1st June 2023

Coagulation pathway

The coagulation pathway consists of a series of reactions, which lead to homeostasis, the blockage of bleeding or haemorrhage. The coagulation cascade is made up of various clotting factors and the liver is the key organ involved in coagulation, being the site of synthesis of the clotting factors. Haemostasis can be primary or secondary. In primary haemostasis, at the site of endothelial damage, the aggregation of platelets form a plug. Secondary haemostasis involves the intrinsic and extrinsic pathways. These both diverge to form the common pathway and lead to fibrin becoming activated; these fibrin units combine and stabilise the platelet plug.
The two pathways, the intrinsic and extrinsic pathways, both converge to activate factor X. This then leads to the common pathway in which activated factor X, in combination with factor V, platelet membrane phospholipids and Ca2+ ions convert prothrombin to thrombin (activated factor II), which in turn results in the activation of fibrin (activated factor I). The fibrin subunits then combine to form a stable fibrin clot.

Regulations of Clotting

Proteins C and S act to prevent coagulation, as these proteins mainly act to inactivate factors V and VIII.

Clotting cascade.

Image Source: Wikimedia Commons (2012). Classical blood coagulation pathway, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Classical_blood_coagulation_pathway.png (Accessed on: 10 January 2023).