Week 4 - Cardiac cycle

Question 1

What is the function of the cardiovascular system?

Answer 1

to supply and remove materials to tissues around the body

examples of these materials include, glucose, oxygen, carbon dioxide

Question 2

What is the basal output of the heart?

Answer 2

5 litres a minute

can be 25-30 when exercising

Question 3

What is the role of the pericardium?

Answer 3

to prevent excessive expansion of the heart

fixes the heart to the mediastinum

protection against infection

Question 4

What are the two atrioventricular valves and where are they located?

Answer 4

mitral - left side of heart

tricuspid - right side of heart

Question 5

How many cusps do the semilunar valves have?

Answer 5

both have 3

Question 6

How many cusps to the atrioventricular valves have?

Answer 6

mitral - bicuspid - 2

tricuspid - 3

Question 7

What are the chordae tendineae?

Answer 7

chord like tendons (80% collagen, 20% elastin) that attach the papillary muscles to the tricuspid valve and mitral valve in the heart

Question 8

What is the purpose of the papillary muscles?

Answer 8

to prevent inversion of the valves during systole

ventricles are contracting, blood must not go back into atria but out to body or lungs

Question 9

What is a chronotrophic change?

Answer 9

a change in rate of contraction

Question 10

What is an inotropic change?

Answer 10

a change in force of contraction

Question 11

What nerve supplies the parasympathetic nerve supply to the heart?

Answer 11

vagus CN X

Question 12

What are the actions of the b1 adrenergic receptor in cardiac muscle?

Answer 12

increase cardiac output by:

increasing heart rate in SA node (chronotropic effect)

increasing strength of atrial and ventricular contraction (inotropic effect)

increases conduction of AV node

Question 13

What is the receptor of the parasympathetic nervous system in the heart?

Answer 13

M2 muscarinic receptor

slow down heart rate

reduce contractile force of atria

reduce conduction velocity of SA and AV nodes

little effect on ventricular muscle due to sparse innervation of ventricles by parasymathetic nervous sytem

Question 14

How long does one cardiac cycle last?

Answer 14

0.8 seconds

Question 15

How long does the heart spend in diastole?

Answer 15

0.4 seconds

Question 16

How long is atrial systole?

Answer 16

0.1 seconds

Question 17

How long is ventricular systole?

Answer 17

0.3 seconds

Question 18

How many heart sounds are produced?

Answer 18

4 - usually only two are audible (S1 and S2)

Question 19

What causes the aortic valve to open?

Answer 19

when aortic pressure is slighly below left ventricular pressure

Question 20

What term is typically used to refer to ventricular contraction while no blood is being ejected?

Answer 20

isovolumetric contraction

Question 21

During what phase does most blood enter the ventricle?

Answer 21

atrial diastole

the movement of blood into the ventricles is passive and caused by a pressure difference

atrial systole ensures the last bit of blood has been ejected

Question 22

The first heart sound represents which portion of the cardiac cycle?

Answer 22

the closing of the atrioventricular valves

Question 23

The second heart sound represents which phase of the cardiac cycle?

Answer 23

closure of the semilunar valves

Question 24

Ventricular relaxation immediately follows:

a) atrial repolarization
b) ventricular depolarization
c) atrial depolarisation
d) ventricular repolarization

Answer 24

d

Question 25

What is stenosis of a heart valve?

Answer 25

valve does not open completely causing turbulent flow associated with calcification

Question 26

What are the characteristics of cardiac muscle?

Answer 26

striated, mononuclear, smaller cells than skeletal muscle, cells connect to each other via **desmosomes** and **gap junctions,** no stem cells

Question 27

What are intercalated discs?

Answer 27

cell junctions that link adjacent cardiac myocytes together to form a **synctium** contain desmosomal junctions, adherent-type junctions and communicating gap junctions

Question 28

What are desmosomes?

Answer 28

cell structure specialised for cell to **cell adhesion**

Question 29

What doesthe term 'calcium induced calcium release' mean?

Answer 29

refers to the trigger Ca²⁺ causing the sarcoplasmic reticulum to release **more** calcium

Question 30

What triggers the initial Ca²⁺ influx into the cell?

Answer 30

a cardiac action potential

Question 31

What are the three patterns of cardiac action potentials?

Answer 31

ventricular, atrial and sino-atrial node

Question 32

What does phase 0 on this graph refer to?

Answer 32

ventricular depolarisation

Question 33

What is the resting membrane potential of the ventricular action potential?

Answer 33

-90mV K⁺ are open and K⁺ moves into the cell creating a negative membrane potential

Question 34

What is a myogenic rhythm?

Answer 34

cardiac muscle can contract rhythmically without nervous input

Question 35

At what rate do action potentials of the sino-atrial node fire?

Answer 35

100 bpm

Question 36

What is the route of conduction of electrical impulses through the heart?

Answer 36

Question 37

What causes phase 2 (prolonged plateau) of the ventricular action potential?

Answer 37

opening of L-type voltage-gated calcium channels causes inward Ca²⁺ current this balances out the outward K⁺ causing a plateau

Question 38

What does an atrial action potential look like?

Answer 38

similar to ventricular, less obvious plateau, slower repolarisation

Question 39

What is the '*pacemaker potential''*?

Answer 39

the slow positive increase in voltage across the cell membrane after each action potential represents the non-contracting time between heart beats (diastole)

Question 40

What are the bipolar (limb) leads?

Answer 40

Lead I Lead II Lead III

Question 41

How is **Lead I** connected?

Answer 41

negative input connected to right arm positive input connected to left arm

Question 42

What does **Lead I** record?

Answer 42

the wave of excitation moving between the right and left sides of the heart REMEMBER: wave of excitation always passes from negative to postive

Question 43

How is **Lead II** connected?

Answer 43

negative input connected to right arm positive input connected to left leg

Question 44

What does **Lead II** record?

Answer 44

records excitation moving between right upper portion of heart to the apex of the venticle

Question 45

How is **Lead III** connected?

Answer 45

positive input connected to left leg negative input connected to left arm

Question 46

What does **Lead III** record?

Answer 46

records excitation moving between left atrium to the apex of the ventricle

Question 47

What are the two types of unipolar lead used in the recording?

Answer 47

3x augmented limb leads 6x chest leads

Question 48

What do unipolar leads do?

Answer 48

record voltage between a single lead and an 'earth' lead

Question 49

What is the general direction of depolarisation of the heart known as?

Answer 49

**the cardiac axis** electrical activity spreads from 11 o clock to 5 o clock

Question 50

What causes an upwards deflection on the ECG trace?

Answer 50

an action potential depolarisation moving **towards** the electrode connected to the **positive input** of the amplifier

Question 51

What does the **P wave** correspond to on an ECG trace?

Answer 51

atrial depolarisation

Question 52

What does the **QRS complex** correspond to on an ECG trace?

Answer 52

ventricular depolarisation

Question 53

What does the **T wave** correspond to on an ECG trace?

Answer 53

ventricular repolarisation

Question 54

What are the septal leads?

Answer 54

V1-V2

Question 55

What are the inferior leads on an ECG?

Answer 55

II, III, aVF

Question 56

What are the anterior leads?

Answer 56

V3-V4

Question 57

What are the lateral leads?

Answer 57

V5, V6, I, aVL

Question 58

What might rarely cause the pathological 4th heart sound?

Answer 58

atrial contraction

Question 59

How do you calculate mean arterial pressure?

Answer 59

diastolic pressure + 1/3 pulse pressure pulse pressure = systolic - diastolic pressure

Question 60

What physical factors affect arterial blood pressure?

Answer 60

arterial blood volume arterial compliance

Question 61

What are the key physiological factors that determine arterial blood pressure?

Answer 61

cardiac output peripheral resistance

Question 62

Why is the mean arterial pressure not simply an average of systolic and diastolic pressures?

Answer 62

diastole lasts longer than systole so has a greater effect on the mean pressure

Question 63

How does aortic valve regurgitation affect stroke volume?

Answer 63

stroke volume increases because there is a greater volume of blood in the ventricle failure of the aortic valve to close properly causes a back flow of blood into the left ventricle increasing stroke volume

Question 64

What is Starling's law of the heart?

Answer 64

an increase in cardiac stretch increases the strength of contraction (greater stretch, greater force if contraction)