Sources of Heme
The majority of heme for degradation comes from these cells.
What are red blood cells?
The enzyme that converts heme into biliverdin.
What is heme oxygenase?
Unconjugated bilirubin is hydrophobic, so it travels in blood bound to this protein.
What is albumin?
Bilirubin enters hepatocytes and is conjugated with this sugar.
What is glucuronic acid?
When hemoglobin is degraded, the globin chains are broken down into these building blocks, which can be recycled.
What are amino acids?
Biliverdin is converted to bilirubin by this enzyme.
What is biliverdin reductase?
Why can’t unconjugated bilirubin appear in urine?
Because it is tightly bound to albumin and water-insoluble.
The enzyme that conjugates bilirubin.
What is UDP-glucuronosyltransferase (UGT1A1)?
This organ is the primary site where aged RBCs are broken down.
What is the spleen?
The cofactor required by biliverdin reductase in this reaction.
What is NADPH?
Albumin binding keeps unconjugated bilirubin in circulation until it reaches this specific organ for uptake and conjugation.
What is the liver?
Conjugated bilirubin is secreted into this organ system.
What is the gallbladder/biliary system?
Why does ineffective erythropoiesis (ex: thalassemias) increase bilirubin production?
Issue with globin chain synthesis, but heme synthesis is fine. You will have proportionally more heme compared to functional hemoglobin to put it in. This excess heme will be degraded into bilirubin.
These color changes reflect sequential enzyme action: heme gives blood its red color, biliverdin appears green, and bilirubin imparts this color as it accumulates.
What is yellow?
What condition can arise if bilirubin builds up and is displaced from albumin in neonates?
Kernicterus
The “15% rule” states that if direct bilirubin is greater than 15% of total (when total is >3mg/dL), the problem is with excretion or obstruction. In contrast, if direct bilirubin is less than 15% of total, the cause may be due to ____ or ____.
Ineffective erythropoiesis or hemolytic disease