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Physiology > Cardiovascular - The Heart > Flashcards

Cardiovascular - The Heart Flashcards

1
Q

Describe cardiac muscle.

A

Cardiac muscle is striated due to the regular arrangement of contractile proteins.

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2
Q

Describe the coupling of cardiac myocytes.

A

They are coupled electrically by gap junctions (as opposed to by neuromuscular junctions)

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3
Q

What are gap junctions?

A

Protein channels which form low resistance electrical communication pathways between neighbouring myocytes.

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4
Q

What is the ‘All or none’ law of the heart?

A

The electrical excitation reaches all the cardiac myocytes.

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5
Q

What is the role of desmosomes?

A

To provide mechanical adhesion between adjacent cells, ensuring that the tension developed by one cell is transmitted to the next.

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6
Q

What provides the contractile properties of muscle fibres?

A

Myofibrils.

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7
Q

What is the structure of myofibrils?

A

Alternating segments of thick myosin and thin actin filaments.

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8
Q

What is a sarcomere?

A

The arrangement of actin and myosin within each myofibril.

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9
Q

How is muscle tension produced?

A

By the sliding of actin filaments on myosin filaments.

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10
Q

When is ATP required?

A

For both contraction and relaxation.

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11
Q

What is required to switch on cross bridge formation?

A

Ca2+

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12
Q

What is the sarcoplasmic reticulum?

A

A specialised endoplasmic reticulum found in muscles which stores and releases Ca2+ ions.

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13
Q

What is the release of Ca2+ from the sarcoplasmic reticulum dependent on?

A

The presence of extra-cellular Ca2+

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14
Q

What is systole?

A

The contraction of ventricular muscle.

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15
Q

What is diastole?

A

The relaxation of ventricular muscle.

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16
Q

What happens when the action potential has passed?

A

Calcium ion influx ceases and the calcium ions are re-sequestered in the sarcoplasmic reticulum by Ca2+-ATPase, and the heart muscle relaxes.

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17
Q

What is the refractory period?

A

The period following an action potential in which it is not possible to produce another action potential.

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18
Q

What is the importance of the refractory period?

A

It prevents generation of tetanic contraction.

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19
Q

What state are the Na+ channels in during the plateau phase of the ventricular action potential and why is this important?

A

They are in the depolarized closed state and are not available for opening, thus preventing another action potential from occurring.

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20
Q

What is the stroke volume?

A

The volume of blood ejected by one (Dr K says each, which is confusing) ventricle per heart beat. This is rougly equal for both ventricles, being approximately 70ml for a 70kg man.

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21
Q

How do you calculate the stroke volume?

A

End Diastolic Volume - End Systolic Volume

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22
Q

How is the stroke volume regulated?

A

Intrinsic mechanisms (within the heart) and extrinsic mechanisms (neuronal and hormonal control).

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23
Q

How are changes in stroke volume brought about?

A

Through changes in the diastolic length of the myocardial fibres.

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24
Q

What is the End Diastolic Volume and how is it determined?

A

The End Diastolic Volume is the volume of blood within each ventricle at the end of diastole, and it is determined by the Venous Return to the heart.

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25
What is the Frank-Starling Mechanism?
It describes the relationship between venous return, end diastolic volume and stroke volume. It states that: 'The more the ventricle is filled with blood during diastole (end diastolic volume), the greater the volume of ejected blood will be during the resulting systolic contraction (stroke volume)'.
26
What effect does stretch have on the affinity of troponin for Ca2+?
Stretch increases the affinity of troponin for Ca2+.
27
What is the difference between skeletal and cardiac muscle with regards to fibre length and muscle tension?
In skeletal muscle the maximum tension is achieved at resting muscle length, whereas in cardiac muscle the optimal tension is achieved by stretching the muscle.
28
How does Starling's Law match the stroke volume of the Right and Left Ventricles?
Increased venous return to the right atrium leads to increased End Diastolic Volume of the right ventricle giving Increased stroke volume into the pulmonary artery increasing Venous return to the left atrium and increased End Diastolic Volume of the left ventricle giving an increased stroke volume into the aorta.
29
What is afterload?
The resistance into which the heart is pumping.
30
What is the effect of increased afterload?
It is imposed after the heart has contracted and because the heart is unable to eject the full stroke volume, the End Diastolic Volume increases. This causes a rise in the force of contraction (Frank-Starling) and will eventually lead to ventricular hypertrophy to overcome the resistance.
31
What is a positive inotropic effect?
Something that increases the force of contraction.
32
How does sympathetic innervation increase contractility?
Innervation of β1 adrenoceptors causes extra calcium channels to open in extracellular membrane and sarcoplasmic reticulum membrane increasing Ca2+ entry
33
How does sympathetic innervation increase heart rate?
1. Increased re-uptake of Ca2+ into the sarcoplasmic reticulum decreases the length of systole 2. Increased conduction velocity in the AV node due to enhanced activity of voltage-dependent Ca2+ channels.
34
What is the effect of sympathetic innervation on cardiac efficiency?
It is decreased because of the increase in oxygen consumption.
35
What is the effect of sympathetic innveration on automaticity?
There is a tendency for non-nodal regions to acquire spontaneous activity.
36
What effect can parasympathetic stimulation have on the atria?
It may cause dysrhythmias.
37
What is the effect of sympathetic nerve stimulation on the Frank-Starling curve?
Frank-Starling curve is shifted to the left and the maximum stroke volume is inceased.
38
What is the effect of heart failure on the Frank Starling curve?
The maximum stroke volume is decreased and the curve shifts to the right.
39
What is the effect of the parasympathetic nervous system on ventricular contraction?
None, the parasympathetic nervous system only stimulates the atria.
40
What is the cardiac output?
The volume of blood pumped by one ventricle per minute.
41
How do you calculate the cardiac output?
Cardiac output = Stroke Volume x Heart Rate
42
How can the cardiac output be regulated?
By regulating the stroke volume and the heart rate.
43
What is the main influence on heart rate?
The autonomic nervous system
44
What is the effect of the sympathetic nervous system on the heart?
Increases heart rate, decreases AV nodal delay and increases the force of contraction.
45
What is the effect of the parasympathetic nervous system on the heart?
Slows the heart rate, increases AV nodal delay.
46
What is vagal tone?
The continuous influence of the parasympathetic nervous system on the SA node under resting conditions.
47
What is the normal resting heart rate?
Between 60 and 100bpm
48
What is bradycardia?
A resting heart rate of less than 60bpm
49
What is tachycardia?
A resting heart rate of more than 100bpm
50
Which parts of the heart does the vagus nerve supply?
SA node and AV node.
51
What neurotransmitters/receptors are used in the parasympathetic nervous system control of the heart?
Acetylcholine on M2 receptors.
52
What is the effect of vagal stimulation on the pacemaker potential?
The cell hyperpolarises resulting in a longer time needed to reach the threshold potential and therefore a lower frequency of action potential.
53
Which parts of the heart do the sympathetic nerves supply?
SA node, AV node and the myocardium.
54
What neurotransmitter/receptors are used in the sympathetic nervous system control of the heart?
Noradrenalin, acting on beta-adrenoceptors.
55
What does the term cardiac cycle refer to?
All events that occur from the beginning of one heart beat to the beginning of the next.
56
What happens during diastole?
The heart ventricles are relaxed and fill with blood.
57
What happens during systole?
The ventricles contract and pump blood into the aorta (LV) and pulmonary artery (RV).
58
What proportion of the cardiac cycle is spent in diastole and systole?
Approximately 2/3 in diastole and 1/3 in systole.
59
What are the 5 events that take place during the cardiac cycle?
Passive Filling Atrial Contraction Isovolumetric Ventricular Contraction Ventricular Ejection Isovolumetric Ventricular Relaxation
60
What is the pressure in the atria and ventricles during Passive Filling?
Close to zero.
61
What is the state of the AV valves during passive filing?
They are open so that venous return flows into the ventricles.
62
What is the state of the aortic valve during passive filling?
It is closed.
63
What is the aortic pressure during passive filling?
Approximately 80mmHg.
64
How full do the ventricles become during passive filling?
Approximately 80%.
65
What is the purpose of atrial contraction?
To complete the End Diastolic Volume.
66
What is isometric ventricular contraction?
The ventricles are contracting whilst all valves are shut, leading to an increased tension around a closed volume.
67
What triggers the AV valves to shut?
When ventricular pressure exceeds atrial pressure.
68
What produces the first heart sound?
The closing of the AV valves.
69
What happens to ventricular pressure during isovolumetric ventricular contraction?
It rises very steeply.
70
What triggers the opening of the aortic and pulmonary valves?
When the ventricular pressure exceeds the aorta/pulmonary pressure.
71
What happens to aortic pressure during ventricular ejection?
It rises.
72
What happens when the aortic/pulmonary valves are opened?
The stroke volume is ejected, leaving behind the end systolic volume (approximately 70ml)
73
When do the aortic and pulmonary valves shut?
When the ventricular pressure falls below the aortic/pulmonary pressure.
74
What produces the second heart sound?
The closing of the aortic and pulmonary valves.
75
What produces the dicrotic notch in the aortic pressure curve?
The vibration occuring when the aortic valve closes.
76
What signals the start of isovolumetric ventricular relaxation?
The closing of the aortic and pulmonary valves.
77
What triggers the opening of the AV valves?
When ventricular pressure falls below atrial pressure.
78
Why does arterial pressure not fall to zero during diastole?
Elastic recoil.
79
Describe the jugular venous pulse.
Bifid pulse, non-palpable. It occurs after the right atrial pressure wave.

Physiology (8 decks)

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