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Flashcards in The Cardiac Cycle Deck (49):
1

What is the length of one cardiac cycle?

0.8s

2

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

0.25s

3

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

0.55s

4

What is the stroke volume of each beat?

70ml

5

What is the circulation time?

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

6

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

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

7

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

Keeping the vascular system under pressure

8

What is the pressure in the major arteries?

80mmHg

9

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

35mmHg

10

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

15mmHg

11

What is the pressure in the veins?

5mmHg

12

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

A system of valves

13

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

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

14

What do the semilunar valves do?

Prevent back flow of blood

15

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

Diastolic blood pressure at 80mmHg

16

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

Systolic blood pressure at 120mmHg

17

What is pulse pressure?

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

18

How do you work out the mean blood pressure?

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

19

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

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

20

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

To stop them being blown out during ventricular contraction

21

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

5 x the pressure

22

What is the dicrotic notch?

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

23

What is the reason for the dicrotic notch?

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

24

Does the heart empty upon ventricular contraction

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

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

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

26

What are the three requirements for contraction of the heart?

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

27

Where is the origin of the heartbeat?

In the sino atrial node

28

Where is the sino atrial node located?

In the right atrium

29

What ensures synchoronised contraction of the left and right atriums?

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

30

Why cant the conduction go straight to the ventricles?

Because of the insulating connective tissue

31

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

0.04s

32

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

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

33

Where does excitation then go after the AV node?

Through to the ventricles

34

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

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

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

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

36

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

The SA and AV nodes

37

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

A negative chronotropic effect

38

What is a chronotropic effect?

A change in heart rate (chronos = time)

39

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

A negative dromotropic effect

40

What is a dromotropic effect?

Changes in condction

41

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

1. The SA node
2. The AV node
3. Ventricles

42

How does the sympathetic nervous system affect the SA node?

Positive chronotropic effect (increase in heart rate)

43

How does the sympathetic nverous system affect the AV nodes?

Postivie dromotropic effect (increase conduction)

44

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

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

45

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

An electrical field is generated

46

What are the three areas on the electrocardiogram?

The P wave
The QRS complex
The T wave

47

What happens during the P wave

The atria contraction (depolarisation)

48

What happens during the QRS complex

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

49

What happens during the T wave

The ventricles relax (repolarise)