1655753
Descripción
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Creado por hadeel.seraj
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Vitamin K (Phylloquinone,
Menoquinone)
- Exists in several forms:
phylloquinone (K1) found in
plants and menaquinone (K2)
formed by bacteria.
- Menadione (K3) is a synthetic
derivative for therapy, used in
the form of intramuscular or
intravenous injections
- All neonates (sterile GIT) should
be given a single prophylactic
dose of vitamin K as
phylloquinone by mouth
- Sometimes
vitamin K is
administrated
before
operations to
reduce bleeding
in surgery
- Anticoagulants (dicumarol and warfarin) are
designed to work as vitamin K antagonists
- Developed for clinical management
in patients at risk of thrombosis
- Functions
- Vitamin K-dependent
carboxylase activity is
necessary for
formation of:
- γ-carboxyglutamate
residues
- γ-carboxyglutamate
residues
- Enhances osteocalcin (protein in bone
matrix, containing γ-carboxyglutamate
residues) synthesis → functions as Ca
binding protein and modifies
crystallization of bone.
- Synthesis of at least 4 blood clotting factors
(contain γ-carboxyglutamate residues),
among them prothrombin (factor II), the
zymogen of blood coagulation enzyme
thrombin → interaction with platelets →
blood clotting
- Vitamin K-dependent
carboxylase activity is
necessary for
formation of:
- Role of Vitamin K
in Blood
Coagulation
- At least 13 proteins and Ca
ions are involved in blood
clotting
- γ-carboxyglutamate residues in
blood clotting factors chelate Ca ions
and so permit their binding to lipid
membranes of platelets
- In vitamin K deficiency or in the presence of its
antagonist → pre-prothrombin is released into
circulation
- Pre-prothrombin is an abnormal precursor of
prothrombin containing few or no
γ-carboxyglutamate residues
- Pre-prothrombin cannot chelate Ca ions or bind to
lipid membrane and so is unable to initiate blood
clotting
- Pre-prothrombin cannot chelate Ca ions or bind to
lipid membrane and so is unable to initiate blood
clotting
- Pre-prothrombin is an abnormal precursor of
prothrombin containing few or no
γ-carboxyglutamate residues
- In vitamin K deficiency or in the presence of its
antagonist → pre-prothrombin is released into
circulation
- γ-carboxyglutamate residues in
blood clotting factors chelate Ca ions
and so permit their binding to lipid
membranes of platelets
- At least 13 proteins and Ca
ions are involved in blood
clotting
- Deficiency
- Deficiency causes increased chance of internal
bleeding (after a minor cut) and uncontrollable
haemorrhage (following a slight trauma).
- The only known symptom is bleeding tendency with a prolonged PT (prothrombin time)
- Combination of antibiotics, inadequate vitamin K intake,
and surgery raises a warning flag that clotting time should
be checked before surgery is performed !!
- Deficiency causes increased chance of internal
bleeding (after a minor cut) and uncontrollable
haemorrhage (following a slight trauma).
- Toxicity
- Excessive bleeding produced by the administration of
oral anticoagulant (overdose) can be corrected by
vitamin K administration
- However, high doses of vitamin K can reduce the
effectiveness of anticoagulants used to prevent blood
clotting
- Symptoms are hemolytic anemia
and jaundice in infants
- Symptoms are hemolytic anemia
and jaundice in infants
- However, high doses of vitamin K can reduce the
effectiveness of anticoagulants used to prevent blood
clotting
- Excessive bleeding produced by the administration of
oral anticoagulant (overdose) can be corrected by
vitamin K administration
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