Stages 1, 2a, and 2b together comprise the "Diastole" period; stages 3 and 4 together comprise the "Systole" period. The unsectioned atria are seen above the ventricles. The heart is a four-chambered organ consisting of right and left halves, called the right heart and the left heart. The upper two chambers, the left and right atriaare entry points into the heart for blood-flow returning from the circulatory systemwhile the two lower chambers, the left and right ventriclesperform the contractions that eject the blood from the heart to flow through the circulatory system.
Cardiac Cycle — Systole and Diastole The mechanical events occurring during one systole and diastole. Events that occur in left chambers of heart, similar events occur in right chambers of heart.
This Cardiac cycle filling of ventricles becomes valuable during physical activity. When pressure in the atrium increases, blood rush into the ventricles through the opened mitral valve. During left atrium contraction, pressure and volume are transferred into left ventricle through opened mitral valve.
Remember aortic valve is closed because pressure in aorta is greater than the pressure in left ventricle at this moment. Isovolumetric Contraction Second Phase This is the early phase of ventricular systole. When ventricles contract, there is a progressive increase in intraventricular pressure.
When intraventricular pressure increase than atrial pressure, This wil leads to closure of mitral valve. Intraventricular pressure progressively increases upto 80mmHg yet it is not competent enough to open the aortic valve.
At this moment ventricle is contracting with closed mitral and aortic valves. Meanwhile, intra atrium pressure is gradually increasing due to accumulation of blood returning from lungs into the left atrium.
During the same phase, aorta pumps whatever blood it contains into more peripheral part of arterial tree due to its elastic nature. This is the stage of ventricular contraction when backward valves are closed yet the forward valves are not opened.
Ventricle is contracting as a closed chamber without any change in volume and size of the ventricle. We call it isovolumetric contraction of early part of ventricular systole.
Third phase of cardiac cycle has started.
Ventricles keep on contracting and there is a progressive increase in intraventricular pressure upto mmHg. During this phase, aortic valve opens and blood is ejected rapidly into aorta.
Now left ventricle and aorta behave as a single chamber. The pressure changes occurred in the ventricles results in faithfully transmission of pressure to aorta. Mitral valve is closed. Ventricles are still contracting but due to ejection of blood intraventricular pressure starts falling.
Hence, pressure in aorta also starts falling, but intraventricular pressure is still more than aortic pressure. Aortic valve remains open leading to slow ejection of blood into aorta. Elastic aorta keeps on squeezing the blood and pumps it into peripheral arterial tree.
Isovolumetric Relaxation Fifth Phase In this phase ventricles start relaxing. Intraventricualr pressure falls rapidly. In the beginning, as soon as the ventricular pressure becomes less than pressure in aorta, aortic valve closes.
Even though pressure in ventricle is falling, it is still high enough compared to pressure in atrium. So ventricle is relaxing with closed valves and it is known as isovolumetric relaxation. During this phase atrium is still behaving as reservoir of blood.Cardiac cycle of the left side of the heart.
The electrocardiogram (EKG) below the diagram shows the corresponding waves with each phase of the cardiac cycle. The bottom line represents the first and second heart sounds. cycle [si´k'l] a succession or recurring series of events. cardiac cycle a complete cardiac movement, or heart beat, including systole, diastole, and the intervening pause.
Cardiac cycle. From Applegate, cell cycle the cycle of biochemical and morphological events occurring in a reproducing cell population; it consists of the S phase, occurring. A cardiac cycle is the sequence of events in a single heartbeat. There are two phases of a heartbeat. There are two phases of a heartbeat.
Diastole is the term used to describe the relaxation of the heart. Phases of Cardiac Cycle Atrial contraction (First Phase) This is the phase of atrial contraction. 80% of ventricular filling has been done passively even before the onset of atrial contraction and the remaining 20% of ventricular filling is due to atrial contraction.
At rest the heart pumps around 5l of blood around the body every minute, but this can increase massively during exercise. In order to achieve this high output efficiently the heart works through a carefully controlled sequence with every heart beat – this sequence of events is known as the cardiac cycle/5(14).
Phases of the Cardiac Cycle. At the beginning of the cardiac cycle, both the atria and ventricles are relaxed (diastole). Blood is flowing into the right atrium from the superior and inferior venae cavae and the coronary sinus.
Blood flows into the left atrium from the four pulmonary veins.