cardiac cycle

what are the 4 stages of the cardiac cycle?

- filling phase

- isovolumetric contraction

- outflow phase

- isovolumetric relaxation

what are the two stages of ventricular filling?

- diastole

- atrial systole

how do the ventricles fill in diastole? (2)

- blood flows from vena cava and pulmonary veins into right and left atria

- blood then flows directly into ventricles at steady rate until pressure of vena cava is equal to ventricles

how do ventricles fill during atrial systole? (4)

- atria contract after diastole

- squirt a small amount of extra blood into ventricles

- this increases ventricular pressure so its higher than atria

- hence atrioventricular (tricuspid and mitral) valves close

what happens in isovolumetric contraction? (2)

- initially both sets of valves are closed

- start of systole the ventricular pressure increases ready to eject blood into aorta/pulmonary trunk

what happens in the outflow phase?

- once ventricular pressure has exceeded aorta/pulmonary trunk pressure the semi-lunar valves open

- blood is pumped into aorta/pulmonary trunk

what happens at the end of the outflow phase? (3)

- ventricles begin to relax

- ventricular pressure decreases so is lower than aorta and pulmonary trunk

- semilunar valves close

what happens in isovolumetric relaxation? (4)

- both sets of valves are closed

- ventricles relax

- ventricular pressure is lower than atrial pressure so atrioventricular valves open

- ventricles fill with blood + cycle begins again

what causes the 'lub' sound? (2)

- AV valves closing

- semilunar valves opening

what causes the 'dub' sound? (2)

- AV valves opening

- semilunar valves closing

where can you auscultate the aortic valve?

right 2nd intercostal space - sternal edge

where can you auscultate the pulmonary valve?

left 2nd intercostal space - sternal edge

where can you auscultate the tricuspid valve?

left 4th intercostal space - sternal edge

where can you auscultate the mitral valve?

left 5th intercostal space - midclavicular line

what are the phases of the cardiac action potential?

phases:

0

1

2

3

4

what happens in phase 0?

rapid depolarisation

what causes rapid depolarisation?

influx of sodium ions

what happens in phase 1?

early repolarisation

what causes early repolarisation?

potassium efflux

what happens in phase 2?

plateau phase

what causes the plateau phase?

slow influx of calcium

what happens in phase 3?

final repolarisation

what causes final repolarisation?

potassium efflux

what happens in phase 4?

restoration of ionic concentrations

what causes restoration of ionic concentrations?

- restored by Na+/K+ ATPase

- slow influx of Na+ decre