Südametsükkel

Südametsükkel, which translates to "heart cycle" or "cardiac cycle" in English, refers to the sequence of events that occur during one complete heartbeat. It encompasses both the relaxation phase, known as diastole, and the contraction phase, known as systole. The cardiac cycle is a continuous, rhythmic process that ensures the efficient pumping of blood throughout the body.

During diastole, the heart muscle relaxes, and the chambers of the heart, specifically the atria and ventricles, fill with blood. This is a passive process, largely driven by the pressure gradient between the veins and the heart. Following diastole, systole begins, during which the heart muscle contracts, forcefully ejecting blood from the ventricles into the arteries. The atria contract just before the ventricles to ensure they are empty of blood before the ventricular contraction begins.

The mechanical events of the cardiac cycle are coordinated by electrical impulses generated by the heart's natural pacemaker, the sinoatrial (SA) node. These electrical signals travel through the heart's conduction system, causing the muscle cells to contract in a synchronized manner. The sounds of the heartbeat, often described as "lub-dub," are produced by the closing of the heart valves. The "lub" sound is caused by the closure of the atrioventricular valves (mitral and tricuspid) at the beginning of ventricular systole, and the "dub" sound is caused by the closure of the semilunar valves (aortic and pulmonary) at the end of ventricular systole. Understanding the südametsükkel is fundamental to comprehending cardiovascular physiology and diagnosing heart conditions.