How does the bilirubin end up in the skin and sclera… even worse the brain?
When old erythrocytes (RBC’s) are removed from the circulation they break down into heme, globin and iron. Heme is converted to biliverdin, which is transformed rapidly into the unconjugated form of bilirubin and released into the plasma (Halamek & Stevenson, 1997). Unconjugated bilirubin is bound to albumin in the plasma until there are insufficient sites or unless the bilirubin has decreased affinity for the albumin. Unbound bilirubin has potential for movement into tissues (skin, sclera, across the blood-brain barrier). Unconjugated bilirubin cannot be excreted. Conjugation is accomplished in the liver with the aid of hepatic ligands, which aid in transport from the albumin across the cell membrane. As luck would have it, hepatic ligands are decreased in the neonate and do not reach adult levels until about 5 days of life. Conjugation also requires oxygen and glucose – no wonder that we see higher bili levels in newborns that have trouble maintaining oxygen and glucose levels. Once
