Cardiac Valve Function & Blood Flow — NEET Biology
📚 Practice ConceptAs the ventricular pressure increases further, the semilunar valves guarding the pulmonary artery (right side) and the aorta (left side) are forced open, allowing the blood in the ventricles to flow through these vessels into the circulatory pathways. 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. As the ventricular pressure declines further, the tricuspid and bicuspid valves are pushed open by the pressure in the atria exerted by the blood which was being emptied into them by the veins. The blood now once again moves freely to the ventricles. The ventricles and atria are now again in a relaxed (joint diastole) state, as earlier. Soon the SAN generates a new action potential and the events described above are repeated in that sequence and the process continues.
Which of the following statements regarding heart sounds and their causes are NOT correct? S1: 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. S3: Closure of the semilunar valves occurs when ventricular pressure declines, preventing backflow of blood into the ventricles. S4: Heart sounds are directly generated by the contraction of the cardiac muscles. S5: A healthy individual experiences approximately 72 'lub-dub' sound pairs per minute. S6: The clinical diagnostic significance of heart sounds is limited as they only indicate the rate of heart beat.
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