Vitamin vision

The lipidic vitamins (ref.84) include vitamin A (32), a substance intrinsic to the physiology of vision, vitamin E (83), a natural protective antioxidant, and vitamins K, (84) with Kj (85), antihemorrhagic compounds, each of which is derivable from an initial natural product intermediate. Although traditionally a -ionone obtained from citral (a major constituent of lemon grass oil) was used for the synthesis of vitamin A, a synthetic source has now replaced this in a process which also gives /g-carotene. In one method the Cl4 aldehyde in that process is reacted with a C6 eneyne component and selective hydrogenation followed by dehydration and isomerisation affords the final product (ref.85). 

Vitamin A also must be obtained in food, especially yellow vegetables. It has many functions in the body, and is essential for good vision. Vitamin A is also needed for the respiratory tract, skin, and for normal growth of bones. Fortunately, vitamin A is fairly abundant in foods. 

Vitamin A is necessary for hearing but not for vision Vitamin A is synthesized in skin... 

See also G Proteins in Vision, Vitamin A, Chemistry of Photo reception... 

Early nutritional studies divided vitamins into two classes water-soluble vitamins and water-insoluble vitamins (Table 25.1). Vitamins A, D, E, and K are water insoluble. Vitamin K is the only water-insoluble vitamin currently known to function as a coenzyme. Vitamin A is required for proper vision, vitamin D regulates calcium and phosphate metabolism, and vitamin E is an antioxidant. Because they do not function as coenzymes, vitamins A, D, and E are not discussed in this chapter. Vitamins A and E are discussed in Sections 9.8 and 26.7, and vitamin D is discussed in Section 29.6. 

Vitamin A plays a crucial role in vision. Vitamin D is necessary for bone integrity because of its role in calcium and phosphorus metabolism. Vitamin E is an important antioxidant, and vitamin K plays a role in blood clotting. 

Photobiology is a discipline separated, if strongly connected, with photochemistiy. Extending the discussion to that topic would go beyond the proposal and the space available. Attention to this issue will thus be limited to a very cursory glance to the historic development of four major topics, chlorophyll photosynthesis, vision, vitamin D and photomedicine, in order to have at least a rough comparison with photochemistry along the time coordinate. 

Upon presenting the Nobel Prize to Karrer, Wilhelm Palmaer, chair of the prize committee at the time, described him as a scientist with the ability to visualize great and important problems as well as their smaller parts and one who in his own unique way approached problems and pursued new ideas by using his own methods [61] . Karrer s methodology has borne much fruit over the decades. The spinoffs from his work on the carotenoids and xanthophylls is still evolving today intense research on vision, vitamins, hormones, metabolic pathways, and enzymes. 

Two molecules of vitamin A are formed from one molecule of -carotene. Vitamin A crystallizes in pale yellow needles m.p. 64 C. It is optically inactive. It is unstable in solution when heated in air, but comparatively stable without aeration. Vitamin A is manufactured by extraction from fish-liver oils and by synthesis from / -ionone. The role of vitamin A in vision seems to be different from its systemic function. See also relincne and rhodopsin. 

Carotenoids absorb visible light (Section 13 21) and dissipate its energy as heat thereby protecting the organism from any potentially harmful effects associated with sunlight induced photochemistry They are also indirectly involved m the chemistry of vision owing to the fact that p carotene is the biosynthetic precursor of vitamin A also known as retinol a key substance m the visual process... 

Vitamins A, D, and E are required by mminants and, therefore, their supplementation is sometimes necessary. Vitamin A [68-26-8] is important in maintaining proper vision, maintenance and growth of squamous epitheHal ceUs, and bone growth (23). Vitamin D [1406-16-2] is most important for maintaining proper calcium absorption from the small intestine. It also aids in mobilizing calcium from bones and in optimizing absorption of phosphoms from the small intestine (23). Supplementation of vitamins A and D at their minimum daily requirement is recommended because feedstuffs are highly variable in their content of these vitamins. 

Conjugation is crucial not only for the colors we see in organic molecules but also for the light-sensitive molecules on which our visual system is based. The key substance for vision is dietary /3-carotene, which is converted to vitamin A by enzymes in the liver, oxidized to an aldehyde called 11-frans-retinal, and then isomerized by a change in geometry of the C11-C12 double bond to produce 11-cis-retinal. 

Vitamin A (retinol) and its naturally occurring and synthetic derivatives, collectively referred to as retinoids (chemical structure), exert a wide variety of profound effects in apoptosis, embryogenesis, reproduction, vision, and regulation of inflammation, growth, and differentiation of normal and neoplastic cells in vertebrates. 

Viking Lander, 355 vinyl chloride, 764 virial coefficient, 168 virial equation, 168 viscosity, 186 visible light, 4, 6 vision, 113 vitamin, 74 vitamin C, F48 volatile, 310 volt, 492, A4 Volta, A., 483 voltage, 490 voltaic cell, 490 voltaic pile, 483... 

Vitamin A (retinol), present in carnivorous diets, and the provitamin (P-carotene), found in plants, form retinaldehyde, utilized in vision, and retinoic acid, which acts in the control of gene expression. Vitamin D is a steroid prohormone yielding the active hormone derivative calcitriol, which regulates calcium and phosphate metaboUsm. Vitamin D deficiency leads to rickets and osteomalacia. 

Alkenes with many double bonds in a row are colored. Some plant pigments are alkenes of this kind. One example is )S-carotene, which gives carrots their distinctive orange color. Animals break down )S-carotene into vitamin A, which is essential for vision. Xanthin molecules, relatives of j6-carotene that contain oxygen atoms, occur in com, orange juice, and shellfish. The xanthin below makes the flamingo pink. 

Vitamin A is essential throughout life, including foetal development, but perhaps its most well researched role is that in vision where 11 -cis retinaldehyde is the initial part of the photoreceptor complex in rods and cones. Retinoic acid induces differentiation in epithelial cells and deficiency leads to... 

Vitamin A (retinol) and retinoic acid are carotenoid oxidation compounds that are very important for human health. The main functions of retinoids relate to vision and cellular differentiation. With the exception of retinoids, it was only about 10 years ago that other carotenoid oxidation products were first thought to possibly exert biological effects in humans and were implicated in the prevention - or promotion of degenerative diseases. A review on this subject was recently published. ... 

AREDS Research Group (2001). A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, 3-carotene, and zinc for age-related macular degeneration and vision loss, AREDS Report No. 8. Arch. Ophthalmol. 119(10) 1417-1436. 

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