Question

Bicuspid and tricuspid valves are open during
A. Ventricular systole B
B. Ventricular diastole C
C. Atrial systole
D. Late joint diastole

Answer 1

The heart is a four-chambered organ which pumps blood to the entire body through systole (contraction) and diastole (relaxation) phases. The bicuspid and the tricuspid valves connect the atria with ventricles and prevent the backflow of blood back into the atria during atrial systole.

Complete answer:
The four chambers of the heart are the left atrium, left ventricle, right atrium, and right ventricle. The bicuspid valve, or also known as the mitral valve allows flow from the left atrium to the left ventricle and the tricuspid valve sends blood from the right atrium to the right ventricle. These valves are mainly present to prevent the backflow of blood back into the atria. The bicuspid valve has two cusps or leaflets and the tricuspid valve has three.

During the cardiac cycle, systole refers to the part where the heart muscles contract to push the blood from one location to the other and diastole refers to when the muscles relax to fill blood within the chambers. At the beginning of the cardiac cycle, both the atria and the ventricle are at an early joint diastole, where the blood is filed within the atria. As the blood fills the chamber the atria contract to push the blood through the valves, and this is known as the atrial systole. It only at this stage does the bicuspid and tricuspid valve open.

After the blood has filled the ventricle, a pressure is built within the ventricle and it contracts to exert pressure which is called the ventricular systole which pushes the blood into the aorta or the pulmonary artery. After this stage, both the ventricle and the atria undergo relaxation or joint diastole where all the valves are closed but blood is being filled within the atria. And as soon as the atrial chamber pressure is crossed the atrial systole occurs and the valves open again and the cycle continues.

Therefore, the correct answer is option C.

Note: Ventricular systole is when the blood within the ventricles is pumped into the aorta or the pulmonary artery. The atrioventricular and the semilunar valve opens during this phase, not the bicuspid and tricuspid valves. The joint diastole occurs only for a very short amount of time. The ventricle has an early and late diastolic component.