Review Note

Last Update: 03/27/2023 06:31 PM

Current Deck: Spring '23::Adv. Principles of Anesthesia I::Exam IV::Coagulation

Published

Cell-Based Model (Tissue Factor Pathway)

{{c1::Initiation}} Phase → {{c1::Amplification}} Phase → {{c1::Propagation}} Phase

Initiation Phase

The initiation phase begins with factors of the faster pathway.
1. The extrinsic pathway requires 15 seconds to form a clot.
2. The intrinsic pathway requires 6 minutes to form a clot.
The process begins with the expression of tissue factor (TF) (factor III, tissue phospholipid, tissue thromboplastin).
TF (factor III) activates factor VII.
Factor VIIa activates factor X.
Prothrombinase (factor Xa, factor Va, calcium [factor IV], and a

phospholipid) activates prothrombin (factor II).
A small amount of thrombin (factor IIa) is produced.
Tissue factor pathway inhibitor (TFPI) limits the amount of tissue factor released and keeps thrombin levels low.
Levels of thrombin (factor IIa) produced in this phase are insufficient to activate fibrinogen (factor I) and produce fibrin (factor Ia).