bilirubin

(noun)

A bile pigment that arises when biliverdin is separated from the iron of old hemoglobin molecules in the liver. Bilirubin becomes part of bile salts in the digestive system and is excreted, while the iron content is reused.

Related Terms

(noun)

A bile pigment that is product of the breakdown of the heme portion of hemoglobin. This happens within macrophages as they digest red blood cells. Extremely high levels of bilirubin cause jaundice.

Related Terms

(noun)

A bile pigment that is a product of the breakdown of the heme portion of hemoglobin, that is processed into bile by the liver.

Related Terms

Examples of bilirubin in the following topics:

  • Jaundice

    • This hyperbilirubinemia subsequently causes increased levels of bilirubin in the extracellular fluid.
    • Concentration of bilirubin in blood plasma does not normally exceed 1 mg/dL (>17µmol/L).
    • Bilirubin is not usually found in the urine because unconjugated bilirubin is not water-soluble; the combination of increased urine-urobilinogen with a lack of bilirubin in urine is suggestive of hemolytic jaundice.
    • Cell necrosis reduces the liver's ability to metabolize and excrete bilirubin, leading to a buildup of unconjugated bilirubin in the blood.
    • Other causes include primary biliary cirrhosis, leading to an increase in plasma conjugated bilirubin because there is impairment of excretion of conjugated bilirubin into the bile.

  • RBC Life Cycle

    • The biliverdin is reduced to the yellow bile pigment bilirubin, which is released into the plasma and recirculated to the liver, then bound to albumin and stored in the gallbladder.
    • The bilirubin is excreted through the digestive system in the form of bile, while some of the iron is released into the plasma to be recirculated back into the bone marrow by a carrier protein called transferrin. 

  • Bile

    • Besides its digestive function, bile serves also as the route of excretion for bilirubin, a waste byproduct of red blood cells recycled by the liver.

  • Skin Color as a Diagnostic Clue

    • The striking colors of a bruise are caused by the phagocytosis and sequential degradation of hemoglobin (red-blue) to biliverdin (green) to bilirubin (yellow) to hemosiderin (golden brown).
    • Also known as icterus, jaundice is a yellowish pigmentation of the skin, the whites of the eyes (sclera), and other mucous membranes caused by increased levels of bilirubin in the blood that builds up in extracellular fluid .

  • Erythroblastosis Fetalis (Hemolytic Disease of the Newborn)

    • Hemolysis leads to elevated bilirubin levels.
    • After delivery, bilirubin is no longer cleared (via the placenta) from the neonate's blood and the symptoms of jaundice (yellowish skin and yellow discoloration of the whites of the eyes) increase within 24 hours after birth.

  • Gallstones

    • Pigment stones are small, dark stones made of bilirubin and calcium salts found in bile.
    • Other common constituents are calcium carbonate, palmitate phosphate, bilirubin and other bile pigments.

  • Cholesterol Metabolism

    • Lecithin and bilirubin gallstones also occur, but less frequently.

  • Blood Plasma

    • Albumins also assist in transport of different materials, such as vitamins and certain molecules and drugs (e.g. bilirubin, fatty acids, and penicillin) due to the force exerted by their oncotic pressure.

  • Waste Management in Other Body Systems

    • The liver is involved in the breakdown and recycling of red blood cells, including the removal of bilirubin from the body by secreting it into the bile, which then functions as a fat emulsifier in the digestive system.