Doctors use a stethoscope to hear the sounds produced during each cardiac cycle. The second sound is heard…

Doctors use a stethoscope to hear the sounds produced during each cardiac cycle. The second sound is heard when:
  1. Ventricular walls vibrate due to gushing in of blood from atria
  2. Semilunar valves close down after the blood flows into vessels from ventricles
  3. AV node receives signal from SA node
  4. AV valves open up

Solution

During each cardiac cycle two prominent sounds are produced which can be easily heard through a stethoscope. There are two prominent heart sounds:

  1. 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.
  2. The second sound is of higher intensity, dup, which is associated with the closure of semilunar valves and mark the end of ventricular systole.

Asked in: NEET 2015 (Phase 2)

Practice more Body Fluids and Circulation questions on Aicharya