Biliverdin is the first product of the process of breaking down aged or abnormal red blood cells. The next stage of this process is the conversion of biliverdin to bilirubin.
Bilirubin is excreted in bile and urine. It is responsible for the yellow color of bruises and the yellow discoloration in jaundice. Its subsequent breakdown products, such as stercobilin, cause the brown color of faeces. A different breakdown product, urobilin, is the main component of the straw–yellow color in urine.
Bile (also known as gall) is a fluid, dark green to yellowish–brown in colour, produced by the livers of most vertebrates. In humans, bile is produced continuously by the liver and stored and concentrated in the gallbladder. It is discharged into the duodenum after eating, and aids the digestion of lipids in the small intestine.
An adult human being produces about 400 to 800 millilitres of bile per day. Bile is about 98% water; bilirubin makes up about 0.2%.
© Haydn Thompson 2020