The semilunar valves prevent backflow of blood into the ventricles of the heart.
These valves are located at the exit points of the heart’s ventricles, specifically the aortic valve (which controls blood flow from the left ventricle into the aorta) and the pulmonary valve (which controls blood flow from the right ventricle into the pulmonary artery). When the ventricles contract, blood is pumped into these arteries, and the semilunar valves open to allow this flow. However, as soon as the ventricles relax, these valves close tightly to prevent any blood from returning back into the heart. This mechanism is crucial for maintaining efficient circulation and ensuring that oxygenated blood is delivered to the body while deoxygenated blood heads to the lungs for re-oxygenation.