Circulatory changes at birth
At birth when the umbilical cord is tight the activity of placenta stopped, the ductus venosus closes, the lungs expand and start to breathe, crossed by crescent volume of blood. The blood running through the lungs is oxygenated by the air and reaches in the left atrium. Even in this cavity there is an increase in blood flow which determines the closure of the foramen ovale valve. The breathe produce an increase in arteriosus blood oxygen concentration which produce first the constriction and then the closure of the ductus arteriosus.

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