CVS Pumping of the heart

Question 1

Define systole and diastole

Answer 1

Systole is the period when the myocardium is contracting (280ms)

Diastole is the relaxation between contractions (700ms)

Question 2

Explain the spread of excitation in systole

Answer 2

The SA node fires an AP which spreads over the atria via the internal tracts
When the AP reaches the AV node there is a brief delay (120ms)
The excitation then travels along the bundle of His down the septum (down left and right bundle branch)
and across the ventricles via the purkinje fibres

Excitation spreads from endo to epicardial surface

Question 3

Why do the ventricles contract from the apex upwards?

Answer 3

Ventricular muscle is organised into figure of eight shaped bands that squeeze in a slight twisting manner most effective for ejection of blood through the outflow valve.

Question 4

Whats the difference between the right and left sides of the heart?

Answer 4

The left side has a much thicker ventricular wall as it must generate enough force to get blood around the entire body whereas the right side only needs to pump to the lungs.
The right side has the SA node pacemaker.

Question 5

What causes the 1st and 2nd heart sounds?

Answer 5

1st sound:
As the AV valves close ‘lup’ (tricuspid + bicuspid)

2nd sound:
As the semilunar valves close ‘dup’ (aortic + pulmonary)

Question 6

What is stroke volume? Give a value for an average resting male

Answer 6

Stroke volume is the volume of blood per minute from each ventricle
At rest stroke volume is ~70ml

Question 7

Give the formula for blood pressure

Answer 7

BP = cardiac output x total peripheral resistance

Question 8

Give an outline of the cardiac cycle

Answer 8

Atrial contraction:
Atrial pressure rises due to atrial systole, accounts for final 10% of ventricular filling
Isovolumetric contraction:
Mitral valve closes, and rise in ventricular pressure as it contracts (all valves closed so no change in volume)
Rapid ejection:
Aortic valve opens, rapid decrease in ventricular volume as blood is ejected. Atrial pressure decreases as atrial base in pulled downwards when the ventricle contracts
Reduced ejection:
Repolarisation of ventricle means rate of ejection falls
Isovolumetric relaxation:
Brief back flow causing aortic valve to close. Rapid decline in ventricular pressure but no change in volume as all valves closed
Rapid filling:
Mitral opens and there is rapid ventricular filling
Reduced filling:
Rate slows down as ventricle reaches its relaxed volume (passive filling at maximum)

Question 9

Where in the cardiac cycle does each valve open and close?

Answer 9

Pulmonary + aortic valve:
Open in systole when ventricular pressure exceeds arterial pressure.
Close towards end of systole, back flow of blood closes the valves

Tricuspid + mitral valves:
Open in early diastole
Remain open in early systole until pressure exceeds atria and brief back flow of blood causes closure

Question 10

What is the cause of a heart murmur?

Answer 10

A murmur is a sound caused by turbulent blood flow, the turbulence is due to stenosis (a narrowed valve) or a leaky valve (regurgitation of blood)

Question 11

What are the different types of heart murmurs?

Answer 11

Systolic murmurs
Diastolic murmurs
Continuous murmurs (patent ductus arteriosus)