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Identify the correct sequence of events in a cardiac cycle.
(a) Diastole, atrial systole, ventricular diastole
(b) Atrial systole, ventricular diastole, ventricular systole
(c) Atrial diastole, atrial systole, ventricular diastole, ventricular systole
(d) Ventricular diastole, diastole, ventricular systole, atrial systole

Last updated date: 13th Jun 2024
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Hint: Heart shows regular contraction and relaxation. Contraction and relaxation take place in the atria and ventricles alternately. The heart receives deoxygenated blood from the body and transfers oxygenated blood to the body.

Complete answer:
The cardiac cycle means one heartbeat, generally, the human heart beats 72 times per minute and pumps out approx 70 milliliters of blood per beat. The phase of contraction of the heart is called systole and the phase of relaxation is called diastole. The sequence of the cardiac cycle are
-Atrial systole- Atrial show contraction due to wave impulse by Sinoatrial node. Both the bicuspid and tricuspid valves get open and blood pumped into ventricles. This process takes 0.1 seconds. After this atria enter into the diastole phase.
-Ventricular systole- After atrial diastole, ventricles enter into the systole stage. Ventricles contraction is stimulated by the atrioventricular node. The bicuspid and tricuspid valves get close to prevent the backflow of blood. After ventricular contraction blood enters into the aorta and pulmonary trunk via the semilunar valve. This process takes 0.3 seconds.
-Ventricular Diastole- semilunar valve gets close and the ventricle enters into a relaxing stage. When the pressure in ventricles get reduced the bicuspid and tricuspid valve get open and blood flow takes place from atria.
-Joint diastole-Both atria and ventricle are in a relaxed state in joint diastole. This phase is also called a general pause. This process takes 0.5 seconds.
The opening and closing of the valve also produce heart sounds lub and dub. Closing of the bicuspid and tricuspid valve produces the first heart sound lub and closing of the semilunar valve generates a second sound dub.
So, the correct answer is ‘Atrial systole, ventricular systole, ventricular diastole’.

Note: Improper cardiac cycle is a symbol of many heart disorders. In this case, the valve does not open and close properly. Due to malfunctioning of the heart oxygen supply to the body also gets affected. In some cases, oxygenated blood gets mixed with deoxygenated blood and it can be fatal.