Quiz 4: Hemoglobin Degradation Flashcards Preview

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Flashcards in Quiz 4: Hemoglobin Degradation Deck (12)
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Extrinsic Hgb Degradation

• Extrinsic (normally 90%): outside of circulatory system, in RES (spleen)
- Hgb loses Fe to transferrin
- Carbon is expired as CO
- Globulin chains return to amino acid pool
- Rest of molecule converts to bilirubin, excreted by liver


Intrinsic Hgb Degradation

• Intrinsic (<10%): Hgb is released directly into blood stream & disassociated into α,β dimers
• Dimers are bound to Haptoglobin, removed from circulation by liver
- If not enough Haptoglobin (hemolytic episodes), dimers go to kidneys, reabsorbed and Fe is stored as Hemosiderin. If renal threshold is met, excess hemosiderin will appear in urine
• If not picked up by haptoglobin, gets oxidized to Methemoglobin


Degradation Process

Hemoglobin gives Iron, Protein, Protoporphyrin
Protoporphyrin gives unconjugated bilirubin
Unconjugated Bilirubin is conjugated in the Liver


Intero-Hepatic Circulation

Conjugated Bilirubin from the liver is sent to the intestines
Some is converted to Urobilinogen, then Urobilin and excreted
The rest is taken back to the Liver, then sent to the intestines again to become Urinary urobilinogen


Excretion In Hemolytic Diseases

Negative Unconjugated Bilirubin
Negative Conjugated Bilirubin
Increased Urobilinogen/Urobilin
All of which are excreted via Urinary Urobilinogen


Excretion in Liver Disease

Positive/Negative Unconjugated Bilirubin
Increased Urobilinogen
Excreted via Urinary Urobilinogen


Excretion with Liver Obstruction

No urinary urobilinogen excreted, because there is something blocking the conjugation of Bilirubin in the Liver so it cannot be excreted (is not sent to the intestines)


Conjugated Bilirubin Transport to the Intestine

Conjugated bilirubin is excreted by the liver into the bile, then excreted into the intestines through the bile duct. Bilirubin is converted to urobilinogen by bacterial action in the GI.
50% of the urobilinogen is reabsorbed into the portal circulation and re-excreted by the liver. Small amounts are normally excreted in the urine but the majority is excreted in the feces.


Bilirubin Testing

Diazotization methods
Evelyn and Malloy: Bilirubin and diazotized sulfanilic acid give azobilirubin; conjugated bilirubin reacts more quickly with the diazo reagent in water
Jendrassik-Grof method: same as Evelyn and Malloy but uses caffeine accelerator


Conjugated Bilirubin

Measured directly and is water soluble


Unconjugated Bilirubin

Measured indirectly and is insoluble in water


Bilirubin Sample Collection

Light sensitive and should be stored in dark glass
Lipemia will falsely elevate results, Hemolysis will falsely decrease results