NEET2015ZoologyBody Fluids and CirculationActual
Doctors use a stethoscope to hear the sounds produced during each cardiac cycle. The second sound is heard when:
Options
- AVentricular walls vibrate due to gushing in of blood from atria
- BSemilunar valves close down after the blood flows into vessels from ventricles
- CAV node receives signal from SA node
- DAV valves open up
Correct answer
B. Semilunar valves close down after the blood flows into vessels from ventricles
Step-by-step solution
During each cardiac cycle two prominent sounds are produced which can be easily heard through a stethoscope. There are two prominent heart sounds: The first sound is of low intensity, lub, which is associated with the closure of mitral and tricuspid valve. This is the beginning of ventricular systole. The second sound is of higher intensity, dup, which is associated with the closure of semilunar valves and mark the end of ventricular systole.