SN5
SHORT NOTE
5M
★ High-yield
Describe bilirubin metabolism. Classify jaundice and give the findings in each type.
Formation of Bilirubin
RBC destroyed after 120 days in res → Haem + globin → Haem oxygenase → Biliverdin + Fe + CO → Biliverdin reductase → Unconjugated bilirubin
- About 300 mg produced daily
- 15% comes from ineffective erythropoiesis and other haem proteins
Transport and Conjugation
Unconjugated bilirubin binds albumin → Taken up by hepatocyte (ligandin) → UDP-glucuronyl transferase → Conjugated bilirubin diglucuronide → Excreted into bile
| Feature | Unconjugated | Conjugated |
|---|---|---|
| Also called | Indirect, prehepatic | Direct, posthepatic |
| Water soluble | No | Yes |
| Bound to albumin | Yes | No |
| In urine | Absent | Present |
| Crosses BBB | Yes → kernicterus | No |
| Normal value | 0.2–0.8 mg/dL | 0.1–0.4 mg/dL |
Intestinal Fate
Conjugated bilirubin in gut → Bacterial action → Urobilinogen → Stercobilinogen → faeces (brown colour)
- Enterohepatic circulation — some urobilinogen is reabsorbed; a small fraction is excreted in urine
- Total serum bilirubin normally 0.3–1.0 mg/dL
Jaundice
Jaundice (icterus) = yellowish discolouration of skin, sclera and mucous membranes due to raised serum bilirubin.Clinically detectable above 2–3 mg/dL.
| Type | Cause | Bilirubin raised | Urine | Stool |
|---|---|---|---|---|
| Prehepatic (haemolytic) | Excess haemolysis | Unconjugated | No bilirubin; ↑ urobilinogen | Dark |
| Hepatic (hepatocellular) | Hepatitis, cirrhosis | Both | Bilirubin present | Normal or pale |
| Posthepatic (obstructive) | Gallstone, carcinoma head of pancreas | Conjugated | Bilirubin present; no urobilinogen | Clay-coloured |
Applied Aspects
- Physiological jaundice of newborn — appears after 24 h, immature UDP-glucuronyl transferase; treated with phototherapy
- Kernicterus — unconjugated bilirubin > 20 mg/dL crosses the immature BBB → basal ganglia damage
- Gilbert syndrome — mild ↓ conjugation, benign. Crigler–Najjar — severe enzyme deficiency
- Van den Bergh test — direct positive in obstructive, indirect in haemolytic jaundice
All questions in Blood (haematology)
- Q1Define erythropoiesis. Describe its sites, stages, and the factors regulating it. Add a note on the fate of red blood cells. ★
- Q2Describe the mechanism of blood coagulation. Explain the intrinsic and extrinsic pathways and the tests used to assess them. Add a note on natural anticoagulants. ★
- Q3Classify blood groups. Describe the ABO and Rh systems and discuss mismatched transfusion reaction. Add a note on erythroblastosis fetalis. ★
- Q4Classify leucocytes and give their normal values. Describe the functions of neutrophils and discuss the types of immunity. ★
- Q5Describe the structure and types of haemoglobin. Outline its synthesis and describe its fate after red cell destruction. ★
- SN1Describe the formation and functions of platelets. ★
- SN2Classify anticoagulants. Describe the mechanism of action of heparin and warfarin. ★
- SN3Define ESR. Give its normal values and enumerate the factors affecting it. ★
- SN4Define anaemia. Classify it morphologically and aetiologically. ★
- SN5Describe bilirubin metabolism. Classify jaundice and give the findings in each type. ★
- SN6Enumerate the plasma proteins with their normal values and describe their functions.
- SN7Write a short note on haemophilia.