The figure represents total period of one cardiac cycle i.e., 0.8 sec and A, B and C represent its stages. Identify A, B, C and select the correct statement regarding them

Options

A. During A, tricuspid and bicuspid valves open and blood flows from atria into the ventricles
B. During B, bicuspid and tricuspid valves close producing first heard sound
C. During C, the semilunar valves close producing second heard sound
D. During B, the atria contract due to a wave of contraction by SA node.

Answer

D

Explanation

In the given figure, A is atrial and ventricular diastole (complete cardiac diastole), B is artrial systole and C is ventricular systole
Druing atrial systole, he atria contract due to wave of contraction, stimulated by the SA node. The blood is forced into te ventricles as the bicuspid and tricuspid valves are open. At the beginning of ventricular systole, the ventricles begin t contract due to a wave of contraction, stimulated by the AV node. The bicuspid and tricuspid valves close immediately producing part of the first heart sound. With complete ventricular systole, the ventricles complete their contraction and the blood flows into the pulmonary trunk and aorta as the semilunar valves open. At the beginning of ventricular diastole, the tricuspid and bicuspid valves open as the pressure in the ventricles fall and blood flows from the atria into the ventricles. Contraction of the heart does not cause this blood flow. It is due to the fact that the pressure within the relaxed ventricles is less than that in the atria and veins.