Final answer:
When the blood flows to the lungs and oxygen level rises, the newborn's heart undergoes changes that close the foramen ovale and ductus arteriosus to establish a proper postnatal circulation, with all blood being sent through the lungs for oxygenation.
Step-by-step explanation:
As blood flows to the lungs and the baby's O2 level increases, several changes occur in the heart to accommodate the switch from fetal to postnatal circulation. The process begins with the first breath, which dramatically decreases lung pressure. This decrease in pressure increases blood flow to the pulmonary arteries, resulting in a higher pressure in the left atrium that closes the foramen ovale. Concurrently, the ductus arteriosus, which previously shunted blood away from the lungs, constricts due to the higher oxygen levels and eventually closes, becoming the ligamentum arteriosum. These closures ensure that all blood pumped by the heart is sent to the lungs for oxygenation.
As blood flows to the lungs and the baby's o2 level increases, several changes occur in the heart:There is decreased resistance in the lungs as the newborn is surrounded by air, allowing more blood to flow into the pulmonary arteries from the right atrium and ventricleLess blood flows through the foramen ovale into the left atrium, as blood now travels to the lungs through the pulmonary arteries and then back to the heart through the pulmonary veinsIncreased pressure in the left atrium forces the foramen ovale to close, preventing blood from bypassing the pulmonary circulation.