METABOLISM OF VITAMIN K HENDRA WIJAYA Esa Unggul University Okt 2012

Chemical form of Vit K

Source of Vit K There are two major natural sources of vitamin K: phylloquinones (vitamin K1) in plant sources menaquinones (vitamin K2) produced by bacterial flora in animals. Endogenous source of vitamin K. The large intestine of healthy adult humans contains a microflora of bacteria.

Benefits of vitamin K Vitamin K: “coagulation vitamin,” “antihemorrhagic vitamin,” and “prothrombin factor.”

Absorption and Transfer Phylloquinone, the major form of vitamin K in the diet, is absorbed in the jejunum, and less effi ciently in the ileum, in a process that is dependent on the normal fl ow of bile and pancreatic juice Like all fat-soluble vitamins, vitamin K is absorbed in association with dietary fats and requires the presence of bile salts and pancreatic juice for adequate uptake from the alimentary canal. Absorption of vitamin K depends on its incorporation into mixed micelles, and optimal formation of these micellar structures requires the presence of both bile and pancreatic juice.

Absorption and Transfer The lymphatic system is the major route of transport of absorbed phylloquinone from the intestine in mammals Ingested phylloquinone is absorbed by an energy-dependent process from the proximal portion of the small intestine Menaquinone is absorbed from the small intestine by a passive non–carrier- mediated process. Efficiency of vitamin K absorption has been measured at 10 to 70%, depending on the form in which the vitamin is administered.

Storage and Excretion About half of the total body pool of vitamin K is in the liver phylloquinone and menaquinones specifically concentrated and retained in the liver Menadione is found to be widely distributed in all tissues and very rapidly excreted. Some breakdown products of vitamin K are excreted in the urine Some vitamin K is re-excreted into the intestine with bile, part of which is excreted in the feces. In humans, 20% of injected phylloquinone was excreted in the urine, and 40 to 50% was excreted in the feces via the bile.

Deficiency The major clinical sign of vitamin K deficiency in all species is impairment of blood coagulation. Clinical signs include low prothrombin levels, increased clotting time, and hemorrhaging. In its most severe form, vitamin K deficiency will cause subcutaneous and internal hemorrhages, which can be fatal. Deficiency can result from insufficient vitamin K in the diet, lack of microbial synthesis within the gut, inadequate intestinal absorption, or inability of the liver to use the available vitamin K.