FAT SOLUBLE VITAMINS

They are soluble in fats and they are needed in bile salts for absorption.

Vitamin A- a fat soluble vitamin, exists in nature as such or in the provitamin form as carotene pigments. Carotene which usually exist in yellow, orange and green vegetables are converted into vitamin A in the intestinal wale. There exist several types of carotenes, none possessing vitamin A activity till converted to vitamin A. These carotenes include a, b and g carotenes. Out of these bcarotene has been found to be most effective precursor of vitamin whereas a and g forms are about half effective.

Vitamin A was isolated in 1931 and has been found to possess the following structure

Vitamin A1 represents one-half of the b-carotene molecule in which the 15-th oxidized to a primary alcohol.

Sources and absorption: vitamin A exists in the animal as well as plant tissues. The richest sources are cod liver oil, oil from liver of other fishes, liver tissue of animals, eggs, butter and cheese. Among the vegetable sources are carrots, yellow, orange, red vegetables and fruits (carrot, red pepper, apricot) and sweet potatoes. Vitamin A is absorbed from the intestine, and absorption is facilitated by bile salts. When provitamins are absorbed, these are converted in the wale of the intestine into vitamin A by most probably hydrolitic or oxidative pathway.

Conversion of provitamin A into vitamin A also occurs in the liver tissue. Each molecule of provitamin A results in the formation of two molecules and sometimes only one molecule of vitamin A. Bile-salts are although helpful in the absorption of vitamin A but are not necessary, whereas, in the case of provitamin A, presence of bile-salts is essential.

Carotene as well as vitamin A are stored in the liver for emergency purposes. In vitamin A deficiency, liver store is exhausted, and complete depletion of this vitamin leads to night blindness.

Retinol is reesterised and stored in liver. Retinol penetrates in cells, jointing with specific receptions.

Functions all forms of vitamin A – retinal, retinol, retinoic acids and their esthers have biological activity.

1. vision cycle retina, which is the innermost membrane of eye, bears [ ] rods and cones. The outer segments of rods and cones possess light sensitive pigments whose formation requires vitamin A . vitamin A is stored in the epithelial cells, surrounding the outer segments of rods and cones. In retina the cisretinol is oxidized in cis-retinal, which joints with opsin and forms chromoprotein rhodopsin (visual purple). The formation of rhodopsin occurs in the darkness. Under the action the light the rodopsin is converted to opsin and trans-retinal, during this process the light energy transforms in visual excitement – electrons, what leads to the beginning electric impulses in visual nerves. Than trans-retinal is reduced to trans-retinol which partially transfers irreversibly to retinoic acid and partially through cis-retinol to cis-retinal, which take part for resynthesis of rhodopsin

Rhodopsin is sensitive to light and upon exposure to light it changes from red to orange then to yellow and to colorless retinol. The eye becomes less sensitive to light upon bleaching of rhodopsin. Rhodopsin is regenerated in dark, consequently the vision sensitivity is restored. In deficiency of vitamin A the rate of recovery is delayed and the individual becomes night-blind.

If the light intensity is constant, the rate of regeneration of rhodopsin equals the rate of its bleaching. Rise in the intensity of light decreases rhodopsin concentration. The time taken in dark adaptation is time required for visualization of the objects when an individual comes from bright light to dim light corresponds to period reqyired for regeneration of rhodopsin. A lack of vA results in increased dark-blindness.

The cones are responsible for color perception. Until now three different cone pigments, all containing retinol have been identified. Deficiency of any one of these pigments or absence makes the individual color blind.

Hence, due to the loss of part of vitamin A (retinoic acid) the animal organism need to enter retinol all time with the food-stuffs.

2. vitamin A regulates the process of keratinazation (the horning of superficial layer of skin and mucosa). During this process the cylindrical epithelium transfers to many layers plane and, which is shelled out biosynthesis of keratin is nedeed in cystin, which is formed by pathway of oxidation cystein by special Cu-containing enzyme catalyses the oxidation of cystein, the retinol is inhibitor for this enzymes and hold the quantity of cystin on the determined level.

3. VA takes part in oxidation-reduction, it formes hydroperoxides, which increases of oxidation of other compounds.

4. VA regulates the normal growth and differentiation the young organism and quickly proliferation tissues, because it rises the level DNA in cells

5. Recent studies have also given clue about involvement of vitamin A in the biosynthesis of mucopolisaccharides, such as chondroitin sulfate. In the presence vA mucopolisaccharide biosynthesis is increased, because in the deficiency of vA the damage and dryness of skin are occured.

6. Retinol and retinal are very important for normal reproduction, because they increases the spermatogenesis at the men and stope the resorption of fetus at the women.

Deficiency symptoms. Deficiency of vitamin A is named kserophtalmicus. There are a dryness of eyes (because there is the keratinization of tear’s canals of mucosa, the tears do not moisten eyes, and their bacteridic action is stopped, because miomalation is occurred, ulcers of cornea and the scars (the wall of eye) are developed. Individual becomes blind. Night blindness is developed as a first symptom. There is keratinization of mucosa of respiratory ways, intestinal, bile gall and . These lead to the development of the chronical diseases of these organs and the appearance of the stones.

Requirement normal daily uptake of vA has been recommended to be 5000 I.U. or 1-1,5 mg of retinol, or 3—4,5mg of carotenes. Hypervitaminosis (more 8000 I.U.) is toxic. It may cause loss of appetite, weight loss, cracking and bleeding of the lips, loss of hair, liver enlargement, pain in bones and joints.

Cholecalciferrol, or vitamin D₃

Vitamins D are fat soluble and are known as antirachitic vitamins. There are 7 vitamers – D2-D9. All of these are derived of steroids, which are formed by solar irradiation. The 2 of the most important are vD2 and vD3

The biologic activity of 25 and 1,25dehydroxycholecalciferol are higher in 3 nad 5 times. The last derivative D3 has been identified as hormone, controlling Ca metabolism.

Sources and absorption the rich sources of vitamin D are cod-liver oil and other fish-liver oils. Other important sources are egg yolk and animal liver. Very little vitamin D is present in the milk. VD can be synthesized in the skin itself from 7-dehydrocholesterol by solar irradiation.

Function the primary function of vD is to regulate the absorption of calcium and phosphorous. In vitamin D deficiency (as in rickets) there occurs a substantial loss of calcium as well as phosphorous in the feces. No matter whether calcium and phosphorous are present in the diet substantially high amounts, normal ossification of the bones does not occur in the absence of vitamin D. Normal ossification occurs even in the presence of low amounts of dietary calcium and phosphorous when vitamin D is present. VD increases both active and passive transport of calcium through small intestine. The transport of phosphorous is also increased. V-s D act by stimulating a “protein carrier”, which is synthesized in the intestinal wall. This suggestion is based upon the fact, that inhibition of protein synthesis by inhibiting RNA synthesis results into loss of response of vD on calcium absorption.

The utilization of calcium in bone ossification to require citrate, which level is low during ricket.

Administration of vD to increase citrate level and to bring about normal ossification of the bones.

Deficiency deseases vD is known as antirachitic vitamin and its prolonged deficiency leads to rickets. In the growingchildren the disease is associated with bow-legs and enlarged joints. Ends of bones show incomplete ossification and irregular patches of phosphorus is decreased and the serum alkaline phosphatase value is increased. Rickets usually develop in infancy or early childhood. There occurs delay in dentition.

Another disease associated with vD deficiency is osteomalacia. In this disease the bones become softer than rickets. The softness of the bones results into deformities. The teeth are destroyed. Serum calcium is reduced that it may cause tetanus. Osteomalacia usually develops due to drainage of calcium by foetus during pregnancy and inadequate replenishment of the calcium and vD and partly due to that woman receives less exposure to sunlight and less vD biosynthesis.

Requirements In the growing children and during pregnancy 400 IU of vD are recommended (» 0,025 mg) besides the amount of vD what is synthesized under the influence of ultraviolet light. It should also be pointed out that smoke prevailing in the atmosphere or the filtration through glass make the sunlight almost useless to synthesize vD. Smoke and glass hinder propagation of ultraviolet light.

Since, vD is not readily excreted and can be stored in circulation for months, its excess is toxic. Toxicity is manifested by nausea, headache, digestive troubles, weakness, polyuria and anorexia. Kidney may get damaged. There might occur ossification of soft-tissues – kidney, liver, lungs, heart.

Vitamin Eare also fat-soluble and are stable to heat and acids. These are however destroyed by alkalis and ultraviolet rays. These vitamins exist in 2 forms, namely a-tocopherol and b-tocopherol (tocopherol denotes child birth bearing alcohol). These forms have been found to be chromane derivatives. Existence of g-tocopherol has also been confirmed and it has also been shown to be a chromane derivative.

Sources and absorption of E-vitamins The vitamins of this group are distributed widely in the plant as well as animal tissues. The rich sources are cotton seed oil, corn oil, oil of wheat germs and plants, green letuce and orange peels. All the green leaves, eggs, meat, butter do also contain these vitamins.

Absorption of E-group vitamins occurs through intestine which is further promoted by bile-salts. Presence of fats also helps in their absorption. Rancid fats destroy vitamin E. These vitamins are mainly stored in the adipose tissue.

Function of E-vitamin.

All tocopherols have different activity. If the potency of a-tocopherol is taken as 100, the relative potencies of b- and g-tocopherols come out to be nearly 25 and 19 respectively.