





After birth, the higher pressure in the left atrium septum firmly presses both heart and they are fused together, closing the hole and forming oval final interatrial septum, which prevents the mixing of venous and arterial blood.
Interventricular septum begins to grow also at the end of the 4th week of intrauterine development.
First septum is not continuous - in the upper part of its retained interventricular foramen later overgrown.
At the same time in the arterial trunk formed two rollers thickened endocardium (inner layer of the heart), which grow towards each other and merge into aortopulmonary septum, while creating the trunks of the aorta and pulmonary artery.
The growth of this partition inside the ventricles leads to its confluence with the interventricular septum and the separation of the right and left heart in the fetus.
Heart valve occurs after the formation of partitions.
On the 5th week of pregnancy starts functioning primary circulatory system of the embryo.
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