vitamin K

vitamin K

n.

a fat-soluble vitamin, synthesized constantly by intestinal bacteria in mammals and occurring in certain green vegetables, fish meal, etc., that promotes blood clotting and is required for the synthesis of prothrombin by the liver: the two naturally occurring varieties are vitamin K₁, C₃₁H₄₆O₂, found chiefly in alfalfa leaves, and vitamin K₂, C₄₁H₅₆O₂, found chiefly in fish meal: vitamin K₃ (MENADIONE) and vitamin K₄ are prepared synthetically

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Any of several fat-soluble compounds essential for the clotting of blood.

A deficiency of vitamin K in the body leads to an increase in clotting time. In 1929 a previously unrecognized fat-soluble substance present in green leafy vegetables was found to be required for coagulation of the blood; its letter name comes from the Danish word koagulation. A pure form was isolated and analyzed structurally in 1939; several related compounds having vitamin-K activity have since been isolated and synthesized. The form of vitamin K that is important in mammalian tissue is of microbial origin. A synthetic vitamin K precursor called menadione is used as a vitamin supplement.

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▪ chemical compound

      any of several fat-soluble naphthoquinone compounds. Vitamin K (from the Danish word koagulation) is required for the synthesis of several blood clotting (coagulation) factors, including prothrombin and factors VII, IX, and X. A form of vitamin K known as phylloquinone (vitamin K₁) is synthesized by plants. A second form of vitamin K known as menaquinone (vitamin K₂) is synthesized by bacteria, including bacteria in the intestines of mammals. These bacteria produce the majority of vitamin K that mammals require. A synthetic vitamin K precursor called menadione (vitamin K₃) is used as a vitamin supplement. First recognized in 1929, the vitamin was isolated and analyzed structurally in 1939 by Danish biochemist Henrik Dam (Dam, Henrik).

       vitaminsA deficiency of vitamin K in the body leads to an increase in clotting time of the blood. Vitamin K deficiency is seldom naturally encountered in higher animals because the vitamin is usually adequately supplied in the diet, besides being synthesized by intestinal bacteria. In humans, deficiency may occur following the administration of certain drugs that inhibit the growth of the vitamin-synthesizing bacteria or as a result of disorders affecting the production or flow of bile, which itself is necessary for the intestinal absorption of vitamin K. In newborn infants (infancy), the absence of intestinal bacteria, low levels of vitamin K in the mother's milk, or the absence of body stores of vitamin K may result in bleeding, which can be prevented by the administration of vitamin K to the infant shortly after birth. (See table (vitamins) of the vitamins.)

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