Final answer:
Physiologic jaundice in newborns is most often due to unconjugated hyperbilirubinemia, where inadequate UDP glucuronyl transferase activity leads to an accumulation of bilirubin in the blood and tissues, resulting in jaundice. Treatment typically involves phototherapy.
Step-by-step explanation:
The mechanism causing physiologic jaundice in newborns is primarily due to unconjugated hyperbilirubinemia. In newborns, the enzyme UDP glucuronyl transferase, which helps process bilirubin, is not fully developed. This leads to an accumulation of unconjugated bilirubin in the blood. When bilirubin levels exceed the binding capacity of albumin, it diffuses into the tissues, causing yellow discoloration known as jaundice. Phototherapy is often used to treat newborns with hyperbilirubinemia because UV light aids in the breakdown of bilirubin, making it easier for the infant's body to eliminate it.