عدد المساهمات : 546
تاريخ التسجيل : 13/08/2008
|موضوع: vitamins الخميس 11 سبتمبر - 12:32|| |
Vitamins are organic compounds that are required for normal growth and development.
General characteristics of vitamins:
Essential for normal growth, differentiation, and development.
Must be supplied by the diet. Their deficiency results in characteristic deficiency diseases.
Not synthesized by humans except:
Vitamin D3, which can be synthesized from cholesterol
And nicotinic acid (niacin) that can be synthesized from the amino acid tryptophan.
Required in small quantities (trace amounts) in the diet
Required for proper metabolism of carbohydrates, lipids and
Prominent function of vitamins B complex is the formation of
coenzymes for various enzymatic reactions.
Not used as a source of energy.
Vitamins are classified according to their solubility into water and fat soluble vitamins
Fat-soluble vitamins: they are insoluble in water, but soluble in non-polar solvents (fate solvents). They are A, D, E, and K.
Water-soluble vitamins: they are soluble in water, but insoluble in non-polar solvents. These vitamins include vitamin C and vitamin B complex.
Sources of vitamins:
Humans have three sources of vitamins:
All vitamins are supplied by foods. The food sources include animal and plant sources except vitamin B12, which has no plant sources.
Some vitamins are synthesized in the body e.g. niacin (nicotinic acid) from the amino acid tryptophan and vitamin D3 (cholecalciferol) from 7-dehydrocholesterol.
Some vitamins e.g. biotin, B12 and K2 are synthesized by the intestinal microorganisms i.e. intestinal bacterial floraبكتريا الامعــاء. Vitamins synthesized by the body or intestinal microorganisms may not supply the entire daily requirement of the vitamin.
Causes of vitamin deficiency:
Decreased intake: famine, poverty, or alcoholism .
Biliary obstructionا decreased absorption of fat-soluble vitamins (A, D, E, and K
Malabsorption syndrome امراض الامتصاص as celiac disease.
Lack of intrinsic factor of vitamin B12 leading to pernicious anemia.
Deficiency of a transport protein e.g. retinol binding protein (RBP) of vitamin A.
Inability to activate the vitamin e.g. vitamin D3 due to renal or liver diseases, and activation of folic acid to tetrahydrofolate, due to deficiency of enzymes required for activation.
Females during pregnancy and lactation.
Children during growth.
During convalescence from diseases.
Increased excretion: as in certain renal diseases.
Drug induced deficiency:
Prolonged antibiotic therapy causes death of intestinal flora and decreased synthesis of the vitamin synthesized in the large intestine.
Treatment of tuberculous patient’s with Isoniazide drug causes vitamin B6 deficiency, due to decreased absorption and
عدد المساهمات : 907
تاريخ التسجيل : 01/08/2008
|موضوع: رد: vitamins الخميس 11 سبتمبر - 19:34|| |
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