Why does a thrombus formed in deep vein thrombosis (DVT) resist initial breakdown better than a fresh superficial clot?

💡 Explanation

Fibrin cross-linking by factor XIIIa increases the mechanical stability and resistance to enzymatic degradation of the clot, because deep vein thrombi undergo more extensive cross-linking compared to superficial clots. Therefore, the deep vein thrombus is more resistant to breakdown rather than being more susceptible due to enzymatic factors.

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