Cardiac Cycle Phases

The cardiac cycle is a series of events in which the heart beats in order to carry out the main functions of receiving and pumping out blood. We are now going to learn more about how does the heart pump blood to our entire body. The cardiac cycle is divided into two phases i.e. the diastole and systole. The descriptions of these two phases along with other events which take place during the cardiac cycle are presented below. All the events which occur during the cardiac cycle are associated/related to the blood pressure/flow of blood which is initiated by heartbeats. The heart rate is derived from the frequency at which cardiac cycle occurs. The cardiac cycle phases are part of this quick action of heat beat. Let us understand more about these phases through this article.

Phases of Cardiac Cycle

As stated earlier, the length of cardiac cycle is divided into the diastole and systole phases. The contractile phase amongst the two is the systole. The cardiac cycle diagram and related information presented in this article should help understand the process in a better manner. Classification of cardiac cycle though divides the process into two main categories (diastole and systole), the diastole and systole too are sub-divided into first and second phases. Let's know more about the cardiac cycle.

First Diastole Phase: In the diastole phase, the heart receives deoxygenated blood from the superior and inferior venae cavae. For blood to enter the heart through the superior and inferior venae cavae, the ventricles and atria get relaxed. With the relaxation of atria and ventricles the atrioventricular open. The opening of atrioventricular valves facilitates blood to reach the ventricles. All the above events are followed by contraction of SA node, which in turn contracts the atria. Blood is then transferred from right atrium to the right ventricle. A valve known as the tricuspid valve is present between the right ventricle and right atrium. It prevents the blood from going back to the atrium.

First Systole Phase: In the first systole phase, right ventricle of the heart contracts as a result of impulses received from the 'Purkinje fibers'. It is followed by the closure of atrioventricular valves and opening of semilunar valves. These actions cause the de-oxygenated blood to get pumped into pulmonary artery. Blood is prevented by the pulmonary valve from entering the right ventricle. Blood is carried to the lungs by the pulmonary artery for oxygenation. The blood after oxygenation, is returned to the heart i.e. in the left atrium. Pulmonary veins carry this purified blood from the lungs to left atrium.

Second Diastole Phase: The beginning of second diastole phase is marked by the closure of semilunar valves and opening of atrioventricular valves. The oxgenated blood brought by pulmonary veins gets accumulated in the left atrium. Simultaneously, the blood present in the vena cava also gets transferred to the right atrium. This is followed by contraction of SA node which in turn causes the contraction of atria. All these actions cause the left atrium depositing the blood into left ventricle. The blood is not allowed to flow back into the left atrium as the mitral valve prevents this from happening.

Second Systole Phase: Closing of semilunar valves and opening of the semilunar valves takes place at the beginning of the second systole phase. Contraction of left ventricle resulting from the reception of Purkinje fiber reception also takes place. This is followed by pumping of oxygenated blood into the aorta. The blood flow cannot revert to left ventricle from aorta since the aortic valve prevents this from happening. The purified/oxygenated blood is distributed to various parts of the body through aorta. Impure/deoxygenated blood is brought in by the network of veins to the heart by means of venae cavae. Knowledge of the cardiac muscle function should help understand the working of heart in a better manner.

The cardiac cycle phases described in this article should help understand about the functioning of the human heart at the time of contraction and relaxation. Details about the flow of blood through different parts/sections of the heart are illustrated in the paragraphs above.