Cardiac Valve Function & Blood Flow — NEET Biology

Correct answer: A — S2, S4 and S6

Let's evaluate each statement: S1: The first heart sound ('lub') is associated with the closure of the tricuspid and bicuspid valves. This statement is correct. NCERT states, "The first heart sound (lub) is associated with the closure of the tricuspid and bicuspid valves." S2: The second heart sound ('dub') is primarily caused by the closure of the atrioventricular valves during ventricular diastole. This statement is NOT correct. The second heart sound ('dub') is associated with the closure of the semilunar valves, not the atrioventricular valves. S3: Closure of the semilunar valves occurs when ventricular pressure declines, preventing backflow of blood into the ventricles. This statement is correct. NCERT states, "The ventricles now relax (ventricular diastole) and the ventricular pressure falls causing the closure of semilunar valves which prevents the backflow of blood into the ventricles." S4: Heart sounds are directly generated by the contraction of the cardiac muscles. This statement is NOT correct. Heart sounds are generated by the closure of the valves, not directly by muscle contraction. S5: A healthy individual experiences approximately 72 'lub-dub' sound pairs per minute. This statement is correct. A healthy heart beats 72 times per minute, with each beat comprising a 'lub-dub' pair of sounds. S6: The clinical diagnostic significance of heart sounds is limited as they only indicate the rate of heart beat. This statement is NOT correct. NCERT states, "These sounds are of clinical diagnostic significance." Deviations from normal sounds can indicate various cardiac abnormalities beyond just heart rate. Therefore, statements S2, S4, and S6 are NOT correct. Option A correctly identifies the incorrect statements. Options B, C, and D include correct statements or miss incorrect ones. This question tests the understanding of the specific events that cause heart sounds and their importance in diagnosis.