16.3 Formation of the cardiac valves - the valve level



The aortic and pulmonary valves (semilunar valves)


As explained in the description of the separation in the outflow tract region, the crease between the truncus and conus has a special meaning. Here the aortic and pulmonary valves (valvulae semilunares) arise. Involved in this are primarily the mesenchymal cushions that are created from immigrated neural crest cells. The septum of the outflow tract leads to a definitive separation of what was initially a common outflow tract. In the area of the conus-truncus-transition it delivers material for the pulmonary truncus and the aorta for the right and the left semilunar valves. In addition, in the ventral area, a new valve forms - the ventral semilunar valve for the truncus pulmonalis. In the dorsal area an additional fold also forms that develops into the dorsal semilunar valve of the aorta.


Fig. 18 - Outflow tract from the front right  Legend

1
2
3
4
5
6
7
8
9		 Aorta
Conotruncal crease
Truncus pulmonalis
Posterior aortic valve
Left aortic valve
Right aortic valve
Right truncus pulmonalis valve
Anterior truncus pulmonalis valve
Left truncus pulmonalis valve

Fig. 18
On the left is the conotruncus as seen ventrally (45° from the right).
In the right image (at A) the truncus is cut away so that the semilunar valve level is visible. Dorsally lies the aorta with right, left and dorsal valves and ventrally lies the truncus pulmonalis with right, left and ventral (anterior) cushions.

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From the common outflow tract, the conotruncus, arise two outflow vessels: the aorta and the truncus pulmonalis.

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Through an additional shift of location the conus is included in the right ventricle. Thus, the semilunar valves come to lie near the av-level with the atrioventricular valves. This is termed the valve plane. In the course of further development a rotation in an anti-clockwise direction also follows so that the aortic dorsal valve comes to the right and the right towards the front. Analogously the anterior pulmonary valve shifts to the left and the left towards the rear. Thus one obtains the nomenclature normally used with adults of a left, right and posterior cusp for the pulmonary valve and a left, right and anterior cusp for the aortic valve. Rotation of the valve planes



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