Question

What prevents backward flow of blood inside the heart during contraction?
A] valves in heart
B] thick muscular walls of ventricles
C] thin walls of atria
D] all of the above

Answer 1

Hint: Cardiac cycle is defined as a repeating pattern of contraction and relaxation of heart. The phase of contraction is called systole and the phase of relaxation is called diastole.
As the ventricles begin their contraction the intraventricular pressure rises , the closure of the bicuspid and tricuspid valve to prevent backward flow of blood to the atria. When ventricular diastole occurs the ventricular pressure falls , closing the semilunar valves to prevent backward flow of blood to ventricles.

Complete answer:
A] valves in heart – these structures prevent backward flow of blood during contraction. On contraction they close ensuring unidirectional flow of blood.
B] thick muscular walls of ventricles- these pump blood out of the heart . hence this option is not correct.
C] thin walls of atria- they carry blood towards the heart and in ventricles . hence this option is not correct.
D] all of the above- as option b and c is not correct. This option is not correct

Our required Ans is a valve in the heart.

Note: The opening between atria And ventricles are guarded by atrioventricular valves. The valve between right atrium and right ventricle is called tricuspid valves due to presence of three cusps and between left atrium and left ventricle has two flaps thus called as bicuspid valves.
Three semilunar valves are found at the point where the pulmonary artery and aorta leaves the heart.