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Pulmonary valve

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The pulmonary valve, essential in preventing blood from flowing back into the right ventricle from the pulmonary trunk, consists of three semilunar cusps. 

Root of pulmonary trunk

The pulmonary valve is located at the root of the pulmonary trunk, a component of the right ventricular outlet supported by the right ventricular outflow tract. It comprises the sinuses of the pulmonary trunk, the pulmonary valve itself, and the interleaflet triangles of the pulmonary.

Pulmonary valve

Upon closer examination, the pulmonary valve is found at the top of the conus arteriosus, forming the opening of the pulmonary trunk and surrounded by the right ventricular myocardium. 

Opening of pulmonary trunk

• Taking a closer look at the opening of the pulmonary trunk reveals that it is circular in shape and positioned at the top of the conus arteriosus.

Focusing our attention on its three cusps, we should know that they are named based on their positions: the left semilunar cusp, right semilunar cusp, and anterior semilunar cusps.

Right semilunar leaflet of pulmonary valve

• The right semilunar leaflet is one of the three leaflets of the pulmonary valve, positioned on the right side.

Left semilunar leaflet of pulmonary valve

• Similar to the right leaflet but located on the left side, we can identify the left semilunar leaflet.

Anterior semilunar leaflet of pulmonary valve

• Positioned anteriorly is the anterior semilunar leaflet. It is also known as the Non-facing leaflet because it is positioned the farthest away from the aortic root.

Nodules of semilunar leaflets of pulmonary valve

• A closer look at the pulmonary valve’s semilunar leaflets, reveals structured components essential for its operation. At the core of each leaflet, positioned midway along the free margin is a central nodule. This is known as nodule of semilunar leaflets or nodule of Arantius.

Lunules of semilunar leaflets of pulmonary valve

• Next to these nodules are the lunles of the pulmonary valve, crescent-shaped areas that extend from the nodule along the free margin of the leaflets. These lunules, allow the valves to seal effectively and prevent backflow of blood.

Commissures of semilunar leaflets of pulmonary valve

• Completing the structure, the commissures of pulmonary valve are the areas where the edges of two leaflets meet and adjoin with the wall of the pulmonary trunk. This junction is fundamental to the cohesive operation of the valve.

Exploring the area surrounding the pulmonary valve reveals the presence of the sinuses of the pulmonary trunk. 

Sinuses of pulmonary trunk

Sinuses of pulmonary trunk are essentially three widenings located at the base of the pulmonary trunk. They create a dilation in the wall of the initial portion of the pulmonary trunk. This structural design plays a crucial role in the heart’s functionality, particularly in facilitating the flow of blood through the pulmonary artery.

Sinuses of pulmonary trunk are categorised based on their spatial orientation relative to the pulmonary trunk. They are known as the right sinus of pulmonary trunk, the left sinus of pulmonary trunk and the anterior sinus of pulmonary trunk.

Right sinus of pulmonary trunk

• The right sinus corresponds to the right semilunar leaflet of pulmonary valve, 

Left sinus of pulmonary trunk

• The left sinus aligns with the left semilunar leaflet of pulmonary valve.

Anterior sinus of pulmonary trunk

• The anterior sinus is associated with the anterior semilunar leaflet of pulmonary valve.

Interleaflet triangles of pulmonary trunk

Taking a closer look between the sinuses of the pulmonary trunk, we can observe the Interleaflet triangles of pulmonary trunk. These are fibrous anatomical structures situated at the base of the pulmonary valve leaflets. Defined by the junctions where the leaflet edges meet and attach.

Relationship to cardiac cycle

During ventricular systole, the phase of the cardiac cycle when the ventricular muscle contracts, the pulmonary valve opens. This opening is essential for allowing the pulmonary artery to fill with blood, which is then pushed into the pulmonary circulation.

In contrast, during ventricular diastole, the relaxation phase of the ventricle, the pulmonary valve closes. This prevents blood from flowing back into the right ventricle from the pulmonary artery.