(a) Heparin (hepar = liver) . It is synthesized by mast cells of connective tissue and liver cells. It is a heteropolysaccharide. It increases the effectivity of antithrombin III (a - globulin) which inactivates the thrombin so prevents conversion of fibrinogen into fibrin.
(b) Hirudin. It is an anticoagulant present in the saliva of salivary glands of leech and is mixed with blood of host during its storage in its crop.
(c) Warfarin. It is an anticoagulant of plant origin, which when given to a patient, lowers the formation of prothrombin and factors VII, IX and X from liver cells by lowering the activity of Vitamin K.
(d) Sodium oxalate, sodium citrate and EDT A (Ethylene diamine tetra acetic acid) are used as anticoagulants in blood banks as these bind Ca++, so these are called chelating agents. .
(e) Chilling of blood also delays blood clotting as it lowers the activity of enzymes involved in blood clotting.
ROLE OF VITAMIN-K IN BLOOD CLOTTING -
Vitamin K, also called anti-haemorrhagic factor, is a fat soluble vitamin and is essential for the formation of prothrombin from the liver. Deficiency of vitamin K causes hypoprothrombinemia which interferes with blood clotting. Vitamin K is also synthesized by intestinal bacteria.