Difference between intrinsic and extrinsic clotting pathway

[medtech]

What is the difference between these pathways? I've looked at a lot of literature for it but it just says extrinsic clotting pathway is the main pathway and involves blood and vessel walls while intrinsic only involves vessel walls.

 

I want to know in what scenario would the intrinsic pathway be initiated as opposed to the extrinsic pathway (ie. would a bruise start the intrinsic pathway and a cut start the extrinsic pathway)

 

This is all for a paper on hemophilia, so I'm also wondering if the VIIIa and IXa complex that acts as a catalyst for cleaving of factor X count as part of the intrinsic, extrinsic or both pathways (ie. when they two initiation pathways merge into the final clotting pathway)

 

Thanks for any help on the subject future doctors or grad students

[Maxime]

You want to write a paper based on information received from premed students on coagulation pathways, coming from this board? Where to start... First, pick any haematology book, you'll easily find your answers. Coagulation pathways aren't anything new. Second, if you're seriously thinking about writing something (to publish?), I'd be sure my sources are reliable...

[medtech]

You want to write a paper based on information received from premed students on coagulation pathways, coming from this board? Where to start... First, pick any haematology book, you'll easily find your answers. Coagulation pathways aren't anything new. Second, if you're seriously thinking about writing something (to publish?), I'd be sure my sources are reliable...

 

I think you missunderstood me. I've read lots of papers on this subject and I know the biochemical mehcanisms behind the two streams (which factor activates which), I want to know if there's different mechanisms that initiate these two streams of clotting deom a clinical point of view.

 

And no, the book of hemophilia 2nd ed, NEJM articles, my phsiology and anatomy notes, and other sources did not help me in this area....

 

Thanks

[alanine]

The physiological pathway (the one functioning normally in our body for hemostasis) is the extrinsic pathway.

 

The intrinsic pathway is an artificial pathway that explains how the PTT works (when phospholipids and activator -celite- are added to the sample). Basically the initiation of the clotting pathway by factor XII doesn't happen physiologically.

 

Basically, the extrinsic pathway is initiated (tissue factor, factor VIIa, etc...you probably know this) all the way to the catalysis of factor II into IIa and subsequent formation of fibrin from fibrinogen. But there's a parallel intermediate pathway in which tissue factor-VIIa complex activate factor IX, which activates factor X (VIII is a cofactor). This intermediate factor is the physiological contribution of the intrinsic pathway to hemostasis.

 

Also, thrombin activates IX and VIII, another amplification pathway.

 

Hope it helps. It usually is quite clear in hematology texts if you look for it!

[DanG8]

From a clinical point of view? The two pathways are activated by exposure to subendothelial surfaces and substrates (intrinsic pathway = negatively charged surfaces, extrinsic pathway = TF). However, the intrinsic pathway itself can use other negatively charged surfaces to activate itself (i.e. bacteria!). This helps, not so much in clotting, but in activation of the complement system (part of the innate immune response).

[Maher]

Quickly: intrinsic pathway arises if the endothelium is damaged (blood contacting collagen + platelets being damaged by cut edges of the vessel wall ultimately activates the pathway)

 

Extrinsic pathway arises if only cells surrounding the blood vessel are damaged (TF leaks in from the damaged cells and into the blood).

 

Usually however, the 2 occur together as it is unlikely that parenchymal and stromal cells are damaged without any damage to capillaries/arterioles/venules.

 

Hope this helps...

[medtech]

Quickly: intrinsic pathway arises if the endothelium is damaged (blood contacting collagen + platelets being damaged by cut edges of the vessel wall ultimately activates the pathway)

 

Extrinsic pathway arises if only cells surrounding the blood vessel are damaged (TF leaks in from the damaged cells and into the blood).

 

Usually however, the 2 occur together as it is unlikely that parenchymal and stromal cells are damaged without any damage to capillaries/arterioles/venules.

 

Hope this helps...

 

Thanks a lot!

[frozenarbitor]

http://en.wikipedia.org/wiki/Clotting

[Maher]

Thanks a lot!

 

No problem