in this video we're going to talk about Billy Rubin metabolism bil Rubin metabolism is important because hyper bilirubinemia is a condition where you have high amounts of bil Rubin that can lead to jaundice which is yellowing of the skin and of the eyes for example and this could indicate something sinister so Billy Rubin is formed uh by breakdown of he present in hemoglobin so the story starts with an old red blood cell which enters What's called the reticular endothelial system which is in your liver and in your spleen here they are engulfed by macrofagos the red blood cells contain many hemoglobin molecules normally which are broken down to heem and globin hence the name hemoglobin heem is further broken down by two enzyme uh he oxygenase followed by Billy verd in redu days forming Billy Rubin and iron the iron and the globin is recycled to make more red blood cells the Billy ribbon formed is in an unconjugated form so it's unconjugated Billy Rubin and it is lipid soluble and so it has to bind to something and alamin is the protein which acts as a transporter so this unconjugated Billy Rubin uh is bound to alamin but it also can bind to other things such as high density lipoproteins and less often it can circulate freely in an Unbound form Billy ruin is also formed by the breakdown of other things such as myoglobin and cytochrome enzymes anyway this Albin Billy Rubin complex circulates around and then enters the liver system where it dissociates the unconjugated Billy Rubin is taken up efficiently by the hepatocytes while the Albin remains in circulation Billy Rubin enters the hepatocytes through facilitated diffusion essentially through a concentration gradient here they undergo what is called glucoronidation this process makes substances such as the Billy Rubin more water soluble which allows it to be excreted in bile and in urine glucuronidation is carried out by a family of enzymes called urine D phosphogluconate glucuronosyl transferase or ugt in the case of Billy Rubin uh it is Billy Ruben ugt the unconjugated Billy Rubin is now conjugated Billy Rubin and is water soluble it is secreted into the bilary system and is a component of bile conjugate B Rubin travels down the bile duct where it joins with the pancreatic duct and into the duodenum through the ampul Vata the conjugated B Rubin is now in the small intestine where it continues its Journey majority of Billy Rubin here is actually conjugated 98% obviously and only a small proportion is unconjugated Billy Rubin conjugated Billy Rubin remember is water soluble and so it is not absorbed across the lipid membrane of the small intestinal epithelium in comparison the unconjugated bil Rubin fraction is partially reabsorbed and under goes uh enterohepatic circulation which is where it travels through the portal system back to the liver so Intero intestine hepatic liver circulation this UNC conjugated bil Rubin can then undergo glucoronidation again to become a conjugated bil Rubin and water soluble going back this conjugated bil Rubin actually continues traveling to the large intestine where it is exposed to so much bacteria here the Billy Rubin is reduced by bacterial enzymes to a series of molecules termed eurobin eurobin are part L absorbed in the bow and under goes again Intero hepatic circulation where the urobilinogen will enter the liver to get processed again now the fraction that is actually not cleared by the liver will enter the general circulation and is partly excreted in urine urine binen gives urine its yellow color majority of eurobin is actually excreted in feces the eurobin here are further oxidized to form eurobin including stco billin oxidized urobilinogen which I mentioned gives feces its brown color so in summary Billy Rubin is a breakdown product of hemoglobin initially it is unconjugated enters the liver and becomes conjugated which is water soluble it then gets further digested oxidized by bacteria and this oxidized form is urobilinogen it can be reabsorbed or excreted in feces and if you have high amounts of bil Rubin this can lead to jaundice which is yellowing of the skin and of the conjunctiva high amount bil rubben hyper rubinia can be an indication of an underlying disease this will be discussed in a separate video [Music]