Fat soluble vitamins passively diffuse into enterocyte (cell of intestinal lining) and form
chylomicrons which enter the lymphatic system
Long-chain fatty acids must form micelles for uptake
Vitamin K absorption (3 main, dietary, and bacterial synthesis) - answer✔Jejunum, ileum, large
intestine (most important bc bacteria's in large intestine produce vitamin K)
Dietary phylloquinone and menaquinone
- mainly jejunum
- passive diffusion into enterocyte
- packaged into chylomicrons
Menaquinone from bacterial synthesis
- ileum and colon
- passive diffusion
- absorption capacity greatly differs among individuals
What negatively impacts vitamin K absorption? - answer✔Fat malabsorption disorders
Excess vitamin A and E
What enhances vitamin K absorption? (when is it best for vitamin K supplementation?) -
answer✔Dietary fat
- for supplementation, better to take vitamin K with main meals as there may be more fat
What is the main circulating form of vitamin K? - answer✔Phylloquinone
Vitamin K transport to blood - answer✔Released from enterocytes in chylomicrons via
exocytosis
Enter the bloodstream via the thoracic duct at a very slow rate
Vitamin K transport from intestine to other tissues - answer✔Chylomicrons deliver some
vitamin K to body cells
Remaining vitamin K to liver in chylomicron remnants
Liver metabolizes vitamin K or repackages vitamin K in VLDL
Liver exports VLDL which deliver lipids and vitamin K to body cells
Vitamin K storage - answer✔Stored in cell membranes
Overall low body storage (because we need a constant/steady intake of it) due to rapid
metabolism in liver
Vitamin K metabolism (degradation) - answer✔Rapid metabolism in liver- packaged into VLDL
for transport to other tissues or degradation/oxidation for excretion- turnover of the pool: 1.5
days
Phylloquinone
- almost completely metabolized: oxidation of side chain (metabolites conjugated with
glucuronic acid)
Menaquinone
- isoprenoid side chain is shortened (metabolites conjugated with glucuronic acid, phosphate,
and sulphate)
Vitamin K excretion - answer✔Conjugated metabolites excreted with bile in feces (main) and
urine
Biochemical role of vitamin K - answer✔Vitamin K required to catalyze the carboxylation of
glutamic acid residues in y-carboxyglutamic acid (Gla) proteins that allows the high-affinity
binding of Ca2+ ions (turning glutamic acid into y-carboxyglutamic acid)
Physiological functions of vitamin K - answer✔Helps to make proteins (ex. Gla) that aid with
normal blood clotting and bone mineralization
Interaction between vitamin K and anti-coagulants - answer✔ex. Warfarin (reduces
strokes/heart attacks)
Interfere with vitamin K cycle
- anticoagulants reduce the activity of quinone reductase and epoxide reductase
- reduction of vitamin K is a critical conversion step for vitamin K to function in gamma
carboxylation reactions
Physiological implications of vitamin K deficiency - answer✔Rare in healthy adults
Vitamin K - Vulnerable population groups - answer✔Newborns
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