What is the cardiac cycle and its phases?

The cardiac cycle is the sequence of events that occurs when the heart beats, comprising the diastole and systole phases.

The cardiac cycle is a fundamental concept in understanding how the heart functions. It refers to the complete sequence of mechanical and electrical events that take place during a single heartbeat. This cycle is divided into two main phases: diastole and systole.

During the diastole phase, the heart muscles are in a state of relaxation. This is the period when the heart fills with blood. It begins with the opening of the atrioventricular (AV) valves, which allows blood to flow from the atria into the ventricles. The atria then contract, pushing any remaining blood into the ventricles. This phase ends when the AV valves close to prevent backflow of blood.

The systole phase follows diastole and is when the heart muscles contract. It begins with the closing of the AV valves and the opening of the semilunar valves, which allows blood to be pumped out of the heart. The ventricles contract, pushing blood into the pulmonary artery and the aorta. The semilunar valves then close to prevent blood from flowing back into the heart, marking the end of systole and the beginning of the next cardiac cycle.

The cardiac cycle is regulated by electrical signals that originate from the sinoatrial node, also known as the heart's natural pacemaker. These signals spread across the heart, causing the muscle cells to contract and relax in a coordinated manner. This ensures that the heart beats in a regular and efficient way, pumping blood throughout the body. Understanding the cardiac cycle is crucial for comprehending how the heart works and how changes in this cycle can lead to cardiovascular diseases.