What are the semilunar valves?

• A. Valves located between the atria and ventricles that prevent backflow into the atria when the ventricles are contracting.
• B. Valves located between the ventricles and arteries that prevent backflow into the ventricles when the ventricles are contracting.
• C. Valves in veins preventing backflow
• D. Valves located between the right and left atria

Answer: (B)

Semilunar valves are the valves at the outflow points of the ventricles, between the ventricles and the great arteries. They include the aortic valve, between the left ventricle and the aorta, and the pulmonary valve, between the right ventricle and the pulmonary artery. They open as the ventricles contract to push blood into these arteries and close when the ventricles relax, preventing a backflow of blood into the heart. This is different from the valves between the atria and ventricles, which prevent blood from flowing backward into the atria, and from valves in veins, which prevent backflow within the venous system.