Stercobilinogen (fecal urobilinogen) is a

chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wi ...

created by bacteria in the gut. It is made of broken-down

hemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...

. It is further processed to become the chemical that gives

feces Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...

its brown color.Stercobilinogen
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Bilirubin Bilirubin (BR) (Latin for "red bile") is a red-orange compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates. This catabolism is a necessary process in the body's clearance of waste products that arise from the ...

is a pigment that results from the breakdown of the

heme Heme, or haem (pronounced / hi:m/ ), is a precursor to hemoglobin, which is necessary to bind oxygen in the bloodstream. Heme is biosynthesized in both the bone marrow and the liver. In biochemical terms, heme is a coordination complex "consisti ...

portion of hemoglobin. The liver conjugates bilirubin, making it water-soluble; and the conjugated form is then excreted in urine as

urobilinogen Urobilinogen is a colorless by-product of bilirubin reduction. It is formed in the intestines by bacterial action on bilirubin. About half of the urobilinogen formed is reabsorbed and taken up via the portal vein to the liver, enters circulation an ...

. Urobilinogen is colourless and is further oxidised to stercobilin which imparts colour to feces. Darkening of feces upon standing in air is due to the oxidation of residual urobilinogens to urobilins. In the intestine, bilirubin is converted by bacteria to stercobilinogen. Stercobilinogen is absorbed and excreted by either the liver or the kidney. Stercobilinogen is oxidized to

stercobilin Stercobilin is a tetrapyrrolic bile pigment and is one end-product of heme catabolism.Boron W, Boulpaep E. Medical Physiology: A cellular and molecular approach, 2005. 984-986. Elsevier Saunders, United States. Kay IT, Weimer M, Watson CJ (1963)� ...

, which is responsible for the pigmentation of feces. In early liver disease, impaired biliary excretion causes stercobilinogen to be absorbed mostly by the kidney, and, therefore, stercobilinogen will appear in the urine in excess as

. This happens because "Stercobilinogen" is simply the name given to Urobilinogen in the GI tract; and in fact its use as a separate term has fallen out of favor due to the confusion.

References

{{Heme metabolism intermediates Pyrroles Gamma-lactams Harpers illustrated biochemistry 28th Ed. Harrison’s principles of internal medicine 20th Ed.