12 Questions
Why is heparin not taken orally?
Because it is destroyed by gastric HCl
What is the mechanism of action of heparin?
Activating Anti-Thrombin III to inhibit clotting factors
What is the effect of warfarin on vitamin K?
Warfarin inhibits vitamin K epoxide reductase
What is the result of warfarin's inhibition of vitamin K epoxide reductase?
Decreased synthesis of clotting factors
What is the duration of action of heparin?
Short duration of action (4-8 hours)
What is the mechanism of action of heparin on clotting factors?
Heparin activates Anti-Thrombin III to inhibit clotting factors
What is the primary function of anticoagulants?
To interfere with the coagulation of blood
How many proteins are responsible for blood coagulation?
12
Which pathway is activated after tissue injury, releasing factor III?
Extrinsic pathway
What is the final product of the coagulation cascade?
Fibrin
What is the source of heparin?
Mast cells
How is heparin administered?
Parenteral (I.V.) administration
Study Notes
Anticoagulants
- Anticoagulants are drugs that interfere with the coagulation of blood.
Blood Coagulation
- There are two pathways: Extrinsic and Intrinsic.
- 12 proteins are responsible for blood coagulation.
Extrinsic Pathway
- After tissue injury, factor III is released from the injured tissue.
- Factor III activates factor VII, which activates factor VIII, then factor X, and finally factor II (prothrombin).
- Prothrombin is converted to thrombin, which activates factor I (fibrinogen) to form fibrin (blood clot).
Intrinsic Pathway
- After tissue injury, factor XII is released from the injured tissue, which activates factor XI, then factor IX, and finally factor X.
- Factor X is activated, leading to the formation of thrombin and fibrin.
Heparin vs Warfarin
- Heparin: natural, stored in mast cells, parenteral (I.V. or S.C.), immediate onset of action, short duration (4-8 hours).
- Warfarin: synthetic, oral (100% absorbed), delayed onset of action (1-2 days), long duration (5-7 days).
Heparin Mechanism
- Inhibits the activity of coagulation factors by activating anti-thrombin III.
- Anti-thrombin III inhibits the activity of factors II, X, XI, XII, and XIII (mainly factor X).
Warfarin Mechanism
- Liver synthesizes clotting factors (1, 9, 7, 2) with the aid of vitamin K.
- Vitamin K is converted to its oxidized form (vitamin K epoxide) during synthesis.
- Warfarin inhibits vitamin K epoxide reductase enzyme, preventing the regeneration of reduced form of vitamin K.
- As a result, the synthesis of clotting factors is stopped.
Learn about anticoagulants, their role in interfering with blood coagulation, and the two pathways of blood coagulation: extrinsic and intrinsic.
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