovolumatric contraction stage of the cardiac cycle
- 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
what produces the first heart sound, and what is it called
at the isovolumetric contraction phase of the cardiac cycle, the av valves snap shut, producing the first sound referred to as lub
150
what is the end diastolic volume
this is the volume of blood in the ventricles at the beginning of the isovolumetric contraction stage
151
what is the pressure of the pulmonary trunk
7-10 mmhg
152
which system is more pressurised, the aorta or the pulmonary trunk
the aorta
153
at what stage do the av valves close
isovolumetric contraction
154
why do the semilunar valves not open in the isovolumetric contraction phase
the arterial pressure is greater than the ventricular pressure
155
what is the third stage of the cardiac cycle
mid to late ventricular systole
156
what is the mid to late ventricular systole stage
the third stage of the cardiac cycle where there is ventricular ejection of blood
157
describe the events that occur in the mid to late ventricular systole stage of the cardiac cycle
- 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
how does mid to late ventricular systole appear on the ECG
QRS complex
159
which phase of the cardiac cycle involves ventricular ejection
mid to late ventricular systole
160
does the right ventricle ever have high pressure
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
are the av valves open in the mid to late systole phase
no
162
which valves open during mid to late ventricular systole
semilunar
163
which valves are open during mid to late ventricular diastole
av valves
164
