What is the role of the pulmonary semilunar valve?

• A. It separates the left ventricle from the aorta.
• B. It separates the right ventricle from the pulmonary artery.
• C. It prevents backflow into the left atrium.
• D. It prevents backflow into the right atrium.

Answer: (B)

The pulmonary semilunar valve sits between the right ventricle and the pulmonary artery, and its main job is to keep blood moving forward into the lungs. When the right ventricle contracts, pressure rises and the valve opens to allow blood to flow into the pulmonary artery. When the ventricle relaxes, the pressure in the pulmonary artery is higher than in the ventricle, so the valve closes to prevent blood from flowing back into the right ventricle. This one-way function is what defines its role.

This fits the correct choice because it precisely describes the connection and purpose: separating the right ventricle from the pulmonary artery and preventing backflow into the ventricle. Other valves have different roles: the valve between the left ventricle and the aorta handles systemic outflow, the valve between the left atrium and left ventricle prevents backflow into the left atrium, and the valve between the right atrium and right ventricle prevents backflow into the right atrium.