The liver is well known to metabolize and excrete into bile many compounds and toxins, thus eliminating them (usually) from the body. Examples can be found among both endogenous molecules (steroid hormones, calcium) and exogenous compounds (many antibiotics and metabolites of drugs). A substantial number of these compounds are reabsorbed in the small intestine and ultimately eliminated by the kidney.
One of the most important and clinically relevant examples of waste elimination via bile is that of bilirubin. Additionally, the mechanisms involved in elimination of bilirubin are similar to those used for elimination of many drugs and toxins.
Bilirubin is a useless and toxic breakdown product of hemoglobin, which also means that it is generated in large quantities. In the time it takes you to read this sentence aloud, roughly 20 million of your red blood cells have died and roughly 5 quintillion (5 x 1015) molecules of hemoglobin are in need of disposal. The dead and damaged red blood cells are picked up by phagocytic cells throughout the body (including Kuppfer cells in the liver) and digested. The iron is precious and is efficiently recycled. The globin chains are protein and are catabolized and their components reused. However, hemoglobin also contains a porphyrin called heme that cannot be recycled and must be eliminated. Elimination of heme is accomplished in a series of steps:
If excessive quantities of either free or conjugated bilirubin accumulate in extracellular fluid, a yellow discoloration of the skin, sclera and mucous membranes is observed - this condition is called icterus or jaundice. Determining whether the excessive bilirubin is free or conjugated can aid in diagnosing the cause of the problem.
"Looking at you with a jaundiced eye"
Next page > Architecture of the Liver > Physiology of the Hepatic Vascular System > Secretion of Bile and the Role of Bile Acids In Digestion > Biliary Excretion of Waste Products > Metabolic Functions of the Liver
Source: Republished with permission by Richard Bowen - Hypertexts for Biomedical Sciences