Transport systems in mammals: Cardiac Cycle

Cardiac cycle

The sequence of events involving the contraction and relaxation of the heart muscles during one heartbeat.

Systole

The contraction of the heart muscle.

Diastole

The relaxation of the heart muscle.

SA node (sino-atrial node)

A group of specialised cells in the wall of the right atrium that acts as the pacemaker and controls the rate of heart contractions.

Atrial systole

The stage when the atria contract and force blood into the ventricles. The tricuspid and bicuspid valves open. It lasts approximately 0.1 seconds.

Ventricular systole

The stage when the ventricles contract. The tricuspid and bicuspid valves close, while the semi-lunar valves open, allowing blood to leave the heart. It lasts approximately 0.3 seconds.

Atrial and ventricular diastole

The stage when both the atria and ventricles relax. The semi-lunar valves close and the chambers fill with blood. It lasts approximately 0.4 seconds.

Lub sound

The sound produced when the tricuspid and bicuspid valves close during ventricular systole.

Dub sound

The sound produced when the semi-lunar valves close during diastole.