The heart is a vital organ responsible for circulating blood throughout the body, primarily by filling its chambers from the veins and then pushing that blood through the arteries. The heart consists of four chambers: the atria and the ventricles. The atria are thinner and less muscular, serving as receiving chambers for blood, while the ventricles are more muscular and act as powerful pumping stations that propel blood into the circulatory system.
The process of pumping blood is known as the cardiac cycle, which encompasses a complete sequence of filling and pumping. This cycle is divided into two main phases: systole and diastole. Systole refers to the contraction phase, during which the heart muscles contract to pump blood out of the heart. Conversely, diastole is the relaxation phase, allowing the heart to fill with blood.
During diastole, blood flows into the atria and ventricles. For instance, blood enters the right atrium from the superior and inferior vena cavae, while the left atrium receives blood from the pulmonary veins. The atria contract (systole) before the ventricles, pushing blood through the atrioventricular (AV) valves into the ventricles. Following this, the atria relax (diastole), and the ventricles contract (systole), pushing blood into the arteries through the semilunar valves.
The entire cardiac cycle is regulated by electrical signals that coordinate the contractions of the heart. These signals can be monitored using an electrocardiogram (ECG), which displays the heart's electrical activity as a waveform. Understanding the cardiac cycle and the role of electrical signals is crucial for comprehending how the heart functions effectively to maintain blood circulation.