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Essay on Vitamin C
Essay Contents:
- Essay on the Historical Review of Vitamin C
- Essay on the Chemical Structure of Vitamin C
- Essay on the Properties of Vitamin C
- Essay on the Distribution of Vitamin C
- Essay on the Functions and Mode of Action of Vitamin C
- Essay on the Deficiency of Vitamin C
Essay # 1. Historical Review of Vitamin C:
In 1753, Captain Lind of the British Navy showed that the disease Scurvy which was common in sailors could be cured by giving them lemons and oranges. Captain Cook (1772-75) kept the sailors free from scurvy by giving them fresh food.
In 1907 scurvy was experimentally produced in guinea-pigs by Hoist and Frolich, and effects of vitamin C were studied on them. It was isolated by Szent-Gyorgyi (1928) and synthesized by Reichstein (1933).
Essay # 2. Chemical Structure of Vitamin C:
Ascorbic acid is an enediol isomer of 2-keto-L-glunolac-tone with a configuration similar to that of L-glucose. The natural variety is the laevo form; the dextro form is physiologically inactive.
Oxidation of ascorbic acid gives rise to dehydroascorbic acid. This reaction is reversible. Both forms are physiologically active. This reaction has provided the basis of oxidation and reduction process (biological oxidation).
Essay # 3. Properties of Vitamin C:
It is white crystal, soluble in water, (insoluble ion fat-sol-vents) and heat-labile. Easily oxidizes at 100° C in presence of oxygen.
Alkali and copper salts help destruction, hence cooking and canning destroy it. Slow cooking is more destructive than rapid cooking, even at high temperature. It can be saved if cooking or canning is carried out anaerobically. It is an actively reducing substance present in the living tissues. Ascorbic acid reduces silver nitrate, ferricyanide, methylene blue, 2, 6-dichlorophenol indophenols etc.
This vitamin can be assayed either chemically or histochemically by this property of ascorbic acid. The oxidation product is dehydroascorbic acid, which also has the biological activity of the vitamin. In the animal system dehydroascorbic acid can again be reduced to ascorbic acid with the help of a tripeptide glutathione. Ascorbic acid is readily absorbed from the intestine and is stored specially in liver, adrenals, pituitary and corpus luteum.
Essay # 4. Distribution of Vitamin C:
i. Vegetable Sources:
Fresh fruits, mainly citrus fruits, e.g., emblic myrobalan (amlaki), orange, lemon, tomato, pine-apple, papaya, etc., fresh vegetables, e.g. cabbage, cauliflower, lettuce, spinach, green peppers, beans etc.; properly sprouted pulses, germinating grams etc., are also rich sources. Potato and seeds are poor, but rich during germination.
ii. Animal Sources:
Generally poor. In the animal body the adrenal cortex contains a good amount. Cow’s milk, meat and fish contain a little. Milk is the only food for infants, so their diet should be supplemented with a good source of ascorbic acid e.g., orange juice or synthetic ascorbic acid.
iii. Blood Serum:
Contains 0.8 mgm of ascorbic acid per 100 ml, but in deficiency only 0.4 mgm or less. It is not much stored in the body.
iv. Most of the Ingested Vitamin C is Promptly Excreted:
Most of the ingested vitamin C is promptly excreted, although vitamin C is a high threshold substance. Daily excretion in urine is 30-35 mgm.
v. The aqueous and vitreous humours are very rich in it.
Biosynthesis of Ascorbic Acid:
Man, primates, guinea-pigs and birds cannot synthesize this vitamin. They presumably lack the enzyme system necessary to convert L-gulonic acid to ascorbic acid. So they require an external supply to meet their body needs. All other animals are capable of synthesizing this vitamin either in liver or in kidney, and do not suffer from ascorbic acid deficiency. The stages of biosynthesis are glucose → glucuronic acid → 2-keto L-gulonolactone → ascorbic acid.
Essay # 5. Functions and Mode of Action of Vitamin C:
i. Ascorbic acid regulates oxidation-reduction potential inside the cell probably by acting as a hydrogen carrier.
ii. It helps in the oxidation of p-hydroxyphenyl pyruvic acid to homogentisic acid which is the intermediate product of tyrosine metabolism.
iii. Ascorbic acid is related to carbohydrate metabolism. Deficient production of insulin takes place in ascorbic acid deficiency. On the other hand, after injection of dehydroascorbic acid in animals diabetic condition is produced.
iv. It is essential for the proper functioning of the formative cells of various tissues, such as fibroblasts, osteoblasts etc.
v. It is at the same time, necessary to maintain the normal state of the intercellular substance (mucoprotein and collagen) in different tissues like bone, cartilage, teeth, skin and connective tissue; also the cementing substance of the capillary endothelium.
vi. It helps in the development of the protein matrix i.e., by synthesizing collagen with special reference to the synthesis of hydroxyproline from a proline precursor. Hydroxyproline is a characteristic constituent of collagen, and it also helps in deposition of calcium and phosphate in the bones
vii. It plays an important role in wound repair. It lays down connective tissues which help in the healing of wounds.
viii. It takes part in the malnutrition of red cells. It helps in the mobilization of iron from its storage from ferritin. The delayed blood clotting, delayed clot retraction and anaemia as seen in Vitamin C deficiency can be explained from this standpoint.
ix. Due to the reducing properties of ascorbic acid, it helps in the absorption of iron form the intestine.
x. It helps in the conversion of folic acid to folinic acid.
xi. This vitamin possibly has some role in enhancing the resistance of animals against different toxins and stress conditions.
xii. It may be involved in the synthesis of adrenal cortical and gonadal hormones. It is observed that the adrenal cortex contains a large amount of vitamin C which is rapidly depleted when it is stimulated by ACTH.
Essay # 6. Deficiency of Vitamin C:
Scurvy:
i. Increased fragility of capillaries causing hemorrhages – under the skin (Fig. 11.9), periosteum, intestine, kidney etc. The gums show erosion of the mucous membrane at their margins and due to the increased fragility of the capillaries there is frequent bleeding (Fig 11.10).
ii. Malformations of bones and teeth. The osteoblasts remain functionless. Many of them are reverted to fibroblasts. There is irregular deposition of bone salts and decrease in the density of long bones. Teeth also show similar changes. The functions of the odontoblasts are impaired. New dentine is not formed and the tissue becomes spongy and porous.
iii. Increased brittleness of bones leading to fracture.
iv. Anaemia Number of red cells and platelets are reduced.
v. Delayed blood clotting and clot retractions.
vi. Skin eruptions
vii. Increased susceptibility to infections.
viii. Impaired healing of wounds
ix. Disturbance in carbohydrate metabolism.
x. Reproductive failure both in males and females.
A daily intake of about 100 mgm is adequate to maintain the normal plasma level. Recommended intake for children are 30 mgm to 80 mgm (adolescents), 75 mgm for adults, 100 mgm during pregnancy and 150 mgm during lactation. Large doses of vitamin C produce no observable ill effects in normal individuals.