Physiology (Cardiovascular)

Question 1

Where does excitation normally originate in the heart?

Answer 1

In the pacemaker cells in the sino-atrial node.

Question 2

Where is the SA node located?

Answer 2

In the upper right atrium close to where the SVC enters.

Question 3

What cells have spontaneous pacemaker potential?

Answer 3

Cells in the SA node.

Question 4

What movement of ions causes the slow depolarisation in the spontaneous pacemaker potential?

Answer 4

Decrease in K+ efflux. Na+ and K+ influx (funny current). Transient Ca2+ influx (T-type Ca2+ channels).

Question 5

Once the threshold is reached, what channel causes the rising phase of the action potential?

Answer 5

Long lasting L-type calcium channels, resulting in calcium influx.

Question 6

What is the falling phase of the action potential caused by?

Answer 6

Inactivation of L-type Ca2+ channels and activation of K+ channels resulting in K+ efflux.

Question 7

Describe the path of cardiac excitation.

Answer 7

SA node -> AV node -> bundle of His -> left and right bundle branches -> purkinje fibres in the ventricles

Question 8

How does excitation spread from cell to cell?

Answer 8

Current flows through gap junctions.

Question 9

Where is the AV node located?

Answer 9

At the base of the right atrium, just above the junction of atria and ventricles.

Question 10

How are AV node cells specialised?

Answer 10

Small in diameter and slow conduction velocity.

Question 11

Other than gap junctions, how can excitation spread from the SA to AV node?

Answer 11

There are some internodal pathways.

Question 12

In cardiac myocytes, what movement of ions causes the rising phase of the action potential?

Answer 12

Na+ influx.

Question 13

Describe the 5 phases of the action potential in cardiac myotcytes.

Answer 13

0 - fast Na+ influx. 1 - closure of Na+ channels and transient K+ efflux. 2 - Mainly Ca2+ influx. 3 - closure of Ca2+ channels and K+ efflux. 4 - resting membrane potential.

Question 14

Describe the graph of action potential in cardiac myocytes at each phase.

Answer 14

0 - rapid upwards y movement. 1 - slight decline in y. 2 - plateau. 3 - rapid decrease in y. 4 - resting potential.

Question 15

What ion movement is the plateau phase mainly caused by?

Answer 15

Influx of Ca2+ through L-type Ca2+ channels.

Question 16

What is the influence of the parasympathetic nervous system on the heart rate at rest?

Answer 16

Vagus nerve exerts a continuous influence on SA node under resting conditions (vagal tone) which slows down the heart rate.

Question 17

What is bradycardia and tachycardia defined as?

Answer 17

Bradycardia - <60bpm. Tachycardia - >100bpm.

Question 18

What is the effect of vagal stimulation on the heart?

Answer 18

Slows heart rate and increases AV nodal delay.

Question 19

What is the neurotransmitter involved in the parasympathetics of the heart and what receptor does it bind to?

Answer 19

ACh, M2 receptor.

Question 20

What is the sympathetic receptor in the heart and what do the sympathetic nerves innervate?

Answer 20

B1. SA node, AV node and myocardium.

Question 21

What effect does noradrenaline have on the heart?

Answer 21

Increases heart rate and decreases AV nodal delay.

Question 22

What effect does the sympathetic and parasympathetic nervous system have on the slope of the pacemaker potential?

Answer 22

Sympathetic increases slope, parasympathetic decreases slope.

Question 23

What does the PR interval, ST segment and TP interval represent?

Answer 23

PR - AV nodal delay. ST - ventricular systole. TP - diastole.

Question 24

Are there neuromuscular junctions in the cardiac muscle?

Answer 24

No.

Question 25

What are protein channels which form low resistance electrical communication pathways between neighbouring myocytes?

Answer 25

Gap junctions.

Question 26

What are the functions of the desmosomes in the intercalated discs?

Answer 26

They provide mechanical adhesion between adjacent cardiac cells which ensures that tension developed by one cells is transmitted to the next.

Question 27

Are myofibrils organelles or muscle cells?

Answer 27

Organelles.

Question 28

What is the functional unit of a muscle cell?

Answer 28

Sarcomeres.

Question 29

What needs to be present for an energised myosin head to bind to an actin filament?

Answer 29

Calcium.

Question 30

Is ATP required for contraction or relaxation?

Answer 30

Both.

Question 31

What are the regulatory proteins that block the myosin binding sites on actin?

Answer 31

Troponin and tropomyosin (troponin-tropomyosin complex).

Question 32

Which of these proteins does calcium bind to?

Answer 32

Troponin.

Question 33

Where is calcium mainly released from in the sarcoplasmic reticulum?

Answer 33

The lateral sacs.

Question 34

What does the long refractory period in cardiac myocytes prevent?

Answer 34

Generation of tetanic contraction.

Question 35

Why can a new action potential not be produced during the plateau phase?

Answer 35

The sodium channels are in the depolarised closed state i.e. not available for opening.

Question 36

Why can a new AP be produced during the descending phase?

Answer 36

The potassium channels are open and the membrane cannot be depolarised.

Question 37

What is the equation relating end diastolic volume, end systolic volume and stroke volume.

Answer 37

SV = EDV - ESV.

Question 38

What is involved in the intrinsic control of stroke volume?

Answer 38

Changes in the diastolic length of myocardial fibres.

Question 39

What is the diastolic length of myocardial fibres determined by?

Answer 39

The volume of blood within each ventricle at the end of diastole.

Question 40

What is the end diastolic volume (EDV, preload) determined by?

Answer 40

Venous return to the heart.

Question 41

What is the Frank-Starling mechanism (Starling's law of the heart)?

Answer 41

The more the ventricle is filled with blood during diastole (EDV), the greater the volume of ejected blood will be during the resulting systolic contraction (SV).

Question 42

What other effect does stretch have inside cardiac myocytes?

Answer 42

The affinity of troponin for calcium.

Question 43

What is the difference between optimal length of muscle fibres in skeletal and cardiac muscle?

Answer 43

Skeletal: optimum length is resting muscle length, stretching the muscle will make it worse. Cardiac: more stretch = more force.

Question 44

Does Starling's law apply to the left ventricle and how?

Answer 44

Yes, more blood in right atrium leads to more blood eventually reaching left ventricle so increases SV into aorta.

Question 45

What is the heart's response to increased afterload in the short term and then long term?

Answer 45

Short term: Heart can't eject full SV so EDV increases so force of contraction increases. Long term: ventricular hypertrophy.

Question 46

What effect does stimulating sympathetic nerves have on force of contraction?

Answer 46

It increases force of contraction (positive inotropic effect).

Question 47

How does sympathetic stimulation decrease the rate of systole and diastole?

Answer 47

Rate of pressure change during systole increases which reduces duration of systole. Rate of ventricular relaxation increases (increased rate of calcium pumping) so reduced duration of diastole.

Question 48

Does the parasympathetic nervous system have any effect on SV?

Answer 48

No.

Question 49

What hormones have a positive inotropic and chronotropic effect and how do these effects compare with the nervous system?

Answer 49

Adrenaline and noradrenaline released from adrenal medulla. Minor effects compared to sympathetic stimulation.

Question 50

Are the pressures in the right heart similar to the left heart?

Answer 50

They have similar patterns but right pressure is much lower.

Question 51

What are the 5 events of the cardiac cycle?

Answer 51

1. Passive filling. 2. Atrial contraction. 3. Isovolumetric ventricular contraction. 4. Ventricular ejection. 5. Isovolumetric ventricular relaxation.

Question 52

What valves open at the starts of passive filling?

Answer 52

AV valves.

Question 53

How full do the ventricles become by passive filling?

Answer 53

Around 80% full.

Question 54

What is the end diastolic pressure of the atria (after atrial contraction)?

Answer 54

A few mmHg.

Question 55

At what part of the ECG does the atria contract?

Answer 55

Between the p-wave and the QRS.

Question 56

When will the AV valve close?

Answer 56

When the pressure in the ventricle is greater than the atria.

Question 57

Does any blood enter or leave the ventricle during isovolumetric ventricular contraction?

Answer 57

No.

Question 58

Describe the ventricular pressure change during isovolumetric ventricular contraction.

Answer 58

Rises very steeply.

Question 59

When will the aortic/pulmonary valves open?

Answer 59

When the ventricular pressure exceeds the aortic/pulmonary pressure.

Question 60

What produces the dicrotic notch in the aortic pressure curve?

Answer 60

The aortic valve vibration.

Question 61

What are the auscultation areas of the heart valves?

Answer 61

Aortic: 2nd intercostal space on right of sternum. Pulmonary: 2nd intercostal space on left of sternum. Tricuspid: 4th intercostal space on left of sternum. Mitral: 5th intercostal space mid-clavicular line.