The pulmonary artery valve

The pulmonary valve is separated from the fibrous framework of the heart by the muscular septum of the right ventricular outlet. It has no fibrous support. Its crescentic base rests on the myocardium of the right ventricular outlet.

The pulmonary valve, similar to the aortic valve, consists of three sinuses and three semilunar cusps, with their bases extending from the fibrous ring. The semilunar cusps originate from the medial edge. There are anterior, left and right semilunar cusps, the proximal edges of which continue laterally in the form of sinuses, and their free edges protrude into the pulmonary trunk. The thickened fibrous part of the central coalescence zone of each cusp is called Morgagni's nodes. The sinuses of the pulmonary valve are also called cusps. The expansion of the initial section of the pulmonary artery is not as well expressed as in the aorta.

The commissures between the cusps are designated as left, right and posterior. The left semilunar cusp directly borders the muscular tissue of the right ventricular outlet, its septum and partially with the upper part of the supraventricular crest. The right cusp also lies next to the myocardium of the right ventricular outlet. The posterior commissure is located opposite the "intercoronary" commissure of the aortic valve. The elements that form the pulmonary valve differ significantly in their structure. The sinotubular junction (arched ring, arched crest), the commissural rods of the valve base are connected to each other in a spatially interconnected elastic framework to which the cusps and sinuses are attached.

The sinus wall in the arched ring area has a structure similar to the pulmonary trunk wall, with a well-defined middle layer consisting of smooth myocytes and surrounded by elastin and collagen fibers. Towards the fibrous ring of the valve base, the sinus wall becomes thinner, the number of elastin fibers and myocytes decreases, collagen increases and at the base it takes the form of a fibrous cord. At the same time, the internal elastic membrane is gradually lost.

The fibrous ring of the base, which has a pulmonary valve, begins with a bifurcation of the fibrous cord of the sinus. One of its parts forms the sinus wall of the fibrous ring, which then passes onto the valve and forms its sinus layer. The other part forms the base of the triangle of the fibrous ring and envelops the cardiomyocytes. The fibrous ring has a triangular shape in cross-section and consists mainly of collagen structures, an elastic membrane along its ventricular surface and, to a lesser extent (about 10%), chondroid tissue. The tissues that make up the middle part of the fibrous ring pass into the valve and form its median layer. The valve has a three-layer structure and consists of a ventricular, median and sinus layer. The thickness of the valve is maximum at the fibrous ring and minimum in the dome. In the area of the nodule of the semilunar valve, the thickness of the valve increases again. Here, the loose middle layer, bordered by the elastic membrane of the ventricular layer, predominates. At the base of the valve, there is a significant number of arterioles, veins and capillaries that provide its blood supply. The commissural rods consist of three sections: an arched section, which has the structure of arched ridges and is their continuation, a fibrous section, consisting mainly of untwisted collagen bundles, braided with sharply twisted collagen fibers, having a structure similar to the fibrous ring of the base, and a section of transition from the first to the second.

The pulmonary valve can be considered as a composite structure consisting of a strong, predominantly collagenous framework and shell elements (cusps and sinuses) with anisotropic properties. The pulmonary valve has the same biomechanics as the aortic valve.

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