جواب سوال لاتین تبیان دوشنبه 24 تیر ماه 87

سوال : The first sound of heartbeat is made after what action

جواب :

It is caused by the sudden block of reverse blood flow due to closure of the atrioventricular valves, i.e. mitral and tricuspid, at the beginning of ventricular contraction, or systole. When the pressure in the ventricles rises above the pressure in the atria, venous blood flow entering the ventricles is pushed back toward the atria, catching the valve leaflets, closing the inlet valves and preventing regurgitation of blood from the ventricles back into the atria. The first sound results from reverberation within the blood associated with the sudden block of flow reversal by the valves]].

The first heart sound is produced by the turbulant flow against the closed AV valves .

First heart sound is caused by atrioventricular valves - Bicuspid/Mitral and Tricuspid .

منبع : http://en.wikipedia.org/wiki/Abraham_Lincoln#Assassination

http://en.wikipedia.org/wiki/Heart_sounds#S3

لینک مسابقه : http://tebyan.net/index.aspx?pid=29855&questionType=5