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Physiology > The Cardiac Cycle > Flashcards

The Cardiac Cycle Flashcards

1
Q

What is the length of one cardiac cycle?

A

0.8s

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2
Q

What length of time of one cardiac cycle is spent in systole (ejecting the blood by contracting)

A

0.25s

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3
Q

What length of time of one cardiac cycle is spent in diastole (heart filling with blood by relaxing)

A

0.55s

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4
Q

What is the stroke volume of each beat?

A

70ml

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5
Q

What is the circulation time?

A

1minute because blood volume is 5L and CO = 5L/min

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6
Q

What kind of blood flow do the tissues require and why is this a problem when it comes to the contractility of the heart?

A

The require a smooth continue flow of blood and blood is pumped from the heart is 72 rapid squirts of 70ml blood

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7
Q

What ensures the tissues get a smooth constant supply of blood?

A

Keeping the vascular system under pressure

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8
Q

What is the pressure in the major arteries?

A

80mmHg

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9
Q

Qhat is the pressure at the start of the capillary bed?

A

35mmHg

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10
Q

What is the pressure at the end of the capillary bed?

A

15mmHg

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11
Q

What is the pressure in the veins?

A

5mmHg

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12
Q

what maintains the pressure gradient that allows a constant flow of blood?

A

A system of valves

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13
Q

What kind of valves are involved in maintaining the pressure in the vascular system?

A

Semilunar valves at the entrance to the aorta, the pulmonary artery and the large veins

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14
Q

What do the semilunar valves do?

A

Prevent back flow of blood

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15
Q

What is the blood pressure in the aorta at rest and what is this called?

A

Diastolic blood pressure at 80mmHg

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16
Q

What is the blood pressure in the aorta during contraction of the left ventricle and what is this called?

A

Systolic blood pressure at 120mmHg

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17
Q

What is pulse pressure?

A

The force that the heart generates each time it contracts (going from systolic to diastolic) so can be worked out by minusing diastolic from systolic so is 40mmHg

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18
Q

How do you work out the mean blood pressure?

A

Diastolic pressure (80) + 1/3rd pulse pressure (40/3=13) = 93mmHg

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19
Q

What are the atrio-ventricular valves and where are they found?

A

The tricuspid valve found between the right ventricle and right atrium and the bicuspid valve between the left ventricle and left atrium

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20
Q

Why are the atrioventricular valves held by chordae tendinae attached to pappilary muscles?

A

To stop them being blown out during ventricular contraction

21
Q

How much more pressure does the left ventricle work at compared to the right?

A

5 x the pressure

22
Q

What is the dicrotic notch?

A

When the pulmonary artery and the aorta show a secondary rise in pressure when the semilunar valves shut

23
Q

What is the reason for the dicrotic notch?

A

Because closing of the valves leads to elastic recoil in the PA and A which causes further pressure change

24
Q

Does the heart empty upon ventricular contraction

A

No 70ml of blood of risidual volume is left when 70ml of blood is pumped out (stroke volume) from the 140ml of blood in the heart

25
Q

Would a sudden change in heart beat upon ventricular filling affect this process?

A

No because most of the filling occurs within the first 1/3rd of diastole

26
Q

What are the three requirements for contraction of the heart?

A
  1. Left and right atrium must contract synchoniously
  2. Left and right ventricles must contract synchronisouly
  3. Ventricles must contract after atria
27
Q

Where is the origin of the heartbeat?

A

In the sino atrial node

28
Q

Where is the sino atrial node located?

A

In the right atrium

29
Q

What ensures synchoronised contraction of the left and right atriums?

A

Rudimentary conducting bundles connecting the two atria ensure rapid conduction and synchronised contraction

30
Q

Why cant the conduction go straight to the ventricles?

A

Because of the insulating connective tissue

31
Q

How long after the origin in the SA node does it travel to the AV node?

A

0.04s

32
Q

How long is the conduction delay at the AV node and why is there a delay?

A

0.125s and because of the small diameter of the conducting cells

33
Q

Where does excitation then go after the AV node?

A

Through to the ventricles

34
Q

What is the reason for the excitation spreading from the AV node to the ventricles?

A

Large diameter purkinje cells leave from the AV node and split at the bundle of His into the left and right bundle branches to spread excitation to the ventricles

35
Q

Where does the excitation spread through the ventricles end up and what is the reason for the whole ventricle contracting?

A

In the cardiac cells (myocytes) which have membrane between them for cell to cell communication

36
Q

What does the vagus nerve of the parasympathetic nervous system act on in order to slow the heart beat?

A

The SA and AV nodes

37
Q

What kind of effect does the vagus nerve have on the SA node?

A

A negative chronotropic effect

38
Q

What is a chronotropic effect?

A

A change in heart rate (chronos = time)

39
Q

What effect does the vagus nerve have on the AV node?

A

A negative dromotropic effect

40
Q

What is a dromotropic effect?

A

Changes in condction

41
Q

What parts of the heart does the sympathetic nervous system act on?

A
  1. The SA node
  2. The AV node
  3. Ventricles
42
Q

How does the sympathetic nervous system affect the SA node?

A

Positive chronotropic effect (increase in heart rate)

43
Q

How does the sympathetic nverous system affect the AV nodes?

A

Postivie dromotropic effect (increase conduction)

44
Q

What two effects does the sympathetic nervous system have on the ventricles?

A

Positive ionotropic effect (increased contractility) and positive leucitropic effect (increased relaxation rate)

45
Q

What is the consequence of the excitation of numerous cardiac cells during the electrical conduction of the heart?

A

An electrical field is generated

46
Q

What are the three areas on the electrocardiogram?

A

The P wave
The QRS complex
The T wave

47
Q

What happens during the P wave

A

The atria contraction (depolarisation)

48
Q

What happens during the QRS complex

A

The ventricles contract (depolarisae) andwhich blocks out the artia relaxing (repolarising)

49
Q

What happens during the T wave

A

The ventricles relax (repolarise)

Physiology (19 decks)

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