Final answer:
Oxygenated blood from a baby's lungs flows through the pulmonary veins to the left atrium, then to the left ventricle, and is distributed throughout the body by the aorta after the resolution of right to left shunting postnatally.
Step-by-step explanation:
Once the right to left shunting resolves in the baby's circulatory system, oxygenated blood from the baby's lungs flows through a distinct postnatal pathway. After the baby takes its first breath, postnatal circulation necessitates that the previously oxygenated blood in the fetal circulation, which bypassed the nonfunctional lungs via the ductus arteriosus and foramen ovale, must now pass through the newly functional lungs. The process is as follows: the right ventricle pumps deoxygenated blood to the lungs via the pulmonary trunk, which splits into left and right pulmonary arteries. There, gas exchange occurs, and carbon dioxide exits the blood while oxygen enters.
Then, the pulmonary veins, which are the only veins carrying highly oxygenated blood in the postnatal body, conduct this oxygen-rich blood into the left atrium. From there, it moves into the left ventricle and is pumped into the aorta, where it will distribute oxygenated blood throughout the systemic circuit to the body's tissues. This efficient circulation is maintained by the closure of the three fetal shunts – the ductus arteriosus, foramen ovale, and ductus venosus – which occur shortly after birth, redirecting blood flow to the lungs and liver as needed in a healthy postnatal circulatory system.