Final answer:
The correct statement about postnatal cardiovascular adjustments in a newborn after the first breath is that the ductus arteriosus constricts and becomes the ligamentum arteriosum, ensuring proper oxygenation of blood in the lungs.
Step-by-step explanation:
Cardiovascular adjustments are crucial as a newborn takes its first breath. The correct statement regarding these adjustments is D) The ductus arteriosus constricts and is converted to the ligamentum arteriosum. As the newborn initiates its first breath, a decrease in blood pressure in the pulmonary system leads to the closure of the foramen ovale through the increased atrial pressure and flaps of tissue obstructing the shunt. Concurrently, the ductus arteriosus constricts due to the elevated oxygen levels in the newborn's blood and gradually becomes the ligamentum arteriosum, ensuring that all blood pumped to the lungs is oxygenated. Postnatal circulation adjustments ensure that the newborn's circulatory system operates independently of the placenta, which was its blood and nutrient source during fetal life.