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The cardiac system is a series of events ensuring that the heart remains beating. The blood that the heart pumps out is circulated through the pulmonary and systemic circuits of the body. There are two main stages in the cardiac cycle. The first one is the diastole cycle, in which the muscles relax and are filled with blood. The second stage is called systole, in which the ventricles pump out the blood when it contracts into arteries. A cardiac cycle definition tells us that it is a chain of events that begins from one heartbeat to another.
Cardiovascular System
The cardiovascular system is responsible for supplying nutrients and removing and cleaning waste from the cells present inside the body. The system consists of circulatory functioning and the human heart. The cardiac cycle needs muscles to supply blood throughout the human body. The blood vessels inside the body act as gateways that help supply blood to various body organs and cells.
Cardiac conduction is defined as the electrical conduction system. It is a group of heart muscles present in the walls of the heart that send signals to its muscles, contracting them. The cardiac cycle definition further gives a deep insight into stages.
Cardiac Cycle Stages
There are phases in which the cardiac cycle performs its functions. The first stage is diastole, in which the muscles relax, and the heart fills with blood. The second stage is called systole, in which the heart pumps out blood, and the muscles start to contract. Both Diastole and Systole occur one after another in stages. The atria and ventricles of the human heart go through these stages separately. There are four stages of the cardiac cycle:
1. Ventricular diastole
When this stage starts, the heart’s ventricle and the atria relax, and atrioventricular valves open and function. Blood without oxygen returns to the heart following the last cardiac cycle. Further, it passes through the inferior and superior vena cava and goes to the respective right atrium.
The atrioventricular valve opens, allowing the blood to go through the atria to the respective ventricles. Now, the two atrioventricular valves are the mitral and tricuspid. Pulses travel from the sinoatrial node (SA) to the atrioventricular node (AV), and then the AV node sends a signal that makes both atria contract. The atrium (right) empties and supplies its contents to the ventricle (right). The valve (tricuspid), situated between the right atrium and the ventricle (right), does not allow the blood to flow back towards the right atrium.
2. Ventricular systole
In the second phase, which is the beginning of the ventricular systole stage, the ventricle (right), filled with blood from the right atrium, receives signals from the fibre branches, carrying electrical signals that cause it to contract. Semilunar valves in the heart get opened up, and the atrioventricular one closes.
Ventricular contraction pumps the oxygen-depleted blood from the ventricle (right) towards pulmonary arteries. The blood does not flow back towards the ventricle (right) due to the presence of a pulmonary valve. A pulmonary artery in the heart carries old, oxygen-depleted blood into the pulmonary circuit towards the lungs. From the same, the blood fills with oxygen and goes back towards the atrium (left) through the pulmonary veins.
3. Atrial diastole
The semilunar valve closes, followed by the opening of the atrioventricular valve. Oxygenated blood in pulmonary veins loads the atrium (left) while blood present in the venae cavae fills the atrium (right). SA nodes send a signal to both atria to get contracted.
Atrial contraction empties the atrium (left) into the left ventricle, and the right atrium empties into the ventricle (right). Mitral valves are present between the atrium (left) and left ventricle, preventing oxygenated blood from going back towards the atrium (left).
4. Atrial systole
During this stage, the atrioventricular valve closes, and the semilunar valve opens. The ventricles receive signals to contract. Oxygenated blood in the left ventricles is pumped to the aorta, and aortic valves prevent the blood from going back towards the left ventricle.
Conclusion
The cardiac cycle defines the chain of events occurring between one heartbeat to the next. There are four stages of the cardiac cycle. The first two stages of the cardiac cycle are called Diastole and Systole. In the first stage, the muscles present in the heart relax, and the heart fills with oxygen-rich blood. In the second stage, the heart muscles start to contract, and the heart pumps out this oxygen-filled blood into different organs and cells of any human body. The last two stages repeat the process to continue the cycle in the segmented heart. The result of this cardiac cycle is blood circulation in human beings.
