Final answer:
The changes in newborn circulation are initiated when the infant takes their first breath, which inflates the lungs and triggers the closing of fetal circulatory shunts.
Step-by-step explanation:
The nurse knows that the changes that take place in the newborn circulatory system after birth are initiated when the infant begins pulmonary ventilation. This act inflates the lungs and dramatically alters the circulatory system by closing the three shunts that directed oxygenated blood away from the lungs and liver during fetal life. Clamping and cutting the umbilical cord leads to the collapse of the three umbilical blood vessels, causing a sequence of anatomical changes that facilitate the newborn's transition to independent respiration and circulation.
Circulatory adjustments occur as a direct result of the first breath, which decreases blood pressure in the pulmonary system and reverses the flow of blood through the foramen ovale. This effectively closes the shunt, and within one year, it becomes the fossa ovalis. Additionally, the ductus arteriosus constricts and eventually forms the ligamentum arteriosum, ensuring oxygenated blood is pumped to the pulmonary circuit.