SN2
SHORT NOTE
5M
★ High-yield
Classify anticoagulants. Describe the mechanism of action of heparin and warfarin.
Definition
Anticoagulants = substances that prevent or delay the coagulation of blood.
Classification
| In vivo (used clinically) | In vitro (used in the laboratory) |
|---|---|
| Heparin | EDTA |
| Warfarin, dicoumarol | Sodium citrate |
| Low molecular weight heparin | Sodium oxalate |
| Direct oral anticoagulants | Heparin |
| — | Siliconised containers |
Heparin
- A sulphated mucopolysaccharide; strongest natural organic acid
- Source — mast cells and basophils; commercially from ox lung and pig intestine
- Mechanism — accelerates antithrombin III about 1000-fold → inactivates thrombin, IXa, Xa, XIa, XIIa
- Acts immediately; works in vitro as well as in vivo
- Given IV or SC only — not absorbed orally
- Monitored by APTT
- Antidote — protamine sulphate
- Safe in pregnancy — does not cross the placenta
Oral Anticoagulants (warfarin)
- Mechanism — inhibits vitamin K epoxide reductase → blocks factors II, VII, IX, X and proteins C and S
- Acts only in vivo; onset delayed 2–3 days
- Monitored by PT / INR (target 2–3)
- Antidote — vitamin K; fresh frozen plasma if urgent
- Contraindicated in pregnancy — teratogenic, crosses placenta
Laboratory Anticoagulants
| Agent | Mechanism | Chief use |
|---|---|---|
| EDTA | Chelates Ca2+ | Best for blood counts — preserves cell morphology |
| Sodium citrate (3.8%) | Chelates Ca2+ | Coagulation studies (1:9); blood banking as CPD-A |
| Sodium/potassium oxalate | Precipitates Ca2+ | Chemical analysis; distorts cells |
| Heparin | Antithrombin III | Osmotic fragility, blood gases |
Applied Aspects
- Heparin-induced thrombocytopenia (hit) — paradoxical thrombosis
- Warfarin has numerous drug interactions — requires regular INR monitoring
- Calcium is essential to coagulation, so all laboratory anticoagulants act by removing it
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.