Lunules of semilunar cusps

The lunules of the semilunar cusps of the pulmonary valve are the thin, crescent-shaped regions located at the free edge of each cusp of the pulmonary valve. These lunules are composed of fibroelastic tissue and are critical for the coaptation of the cusps during valve closure, ensuring a tight seal to prevent regurgitation from the pulmonary artery into the right ventricle. The central thickening at the midpoint of each lunule is known as the nodule, which further aids in complete closure of the valve. The lunules are structurally analogous to those found in the aortic valve and are essential for normal valve function