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Coagulation cascade
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When a vessel breaks, a plug of platelets forms. What makes it firm is the coagulation cascade, a chain of blood proteins, the factors, in which each one activates the next.
But it is not a single chain. There are two ways in. The extrinsic pathway starts when the cells that line the inside of the vessel, the endothelium, are damaged and release a substance called tissue factor. The intrinsic pathway starts when the collagen in that same wall is exposed. They are two different starting points, but both end up activating the same protein, factor X.
Think of two different roads that empty onto the same bridge. From there on everything runs together: activated factor X converts prothrombin into thrombin, and thrombin converts fibrinogen into fibrin, threads that weave together over the platelet plug and make it firm.
In brief
The coagulation cascade has two pathways, the intrinsic and the extrinsic, that start separately and converge into a common pathway.
Two different roads that empty onto the same bridge.
The extrinsic pathway begins with tissue factor released by damaged endothelial cells; the intrinsic one, with exposed endothelial collagen. Both end by activating factor X.
In the common pathway, factor Xa converts prothrombin into thrombin, and thrombin converts fibrinogen into fibrin, which stabilizes the platelet plug.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Coagulation Pathways, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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