LO4: Describe atrial and ventricular systole and diastole in the cardiac cycle, using mechanical actions and electrical actions.

What is systole?

Systole is the contraction phase of the heart chambers, pumping blood out.

What is diastole?

Diastole is the relaxation phase of the heart chambers, allowing them to fill with blood.

What causes the "lub" and "dub" heart sounds?

"Lub" = AV valves closing during ventricular systole.
"Dub" = Semilunar valves closing during ventricular diastole.

What triggers each heartbeat and sets the rhythm?

The SA node initiates the electrical impulse, acting as the heart’s natural pacemaker.

What happens during early ventricular diastole?

Ventricles relax, semilunar (SL) valves close to stop backflow. Atria are relaxed. No electrical activity.
Valves: AV open / SL closed

What happens during mid ventricular diastole?

Atria and ventricles are relaxed. Blood flows from veins → atria → ventricles. No electrical signals.
Valves: AV open / SL closed

What happens during atrial systole (still part of diastole)?

Atria contract to top-up the ventricles. This completes ventricular filling (end diastolic volume or EDV). SA node has fired.
Valves: AV open / SL closed

What happens during early ventricular systole?

Ventricles start contracting, pressure rises → AV valves close. SL valves still closed. Atria relax. AV node passes signal to ventricles.
Valves: AV closed / SL closed

What happens during late ventricular systole?

Ventricles fully contract → SL valves open, blood is pumped out to lungs and body. Some blood remains (end systolic volume or ESV).
Valves: AV closed / SL open