Cardiac cycle
The human body is composed of many organs. Every part is equally important; these parts need blood for proper functioning, which involves a series of the cycle to manage the functioning. The cardiac cycle is defined as altering the relaxation and contraction of the ventricles and the atria for proper pumping of blood into the body parts. Generally, the sequence starts at the beginning of a heartbeat and ends at the commencement of another. The cardiac cycle has two phases; diastole (diastolic phase) and systole (systolic phase). The diastolic phase involves relaxation of the heart chamber filled with blood from the veins.
In contrast, the systolic phase requires the heart chamber’s contraction, and blood is pumped through the arteries towards the periphery. In other words, when the ventricles are in systole, the atria are in diastole and the other way round. The aim of this paper, therefore, is to understand the cardiac cycle.
The heart contains cells (myocardiocytes) unique and operates independently to generate electrical activity from one section to the other. It also has an area called the sinoatrial node (SN), which contains sub-specialized cells. This node can contract faster than the other heart tissues, and therefore it sets the pace for cardiac contraction; it is the pacemaker of the heart. The atrioventricular (AV) node, on the other hand, can produce an action potential in which the cells are a bit slower and act in the response of the sinoatrial nodes.
The cardiac cycle’s first process is atrial diastole, which occurs within very few seconds before SA electrical signaling. It enables blood transmission into the ipsilateral ventricle, which also pumps residual blood into the ventricles. During the process, blood is pumped in the right atrium via the inferior and superior vena cava and the left atrium through the pulmonary veins. At the beginning of the phase, the atrioventricular valves are closed, and blood is pumped into the atria. When the pressure is much from the atrium to the ventricle’s pressure, it results in the opening of the valves, which allows blood to flow into the ventricles. The SA allows the residual blood to flow in the lower chambers through contractions and leads to pressure increase through atrial systole.
The second process involves the closure of semilunar and atrioventricular valves in that there is no change in the amount of blood, resulting in isovolumetric relaxation. Low pressure causes the valves to open, and little blood flows into the ventricles, which results in preload. When the ventricles contract, the AV node allows complete contraction, and when the pressure is not sufficient, it results in isovolumetric contraction. When pressure exceeds, the valves open, resulting in end-systolic volume. The whole cycle continues to repeat as long as there is life.