Fibinolysis

[steeplesign]

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Hi guys,
I'll preface this post with a potential apology if this question is completely ridiculous, but heme is not really my thing (i.e. everything about blood confuses me). So here goes...

Pathoma states that plasmin is responsible for cleaving fibrin and fibrinogen, which in turn has an anti-thrombotic effect. I get why cleaving fibrin would help with clot breakdown and inhibition, but why fibrinogen?
I thought the whole point of the coagulation cascade was to cleave fibrinogen to fibrin, thereby allowing formation of a stable clot. So why does cleavage of fibrinogen by plasmin cause the opposite by actually helping with degradation and prevention of a clot?

I would appreciate any clarification! For whatever reason, my IQ score temporarily drops by 30 points the moment I try learning anything about blood, so feel free to explain like I'm five - it'll probably be for the best, anyways 🙄

 

[zhopv10]

Hey so I'm not sure on a couple things in your post. So you got that plasminogen is converted to plasmin and plasmin breaks down the fibrin clot. But i've never heard of plasmin converting fibrin to fibrinogen (I could be off though, somebody else could comment). I'll give you my understanding and hopefully it helps. So plasmin breaks down the fibrin in the fibrin clots to fibrin breakdown products (FBP's). These include things like D-dimer that is used for screening for possible clotting pathology, and others. These FBP's then can feed back and compete with thrombin thus decreasing the actual continued formation of the clot too. Also it perpetuates itself as it can convert Plasminogen to plasmin. Hopefully that helps.

 

[DerpStore]

Hi guys,
I'll preface this post with a potential apology if this question is completely ridiculous, but heme is not really my thing (i.e. everything about blood confuses me). So here goes...

Pathoma states that plasmin is responsible for cleaving fibrin and fibrinogen, which in turn has an anti-thrombotic effect. I get why cleaving fibrin would help with clot breakdown and inhibition, but why fibrinogen?
I thought the whole point of the coagulation cascade was to cleave fibrinogen to fibrin, thereby allowing formation of a stable clot. So why does cleavage of fibrinogen by plasmin cause the opposite by actually helping with degradation and prevention of a clot?

I would appreciate any clarification! For whatever reason, my IQ score temporarily drops by 30 points the moment I try learning anything about blood, so feel free to explain like I'm five - it'll probably be for the best, anyways 🙄

Hey so I think I understand your confusion. Fibrinogen is indeed cleaved by thrombin into fibrin which is the more active/cross-linkable form. However plasmin will cleave fibrinogen at a different site, and it will not result in fibrin, but in fibrinogen split products. So since it is degrading/cleaving fibrinogen into an inactive compound (fibrinogen split products as opposed to fibrin), there is less precursor fibrinogen for thrombin to work with and so it decreases clot formation.

So yes, plasmin does cleave serum fibrinogen, but this does not result in formation of fibrin.
When thrombin cleaves fibrinogen, this results in the formation of fibrin.

In addition when plasmin acts on fibrin (again, which is created by cleavage of fibrinogen by thrombin), this will result in formation of d-dimers. Hopefully this is clear now!

 

[steeplesign]

Hey so I'm not sure on a couple things in your post. So you got that plasminogen is converted to plasmin and plasmin breaks down the fibrin clot. But i've never heard of plasmin converting fibrin to fibrinogen (I could be off though, somebody else could comment). I'll give you my understanding and hopefully it helps. So plasmin breaks down the fibrin in the fibrin clots to fibrin breakdown products (FBP's). These include things like D-dimer that is used for screening for possible clotting pathology, and others. These FBP's then can feed back and compete with thrombin thus decreasing the actual continued formation of the clot too. Also it perpetuates itself as it can convert Plasminogen to plasmin. Hopefully that helps.

Thank you very much for your reply. That explanation actually helped me understand D-dimer a bit better too, which is a big bonus! haha I need all the help I can with this subject, as you can see.
I think I just got tripped up on the wording in Pathoma, but thanks to you and DerpStore, I get it now!

 

[steeplesign]

Hey so I think I understand your confusion. Fibrinogen is indeed cleaved by thrombin into fibrin which is the more active/cross-linkable form. However plasmin will cleave fibrinogen at a different site, and it will not result in fibrin, but in fibrinogen split products. So since it is degrading/cleaving fibrinogen into an inactive compound (fibrinogen split products as opposed to fibrin), there is less precursor fibrinogen for thrombin to work with and so it decreases clot formation.

So yes, plasmin does cleave serum fibrinogen, but this does not result in formation of fibrin.
When thrombin cleaves fibrinogen, this results in the formation of fibrin.

In addition when plasmin acts on fibrin (again, which is created by cleavage of fibrinogen by thrombin), this will result in formation of d-dimers. Hopefully this is clear now!

Thank you so much for the explanation! That's exactly what I needed to hear to have my confusion cleared up. I appreciate it 🙂