Abnormalities of the truncus and conus

The most frequently seen abnormality of this.region is the tetralogy of Fallot classically this cardiac abnormality is described as consisting .

1-pulmonary stenosis
2-ventrical septal defect
3-overridding aorta and
4-hypertrophy of he right.ventricle 

Hence the term tetralogy .the basic defect in the cardiac malformation is in unequal division of the conus due to an anterior displacement of the truncoconal septum.this results in a narrow right ventricular outflow region that is an infludibular stenosis and a large defect of the interventriculer septum.the aorta arises directly above the sepal defect from both ventricular cavities and the resulting high pressure on the right side causes hypertrophy of the right ventricular wall.this abnormality is regarded as the most important type of malformation Saudi cyanosis.the defect is compatible with life.
Under normal conditions the truncus and conus are divided into the aorta and pulmonary artery by the fusion and descent of the two spiral ridges if these fail to fuse and to descend toward the ventricular anoresistent truncus artetious results .in such a case the pulmonary artery arises some distances above the origin of of the undivided truncus since the ridges also participate in the fornation of the interventriculer septum the persistent truncus is always accompanied by a defective interventriculer septum the undivided truncus thus overrides both ventricles and receives blood from both sides  Some times the truncoconal septum fails to follow its normal spiral course and descends straight downward as a consequence the aorta originates from the right ventricle and the pulmonary aaertey from the left. This condition known as transposition
transpositionof the great vessels is one of the most common cardiac abnormalities . sometimes it is associated with a defect in the membranous part of the interventriculer Sept it is usually combined with an open ducts artetious.

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