hi in this tutorial I'm going to explain the Billy rubben pathway the Billy rubben pathway is really important because excess Billy Rubin in the blood is the source of jaundice which is a yellowing of the skin many diseases can cause jaundice and understanding the Billy rubben pathway helps us to diagnose these diseases so Billy Ruben is a product of heem catabolism that is the breakdown of heem found in red blood cells so our pathway begins with a red blood cell and when this red blood cell gets old and weary then a maccrage eats the red blood cell and this initiates hem catabolism now hemoglobin found in the red blood cell is made up of four subunits and each of these subunits consists of a protein element called globin and a porin ion complex called he this ion is the molecule which carries oxygen through the blood the globin and the he dissociate so this is a globin part and the protein gets broken down and re recycled and this is the he part this is also spelled h e m in North America the ion dissociates from the he and it gets reused for making new red blood cells and so we're left with this organic ring which is known as a porine the structure of the porer and ring is quite complex and Beyond the scope of this tutorial but it's basically a carbon ring with nitrogen Elements which coordinate with the ion now through a couple of steps which I haven't shown here this porin ring is opened up and this molecule is Billy Ruben it is a bright yellow molecule hence why excess causes yellow skin pigmentation in jaundice it's also a toxic molecule which is why it is so important to remove it from the body now Billy Rubin is not a very water soluble molecule so it gets attached to this protein albumin which carries it through the blood the albumin carries Billy Rubin to the liver once inside the liver an enzyme called UDP glucuronyl transferase attaches glucuronic acid to the Billy Rubin in this way it makes Billy Rubin less toxic and more water soluble we call these molecules conjugated Billy Rubin as opposed to the unconjugated Billy ruin prior to the attachment of the glucuronic acid we'll discuss this process in more detail in the next video the conjugated Billy Rubin then gets excreted in the bile into the intestines it then gets acted upon by the bacteria in the intestines to produce stco binen this is a precursor to stoin this occurs by oxidation and Cobin is the molecule that gives feces its characteristic brown color however not all stco binen gets excreted a closely related form called urobilinogen gets absorbed back into the blood which in turn is filtered by the kidneys you urobilinogen can be converted to eurobin Via oxidation and these get excreted in the urine eurobin is the molecule which gives urine its yellow color in the next video we'll be looking at the metabolism of Billy Rubin in the liver and the diseases associated with dysfunction of this process for more free tutorials and the PDF for this tutorial visit www.h handwritten tutorial.com