Q.Explain heart sounds.

Heart sounds are the two distinct sounds produced during each cardiac cycle, heard easily with a stethoscope.

• The first heart sound, described as 'lub', is produced by the closing of the tricuspid and bicuspid valves.
• The second heart sound, described as 'dub', is produced by the closing of the semilunar valves.
• Both sounds arise from valves shutting as blood is prevented from flowing backward during the cycle. …

During every cardiac cycle the heart produces two clear sounds that can be heard easily with the help of a stethoscope. Both of them come from the same underlying event — the shutting of valves as the heart works to keep blood moving in one direction only.

The first heart sound is described by the syllable 'lub'. It accompanies the closing of the tricuspid and bicuspid valves, the valves that lie between the atria and the ventricles. As the ventricles begin to contract, blood tries to flow back toward the atria, and this backflow snaps these valves shut, producing the sound.

The second heart sound is described by the syllable 'dub'. It accompanies the closing of the semilunar valves, which guard the openings of the ventricles into the pulmonary artery and the aorta. As the ventricles relax and their pressure falls, blood is prevented from flowing back into them by the closing of these valves, and that closure gives the second sound. …

Method: Correlating Two Related Events (a Sound and the Valve Action That Causes It)

Use this approach whenever a question asks you to explain an audible or observable event caused by an underlying structural action.

Steps

Step 1: Recall the general principle that generates the event

A valve closing under backflow pressure produces sound; a valve simply staying open produces none. State this principle before naming which valve is involved.

Step 2: List the events being asked about, in the order they occur within one cycle

Here: the first sound occurs early in the cycle, the second sound later, so treat them in that order.

Step 3: Name the specific valve set that closes for each event, and WHY it closes at that moment …