Final answer:
After birth, the infant's blood supply comes from multiple sources, including the lungs, umbilical arteries, and breast milk or formula.
Step-by-step explanation:
After birth, the infant's blood supply comes from multiple sources. The first breath taken by the newborn inflates the lungs and closes the three shunts that directed oxygenated blood away from the lungs and liver during fetal life. Clamping and cutting the umbilical cord collapses the three umbilical blood vessels, and the proximal umbilical arteries remain as part of the circulatory system. Additionally, the lactating mother supplies all the hydration and nutrients needed by the infant for the first 4-6 months of life through breast milk or formula.