Download Fat Soluble Vitamins

Fat Soluble Vitamins
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Fat soluble vitamins include: A and carotenoids, E, K, D
Associated with fat absorption
Needed in small amounts
Stored in fatty tissues
Excess intake has toxic consequences
Retinol and caroteinoids
•
Lipid-soluble red,
orange, and yellow
pigments produced by
plants
•
Fewer than 10% have
vitamin A activity
•
B carotene, a
carotene, b
cryptoxanthin
•
Others also have
physiological
importance
•Lycopene
•Canthaxanthin
•Zeaxanthin
Fig. 10-1a, p. 327
Fig. 10-1b, p. 328
70-90% vitamin A absorption if fat is present
<5% to 60% for carotenoids; vitamin E interferes
CRBPII = cellular retinol
binding protein
Specfic protein carrier- vitamin A
Passive diffusion - carotenoids
LRAT = lecithin retinol acyl
transferase
Fig. 10-2, p. 329
‘‘Outer limiting
membrane’’
Photoreceptor
(rod) cell
Müller cell
Outer
segment
Inner
segment
Capillary
Pigment epithelium
Nucleus
Outer of photoreceptor
(rod) cell Segment
Functions: Vitamin A
• Vision
• Cell differentiation, growth, reproduction
• Bone development
• Immune system
Fig. 10-7, p. 334
Fig. 10-8, p. 334
Functions: Vitamin A
•Vision
•Cell differentiation, growth, reproduction
•Bone development
•Immune system
Fig. 10-9, p. 335
Functions: Vitamin A
•Vision
•Cell differentiation, growth, reproduction
•Bone development
•Immune system
Functions: Vitamin A
•Vision
•Cell differentiation, growth, reproduction
•Bone development
•Immune system
Function: Carotenoids
• Antioxidants for singlet oxygen;
Lycopene > vitamin E > a carotene >
bcryptoxanthin > zeaxanthin, b carotene >
lutein
(also work better when used together)
• Antioxidant for lipid peroxides (works with
vitamin E)
• Lower incidence of atherosclerosis through
prevention of oxidation of LDLs
Interaction with other nutrients:
• Vitamins E and K (inversely related; high A, low E and K)
• Zinc and iron
• Protein
Excretion: most in urine as oxoretinoic acid, small amounts in expired air, some in
feces
Fig. 10-10, p. 339
Deficiency:
• increased morbidity in children under age 5 with no evident clinical signs of
deficiency
• Signs, when present include xeropthalmia, anorexia, retarded growth,
increased susceptibility to infections, enlargement of hair follicle, and
keratinization of epithelial (mucous cells) of the skin.
Toxicity:
• Hypervitaminosis A
• Nausea, vomiting, double vision,
headache, dizziness, and
desquamation of the skin
• Teratogen
Vitamin D (a seco-steroid)
plants
animals
Fig. 10-11, p. 344
Table 10-2, p. 345
• Dietary Vitamin D is absorbed from a
micelle, along with other fats.
• About 50% of dietary D3 is absorbed.
Most absorbed in distal small intestine.
• Incorporated into chylomicrons
• Cholecalciferol from the skin is bound to
DBP and travels primarily to the liver, but
can be picked up by other tissues as well
(muscle and adipose)
• Blood is the major storage site; half-life
of 10-21 days
• Hydroxylases generate
the active form of the
vitamin (25-OH
cholecalciferol)
• Release by the kidney
of active forms; a
half-life of 4-6 hours
in the blood
Fig. 10-12, p. 346
Functions:
• Acts as a steroid hormone in calcium homeostasis
•Intestinal effects
•Effects on the kidney
•Effects on bone
Fig. 10-13, p. 347
Fig. 10-14, p. 348
Fig. 10-15, p. 349
Deficiency: rickets, osteomalacia
Interaction with other nutrients:
•Calcium, phosphorus, vitamin K
Excretion:
• Bile > feces > urine
Toxicity:
• Not possible from excess exposure to sunlight
• Few cases; calcification of soft tissues, hypertension, anorexia, renal
dysfunction
Only form with biologic activity
Fig. 10-17, p. 353
Digestion and Transport:
• Synthetic forms are deesterified
• Free alcohol forms are
absorbed passively in micelles;
non-saturable
• 20-80% absorption; better
with fats
• Incorporated into chylomicrons
in intestinal cell and sent out
into lymph
• Transfer between
chylomicrons, HDLs and LDLs
occurs in the blood. HDLs and
LDLs contain highest
concentration of the vitamin
• Half-life of about 48 hrs.
• Some stored in adipose, liver,
lung, heart, muscle, adrenals
Table 10-3, p. 354
Functions:
• Maintenance of membranes - prevents oxidation of unsaturated fatty acids contained in
the phospholipids (includes membranes of mitochondria and ER)
•Reduced LDL oxidation; decreased plaque formation
•Reduction in cataract formation
•Reduced oxidation in diabetics
• Suppression of activity of HMGcoA reductase (cholesterol synthesis)
1
2
Fig. 10-18, p. 356
Regeneration
Nutrient Interactions:
• Function closely linked to selenium (needed for GSH peroxidase), vitamin C, sulfur
containing amino acids,
• Inhibits carotene absorption and conversion to retinol; may impair vitamin K absorption;
may cause vitamin -D dependent bone mineralization problems
Deficiency:
Rare except in populations with fat malabsorption (cystic fibrosis)
myopathy and weakness, croid pigment accumulation, and degenerative neurologic
problems
Toxicity: one of the least toxic; bleeding problems
Fig. 10-19, p. 356
Vitamin K
Absorption: in micelles; incorporated into chylomicrons, then chylomicron
remnants, then VLDLs, then HDLs and LDLs.
Found mainly in liver and heart. Turnover is once every 2.5 hrs.
Synthetic form
From green plants
Synthesized by bacteria
Fig. 10-20, p. 361
Table 10-4, p. 361
Functions:
blood clotting and bone mineralization
Fig. 10-21, p. 363
Vitamin K cycle
Needed for protein
carboxylation
Vit. K usually only
present in this form in
the body
Osteocalcin or Bone Gla protein
Matrix Gla protein
Fig. 10-23, p. 364
Deficiency: rare in adults; newborns, chronic antibiotic
administration, and malabsorption can result in deficiency
Bleeding episodes
Osteoporosis
Toxicity:
none known
Table 10-1, p. 326