Flashcards in Heme synthesis, degradation and porphyrias - Part 4 Deck (22):
Conjugated Bilirubin is also known as what?
Where and how is urobilinogen formed?
Bilirubin diglucuronide is released from liver into bile. It reaches intestine, & after deconjugation of glucuronic acid, intestinal bacteria form the colorless urobilinogen from bilirubin.
What leads to the brown sterobilin in the large intestine where it is formed by bacteria?
How does urobilinogen reach the kidney?
Before reaching the large intestine, some urobilinogen can be taken up into the liver via the enterohepatic circulation. This urobilinogen is either secreted by the liver into the bile or it is released by the liver into the blood stream and reaches the kidney.
In regards to heme degradation products, what is found in the urine?
-mixture of urobilinogen and urobilin.
Where is urobilin formed and how?
Urobilin is light yellow and formed in the kidney and also by contact of urobilinogen in urine with oxygen and light. That is why the yellow color can intensify in urine after release.
What causes hemolytic jaundice?
Extreme hemolysis of RBCs
What genetic defects can lead to hemolytic jaundice?
-glucose 6-P dehydrogenase deficiency, --pyruvate kinase deficiency
In patients with hemolytic jaundice, is the bilirubin in the blood conjugated or unconjugated?
The high level of bilirubin in the blood is due to unconjugated bilirubin as the liver is overloaded with the project to conjugate bilirubin and some unconjugated bilirubin stays in the blood complexed to albumin or accumulates in sclerae and skin.
In patients with hemolytic jaundice, what is characteristic of the urobilinogen levels?
higher urobilinogen levels than normal
Why do you find in patients with complete obstructive jaundice high blood levels
of conjugated (direct) bilirubin?
Bilirubin diglucuronide accumulates in the liver as it cannot be totally released into the intestines, as the bile ducts are obstructed by gallstones (extrahepatic cholestasis). The conjugated bilirubin is then spilled from the liver into the blood (regurgitation).
What is a characteristic serum injury marker in patients with complete obstructive jaundice?
sALP is elevated due to irritated bile ducts
Which color of the urine and feces would you expect in patients with complete obstructive jaundice?
-The color of the urine would be orange reddish brown due to conjugated bilirubin released by the kidney into urine. The feces are of pale, clay color as the bacteria of the large intestine lack urobilinogen for stercobilin formation.
-Urobilinogen would be undetectable in urine as most of the conjugated bilirubin did not reach the intestines and less urobilinogen is taken up into the liver.
Why do you find in patients with hepatocellular jaundice high blood bilirubin levels in form of both unconjugated and conjugated bilirubin?
-Hepatocellular jaundice results from defective hepatocytes. These cells are damaged and cannot conjugate bilirubin as usual, so unconjugated bilirubin will accumulate in blood
-Some bilirubin, however, is conjugated, but then it cannot be released as normally by active transport into the bile, which needs ATP
-In addition, the liver plasma membranes are leaking, shown by increased sALT and sAST as hepatocellular injury markers and the conjugated bilirubin leaks out of the hepatocyte and is found in serum
In patients with hepatocellular jaundice, would you find bilirubin in the urine and why?
-The urine contains bilirubin, as conjugated bilirubin leaked from the liver into the blood and was released by the kidney into urine
-On the other hand, urobilinogen in the urine would be undetectable, due to the fact that less conjugated bilirubin reached the intestines. This can also lead to pale, clay color feces.
Which liver injury markers in serum can be used to distinguish between
hepatocellular and obstructive jaundice?
-Hepatocellular jaundice is due to hepatocyte injury. This is indicated by increased blood levels of ALT and AST, whereas the level of ALP is mostly normal.
-Obstructive jaundice is characterized by mostly normal or slightly elevated blood levels of ALT and AST but by increased levels of ALP.
What are often the causes for total obstructive jaundice?
often the blockage of the main bile duct by gallstones or by a pancreatic tumor.
Pre-hepatic jaundice is caused by?
Excessive destruction of RBCs
Hepatocellular jaundice is caused by?
Liver diseases due to defective hepatocytes
Post-hepatic jaundice is caused by?
-Pancreatic tumor (extrahepatic cholestasis)
What is the name of the test that measures total and direct bilirubin in serum?
The blood test is the van den Bergh reaction