Pulmonary valve
Semilunar valve of the heart
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Through Cardiac cycle and Inhalation
The closure of the pulmonary valve contributes to the P2 component of the second heart sound (S2).
Structure
The pulmonary orifice lies nearly in the horizontal plane, and is situated at a superior level than the aortic orifice.
Cusps
At the apex of the infundibulum, the pulmonary orifice is guarded by three semilunar cusps - two anterior and one posterior, with free edges projecting upward into the lumen of pulmonary trunk. The cusps are named according to their positions during foetal development: the anterior, the posterior, and the septal cusp. The free edge of each cusp presents a fibrous nodule of semilunar cusp at the centre with two lateral thin portions, the lunule of semilunar cusp. Each cusp forms pocket like dilatation called pulmonary sinus at the initial portion of pulmonary trunk.
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Clinical significance
The right heart is a low-pressure system, so the P2 component of the second heart sound is usually softer than the A2 component of the second heart sound. However, it is physiologically normal in some young people to hear both components separated during inhalation.