Answer: Closure of the semilunar (aortic and pulmonary) valves at the start of diastole.
- A Contraction of the ventricular myocardium during systole as generally observed
- B Opening of the atrioventricular valves during diastole in typical laboratory settings
- C Closure of the atrioventricular valves at the start of systole under normal conditions
- D Closure of the semilunar (aortic and pulmonary) valves at the start of diastole
Correct answer: D. Closure of the semilunar (aortic and pulmonary) valves at the start of diastole
Explanation: The second heart sound ('dub') is produced by the closure of the semilunar valves (aortic and pulmonary) at the beginning of ventricular diastole.
A single ECG cycle: the P wave marks atrial depolarisation (contraction signal), the large QRS complex marks ventricular depolarisation, and the T wave marks ventricular repolarisation (recovery) before the next cycle begins.
Concept context
Blood, lymph, the heart, the cardiac cycle, blood pressure, and ECG. High NEET weightage.