Cardiac Physiology Flashcards
1
Q
The heart pumps from?
A
Low pressure veins to high pressure arteries
2
Q
Blood pressure in the pulmonary circuit is approximately?
A
28/8 mmHg
3
Q
Blood pressure in the systemic circuit is approximately?
A
120/80mm Hg
4
Q
Define heart failure
A
The pathological state in which the heart is unable to pump blood at a rate required by metabolizing tissues or can do so only with an elevated filling pressure
5
Q
In adults heart failure most frequently results from inability of the left ventricle to?
A
Fill – Diastolic performance
Eject blood – Systolic performance
6
Q
What is the Cardiac cycle?
A
The cardiac cycle can be described as a coordinated sequence of electrical and mechanical events occurring from the start of one heartbeat to the start of the next
7
Q
A single cardiac cycle includes?
A
A complete relaxation and contraction of both atria and ventricles
8
Q
What is the relaxation phase?
A
DIASTOLE
9
Q
What is the contraction phase?
A
SYSTOLE
10
Q
What directs movement of blood in the heart?
A
Valves within the heart
11
Q
Pressure changes are brought about by ?
A
Conductive electrochemical changes within the myocardium that result in contraction of cardiac muscle
12
Q
Which valve closes during atrial contraction?
A
Mitriai valve closes
13
Q
Ventricular isovolumetric contraction occurs ?
A
When both valves are closed and aortic valve opens
14
Q
Ventricular isovolumetric relaxation occurs?
A
When both valves are closed - mistrial valve opens
15
Q
Phases of the cardiac cycle
A
- Atriole systole begins
- Ventricular systole - first phase
- Ventricular systole - second phase
- Ventricular diastole - early
- Ventricular diastole - late
16
Q
Which ECG wave corresponds to when atriole systole begins ?
A
P wave
17
Q
Which wave corresponds to Atrial depolarisation in ECG?
A
P wave
18
Q
Which wave corresponds to Ventricle depolarisation in ECG?
A
QRS complex
19
Q
Which wave corresponds to Ventricular repolarization?
A
T wave
20
Q
Function of Gap junctions
A
Gap junctions allow passage of action potentials from one cell to the next, very quickly – allows the cardiac muscle to function together as a SYNCTIUM
21
Q
What structures allow the cardiac muscle to function as a SYNCTIUM?
A
GAP junctions
22
Q
Function of Intercalated discs
A
Intercalated discs link muscle cells together and contain desmosomes and gap junctions
23
Q
Function of Desmosomes
A
Desmosomes hold the muscle cells together tightly
24
Q
What is the name of the process by which Myocardial cells can spontaneously depolarize?
A
Automaticity
25
Which structures allow action potential to pass to adjacent cells?
Intercalated discs
26
Spontaneous depolarisation generates?
Pacemaker potential
27
How many syncytiums does the heart have?
2
28
Heart composed of two syncytiums
Atrial
Ventricular
29
Atrial syncytium
Constitutes the walls of the two atria
30
Ventricular syncytium
Constitutes walls of the two ventricles
31
Function of fibrous tissue that seat the cardiac valve
It lacks gap junctions and electrically isolates atria from ventricles: provides a border
32
Phases of the cardiac action potential are associated with changes in cell membrane permeability, mainly by which ions?
Na + , K + , and Ca ++ ions.
33
Changes in cell membrane permeability alter the rate of movement of these ions across the membrane and thereby change the membrane voltage (V m ).
True or false?
True
34
Changes in permeability are accomplished by?
Opening and closing of ion channels that are specific for individual ions
35
Why do cells have a Resting potential?
Due to distribution of ions across the cell membrane
36
The resting is ?
NEGATIVE- inside the cell relative to the outside
37
Find the term:
This is the electrical potential difference (voltage) between the inside and the outside of a cell
Transmembrane potential =TMP
38
When there is a net movement of +ve ions into a cell, the TMP becomes?
More POSITIVE
39
When there is a net movement of +ve ions out of a cell, TMP becomes?
MORE negative
40
Two main forces drive ions across cell membranes?
Chemical potential
Electrical potential
41
Name the process when an ion will move down its concentration gradient.
Chemical potential
42
Name the process when an ion will move away from ions/molecules of like charge
Electrical potential
43
Ionic movements or conductances across the myocardial membrane occur in response to?
The electrochemical potential gradient
44
Ionic movements or conductances are controlled by?
selective ion permeability
45
Properties of cardiac ion channels
- Selectivity
- Voltage- sensitive gating
- Time-dependence
46
Name the property of cardiac ion channels:
They are only permeable to a single type of ion based on their physical configuration.
Selectivity
47
Name the property of cardia ion channels:
A specific TMP range is required for a particular channel to be in open configuration; at all TMPs outside this range, the channel will be closed and impermeable to ions. Therefore, specific channels open and close as the TMP changes during cell depolarization and repolarization, allowing the passage of different ions at different times.
Voltage-sensitive gating
48
Name the property of cardiac ion channels:
Some ion channels (importantly, fast Na+ channels) are configured to close a fraction of a second after opening; they cannot be opened again until the TMP is back to resting levels, thereby preventing further excessive influx.
Time - dependence
49
The cells of the SAN depolarise over time, with movement of ions causing ?
The resting membrane potential to gradually decrease (pacemaker potential)
50
What happens once the membran potential exceeds a threshold?
An action potential is triggered
51
An action potential is triggered automatically every?
0.8 seconds (approx.) at rest
52
The cells of the AVN depolarise like the cells of the SAN, but more slowly. What does this result into?
An action potential is triggered in the AVN cells before they depolarise enough to trigger their own
53
Name the process by which an electrical action potential leads to contraction of cardiac muscle cells
Excitation-contraction coupling
54
How is Excitation-contraction coupling achieved?
By converting a chemical signal into mechanical energy via the action of CONTRACTILE PROTEINS
55
What is the crucial mediator that couples electrical excitation to physical contraction by cycling in and out of the myocyte’s cytoskeleton during each potential?
Calcium
56
At what membran potential do SAN cell membrane ‘funny channels’ open?
-60 mV
57
What happens at -60 mV?
Sodium enters the cell through the ‘funny channels’, taking a positive charge into the cell
58
What effect does Sodium have once entering the cell?
The inside of the cell becomes less negative in relation to the outside
59
Once the inside of the cell becomes less negative in relation to the outside what happens next?
A type of voltage – gated calcium channels open, and calcium enters the cell slowly
The cell continues to depolarise gradually (pacemaker potential)
60
What happens when the threshold is reached?
Another type of voltage- gated calcium channels opens and calcium enters the cell rapidly
61
What is the result of calcium entering the cell rapidly ?
This results in rapid depolarisation – the cardiac action potential
62
Depolarisation is due to?
K+
63
The initial influx of Ca2+ into myocytes through L-type Ca2+ channels during phase 2 of the action potential is insufficient to trigger contraction of myofibrils. This signal is amplified by?
CICR mechanism
64
What is the purpose of the CICR mechanism
It triggers much greater release of Ca2+ from the sarcoplasmic reticulum
65
The cell membrane of cardiomyocytes are called?
Sarcolemma
66
Name the specialized Ca2+ release receptors in the sarcoplasmic reticulum (SR)
Ryanodine receptors
67
The influx of Ca2+ into mycocytes is through?
L-type Ca2+ channels during phase 2 of the action potential
68
What is the name of this mechanism?
The cell membrane of cardiomyocytes, called sarcolemma, contains invaginations (T-tubules) that bring L-type Ca2+ channels into close contact with ryanodine receptors, specialized Ca2+ release receptors in the sarcoplasmic reticulum (SR).
• When Ca2+ enters the cells through L-type channels, ryanodine receptors change conformation and induce a larger release of Ca2+ from abundant SR stores.
• Large levels of intracellular Ca2+ act on tropomyosin complexes to induce myocyte contraction.
CICR MECHANISM
69
The trace in EINTHOVENS TRUANGLE depends on?
a) The direction of travel
b) Whether the cells are depolarising or repolarising
c) The size of the change in potential
70
Electrical trace resulting from action potentials in all the heart muscle fibres
ECG
71
Atrial contraction on ECG
P wave
72
Depolarisation of ventricular muscle on ECG
QRS complex
73
Repolarization of ventricular muscle on ECG
T wave
74
The ECG represents?
The electrical vectors of the cardiac cycle
75
The baseline of the ECG is the?
Isoelectric line - denotes resting membrane potential
76
What denotes resting membrane potential in the ECG
Isoelectric Line
77
Atrial repolarization is too minor in amplitude to be recorded by surface electrodes
True or false
True
78
What is the isoelectric point in the QRS complex ?
S
79
Contraction commences at PEAK of which portion in the QRS complex?
R portion
80
Which interval in ECG starts with atrial muscle depolarization ends with the start of ventricular depolarization ?
PR interval- it is assumed that the impulse passes through the AV node into the ventricle during this interval
81
A prolonged PR interval may suggest?
AV block is present
82
What is used as a baseline - reference line or isoelectric line of the ECG trace?
PR segment
83
Volume of blood In the ventricles at the end of diastole is?
End diastolic voluMe = EDV
84
How much is EDV ?
130 ml at rest
85
Volume of blood at the end of systole is?
End of systolic volume = ESV
86
How much is ESV at rest?
60 ml
87
Amount if blood elected from the ventricles in one beat is?
Stroke volume= SV
88
Formula for SV (STROKE VOLUME)
SV=EDV-ESV
Stroke volume= End of diastolic volume - End of systolic volume
89
Formula for Cardiac Output CO?
CO= SV x HR (heart rate)
90
Units for HR
bpm = beats per minute
91
The higher the arterial pressure, SV is
Lower
92
Regulation of SV
Preload
Afterload
Contractility
93
The extent of stretch of the heart muscle is called?
PRELOAD
94
The pressure against which the heart need to pump, to expel blood is called?
AFTERLOAD
95
The ability of the muscle to produce a force is called?
CONTRACTILITY
96
What increases contractility ?
Inotropic agents such as adrenalin , and the influence of the sympathetic nervous system
97
Force of contraction is proportional to?
The INITIAL fibre length in diastole
98
According to the Starlings Law:
Increased stretch of ventricular muscle results in?
Increased overlap of actin and myosin filaments so that a greater number of cross bridges are formed
99
Le get tension relationship states that ?
There is an optimal sarcomere length for maximum contraction
100
Intracellular calcium required to generate 50 % max tension is lower when?
Muscle fibres is stretched
101
Why is Frank-Starling effect important?
* Allows the heart to adapt its pumping capacity to changes in venous return and to changes in arterial blood pressure
* Helps to match the output of right and left sides of the heart
102
The cardiovascular center in the medulla oblongata controls?
Sympathetic and parasympathetic nerves that innervate the heart
103
Which system:
* Decreases rate of influx of Na+ through the funny channels, and slow Ca2+ influx
* This means it takes longer for the pacemaker potential to reach the threshold for an action potential
Parasympathetic NS (slows heart rate)
104
Which system:
Increases rate of influx of Na+ and Ca2+
This means that pacemaker potentials develop quickly, so cardiac action potentials
Sympathetic NS (increases heart rate)
105
What represents the pressure of the blood as it moves through the arterial system?
Systemic hypertension
SVR
106
Formula for Blood pressure BP
BP=COxSVR
With CO= SV x HR
107
Systolic BP is largely determined by?
Characteristics of SV being ejected by the heart and the ability of aorta to stretch to accommodate the SV
108
Diastolic pressure is determined by?
The energy that is stored in the elasticity of fibres that are stretched during systole
109
Withouttheelasticrecoil,pressure would?
Fall dramatically between beats, as would blood flow
110
Blood pressure is regulated by?
A baroreceptor reflex
111
Longtermbloodpressureismaintainedmainlythroughthe?
Renin-angiotensin- aldosterone mechanism
112
Stretch - sensitive sensory nerve roots endings are located in the?
Carotid sinuses and aortic arch
113
As arterial pressure decreases what happens to HR?
HR decreases
114
What happens is blood pressure remains elevated?
It can reset or down regulate the reflex to a higher set point
115
Name the process:
* Contraction of smooth muscle in the vessel walls, also precapillary sphincters in arterioles
* Causes narrowing of the diameter of the blood vessel
* Caused by sympathetic nerve activity and the hormone angiotensin II
* Increases the resistance of blood vessels to blood flow
Vasoconstriction
116
Name the process:
* relaxation of smooth muscle in the vessel walls, also precapillary sphincters in arterioles
* Causes widening of the diameter of the blood vessel
* Caused by withdrawal of sympathetic nerve activity and locally released chemicals e.g. nitrous oxide and lactic acid
* decreases the resistance of blood vessels to blood flow
Vasodilation
117
Arterial pressure I’d the product if ?
Cardiac output and peripheral resistance
118
Pressure receptors are called?
Baroreceptors
119
The response to injury hypothesis states that the initial event in the pathogenesis of atherosclerosis is?
Injury to epithelium
120
Atherosclerosis development
- Injury to vascular endothelium
- Lipoprotein deposition
- Inflammatory reaction
- Cap formation
121
Time between atrial depolarisation and ventricular depolarisation in ECG is defined by?
PR interval
