Cardiovascular system Flashcards
(306 cards)
1
Q
Of what does cardiac muscle consist?
A
Of short, striated muscle fibres (cells).
2
Q
What do sliding filaments allow?
A
Shortening of the muscle.
3
Q
Due to which factors’ action are filaments arranged in bundles?
A
Due to the action of actin and myosin.
4
Q
What is actin?
A
Thin.
5
Q
What is myosin?
A
Thick.
6
Q
What are the bundles where filaments are arranged called?
A
Myofibrils.
7
Q
What are the energy demands on the cell?
A
So high.
8
Q
What is 40% of cell volume?
A
Mitochondria.
9
Q
What is the outer layer of the ventricle wall called?
A
The pericardium.
10
Q
With what does the inner layer or the ventricle make contact with?
A
The blood.
11
Q
How is the inner layer of the ventricle called?
A
The endocardium.
12
Q
What is in the middle of the ventricle?
A
The thick myocardium/muscle layer.
13
Q
Of what is the muscle/myocardium composed?
A
Of myocytes.
14
Q
Of what is each myocyte composed?
A
Of myofibrils.
15
Q
What are myofibrils?
A
Cylindrical organelles.
16
Q
What are the cylindrical organelles of muscles?
A
The contractile unit.
17
Q
What are the cardiac muscle cells/myocardial cells?
A
Striated.
18
Q
What do myocardial cells contain?
A
Actin and myosin filaments.
19
Q
How areactin and myosin filaments arranged?
A
In the form of sarcomeres.
20
Q
By what do actin and myosin filaments contract?
A
By means of the sliding filament mechanism.
21
Q
How are myocardial cells characterised?
A
Short.
Branched.
Interconnected.
22
Q
What is each myocardial cell in structure?
A
Tubular.
23
Q
To what is each myocardial cell joined?
A
To adjacent myocardial cells.
24
Q
By what is each myocardial cell joined to adjacent myocardial cells?
A
By electrical synapses/gap junctions.
25
Where are the gap junctions concentrated?
At the ends of each myocardial cell.
26
What does each myocardial cell permit?
Electrical impulses.
27
Where are electrical impulses of myocardial cells conducted?
Along the long axis from cell to cell.
28
For what do gap junctions in cardiac muscle have an affinity?
For stain.
29
As what does stain make the gap junctions appear in cardiac muscle?
As dark lines between adjacent cells.
30
When do gap junctions appear as dark lines between adjacent cells?
When they are viewed in the light microscope.
31
As what are the dark-staining lines known?
As intercalated discs.
32
Where do action potentials originate?
At any point in a mass of myocardial cells.
33
How are the actions potential from myocardial cells called?
Myocardium.
34
Where is myocardium spread?
To all cells in the mass that are joined by gap junctions.
35
What are all cells in a myocardium?
Electrically joined.
36
As what does a myocardium behave?
As a single functional unit.
37
What do skeletal muscles produce?
Contractions.
38
Depending on what are skeletal muscles graded?
On the number of cells stimulated.
39
To what does a myocardium contract each time?
To its full extent.
40
Why does myocardium contract to its full extend each time?
Because all of its cells contribute to the contraction.
41
What can the ability of the myocardial cells to contract do?
Increased by the hormone adrenaline.
| By stretching of the heart chambers.
42
Of what is a myocyte made?
Of many myofibrils.
43
To what does the outer sarcolemma membrane serve?
To bundle the fibrils.
44
To what is the sarcolemma similar?
To a typical plasma membrane.
45
For what does the sarcolemma have specialised functions?
For the muscle cell.
46
By what is the dark and light banding pattern cause?
By the regular arrangement of actin and myosin filaments.
47
Where does depolarisation of the membrane proceed?
Down the longitudinal tubules to all the myofibrils.
48
Across what does depolarisation spread?
Across the sarcoplasmic reticulum.
49
Via what does the depolarisation spread across the sarcoplasmic reticulum?
Via the transverse/T tubules.
50
What is the SR?
The store of cellular calcium ions.
51
Thanks to what a more detailed banding pattern can be observed?
Thanks to the arrangement of the tubules.
52
Of what do triads consist?
Of two terminal cisterns of the L-system. associated with a central T-tubule segment.
53
What is the main function of the triads?
To translate the action potential from the plasma membrane to the sarcoplasmic reticulum.
54
What does action potential from the plasma membrane to the sarcoplasmic reticulum affect?
Calcium flow into the cytoplasm.
| Initiation of muscle contraction.
55
Where do T tubules project?
Into the depths of the myocyte.
56
Of what id each myofibril composed?
Of a thick and thin filaments.
57
To what do thick and thin filaments of myofibril give rise?
To the banding pattern of the muscle.
58
What do the voltage-gated Ca channels in the plasma membrane and the Ca release?
Channels in the sarcoplasmic reticulum.
59
What do voltage-gated Ca channels and the Ca do not?
Directly interact.
60
To what region do the transverse T tubules come very close to?
To the sarcoplasmic reticulum.
61
During what does depolarization of the T tubules occur?
During an action potential.
62
What does depolarization of the T tubules open?
Voltage-gated Ca channels in their plasma membrane.
63
Where does Ca diffuse?
Into the the cytoplasm.
64
With what does the Ca that diffuses into the cytoplasm interact?
With the nearby Ca.
65
What do Ca diffused into the cytoplasm and the nearby Ca that interact with, release?
Channels in the sarcoplasmic reticulum.
66
What does the release of channels in the sarcoplasmic reticulum causes the Ca channels?
To pen and release the stored Ca into the cytoplasm.
67
What does the release of the stored Ca into the stimulate stimulate?
Contraction.
68
What is contraction?
A process termed: calcium-induced calcium release.
69
As what does Ca serve?
As a second messenger.
70
From where to where does Ca serve as a second messenger?
From the voltage-gated Ca channels to the Ca release channels.
71
Where is excitation-contraction coupling slower as a result of Ca serving as a second messenger?
In cardiac than in skeletal muscle.
72
Through where does Ca diffusion take place?
Through the plasma membrane of the transverse tubules.
73
Where does Ca diffusion serve mainly?
To open the channels in the sarcoplasmic reticulum.
74
Where does Ca release channels?
In the sarcoplasmic reticulum.
75
For what is the Ca release responsible?
For the rapid diffusion of Ca into the cytoplasm.
76
Where does Ca bind to after is diffused into the cytoplasm?
To troponin.
77
What does Ca stimulate after is diffused into the cytoplasm and binds to troponin?
Contraction.
78
What must the Ca in the cytoplasm be in order for the muscular chambers of the heart to relax?
They must be actively transported back into the sarcoplasmic reticulum by the Ca ATPase.
79
What does tropomyosin block in a relaxed muscle?
The attachment of cross bridges to actin .
| Concentration of Ca.
80
What is the calcium concentration in the sarcoplasm?
Very low.
81
What happens to the Ca concentration in the sarcoplasm when the muscle cell is stimulated to contract?
It rises sharply.
82
What does some of the Ca attach?
Troponin.
83
What does the Ca attachment to troponin cause?
A conformational change.
84
What does the conformational change caused by Ca and troponin attachment move?
The troponin complex --> attached to tropomyosin.
85
Why does conformational change move troponin complex and its attached it out of the way?
So that the cross bridges can attach to actin.
86
Where do cross bridges bind to once the attachment sites on the actin are exposed?
To actin.
87
What do cross bridges that bind to actin undergo?
Power strokes.
88
What do cross bridges that bind to actin produce?
Muscle contraction.
89
What is now the preferred test for detecting myocardial infarction or heart attack?
Measurement of cardiac-specific troponin T/troponin I.
90
What happens to the myocardial cells in the measurement of cardiac-specific troponin T blood test?
They die and release troponin T/I proteins into the blood.
91
Where do blood tests for troponin T/I rely on?
Binding to specific antibodies.
92
What are the blood tests for troponin T/I?
Heart specific.
93
What does an abnormally increased plasma troponin T/I may indictaed?
That an myocardial infarction (MI) has occurred.
94
What has cardiac troponin become?
A continuous variable.
95
What is the accurate measurement of cardiac troponin?
Below the 99th percentile.
96
How many changes do occur in cardiac toponin?
Small changes within 1/2 hours.
97
What does cardiac troponin measurement and changes enable?
Development of algorithms for reliable rule-out and rule-in of acute MI within 2 hours.
98
What is the cardiac muscle?
Striated.
99
What does the cardiac muscle contain?
Sarcomeres that shorten.
100
By what do the sarcomeres in the cardiac muscle shorten?
By sliding of thick and thin filaments.
101
Of what might the detection of elevated troponin be indicative?
Of heart damage.
102
What do the sarcolemma and T-tubules conduct?
Electrical impulse to the muscle.
103
What does the conduction of sarcolemma and T-tubules that conduct electrical impulse to the muscle trigger?
Calcium release from SR.
104
To what does calcium bind?
To troponin.
105
How are the Bundles of cardiac muscle fibres arranged?
Spirally around the ventricles.
106
How are adjacent cardiac muscle cells joined?
End to end.
107
By what are the cardiac muscle cells joined end to end ?
By intercalated discs.
108
What do intercalated discs contain?
Two types of specialized junctions.
109
Which are the 2 types of specialized junctions that are contained in the intercalated discs?
1. Desmosomes.
| 2. Gap junctions.
110
How do desmosomes act?
Like rivets.
111
How do desmosomes hold the cells together?
Mechanically.
112
What do gap junctions permit?
Action potentials to spread from one cell to adjacent cells.
113
Of what is the heart composed?
Of spiral clockwise and counter clockwise arrangement of muscle fibres.
114
What does the physiological sequence of ventricular function involve?
An isovolumic contraction phase to develop preejection tension.
115
What does pre-ejection tension mean?
The muscle begins to contract without expelling the blood.
116
What does follow the ejection phase?
Post-ejection isovolumic phase.
117
When does post-ejection isovolumic phase occur?
When there is no change in volume.
118
What do occur after post-ejection phase?
Rapid and slow periods for filling.
119
How does LV volume decrease in systole?
Rapidly.
120
What is systole?
The name for contraction.
121
How does LV volume decrease after contraction?
Slowly.
122
How does the volume increase in early filling?
Rapidly.
123
How does the volume increase during late filling?
More slowly.
124
Of what does the heart consist?
4 chambers.
2 atria.
2 ventricles.
major vessels.
125
What do inferior and superior venae cavae bring?
Deoxygenated blood back to the right atrium.
126
With what does the left atrium fill?
With oxygenated blood from the pulmonary vein.
127
Into where id the blood pumped upon simultaneous contraction?
Into the ventricles.
128
Through what is the blood pumped into the ventricles upon simultaneous contraction?
Through the tricuspid and bicuspid valves.
129
What do the pulmonary semilunar valve and aortic semilunar valves do as the ventricles contract?
They open.
130
Into where is the deoxygenated blood pumped?
Into the pulmonary artery.
131
To where is the pumped blood into the pulmonary artery be taken?
To the lungs.
132
Into where is the oxygenated blood pumped?
Into the aorta.
133
Where is the pumped blood into the aorta carried?
Around the body.
134
By what is the eversion of the AV valves prevented?
By tension on the valve leaflets.
135
By what are the valve leaflets exert?
By the chordae tendineae.
136
When do the valve leaflets exert by the chordae tendineae?
When the papillary muscles contract.
137
What happens to the upturned edges of the semilunar valves when they are swept closed?
They fit together in a deep, leakproof seam.
138
What does the deep, leakproof seam prevent?
Valve eversion.
139
What is the difference between a cyclist and a patient with morphologically mild hypertrophic cardiomyopathy?
The cyclist has an enlarged left ventricular cavity.
140
How is cardiac output measured?
Volume of blood pumped by the left ventricle + right ventricle per unit time.
141
By what is the cardiac output determined?
By the heart rate * stroke volume.
142
By what factors is heart rate influenced?
By hormones: adrenaline.
Fitness.
Age.
Autonomic activity.
143
What do fitter people normally have?
A lower heart rate.
144
What do older people usually have?
A higher heart rate.
145
What happens to the heart rate if parasympathetic activity is high?
It is lower.
146
By which factors is stroke volume influenced?
By many factors.
147
What can a larger athletic heart pump?
A larger volume.
148
What do males usually have?
A larger stroke volume.
149
What do a longer duration and stronger contraction increase?
SV.
150
What does a larger end diastolic volume increase?
SV.
151
What does a lower vessel resistance permit?
A larger volume of blood to be ejected.
152
In response to which factor does stroke volume increase according to the Frank-Starling law?
To increased EDV.
153
What is diastole?
The relaxation of the heart.
154
When does SV increase?
As EDV and pressure increase.
155
With what does the slope increase?
With sympathetic activity.
156
What does the slope cause when increases?
Increased stroke volume.
157
What happens to the slope and stroke volume with parasympathetic activity?
They decrease.
158
When is the heart muscle subjected to an increasing degree of stretch?
As EDV increases.
159
How does the heart muscle contract s in strecth?
More forcefully.
160
What is the sarcomere?
A unit of striated muscle tissue.
161
What does the sarcomere do as EDV increases?
It stretches.
162
What happens to the actin filaments attached to parallel Z-lines as EDV increases?
They are pulled apart.
163
What does the sympathetic activity increase?
The strength of myocardial contraction.
164
What effect does the sympathetic activity that increases the strength of myocardial contraction?
It has a positive inotropic effect.
165
What happens to the sarcomere beyond a certain volume ?
It stretches to a degree.
166
What does the sarcomere degree impair?
The amount of force it can generate.
167
Through where does blood flow to reach the organs of the body?
Through arteries.
168
By what does is the blood pumped?
By action of the heart.
169
What do the arrows indicate?
The direction of blood flow.
170
How are all of the heart valves shown to illustrate the direction of blood flow through the heart?
Open.
171
What does the right side of the heart receive?
Oxygen poor blood from the systemic circulation.
172
Into where does the right side of the heart pump oxygen poor blood?
Into the pulmonary circulation.
173
What does the left side of the heart receive?
Oxygen rich blood from the pulmonary circulation.
174
Where does the left side of the heart pump oxygen rich blood?
Into the systemic circulation.
175
Through where do the parallel pathways of blood flow?
Through the systemic organs.
176
What is the difference between the left ventricular wall and the right wall?
The left is much thicker.
177
By what side of the heart do the lungs receive all the blood pumped out?
By the right side.
178
What do the systemic organs receive?
Some of the blood pumped out by the left side of the heart.
179
How is the percentage of pumped blood received by the various organs under resting conditions characterised?
Indicated.
180
What can happen to the distribution of cardiac output?
It can be adjusted as needed.
181
What are the carotid arteries?
The blood vessels that carry oxygenated blood to the head, brain and face.
182
What is the carotid sinus?
A dilated area at the base of the internal carotid artery superior to the bifurcation of the internal and external carotid.
183
What does the sinus contain?
Many baroreceptors.
184
What do the baroreceptors sense?
Change in blood pressure.
185
What is the carotid body?
The main peripheral chemoreceptor.
186
What does the carotid body sense?
The arterial PO2, PCO2 and pH.
187
What does carotid chemosensory discharge in response to hypoxemia, hypercapnia and acidosis?
Reflex respiratory, autonomic and cardiovascular adjustments.
188
Where is carotid chemosensory located?
In the adventitia.
| In the bifurcation of the common carotid artery.
189
What do the baroreceptor and chemoreceptors constantly monitor?
The blood supply.
190
What do the baroreceptor and chemoreceptors send?
Signals to the brain.
191
What do the signals sent to the brain from the baroreceptors and chemoreceptors increase?
Parasympathetic or sympathetic nervous system output.
192
Why do the signals sent to the brain from the baroreceptor and chemoreceptor increase parasympathetic and sympathetic nervous system output?
To regulate heart rate and breathing appropriately.
193
Due to what there might be a decrease in pH?
Due to elevated hydrogen ions in circulation from exercise.
194
How does the brain respond if there is a decrease in pH?
With increased heart rate, force and breathing rate.
195
What events occur when the baroreceptors sense a decrease in stretching and chemoreceptors sense a decrease in oxygen along with an increase in carbon dioxide and hydrogen ion levels?
Homeostatic sequence of events.
196
What happens when parasympathetic stimulation of heart is decreased?
There is an increase in HR and SV.
197
Due to which factor is there an increase in blood flow and pressure?
Due to increased cardiac output.
198
Due to which factor is there an increase in blood flow and pressure?
Due to increased cardiac output.
199
What is the response to chemoreceptor stimulation?
Increased sympathetic stimulation of the hear to increase HR and SV.
200
What else does increased HR and SV cause?
An increase in blood flow and pressure.
201
What is the heart?
One continuous piece of specialised muscle.
202
What is a heart beat?
A coordinated relaxation and contraction of atria and ventricles.
203
To what do a series of valves and muscles contribute?
To formation of four chambers and compartmentalisation of blood within the heart.
204
By what is cardiac output determined?
By stroke volume and heart rate.
205
Under what influence is stroke volume and heart rate?
Of various physiological inputs.
206
What does Frank-Starling law explain?
The intrinsic contractile behaviour of the heart in response to increased EDV.
207
What are the mechanical events of the heart muscle contraction?
Perfectly coordinated in order.
208
Why are the mechanical events of the heart muscle contraction perfectly coordinated in order?
For the correct sequence of events to occur.
209
What happens first in the events of heart muscle?
Receiving blood into the atria.
210
What happens after the blood is received into the atria?
It enters into the ventricles and then out of the heart.
211
What is the hart after the previous ventricular contraction?
Relaxed.
212
What does the pressure in the venae cavae and pulmonary artery begin to do when the heart is relaxed?
It begins to force blood into the atria.
213
What does the pressure do when blood begins to fill the atria?
It builds up.
214
What do the atrio ventricular valves do, as blood begins to fill the atria?
They open.
215
What do the ventricles begin to do, as the blood begins to fill the atria?
They fill passively.
216
Due to which factor does the atria contract spontaneously?
Due to the cardiac pacemaker potential in sinus node.
217
How much time doe the atria contraction take?
0.5 seconds.
218
What happens to the muscle, as the blood fills the ventricles?
It tightens but don't shorten.
| It is not yet contracting.
219
What does the tightening of the muscle raise?
The pressure in the ventricles.
220
Due to which factor do the atrioventricular valves close?
Due to the pressure.
221
As what does the closure of the atrioventricular valves heard?
As the first heart sound.
222
What does the cardiac action potential cause?
The ventricles to contract.
223
What does the cardiac action potential generate?
Sufficient pressure.
224
Why does the cardiac action potential generate sufficient pressure?
To force the blood out through the semilunar valves and into the aorta and pulmonary artery.
225
What does the back pressure in the vessels do, when the ventricles are relaxed?
It forces the semilunar valves shut and the cycle begins again.
226
Where does the action potential initiated at the SA first spread?
Throughout both atria.
227
By what is the spread of action potential throughout both atria facilitated?
By 2 specialised atrial conduction pathways.
228
Which are the 2 specialised atrial conduction pathways that facilitate the spread of the action potential initiated at the SA?
1. Interatrial / Bacmanns bundle.
| 2. Internodal pathways.
229
What is the AV node?
The only point where an action potential can spread from the atria to ventricles.
230
Where does the action potential from the AV node spread?
Throughout the ventricles.
231
How does the action potential from the AV node spread throughout the vetricles?
Rapidly.
232
By what is the action potential from the AV node dispatched?
By a specialised ventricular conduction.
233
Of what does the ventricular conduction through where the action potential from the AV node is dispatched consist?
Of the bundle of His and Purkinje fibres.
234
What is the first half of the pacemaker potential?
The result of simultaneous opening of unique funny channels.
235
What does the simultaneous opening of unique funny channels permit?
Inward Na+ current..
| Closure of K+ channels.
236
What does the closure of K+ channels reduce?
Outward K+ current.
237
What is the second half of the pacemaker potential?
The result of opening of T-type Ca2+ channels.
238
What is the result, once threshold potential of -40mV is reached?
The rising phase of the action potential.
239
What is the result of the rising phase of the action potential?
The opening of L-type Ca2+ channels.
240
What is the result of opening of K+ channels and closing of the calcium channels?
The falling phase.
241
What does begin once the cell has repolarised to -60mV?
Another slow depolarisation.
242
What does the last slow depolarisation restart?
The cycle.
243
From what does the action potential in cardiac contractile cells differ?
From the action potential in cardiac autorhythmic cells.
244
What is the rapid rising phase of the action potential in contractile cells?
The result of Na+ entry on opening of fast Na+ channels at threshold phase 0.
245
About what value is the resting membrane potential?
About -90mV.
246
When is the action potential triggered?
When depolarisation occurs beyond -70mV.
247
How is the influx of sodium characterised?
So great.
248
What happens to the membrane potential during influx of sodium?
It depolarised to 30mV.
249
Why does the early, brief repolarization occur after the potential reaches its peak?
Because of limited K+ efflux on opening of transient K+ channels.
And chloride ion efflux accompanied with inactivation of the Na+ channels.
250
The result of what is the prolonged plateau phase, phase 2?
Of slow Ca2+ entry on opening of L-type Ca2+ channels, coupled with reduced K+ efflux on closure of several types of K+ channels.
251
What is the rapid falling?
Phase 3.
| The result of K+ efflux on opening of ordinary voltage-gated K+ channels.
252
By what are the ion concentration and membrane potential restored?
By the activity of Na/K ATPase and Na/Ca exchanger.
253
By what is resting potential maintained?
By opening of leaky K+ channels.
254
Why can the electrical activity of the heart monitored?
To check for signs of pathology.
255
What has been developed as monitoring the electrical activity of the heart is not done directly?
An indirect method called 'electrocardiogram'.
256
What is the use of the electrocardiogram?
To record the electrical activity of the heart from different angles to identify and locate pathology.
257
Where are electrodes placed?
On different parts of a patient's limbs and chest.
258
Why are electrodes placed on different parts of a patient's limbs and chest?
To record the electrical activity.
259
What does the reading represent?
A graph of voltage versus time of the electrical activity of the heart.
260
How many main components to an ECG are there?
3.
261
Which are the 3 main components to an ECG?
1. P wave.
2. QRS complex.
3. T wave.
262
What does the P wave represent?
The depolarization of the atria.
263
What does the QRS complex represent?
The depolarisation of the ventricles.
264
What does the T wave represent?
The repolarisation of the ventricles.
265
What does the reading represent?
The sum of the electrical activity.
266
Where do depolarisation, repolarisation and maintenance of resting membrane potential happen?
In different regions of the heart.
267
What do the ventricles do during atrial systole?
They are relaxed and repolarised.
268
What happens when the ventricles are relaxed and repolarised?
Inward sodium conductance in the atria.
| Outward K conductance in the ventricles.
269
Which are the dominant ion flows during atrial systole?
Na+ and K+.
270
What does the cardiac action potential contract?
The ventricles.
271
What can the ECG help detect?
Arrhythmias.
Coronary heart disease.
Heart attacks.
Cardiomyopathy.
272
What happens in arrhythmias?
The heart beats too slowly, too quickly, or irregularly.
273
What happens in coronary heart disease?
The heart's blood supply is blocked or interrupted by a build-up of fatty substances.
274
What happens in heart attacks?
The supply of blood to the heart is suddenly blocked.
275
What happens in cardiomyopathy?
The heart walls become thickened or enlarged.
276
Which are the 3 main types of ECG?
1. A resting ECG.
2. A stress or exercise ECG.
3. An ambulatory ECG.
277
When is a resting ECG carried out?
While you're lying down in a comfortable position.
278
When is a stress or exercise ECG carried out?
While you're using an exercise bike or treadmill.
279
What happens in an ambulatory ECG?
The electrodes are connected to a small portable machine worn at your waist so your heart can be monitored at home for 1 or more days.
280
Why do the ventricles depolarise and contract?
To eject blood into the aorta.
281
What happens to pressure in the arteries, as the ventricles depolarise and contract?
It rises.
282
Where does a slight lab occur?
In the initiation of depolarisation.
The initiation of the QRST complex.
The peak arterial pressure.
283
When does the pressure rise in the vessels?
When the blood is pumped.
284
What does the parasympathetic stimulation decrease?
The rate of SA nodal depolarisation.
285
Why does the parasympathetic stimulation decrease the rate of SA nodal deporisation?
So that the membrane reaches threshold more slowly and has a fewer action potentials.
286
What does the sympathetic stimulation increase?
The rate of depolarisation of the SA node.
287
Why does the sympathetic stimulation increase the rate of depolarisation of the SA node?
So that the membrane reaches threshold more rapidly and has more frequent action potentials.
288
To what does each SA done action potential lead?
To a heartbeat.
289
What does increased parasympathetic activity decrease?
The heart rate.
290
What does the increased sympathetic activity increase?
The heart rate.
291
What does the valve closing produce?
2 normal heart sounds.
292
By what is the first heart sound (S1)/ ' lub' caused?
By closing of the AV valves.
292
By what is the first heart sound (S1)/ ' lub' caused?
By closing of the AV valves.
293
By what is the second heart sound (S2) / 'dub' caused?
By closing of the aortic and pulmonary valves.
294
What does a defective valve function produce?
Turbulent blood flow.
295
As what can the turbulent blood flow be heard?
As a heart murmur.
296
What might the abnormal valves be?
Stenotic or insufficient.
297
What are the stenotic valves?
The do not open completely.
298
What are the insufficient valves?
They do not close completely.
299
What is a cardiac arrest?
An abnormal electrical event.
300
By what is a heart attack caused?
By restriction of the blood supply to the myocardium.
301
Where does the pacemaker potential originate?
In the SA node.
302
What does the pacemaker potential determine?
The intrinsic heart rate.
303
What does SA node receive?
Sympathetic and parasympathetic input.
304
What does coordinated activation of Na+, K+ and Ca2+ channels regulate?
The electrical activity of SA node and cardiac muscle.
305
What is ECG?
A graph of voltage versus time of the electrical activity of the heart using electrodes placed on the skin.
