Vitamins. dr.basima s.jaff

Transcription

1 Vitamins dr.basima s.jaff

2 1 Introduction The term vitamin was introduced in 1911, and the first vitamin discovered and isolated in a pure crystalline form was effective in preventing and curing a dietary deficiency disease called [polyneuritis]. The name vitamin was proposed for this compound because of its vital need in the preventing and curing of the above pathological condition and because chemically it was found to be an amine. Now a days,the term vitamin is used to a group of biologically essential organic chemical compounds have no chemical resemblance to each other,but because of a similar general function in metabolism.

3 Generally,the vitamins can not be synthesized by man and most other animals and they must be supplied in the diet, however,no single food is a rich source of all vitamins. Before the chemical structures of the vitamins were known,they were identified by letters of alphabete.this system is gradually being replaced by a nomenclature based on the chemical nature of the compound or a description of its source or function. Vitamins are usually needed in small amounts for normal growth,development and maintenance of health.inside the human body,vitamins undergo biotransformation and converted to more complex compounds [co-enzymes] that playa key role in many cellular reactions. The average daily requirement for vitamins differs from one vitamin to another and its influenced by age,sex[gender], pregnancy, lactation, physical stress and nutritional state.

4 II Hypovitaminosis [vitamins deficiency] -Avitaminosis Lack of one or more vitamins produces characteristic syndromes and generally.hypovitaminosis is divided into two principal types : I - Primary hypovitaminosis - This results from deficient intake or deficiency of the vitamin[s] in the diet. 2- Secondary [conditioned] hypovitaminosis This arises not because of a lack of vitamin[s] in the diet,but because of:

5 1. Decreased [inadequate] intake :such as those occur in cases of: prolonged vomiting, loss of teeth,long standing organic diseases etc. 2. Decreased[inadequate] absorption : such as those occur in cases of malabsorption [diarrhea,biliary obstruction and intestinal diseases]. 3. Impaired [inadequate]utilization when the vitamin[s] are not used properly. 4. Increased elimination :such as those occur in cases of diarrhea. diuresis,lactation and blood loss. 5. Increased requirement :certain vitamins are needed in excess in cases of growth,pregnancy,lactation,wound healing,excess alcohol consumption and diet rich in carbohydrates.

6 6- Faulty bacterial synthesis:the biosynthesis of certain vitamins which are made up by certain intestinal bacteria is inhibited,when antibiotics are used.. 7- Bacterial destruction :such as decomposition of vitamin c by intestinal bacteria. 8- Inadequate conversion of the pro vitamin into active vitamin. 9- Vitamin inhibitors[antagonists] :such as PABA and Sulphonamides,Thiaminase present in raw fishes that hydrolyzes vitamin B Imbalance :its known that is necessary to make a balnce between water and fat soluble vitamins.

7 11- therapeutic diet [total parenteral nutrition ] : when therapeutic diet is used for long periods,there will he vitamin deficiency such as glucose saline. 12. Chronic alcoholism for example alcohol inhibits intestinal absorption. of Vit.B1 causing it's deficiency.

8 Hypovitaminosis of any type if prolonged, leads to avitaminosis,which is characterized by : 1. A gradual decrease in tissue level of vitamins. 2. Biochemical lesions. 3. Anatomic lesions. 4. Cellular pathology [diseases]. 5. Death.

9 III Hyper vitaminosis Generally,fat soluble vitamins are more storable in human body,so excessive intake can result in toxic conditions.however,with the exception of vitamins A,D and E,there is little danger of toxic manifestations from the usual amount of vitamins,present, either in the diet or in the ordinary vitamin supplements,for example : The minimum lethal dose for Niacin is 6 G./Kg. body wt./day, so for a person of 60 Kg body wt. this is equal to 6*60=360 G/day,no one takes this quantity.

10 IV-Biosynthesis of vitamins Generally,the vitamins can not be synthesized by man and most other animals and they must be supplied in the diet,however, certain vitamins are synthesized to greater or less extent in the human body : 1- This may occurs as a result of bacterial growth in the intestinal tract.for example bacteria produce considerable amounts of vitamins K2,B5, B7 and B Metabolic biotransformation of the essential amino acid [tryptophan] to niacin. 3- Vitamin D3 may be synthesized from cholesterol by the skin,if its properly exposed to adequate sun shine

11 VII-Classification of vitamins: 1 - Fat soluble vitamins :this group includes :vitamins A,D,E and k,they are usually associated with the lipids of natural foods. 2- Water soluble vitamins :vitamin C and B complex vitamins.

12 1 - Fat soluble vitamins 1- Vitamin A 1 - Properties : soluble in fat and fat solvents discovered in 1913, stable at high temperature,destroyed by U.V. light, found either as vitamin A or as its precursor which is called pro vitamin A or Beta-carotene,which is converted after its absorption to vit. A in the intestinal wall and liver. 2- Chemistry : vit.a is a complex primary alcohol,the terminal [OH] group is esterified mostly with palmitic acid [C16 :0],its structural formula is characterized by the presence of beta ionone ring.

13 There are two principal types of vit.a : 1-Vit.Al or Retinol = Retinal 2-Vit.A2 or 3-dehydroretinol,which has a potency of 40% of that of vit.al and its structural formula differs from that of vit.a1, only in the presence of an additional double bond between C3 and C4 in the beta ionone ring. Vit.Al may be derived from beta-carotene by cleavage of the chain in a dioxygenase reaction in the presence of oxygen yielding two molecules of vit.al.

14 5- Physiologic roles : Includes : I -Vit.A has antioxidant property,so it has an important role in preventing certain. types of cancer,mainly lung cancer. 2-maintenance of epithelial tissues. 3-Promotes the formation of skeleton, so its important for growth 4-Vit.A is necessary for reproduction and lactation. 5-Certain derivatives of vit.a are used for the treatment of acne and psoriasis. 6-It has a specific role in the physiologic mechanism of vision [its involved in optic nerve transmission]. Rhodopsin opsin + Retinal visual purple, protein part non protein part retinal pigment, photoreceptor molecule,conjugated protein found in rode and cone cells of the retina of the eyes

15 When light stricks on the rode and cone cells of the retina of the eyes which contains Rhodopsin,the latter is coverted to opsin and retinol. Normally,equilibrium is maintained in the retina of the eyes such that the rate of breakdown of rhodopsin is equaled by the rate of regeneration. When there is deficiency of vit.a,the rate of rhodopsin regeneration is retarded,and this affects the process of vision and the patient may be a night blind [Nyctalopia].

16 7-Hypovitaminosis A : this may be either primary or secondary and characterized by : 1 -Slowing or stopping of growth in young animals. 2-Avoidance of light[photophobia],and [xerophthalmia] which is characterized by drying of the eyes,the cells of the lacrimal glands become keratinized and stop secreting tears, this may cause blidness if its not treated. 3-Vit.A deficiency has similar effects on the other epithelial tissues, mainly those of the respiratory and alimentary tracts. 4-Vit.A deficiency lowers body resistance against bacterial infections. 5-It causes nyctalopia. 6-There will be deposition of carotene in the skin.

17 7-There are also dryness and scaliness of the skin. 8-Vit.A deficiency leads to the formation of urinary caculi. 9-There is a defective in the formation of the enamel of the teeth. 10-VitA deficiency causes paralysis and nerve degeneration. 11 -There will be atrophy of the testis. 12-Vit. A deficiency causes also a delay of wound healing. 13-The risk of cancer isincreased

18 8-Hypervitaminosis : ingestion of an excess of vita causes : 1 -Anorexia[loss of appetite]. 2-Irritability[bone pain]. 3-Fissuring at the corner of the mouth. 4-Cracking and bleeding of the lips. 5-Loss of hair. 6-Hepatosplenomagaly and liver damage. 7-Headache and muscle stiffness. 8-Abortion. 9-Menstrual irregularities

19 9-Recommended Dietary Allowance [RDA] : It varies according to age, individual condition, sex and.and normally its : 4000 I.U. for women I.U. for men. This quantity must be increased to 6000 I.U./day in cases of lactation and pregnancy. lug. = 3 I.U.

20 Vitamin D Vitamin D =Steroid pre[o]-hormone = Anti-rachitic vitamin =Calciol= Calcitriol = sun shine Vitamin. 1- Properties : Vit. D is a white crystalline compound,soluble in fat and fat solvents,discovered in Vitamins D are a group of compounds that are sterols occurring in nature, principally in animal organisms. Certain of these sterols are pro-vitamin D, and when subjected to long wave U.V. light acquire the physiologic properties of preventing and curing [Rickets] a disease Characterized by skeletal abnormalities including failure of calcification

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22 2- Chemistry : For nutritional purposes the two principal D vitamins are : - Vit. D2 [activated Ergosterol] or Ergocalciferol or Viosterol,which is of vegetable origin. Vit. D3 [activated 7-dehydrocholesterol] or cholecalciferol,which is of animal origin.. Man and other mammals can synthesize pro-vit. D3 in their bodies.both vitamins D2 and D3 have equal potencies. 3- Occurrence : Vitamins D are found mainly in : cod liver oi1,other fish oils. eggs,liver,milk,mush rooms and cereals

23 5-Physiologic roles : includes : 1-Vit. D increases the intestinal absorption of Ca and P. 2-It has a direct effect on calcification process. 3-It affects the clearance and excretion of P by the kidneys. 4-Its also essential for normal Insulin secretion,cell differentiation and immunity. 6-Hypovitaminosis : its characterized by : 1-Rickets in children and Osteomalacia in adult. 2-An increase in the level of serum alkaline phosphatase. 3-A delay in dentition in children. 4-Hypoplasia [poor structural development].

24 7-Hypervitaminosis : ingestion of an excess of vit.d causes : 1 -Anorexia and weakness. 2-Nausea and headache. 3-Digestive disturbances[constipation] and polyuria. 4-Irreversible damage of kidneys. 5-Calcification of soft tissues. 6-Hypercalcuria,resulting in kidney stones. 8-RDA : varies according to age,sex and individual conditions and normally its about : 2.5 Mg. in adult and 10 Mg. in infant,children,pregnant and nursing women.lug.= 10 I.U.

25 Vitamin E = Alpha tocopherol 1-Properties : fat soluble vit.,soluble in fat and fat solvents,known also as anti-sterility vit Or fertility factor,discovered in The name tocopherol is a Greek word-means Child-bearing plus an ol for an alcohol. 2-Chemistry : There are several tocopherol isomers,like alpha,beta,gamma,delta----etc., of which the alpha isomer is the most potent and it has the following structural formula :

26 Interaction and synergism between antioxidant systems operating in the lipid phase (membranes) and the aqueous phase (cytosol) Free radical chain reaction PUFA-H = polyunsaturated fatty acid PUFA-OO = peroxyl radical of polyunsaturated fatty acid PUFA-OOH = hydroxyperoxy polyunsaturated fatty acid PUFA-OH = hydroxy polyunsaturated fatty acid

27 3- Occurrence: good sources of vit E are eggs,muscle,liver, fish.chicken,oat meal,corm oil,soya,cotton seeds and wheat germ oils 4-physiological roles : 1. Vit.E prevents auto-oxidation[ peroxidation] of polyunsaturated fatty acids,so it can be used as an anti - oxidant. 2. It prevents damage of lung tissues caused by various oxidants found in the air 3. Vit. E serves as a co-factor inelectron transfer system. 4. Its essential for normal immune system.

28 5-Hypovitaminosis : its characterized by: 1 - Resorption of the foetus in females. 2 Atrophy of the spematogenic tissues and permanent sterility in males, 3-RBC haemolysis and anemia. 4-Abnormal metabolism of nucleic acids. 5-An increase in urinary excretion of creatine. 6-Steatorrhea,cystic fibrosis and pancreatitis. 6-Hpervitaminosis : its characterized by : malaise and fatigability.

29 RDA : It varies according to age,sex,individual conditions and the amount of P.U.S.F.A in the diet. [vit.e/p.u.s.f.a.]= 0.6. Normally its about 10 Mg./day. 1 I.U. =0.67Mg. Tocopherol.

30 Vitamins K: Chemistry : a large number of chemical compounds which are related to 2-methyl-1,4 naphthoquinone posses some degree of vit.k activity.the principal types of vit.k are : 1 - Vit. K1= Mephyton = Phytonadione =Phylloquinone = 2- methyl-3-phytyl 1,4- naphthoquinone,this type of vit.k is of plant origin.

31 2- Vit.K2 =Menaquinone =Farnoquinone =2-methyl-3- difamesyl 1,4naphthoquinone,it occurs as a metabolic product of intestinal bacteria as well as in animal tissues

32 3- Vit.K3 -Menadione = 2-methyl-1,4 naphthoquinone,is a synthetic compound.this suggested that this portion[2- methyl 1,4-naphthoquinone] of the molecule is essential for biologic effects.

33 Physiological Effects of Vitamin K Vitamin K serves as an essential cofactor for a carboxylase that catalyzes carboxylation of glutamic acid residues on vitamin K- dependent proteins. These proteins are involved in: 1) Coagulation 2) Bone Mineralization 3) Cell growth

34 4- Occurrence : vit.k is found mainly In : liver,g.i.t., skeletal muscles,cows milk, cheese,kale, cabbage, cauliflower,alfalfa,peas, and cereals. 5-Physiologic roles : include : 1 -Vit.K catalyzes the biosynthesis of several plasma clotting factors such as factors :11 [prothrombin]. V11,1X and X. 2-It catalyzes the oxidative phosphorylation. 3-It induces RNA formation. 4-VitK has an important role in Ca metabolism. 5-It may be used as anti-dote for anti-coagulant drugs such as coumarine derivatives. 6-It has also an important role in mineralization process.

35 6-Hypovitaminosis : its characterized by : 1-Episiaxis and excessive menstrual loss. 2-Haematuria. 3- G.I.T. harmorrhage. 4-Hypoprpothrombinemia. 7-Hypervitaminosis :its characterized by : 1 -Hyperbilirubinemia and haemolytic anemia. 2-Liver damage. 3-Reduced effectiveness of anti-coagulants

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