Question

The heart sound “dub” is produced during which of the following stages of the cardiac cycle?

• A. End of atrial systole
• B. End of ventricular diastole
• C. Joint diastole
• D. End of ventricular systole

Answer 1

The correct option is D End of ventricular systole

The sinoatrial node generates an action potential due to which the left and right atrium contracts and undergoes atrial systole. The action potential is then further conducted to the atrioventricular node (AV node). AV node conducts the impulse to the bundle of His and purkinje fibres.

Due to the transmission of the action potential, the ventricles contract and it is called ventricular systole. At this stage, the atriums also relax and undergo diastole.
Due to the ventricular systole, the pressure inside the ventricles increase which results in closure of the bicuspid and tricuspid valve. The closure of the atrioventricular valves produces the sound lub at the start of the ventricular systole.
As the pressure inside the ventricles increases, the semilunar valves open up and blood is released into the circulatory system. Then the semilunar valves close to prevent the backflow of blood into the ventricles. The closure of semilunar valves produces the heart sound “dub”. This occurs at the end of ventricular systole.