The cardiac cycle is the sequence of events in one heartbeat. – It involves contraction and relaxation of the heart chambers. – Master it to understand how blood flows and pressure changes. – Let’s break it down step by step.
– Diastole: Heart muscles are relaxed. – Atria fill with blood from veins (vena cava, pulmonary veins). – AV valves (tricuspid & mitral) are open. – Ventricles are filling with blood.
– Atrial Systole: Atria contract to push blood into ventricles. – This adds 20-30% more blood to ventricles (atrial kick). – AV valves still open, ventricles now nearly full. – Right atrium pushes blood to right ventricle, left to left ventricle.
– Isovolumetric Contraction: Ventricles contract, but valves are still closed. – Pressure in ventricles rises. – Both the AV valves and semilunar valves (pulmonary/aortic) are closed. – No blood is ejected yet.
– Ejection Phase: Pressure in ventricles exceeds aortic/pulmonary pressure. – Semilunar valves open. – Blood is ejected into the aorta (left ventricle) and pulmonary artery (right ventricle). – Ventricular volume decreases as blood exits.
– Isovolumetric Relaxation: Ventricles relax, and pressure drops. – Semilunar valves close to prevent backflow. – AV valves are still closed. – No blood enters or exits yet, ventricles are still full.
– End of Cycle: AV valves open again as ventricular pressure drops. – Blood flows from atria into ventricles, starting the cycle again. – Heart rate governs the speed of the cycle. – Proper coordination ensures efficient blood flow and oxygen delivery.