MLT GlobeChemistry: Liver function & bilirubin – page 2
84 Chemistry MCQs on Liver function & bilirubin with answers and explanations.
The primary bile acids synthesized by the liver from cholesterol are:
The liver makes cholic and chenodeoxycholic acids and conjugates them with glycine or taurine. Gut bacteria convert them to the secondary bile acids deoxycholic and lithocholic acid.
In a healthy term newborn, physiological jaundice typically peaks at:
Physiological unconjugated hyperbilirubinemia peaks around days 3–5 and settles within about 2 weeks in term babies. Jaundice in the first 24 hours is pathological.
Which enzyme converts biliverdin to bilirubin?
Heme oxygenase opens heme to biliverdin, and biliverdin reductase then reduces it to unconjugated bilirubin. UGT1A1 conjugates bilirubin in the liver.
A patient with advanced cirrhosis has low urea, normal creatinine and high ammonia. The low urea is best explained by:
The failing liver cannot convert ammonia to urea, so urea falls while ammonia rises. Kidney injury and dehydration raise urea, and a high-protein diet increases it.
A total bilirubin of 3.0 mg/dL is equal to about how many µmol/L? (1 mg/dL = 17.1 µmol/L)
3.0 × 17.1 = 51.3 µmol/L. Dividing instead of multiplying gives the wrong value of about 0.18.
Which enzyme conjugates bilirubin with glucuronic acid in the liver?
UDP-glucuronyltransferase (UGT1A1) adds glucuronic acid to bilirubin in hepatocytes. Heme oxygenase and biliverdin reductase act earlier, in bilirubin formation.
Within the hepatocyte, bilirubin is conjugated mainly in the:
UDP-glucuronyltransferase is an endoplasmic reticulum enzyme, so bilirubin conjugation takes place there before secretion into bile.
The approximate upper reference limit for total serum bilirubin in adults is:
Adult total bilirubin is normally below about 1.0–1.2 mg/dL (17–21 µmol/L); exact limits vary slightly by method.
Which of these plasma proteins is made by plasma cells rather than by the liver?
Immunoglobulins are produced by plasma cells. Albumin, fibrinogen and transferrin are synthesised by hepatocytes.
Which serum enzyme rises most characteristically when bile flow is obstructed (cholestasis)?
Cholestasis stimulates synthesis of ALP by bile duct cells, so ALP (with GGT) rises markedly. CK is a muscle enzyme and amylase a pancreatic/salivary enzyme.
In physiological jaundice of the newborn, which bilirubin fraction is mainly increased?
Newborns have immature UDP-glucuronyltransferase and a high red cell turnover, so unconjugated bilirubin accumulates.
Serum albumin is used as a marker of which liver function?
Albumin is made only by the liver, so a low level in chronic liver disease reflects reduced synthetic function. Because its half-life is about 3 weeks, it changes slowly.
Hay's sulfur test detects bile salts in urine because bile salts:
Bile salts are detergents that reduce surface tension, the same property that emulsifies fat in the intestine. Sulfur powder therefore sinks instead of floating; no chemical reaction is involved.
A patient has low blood urea and high blood ammonia. Failure of the urea cycle in which organ best explains this?
The complete urea cycle functions in hepatocytes, converting ammonia to urea. Kidney failure raises urea because excretion falls, the opposite pattern.
Deficiency of which lipotropic nutrient causes fatty liver by impairing phosphatidylcholine synthesis and VLDL export?
Phosphatidylcholine is needed to assemble and secrete VLDL. Without choline, triglyceride builds up in hepatocytes.
During fasting, lipolysis releases glycerol from adipocytes. Where is most of this glycerol used?
Adipocytes have little glycerol kinase, so glycerol goes to the liver. There it is phosphorylated and used for gluconeogenesis.
When amino acids reach the liver for breakdown, what is usually the first reaction that removes their alpha-amino group?
Most amino acids first pass their amino group to alpha-ketoglutarate to form glutamate. Glutamate dehydrogenase then releases the nitrogen as ammonia.
Most of the body's vitamin A is stored as retinyl esters in which cells?
Hepatic stellate cells store about 80% of body vitamin A as retinyl esters. When these cells are activated in liver injury, they lose this store and lay down fibrous tissue.
A patient with viral hepatitis has raised serum conjugated AND unconjugated bilirubin. Which type of jaundice is this?
Damaged hepatocytes both conjugate and excrete bilirubin poorly, so both fractions rise. Haemolysis and Gilbert syndrome mainly raise unconjugated bilirubin.
A healthy 20-year-old has mild unconjugated hyperbilirubinemia that rises during fasting, with normal liver enzymes and no hemolysis. The most likely diagnosis is:
Gilbert syndrome is a common, harmless reduction in UDP-glucuronyl transferase activity. Unconjugated bilirubin rises mildly with fasting, illness or stress; Dubin-Johnson causes conjugated hyperbilirubinemia.