BASI EXAM 9: Heme Catabolism exam Already Passed!!

Heme is catabolized from this type of molecule to this type of molecule in order for excretion - Answer-hydrophobic, toxic to amphipathic, non-toxic and soluble What are the 5 general steps in heme catabolism? - Answer-1. formation and transport of bilirubin 2. uptake of bilirubin in liver 3. secretion and catabolism of conjugated bilirubin 4. enterohepatic reabsorption of urobilinogen from intestines 5. urinary excretion of absorbed urobilinogen or urobilin Explain the first step in heme catabolism: the formation and transport of bilirubin - Answer--RBCs in spleen, bone marrow or liver are phagocytized by macrophages -converted to BILIVERDIN (green) -converted to BILIRUBIN (orange) that in UNCONJUGATED Free heme is toxic and _____ - Answer-non-recyclable What is UCB? when is it made? where? - Answer-unconjugated bilirubin in macrophages hydrophobin, carried through circulation by serum albumin What carries UCB in the circulation? - Answer-albumin Where does conjugation of bilirubin occur? - Answer-in liver hepatocyte after entering from hepatic artery Explain the second step of heme catabolism: uptake of bilirubin in the liver and conjugation - Answer--UCB travels in blood w/ albumin -UCB alone enters hepatocyte using OATP transporters (facilitated diffusion)-sugar molecules added to UCB to conjugate it (CB) -CB is excreted into bile duct using ATP-dependent transporter called MRP2 CB is found _____ in the peripheral circulation in the absence of pathology - Answer-conjugated bilirubin; not found in circulation or very small amounts in circulation Which step in heme catabolism is the OATP (organic-anion-transporting polypeptides) transporters found? where? what type of transport? - Answer-UCB entering into hepatocytes from circulation through facilitated diffusion Which step in heme catabolism in the MRP2 transporters found? where? what type of transport? - Answer-CB entering into bile duct from hepatocytes, active transport (ATP-dependent) Explain the third step in heme catabolism: secretion and metabolism of conjugated bilirubin - Answer--in intestine, by colonic bacteria to yield UROBILINOGEN (colorless) -urobilinogen undergoes AUTO-OXIDATION yielding STERCOBILIN (brown=feces) What molecule gives feces its brown color? - Answer-stercobilin How much of urobilinogen is excreted in the feces? - Answer-90% What happens to the urobilinogen that is not excreted in the feces? - Answer-enters gut and picked back up into bloodstream via portal vein In relation to heme catabolism, what does bile obstruction cause? - Answer-CB is unable to flow into the intestine, and urobilinogen synthesis is minimal In relation to heme catabolism, what happens in the case of liver damage? - Answer-liver cannot reabsorb excess urobilinogen and circulating urobilinogen levels increase Explain step 4 in heme catabolism: What happens to the 10% urobilinogen that is not excreted initially as feces? - Answer-re-enters circulation 9%= back to liver 1%= to kidneysExplain step 5 in heme catabolism: what happens to the urobilinogen that is not initially excreted in feces, and then is not taken up again by liver? - Answer-through kidneys for excretion into urine -goes through AUTO-OXIDATION =UROBILIN (yellow) -excreted in urine What molecule gives urine its yellow color? - Answer-Urobilin What is TBIL? how is it measured? - Answer-it is the total bilirubin including unconjugated and conjugated. determined directly through two dye reactions What is DBIL? how is it measured? - Answer-direct bilirubin: mostly conjugated determined directly through one dye reaction What is IBIL? how is it measured? - Answer-indirect bilirubin: mostly unconjugated determined INDIRECTLY by TBIL-DBIL what is jaundice? - Answer-yellow discoloration of skin, nail beds and conjunctiva caused by DEPOSITION OF BILIRUBIN aka HYPERBILIRUBINEMIA What are the four types of jaundice? - Answer-1. neonatal 2. pre-hepatic jaundice 3. hepatic 4. post-hepatic What is neonatal jaundice caused by in general? - Answer-multiple factors