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Urobilinogen is a yellow by-product of bilirubin reduction. It is formed in the intestines by the bacterial enzyme bilirubin reductase. [ 1 ] About half of the urobilinogen formed is reabsorbed and taken up via the portal vein to the liver, enters circulation and is excreted by the kidney.
Because there is no problem with the liver or bile systems, this excess unconjugated bilirubin will go through all of the normal processing mechanisms that occur (e.g., conjugation, excretion in bile, metabolism to urobilinogen, reabsorption) and will show up as an increase of urobilinogen in the urine. This difference between increased urine ...
Urobilin is generated from the degradation of heme, which is first degraded through biliverdin to bilirubin. Bilirubin is then excreted as bile, which is further degraded by microbes present in the large intestine to urobilinogen. The enzyme responsible for the degradation is bilirubin reductase, which was identified in 2024.
Stercobilinogen (fecal urobilinogen) is a chemical created by bacteria in the gut. It is made of broken-down hemoglobin. It is further processed to become the chemical that gives feces its brown color. [1] Bilirubin is a pigment that results from the breakdown of the heme portion of hemoglobin.
Although 20% of the secreted bilirubinoid bile is reabsorbed by the small intestine, [2] conjugated bilirubin is not reabsorbed in small intestine. All conjugated bilirubin in the large intestine is metabolised by colonic bacteria to urobilinogen, which is then further oxidized to urobilin and stercobilin. Urobilin, stercobilin and their ...
Urobilinogen refers to a group of compounds produced from bilirubin by the intestinal flora. Under normal conditions, most of the urobilinogen produced is absorbed into the bloodstream and secreted into the bile by the liver, or excreted in the feces as stercobilin and other compounds. A small fraction is excreted in the urine.
Intestinal bacteria reduce the bilirubin to urobilinogen, which is later oxidised and either excreted with the faeces as stercobilin or in the urine as urobilin. Conjugated bilirubin appears in urine when the normal degradation cycle is altered due to the obstruction of the biliary ducts or when the kidney's functional integrity is damaged.
Conjugated bilirubin is then secreted along with bile into the intestine and is either excreted in faeces as urobilinogen or reabsorbed into blood and transported back to the liver. The varied causes of hyperbilirubinemia are best understood from bilirubin metabolism.