Why blood does not clot in circulation?

Answer 1

I. Endothelial surface factors-

a) Smoothness of endothelial surface,which prevents contact activation of intrinsic system.

b) Layer of glycocalyx on endothelium.

c) a protein bound with the endothelium membrane, thrombomodulin, which binds thrombin.

II. Antithrombin action of fibrin & Antithrombin-III

a) when a clot is forming, about 85-90% of thrombin becomes adsorbed to fibrin fibers.

b) some thrombin 10-15%, combines with antithrombin-III, which urther blocks effect of thrombin on fibrinogen.

III. Heparin-

heparin is a highly negatively charged conjugated polysaccharide.