Atrial Diastole

The cardiac cycle is an electrical cycle of the heart where the heart expands and relaxes to receive and pump out blood respectively. The cardiac cycle is divided into the systole and the diastole. The systole is the contraction phase of the cardiac cycle, where the chambers of the heart contract to push the blood forward. The diastole is the loosening phase of the heart, where the chambers of the heart relax and fill in blood. Both atria and ventricle take part in systole and diastole to maintain the proper blood supply throughout the body. 

Cardiac Cycle

As the name suggests, the cardiac cycle is the cycle of the human heartbeat. It comprises two parts: systole and diastole. Systole is the stage where the heart forces out blood to the lungs and the body. Diastole is the phase where the heart receives blood from the lungs and the body. A heart beats 70-75 times in a minute, and one cardiac cycle lasts up to 0.8 seconds approximately. 

The right atria receive deoxygenated blood from the body via the superior and inferior vena cava. It then enters the right ventricle of the heart, from which the blood is transferred to the lungs for purification. The purified blood is collected by the left atria and is pumped forward to the left ventricle. Then the blood is transported to the whole body through the aorta. To perform all these transfers, the heart requires strong electrical signals so that the chambers can contract and pump the blood forward.

Divisions of the Cardiac Cycle

• Systole: it is the contraction phase of the cardiac cycle where the chambers of the heart contract to push the blood forward. The Atria shrinks to move blood to the ventricles. The right atria contract to push deoxygenated blood to the right ventricle. The right ventricle further contacts to push blood to the lungs. At the same time, the left atria receive purified blood from the lungs and contract to push the blood to the left ventricle. The purified blood from the left ventricle is moved to the whole body through the aorta.

The systole is further divided into Atrial systole and ventricular systole, which means the contraction of the atria and ventricles, respectively.

• Diastole: is the relaxation phase of the cardiac cycle where the chambers of the heart relax to fill in blood. Initially, when the right atria are relaxed (atrial diastole), the blood from the superior and inferior vena cava enters the atria; then, as the left atria contracts, the left ventricle relaxes, due to which the blood from the left atria is transferred into the left ventricle. Likewise, when the left atria are relaxed (atrial diastole), blood from the lungs enter the left atria. At this time, the left ventricle relaxes, and the left atria contracts, due to which the blood occupies the left ventricle and then is transferred to the whole body.

The diastole is further divided into ventricle diastole and atrial diastole, where the atria and ventricles relax.

Atrial Diastole Explanation

In the beginning, all the four chambers of the heart relax and contract in a synchronised manner. When both the left and right atria relax, it receives blood from the lungs and the superior and inferior vena cava. Due to pressure, the atria contract, and the tricuspid and bicuspid valves open, which forces the blood into the relaxed left and right ventricles, respectively. When the ventricles are filled, the bicuspid and the tricuspid valves close to avoid the backflow of blood. The blood is pushed forward from the ventricles, the left ventricle transfers blood from the aorta to the whole body, and from the right ventricle, the blood is transferred to the lungs through the pulmonary artery.

Conclusion

The cardiac cycle is a cycle of events that the heart undergoes in one heartbeat. It lasts about 0.8 secs. A heart beats approximately 70-75 times in a minute. Systole means contraction of the chambers of the heart, whereas diastole means relaxation of the chambers of the heart. The systole can be further divided into atrial systole and ventricular systole. The diastole can also be divided into atrial diastole and ventricular diastole. 

In atrial systole, the atria contract to pump blood to the ventricles, and in ventricle systole, the ventricles contract to move blood forward to their respective target area. In the atrial diastole, the atria relax to receive blood from their respective target areas, and in the ventricle diastole, the ventricles relax to receive blood from the atria. This whole cardiac cycle lasts about 0.8 seconds. 

The four phases occupy different times:

Atrial systole lasts about 0.1 secs

Ventricle Systole lasts about 0.3 secs

Atrial diastole: lasts about 0.7 secs

Ventricle diastole lasts about 0.5 secs.