Question

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

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 heart sound
D)During B, the atria contract due to a wave of contraction by SA node

Answer 1

The cardiac cycle is the function of heart from one heartbeat to the next. The cardiac cycle consists of two phases: the contraction phase pumping of blood or the systole and the relaxation phase or the diastole when the heart refills with the blood.

Complete answer:
To solve this question, we must know about the cardiac cycle.
The cardiac cycle has three phases-
Atrial and Ventricular diastole which lasts for 0.4 sec
Atrial systole which lasts for 0.1 sec
Ventricular systole which lasts for 0.3 sec
A is represented as the atrial and ventricular diastole in which the chambers are relaxed and fills with blood. In this no contraction of any part takes place. Due to the increase in the pressure, A-V valves are open.
B is represented by atrial systole which lasts for 0.1 sec. The atrium contracts and the blood pushes through the ventricles. The atrium contracts due to the contraction by the SA node.

C is represented by ventricular systole which lasts for 0.3 sec. The ventricles contract and push the blood through the aorta and pulmonary artery.

Hence, the correct answer is option (D)

Note: The first heart sound is produced by the closure of atrioventricular valves and the second heart sound is produced by opening of semilunar valves. The second sound is louder than the first one due to the pressure difference in the aorta and pulmonary artery.