The plasma contains fibrinogen and platelets, which are destroyed when they encounter rough vessel wall wounds and release prothrombin that promotes blood coagulation. The predecessor of this enzyme is prothrombin, and with the participation of Ca2+, the activator of prothrombin can catalyze the conversion of prothrombin into active thrombin. Under the action of thrombin, Ca2+ and other factors, the soluble fibrinogen is transformed into insoluble filamentous fibrin through a series of changes. After the formation of this protein, it intertwines with each other to form a net, and nets the blood cells, causing the original blood to clot.1. Adding an appropriate amount of anticoagulant (e.g., sodium citrate) to the blood takes away the Ca2+ and makes it calcium-losing blood, which prevents fibrinogen from turning into fibrin, and thus avoids blood clotting.2. Natural hirudin can affect blood coagulation and thrombosis in a number of ways: (1) Antithrombin effectThe antithrombin effect of hirudin is seen in blood-sucking leeches. Hirudin contains 6 cysteine residues with similar distribution, and this structure can achieve a 1:1 ratio between hirudin and thrombin to form a stable complex, which has a highly specific inhibitory effect on thrombin and plays an anticoagulant role to inhibit thrombin. (2), other anticoagulant effects in the 1980s, from the Mexican leech salivary glands extracted from a peptide consisting of 119 amino acid residues, which contains cysteine amino acid residues, can be specific, reversible and factor Xa combination to form a complex, to play the role of anticoagulant. Recently, an anticoagulant factor Xllla containing 66 amino acid residues was found in the giant Amazonian leech. It is the strongest specific inhibitor of factor Xllla found so far, and also has an inhibitory effect on other glutamine transferase enzymes, so that it can fully inhibit the cross-linking reaction of fibrin monomers and play an anticoagulant role. (3) Antiplatelet effect at the same time the Mexican leech extracted a leech antiplatelet protein. It has specific inhibition of collagen-induced platelet aggregation, from the North American leech extracted a peptide containing 39 amino acid residues, its three-dimensional conformation and hirudin is very similar to inhibit fibrinogen-mediated platelet aggregation.