Vitamin K

One of two naturally occurring fat-soluble vitamins (vitamin K1 and vitamin K2) needed for the clotting of blood because of an essential role in the production of prothrombin (a clotting factor). The term vitamin A may also refer to a synthetic compound that is closely related chemically to the natural vitamins K1 and K2 and has similar biological activity. Vitamin K is required (as a cofactor) for the body to make four of the blood's coagulation (clotting) factors: particularly prothrombin and also factors VII, IX, and X. Vitamin K1 is made by plants, whereas vitamin K2 is of bacterial origin and is the important form for people. All other forms of vitamin K are converted to vitamin K2 in the body. There are a number of closely related compounds of the vitamin K2 series. Vitamin K deficiency only rarely occurs because an adequate supply of the vitamin is usually present in the diet and the vitamin is synthesized by bacteria in the intestine. Deficiency of vitamin K 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 is necessary for the intestinal absorption of vitamin K. In newborn babies, the absence of large intestinal bacteria coupled with the absence of body stores of vitamin K may result in hemorrhagic disease of the newborn. This is a dangerous condition because there can be bleeding into critical organs such as the brain. This disorder can be prevented by the administration of vitamin K to the baby shortly after birth or to the mother during labor. A fat-soluble substance present in green leafy vegetables was found in 1929 to be needed for coagulation of the blood to take place. The substance came to be named vitamin K. The K was for Koagulation (Danish for coagulation). A pure form of the vitamin was isolated and analyzed in 1939. Several related compounds with vitamin K activity have also been synthesized. The 1943 Nobel Prize in physiology or medicine was shared by the Danish researcher Henrik Carl Peter Dam (1895-1976) for his (original) discovery of vitamin K and the American worker Edward Adelbert Doisy (1893-1986) for his discovery of the chemical nature of vitamin K.

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vitamin K n
1) either of two naturally occurring fat-soluble vitamins that are essential for the clotting of blood because of their role in the production of prothrombin in the liver and that are used in preventing and treating hypoprothrombinemia and hemorrhage:
a) a yellow oily naphthoquinone C31H46O2 that is obtained esp. from alfalfa or made synthetically and that has a fast, potent, and prolonged biological effect, is effective orally, and is useful esp. in treating hypoprothrombinemia induced by anticoagulant drugs called also phylloquinone, phytonadione, vitamin K1 see MEPHYTON
b) a pale yellow crystalline naphthoquinone C41H56O2 that is obtained esp. from putrefied fish meal and is synthesized by various bacteria (as in the intestines of humans and higher animals) and that is much more unsaturated than vitamin K1 and slightly less active biologically called also menaquinone, vitamin K2
2) any of several synthetic compounds that are closely related chemically to vitamins K1 and K2 but are simpler in structure and that have similar biological activity esp MENADIONE

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a fat-soluble vitamin occurring in two main forms: phytomenadione (of plant origin) and menaquinone (of animal origin). It is necessary for the formation of prothrombin in the liver, which is essential for blood clotting, and it also regulates the synthesis of other clotting factors. A dietary deficiency does not often occur as the vitamin is synthesized by bacteria in the large intestine and is widely distributed in green leafy vegetables and meat.

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any of a group of structurally similar fat-soluble compounds that promote blood clotting by increasing hepatic biosynthesis of prothrombin and other coagulation factors, activating these factors by γ-carboxylation of glutamic acid moieties in inactive precursor proteins. Two forms exist naturally, phytonadione (vitamin K1) and menaquinone (vitamin K2), as well as one synthetic provitamin form, menadione (vitamin K3). The best sources are green leafy vegetables, liver, cheese, butter, and egg yolk, and as menaquinone it is synthesized by the intestinal flora. Deficiency, usually seen only in neonates, in disorders of absorption, or during antibiotic therapy, is characterized by hemorrhage.

Medical dictionary. 2011.

Look at other dictionaries:

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