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13 Cards in this Set

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Most of the bilirubin in the body is formed in the tissues by the breakdown of hemoglobin. TRUE/FALSE
TRUE. The bilirubin is bound to albumin in the circulation.
Is all bilirubin tightly bound?
NO. Some of it is, but most can dissociate in the liver, and free bilirubin enters liver cells, where it is bound to cytoplasmic proteins.
What happens next to bilirubin?
It is next conjugated to glucoronic acid in a reaction catalyzed by the enzyme, glucoronyl transferase.
Where is this enzyme located?
In the smooth endoplasmic reticulum. Each bilirubin molecule reacts with 2 uridine diphosphoglucuronic acid molecules to form bilirubin diglucoronide.
Is this glucoronide more water soluble?
It is more water soluble than than free bilirubin is then transported to the bile canaliculi.
Does a small amount of the bilirubin glucoronide escape into the blood?
Yes. It is bound less tightly here to albumin than is free bilirubin and is excreted in the urine.
The total plasma bilirubin normally includes free bilirubin plus a small amount of conjugated bilirubin. TRUE/FALSE
TRUE. Most of the bilirubin glucoronide passes via the bile ducts to the intestine.
Is the intestinal mucosa impermeable to conjugated bilirubin?
It is relatively impermeable to conjugated bilirubin but is permeable to unconjugated bilirubin and to urobilinogens.
What are urobilinogens?
They are a series of colorless derivatives of bilirubin formed by the action of bacteria in the intestine. Some are reabsorbed into the portal circulation. Some of the reabsorbed substances are reexcreted by the liver and excreted in the urine.
What exactly is jaundice?
When free or conjugated bilirubin accumulates in the blood, the skin, sclera and mucus membranes turn yellow.
When is jaundice detectable?
When the total plasma bilirubin is greater than 2mg/dl(34umol/L).
What can cause hyperbilirubinemia?
1. excess production of bilirubin(hemolytic anemia)
2. decreased uptake of bilirubin into hepatic cells
3. disturbed intracellular protein binding or conjugation
4. disturbed secretion of conjugated bilirubin into the bile canaliculi
5. intrahepatic or extrahepatic bile duct obstruction.
When does the free bilirubin rise?
When it is due to the first three processes listed above. When due to disturbed secretion of conjugated bilirubin or bile duct obstruction, bilirubin glucoronide regurgitates into the blood, and it is the conjugated bilirubin in the plasma that is elevated.