Ans. is 'c' i.e.. VIII o Vit K acts as a cofactor at a late stage in the synthasis of coagulation factors by liver - Prothrombin (factor II), Factor VII, IX and X (also protein 'C' & Protein 'S').Vitamin-Ko It is a fat soluble vitamin.o It is the major coagulant of human body (coagulants are substances which promote coagulation),o It is of three types -K1 (from plants) - PhytonadioneK2 (Produced by bacteria) - MenaquinonesK3 (Synthetic) - Menadioneo Half life of vit K is 72 hours - Mahenderbhan Singh 5th/e - 348o l it K acts as a cofactor at a late stage in the synthasis of coagulation factors by liver - Prothrombin (factor II), Factor VII, IX and X (also protein & Protein 'S')o It catalyzes the final step in activation of these factors i.e. gamma carboxylation of glutamate residues which confers on them the capacity to bind Ca+2 and to get bound to phospholipids surfaces - properties essential for participation in the coagulation cascade.Uses1. Deficiency stateDietry deficiency, prolonged antimicrobial therapy, obstructive jaundice or malabsorption syndrome.2. Liver diseaseVit K is usually ineffective because synthesis of clotting factor in liver is impaired.It may be helpful if there is deficiency due to decreased absorption because of lack of bile salts (bile salts promote absorption of fat soluble vitamin).3. NewbornsNewborns have deficiency of vit K as well as has limited capacity to synthesize clotting factors.Haemorrhagic disease of newborn can be prevented and treated with Vit K.4. Overdose of oral anticoagulantsThis is the most important indication of lit K.Oral anticoagulant interfere with the synthesis of Vit K dependent clotting factor - Vit K can be used to reverse the effect.o Phytonadione (Kj) is the preparation of choice for these indications, because it acts most rapidly.o lit Kj (Menadione) can cause hemolysis-contraindicated in G-6-PD deficiency and neonates.o In the newborn menadione can precipitate kemicterus by -Inducing hemolysis.Competitively inhibiting glucronidation of bilirubin.