Factors retarding (slowing down) clotting:
1. Cooling : Lowering of temperature retards coagulation Blood banks are maintained at low temperatures to keep the transfusion blood in a fluid state
2. Smooth surface: A voiding direct contact with water wettable surface e.g parafinised test tubes can retard the clotting of blood since TC do not break as the smooth surface is frictionless
3. Precipitation of Fibrinogen: fibrinogen can be precipitated out by adding various salt like sodium sulphate or magnesium sulphate this would prevent or slow down the process of clotting
4. Removal of lonic calcium : precipitation of calcium by addition of citrates or oxalates of k or Na retards clotting sodium fluoride (0.4%) also retards clotting but is not used because of fluoride toxicity complex compounds are formed by ethylene diamine tetra acetic acid (EDTA) di-sodium and trisodium citrate these compounds also prevent clotting of the blood
5. Use of anticoagulants: There are many other substance that prevent clotting of blood by various mechanisms they are known as anticoagulants these substances are as follows:
(a) Dyes: Azo dyes and other synthetic compounds like trypan red trypan blue chicago blue etc act as anticoagulants (i.e.prevent clotting )
(b) biological extracts:
(1) Intravenous peptone injection
(2) A fish protein called protamine
(3) A mino acid cysteine
(4) Heparin : howel found a substance in liver which prevents clotting of the blood hepar means liver so he named it heparin heparin is also found in mast cells which are hardly 1% of the total WBCs of blood but abundant in RES and along the blood vessels heparin has anti prothrombin type of action heparin however does not play significant role in preventing intravascular clotting
(5) Hirudin: it is obtained from the salivary gland of the leech it is anti thrombin in nature and therefore prevents clotting but is not used therapeutically because of its toxicity
(c) Dicoumarin is also named as dicoumarol dicoumarol has anti vit K action antagonist to naphthaquinone it thus prevents biosynthesis of prothrombin in the liver and acts as anticoagulant
(d) phenindione retards factors 7 and retards somewhat prothrombin it is like dicoumarol but quicker in action
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