Urine urobilinogen is absent in:
Correct Answer: Obstructive jaundice
Description: Formation and Fate of Urobilinogen:
Once in the intestine, about half of the “conjugated” bilirubin is converted by bacterial action into the substance urobilinogen, which is highly soluble.
Some of the urobilinogen is reabsorbed through the intestinal mucosa back into the blood, and most is re-excreted by the liver back into the gut, but about 5 percent is excreted by the kidneys into the urine.
After exposure to air in the urine, the urobilinogen becomes oxidized to urobilin; alternatively, in the feces, it becomes altered and oxidized to form stercobilin.
Obstructive jaundice:
Occurs due to obstruction of bile flow at any level of biliary system - Eg: Gall stones, CA biliary system or pancreas.
Thus, bile cannot be excreted into small intestine, instead released into circulation. Hence, the blood contains more amount of conjugated bilirubin.
When total obstruction of bile flow occurs, no bilirubin can reach the intestines to be converted into urobilinogen by bacteria. Therefore, no urobilinogen is reabsorbed into the blood, and none can be excreted by the kidneys into the urine.
Consequently, in total obstructive jaundice, tests for urobilinogen in the urine are completely negative. Also, stools become clay colored owing to a lack of stercobilin and other bile pigments.
Category:
Physiology
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