MLT GlobeChemistry: Liver function & bilirubin
84 Chemistry MCQs on Liver function & bilirubin with answers and explanations.
Which bilirubin fraction gives a direct van den Bergh reaction and is the main pigment excreted in bile?
Hepatic UGT1A1 conjugates bilirubin with glucuronic acid; this water-soluble form reacts directly with diazo reagent and enters bile. Unconjugated bilirubin needs an accelerator; urobilinogen forms in the gut.
In advanced liver failure, rising blood ammonia is most damaging to which organ?
Ammonia crosses the blood–brain barrier and disturbs astrocyte glutamine metabolism and neurotransmission, causing hepatic encephalopathy. Other organs tolerate hyperammonaemia far better.
During prolonged fasting, which organ makes ketone bodies but cannot use them itself?
Hepatic mitochondria make acetoacetate and beta-hydroxybutyrate. The liver lacks succinyl-CoA:3-ketoacid CoA transferase (thiophorase), so it exports ketones to other tissues.
Where are the body's vitamin B12 stores mainly held?
The liver holds several milligrams of B12, enough for years. This is why dietary deficiency takes a long time to cause megaloblastic anaemia.
Jaundice usually becomes visible in the sclerae once serum total bilirubin exceeds about what level?
Normal total bilirubin is up to about 1.2 mg/dL. Scleral icterus usually appears above 2–3 mg/dL, and the range between is subclinical hyperbilirubinaemia.
Yellow discoloration of skin and sclera (jaundice) is due to:
Jaundice appears when bilirubin exceeds about 2-3 mg/dL. ALT indicates liver cell injury but does not cause yellow color.
Which pattern is typical of hemolytic (prehepatic) jaundice?
Excess heme breakdown floods the liver with unconjugated bilirubin, which is not water soluble and does not enter urine. More bilirubin reaches the gut, so urobilinogen rises.
During heme breakdown in macrophages, which enzyme opens the heme ring to form biliverdin?
Heme oxygenase cleaves the heme ring, releasing iron and carbon monoxide and forming biliverdin; biliverdin reductase then forms bilirubin. Ferrochelatase inserts iron during heme synthesis.
Unconjugated bilirubin is carried in plasma to the liver mainly bound to:
Unconjugated bilirubin is water-insoluble and travels tightly bound to albumin. Ligandin is an intracellular carrier protein inside hepatocytes, not a plasma carrier.
In the hepatocyte, bilirubin is conjugated with which substance?
UDP-glucuronosyltransferase 1A1 attaches glucuronic acid to bilirubin, forming water-soluble mono- and diglucuronides. Glycine and taurine conjugate bile acids, not bilirubin.
A patient reports pale, clay-coloured stools. This finding reflects reduced formation in the gut of:
Stercobilin, formed from urobilinogen, gives stool its brown colour. When bile flow to the intestine is blocked, little stercobilin forms and stools become pale.
Why does unconjugated, not conjugated, bilirubin cause kernicterus in newborns?
Free (unbound) unconjugated bilirubin is lipophilic and enters the brain, especially when albumin binding is exceeded. Conjugated bilirubin is water-soluble and does not cross easily.
A healthy, breastfed 2-week-old has persistent mild unconjugated hyperbilirubinemia, normal stools and no hemolysis. The most likely cause is:
Breast milk jaundice begins after the first week and can last several weeks, with unconjugated bilirubin in a thriving baby. Biliary atresia gives conjugated bilirubin and pale stools.
A patient with long-standing cirrhosis has a rising serum alpha-fetoprotein and a new liver mass. The most likely diagnosis is:
AFP is used with imaging to detect hepatocellular carcinoma in cirrhosis. Benign lesions such as abscess or hemangioma do not typically raise AFP.
Why is unconjugated bilirubin not found in urine even when its serum level is high?
Unconjugated bilirubin is water-insoluble and tightly bound to albumin, so it is not filtered. Only conjugated bilirubin, which is water-soluble, can appear in urine.
Jaundice of the skin and sclera usually becomes clinically visible when total serum bilirubin exceeds about:
Adult total bilirubin is normally below about 1.2 mg/dL; visible jaundice usually appears above about 2.5–3 mg/dL. Values between are called latent or subclinical hyperbilirubinemia.
A neonatal bilirubin sample was left uncovered on a sunny bench for 2 hours before testing. The result will most likely be:
Bilirubin is photo-oxidized by light and can fall by up to about 50% per hour in bright light. Samples should be protected with amber tubes or foil.
In diazo methods, bilirubin reacts with diazotized sulfanilic acid to form:
The diazo reaction splits bilirubin into two colored azobilirubin (azopigment) molecules, whose absorbance is measured. Glucuronidation happens in the liver, not in the assay.
Total bilirubin is 5.2 mg/dL (89 µmol/L) and direct bilirubin is 0.8 mg/dL (14 µmol/L). What is the indirect bilirubin?
Indirect (mostly unconjugated) bilirubin = total − direct = 5.2 − 0.8 = 4.4 mg/dL (75 µmol/L). A mainly indirect rise suggests hemolysis or reduced conjugation.
In the liver, ammonia is detoxified mainly by conversion to:
The hepatic urea cycle converts ammonia to urea, which the kidneys excrete. Uric acid comes from purine breakdown and creatinine from creatine in muscle.