إعـــــــلان

تقليص
لا يوجد إعلان حتى الآن.

فيتامين k وكل مايتعلق بة

تقليص
X
 
  • تصفية - فلترة
  • الوقت
  • عرض
إلغاء تحديد الكل
مشاركات جديدة

  • فيتامين k وكل مايتعلق بة

    Vitamin K
    Vitamin K (K from "Koagulations-Vitamin" in German and Scandinavian languages) denotes a group of lipophilic, hydrophobic vitamins that are needed for the posttranslational modification of certain proteins, mostly required for blood coagulation. Chemically they are 2-methyl-1,4-naphthoquinone derivatives.
    Vitamin K1 is also known as phylloquinone or phytomenadione (also called phytonadione). Vitamin K2 (menaquinone, menatetrenone) is normally produced by bacteria in the Large Intestine, and dietary deficiency is extremely rare unless the intestines are heavily damaged, are unable to absorb the molecule, or due to decreased production by normal flora, as seen in broad spectrum antibiotic use.
    There are three synthetic forms of vitamin K, vitamins K3, K4 and K5, which are used in many areas including the pet food industry (vitamin K3) and to inhibit fungal growth (vitamin K5)
    Chemical structure
    All members of the vitamin K group of vitamins share a methylated naphthoquinone ring structure, and vary in the aliphatic side chain attached at the 3-position (see figure 1). Phylloquinone (also known as vitamin K1) invariably contains in its side chain four isoprenoid residues, one of which is unsaturated.
    Menaquinones have side chains composed of a variable number of unsaturated isoprenoid residues; generally they are designated as MK-n, where n specifies the number of isoprenoids.
    It is generally accepted that the naphthoquinone is the functional group, so that the mechanism of action is similar for all K-vitamins. Substantial differences may be expected, however, with respect to intestinal absorption, transport, tissue distribution, and bio-availability. These differences are caused by the different lipophilicity of the various side chains, and by the different food matrices in which they occur.

    Sources
    Food sources
    Phylloquinone (vitamin K1) is the major dietary form of vitamin K. Green leafy vegetables and some vegetable oils (soybean, cottonseed, canola, and olive) are major contributors of dietary vitamin K. Hydrogenation of vegetable oils may decrease the absorption and biological effect of dietary vitamin K. If you wish to check foods for their nutrient content, including vitamin K, search the USDA food composition database or view a list of foods containing a specific nutrient. A number of good sources of vitamin K are listed in the table below along with their vitamin K content in micrograms (mcg).
    Food Serving Vitamin K (mcg)
    Olive oil 1 Tablespoon 8.1
    Soybean oil 1 Tablespoon 25.0
    Canola oil 1 Tablespoon 16.6
    Mayonnaise 1 Tablespoon 3.7
    Broccoli, cooked 1 cup (chopped) 220
    Kale, raw 1 cup (chopped) 547
    Spinach, raw 1 cup 145
    Leaf lettuce (green), raw 1 cup (shredded) 62.5
    Swiss chard, raw 1 cup 299
    Watercress, raw 1 cup (chopped) 85
    Parsley, raw 1/4 cup 246

    Function
    The only known biological role of vitamin K is as a cofactor for an enzyme that catalyzes the carboxylation of the amino acid, glutamic acid, resulting in its conversion to gamma-carboxyglutamic acid (Gla). Although vitamin K-dependent gamma-carboxylation occurs only on specific glutamic acid residues in a small number of vitamin K-dependent proteins, it is critical to the calcium-binding function of those proteins.
    Coagulation (clotting)
    The ability to bind calcium ions (Ca2+) is required for the activation of the seven vitamin K-dependent clotting factors, or proteins, in the coagulation cascade. The term, coagulation cascade, refers to a series of events, each dependent on the other, that stop bleeding through clot formation. Vitamin K-dependent gamma-carboxylation of specific glutamic acid residues in those proteins makes it possible for them to bind calcium. Factors II (prothrombin), VII, IX, and X make up the core of the coagulation cascade. Protein Z appears to enhance the action of thrombin (the activated form of prothrombin) by promoting its association with phospholipids in cell membranes. Protein C and protein S are anticoagulant proteins that provide control and balance in the coagulation cascade; protein Z also has an anticoagulatory function. Control mechanisms for the coagulation cascade exist, because uncontrolled clotting may be as life threatening as uncontrolled bleeding. Vitamin K-dependent coagulation factors are synthesized in the liver. Consequently, severe liver disease results in lower blood levels of vitamin K-dependent clotting factors and an increased risk of uncontrolled bleeding (hemorrhage).
    Bone mineralization
    Three vitamin-K dependent proteins have been isolated in bone: osteocalcin, matrix Gla protein (MGP), and protein S. Osteocalcin (also called bone Gla protein) is a protein synthesized by osteoblasts (bone-forming cells). The synthesis of osteocalcin by osteoblasts is regulated by the active form of vitamin D, 1,25(OH)2D3 or calcitriol. The mineral-binding capacity of osteocalcin requires vitamin K-dependent gamma-carboxylation of three glutamic acid residues. The function of osteocalcin is unclear but is thought to be related to bone mineralization. MGP has been found in bone, cartilage, and soft tissue, including blood vessels. The results of animal studies suggest MGP prevents the calcification of soft tissue and cartilage, while facilitating normal bone growth and development. The vitamin K-dependent anticoagulant protein S is also synthesized by osteoblasts, but its role in bone metabolism is unclear. Children with inherited protein S deficiency suffer complications related to increased blood clotting as well as decreased bone density.
    Cell growth
    Gas6 is a vitamin K-dependent protein that was identified in 1993. It has been found throughout the nervous system, as well in the heart, lungs, stomach, kidneys, and cartilage. Although the exact mechanism of its action has not been determined, Gas6 appears to be a cellular growth regulation factor with cell-signaling activities. Gas6 appears to be important in diverse cellular functions, including cell adhesion, cell proliferation, and protection against apoptosis. It may also play important roles in the developing and aging nervous system. Further, Gas6 appears to regulate platelet signaling and vascular homeostasis.

    Deficiency
    Overt vitamin K deficiency results in impaired blood clotting, usually demonstrated by laboratory tests that measure clotting time. Symptoms include easy bruising and bleeding that may be manifested as nosebleeds, bleeding gums, blood in the urine, blood in the stool, tarry black stools, or extremely heavy menstrual bleeding. In infants, vitamin K deficiency may result in life-threatening bleeding within the skull (intracranial hemorrhage).
    Adults
    Vitamin K deficiency is uncommon in healthy adults for a number of reasons: 1) vitamin K is widespread in foods (see Food sources); 2) the vitamin K cycle conserves vitamin K; and 3) bacteria that normally inhabit the large intestine synthesize menaquinones (vitamin K2), although it is unclear whether significant amounts are absorbed and utilized. Adults at risk of vitamin K deficiency include those taking vitamin K antagonist anticoagulant drugs and individuals with significant liver damage or disease. Additionally, individuals with disorders of fat malabsorption may be at increased risk of vitamin K deficiency.
    Infants
    Newborn babies who are exclusively breast-fed are at increased risk of vitamin K deficiency, because human milk is relatively low in vitamin K compared to formula. Newborn infants, in general, have low vitamin K status for the following reasons: 1) vitamin K is not easily transported across the placental barrier; 2) the newborn's intestines are not yet colonized with bacteria that synthesize menaquinones; and 3) the vitamin K cycle may not be fully functional in newborns, especially premature infants. Infants whose mothers are on anticonvulsant medication to prevent seizures are also at risk of vitamin K deficiency. Vitamin K deficiency in newborns may result in a bleeding disorder called vitamin K deficiency bleeding (VKDB) of the newborn. Because VKDB is life-threatening and easily prevented, the American Academy of Pediatrics and a number of similar international organizations recommend that an injection of phylloquinone (vitamin K1) be administered to all newborns.
    Lower doses of vitamin K1 for premature infants: The results of two studies of vitamin K levels in premature infants suggest that the standard initial dose of vitamin K1 for full term infants (1.0 mg) may be too high for premature infants. These findings have led some experts to suggest the use of an initial vitamin K1 dose of 0.3 mg/kg for infants with birth weights less than 1,000 g (2 lbs, 3 oz), and an initial dose of 0.5 mg would probably prevent hemorrhagic disease in newborns.
    The Adequate Intake (AI)
    In January 2001, the Food and Nutrition Board (FNB) of the Institute of Medicine established the adequate intake (AI) level for vitamin K in the U.S. based on consumption levels of healthy individuals. The AI for infants was based on estimated intake of vitamin K from breast milk.
    Adequate Intake (AI) for Vitamin K
    Life Stage Age Males (mcg/day) Females (mcg/day)
    Infants 0-6 months 2.0 2.0
    Infants 7-12 months 2.5 2.5
    Children 1-3 years 30 30
    Children 4-8 years 55 55
    Children 9-13 years 60 60
    Adolescents 14-18 years 75 75
    Adults 19 years and older 120 90
    Pregnancy 18 years and younger - 75
    Pregnancy 19 years and older - 90
    Breast-feeding 18 years and younger - 75
    Breast-feeding 19 years and older - 90

    Physiology
    Vitamin K is involved in the carboxylation of certain glutamate residues in proteins to form gamma-carboxyglutamate residues (abbreviated Gla-residues). The modified residues are often (but not always) situated within specific protein domains called Gla domains. Gla-residues are usually involved in binding calcium. The Gla-residues are essential for the biological activity of all known Gla-proteins.
    At this time 14 human proteins with Gla domains have been discovered, and they play key roles in the regulation of three physiological processes:
    • Blood coagulation: (prothrombin (factor II), factors VII, IX, X, protein C, protein S and protein Z).
    • Bone metabolism: osteocalcin, also called bone Gla-protein (BGP), and matrix gla protein (MGP).
    • Vascular biology.

    Symptoms of Vitamin K Deficiencies
    Vitamin K is known to be needed to coagulate blood and to maintain proper bone density. It plays a key role in proper development of the fetus. Deficiencies of vitamin K have been linked to:
    Heavy menstrual bleeding*
    Gastrointestinal bleeding
    Hematuria (blood in the urine)
    Nosebleeds
    Eye hemorrhages
    Anemia
    Gum bleeding
    Prolonged clotting times
    Hematomas
    Hemorrhaging
    Ovarian Hemorrhaging
    Easy bruising
    Purpura
    Osteopenia
    Osteoporosis
    Fractures
    Hypercalciuria
    Liver Cancer
    Calcification of soft tissue, especially heart valves (See my section on Calcium Deposits for more on this topic).

    Birth defects linked directly to vitamin K deficiencies include:
    Underdevelopment of the nose, mouth and mid face
    Shortened fingers
    Cupped ears
    Flat nasal bridges
    The following birth defects have been linked to anticonvulsant drugs, which block vitamin K:
    Epicanthal folds
    Flat nasal bridge
    Short noses
    Variety of craniofacial abnormalities
    Neural tube defects
    Mental retardation
    Learning disabilities
    Long, thin overlapping fingers
    Hypertelorism
    Upslanting palpebral fissures
    Microcephaly
    Cardiac abnormalities
    Distal digit hypoplasia (shortened pinkie fingers)
    Growth deficiency
    Also see my sections on:
    Menorrhagia: Overlooked Causes of Heavy Menstrual Bleeding for more information on this topic.
    Nose bleeds: Overlooked Causes of Epistaxis
    Ovarian Pain from Vitamin K Deficiency

  • #2
    شكراااااااااااااااااااااااااااا

    تعليق


    • #3
      الف شكر على الموضوع
      جاني ف وقته اليوم اخدنا المحاضره عنvitamin K deficiency
      بارك الله فيك

      تعليق


      • #4
        مشكوررررررررررررر

        تعليق


        • #5
          الله يعطيك العافيه

          تعليق

          يعمل...
          X