| vitamin A | <biochemistry> Deficiency of this vitamin interferes with the production of rhodopsin in the eye resulting in night blindness and xerophthalmia. (27 Sep 1997) |
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| vitamin A1 | Vitamin A1alcohol; 2,6,6-trimethyl-1-(9'-hydroxy-3',7'-dimethylnona-1',3',5',7'-tetraenyl)cyclohex-1-ene;a half-carotene bearing the b (or beta-ionone) form of the cyclic end group and a CH2OH at the C-15 position (numbering as in carotenoids) or 9'-position (numbering as a nonyl side chain on a cyclohexene ring); an intermediate in the vision cycle, it also plays a role in growth and differentiation. See: dehydroretinol. Synonym: vitamin A1 alcohol, vitamin A1. Retinol dehydrogenase, an oxidoreductase catalyzing interconversion of retinal and NADH to retinol and NAD+. (05 Mar 2000) |
| vitamin A1 acid | <biochemistry> The aldehyde (retinal) has long been known to be involved in photoreception, but retinoic acid has other roles. There are cytoplasmic retinoic acid binding proteins and retinoic acid response elements that regulate gene transcription. Retinoic acid is thought to be a morphogen in chick limb bud development and in early development of the chick that probably accounts for its potent teratogenic action. Synonym: vitamin A. (03 Jul 1999) |
| vitamin A1 alcohol | Vitamin A1alcohol; 2,6,6-trimethyl-1-(9'-hydroxy-3',7'-dimethylnona-1',3',5',7'-tetraenyl)cyclohex-1-ene;a half-carotene bearing the b (or beta-ionone) form of the cyclic end group and a CH2OH at the C-15 position (numbering as in carotenoids) or 9'-position (numbering as a nonyl side chain on a cyclohexene ring); an intermediate in the vision cycle, it also plays a role in growth and differentiation. See: dehydroretinol. Synonym: vitamin A1 alcohol, vitamin A1. Retinol dehydrogenase, an oxidoreductase catalyzing interconversion of retinal and NADH to retinol and NAD+. (05 Mar 2000) |
| vitamin A2 | 3-Dehydroretinol;retinol with an additional double bond in the 3-4 position of the cyclohexane ring. Synonym: vitamin A2. (05 Mar 2000) |
| vitamin A2 aldehyde | 3-Dehydroretinaldehyde;dehydroretinol with -CHO instead of -CH2OH at the terminal carbon of the side chain. Synonym: retinene-2, vitamin A2 aldehyde. (05 Mar 2000) |
| vitamin A aldehyde | <chemical> A carotenoid constituent of visual pigments. It is the oxidised form of retinol which functions as the active component of the visual cycle. It is bound to the protein opsin forming the complex rhodopsin. When stimulated by visible light, the retinal component of the rhodopsin complex undergoes isomerization at the 11-position of the double bond to the cis-form; this is reversed in "dark" reactions to return to the native trans-configuration. Chemical name: Retinal (03 Jul 1999) |
| vitamin a deficiency | A nutritional condition produced by a deficiency of vitamin a in the diet, characterised by night blindness and other ocular manifestations such as dryness of the conjunctiva and later of the cornea (xerophthalmia). Vitamin a deficiency is a very common problem worldwide, particularly in developing countries as a consequence of famine or shortages of vitamin a-rich foods. In the united states it is found among the urban poor, the elderly, alcoholics, and patients with malabsorption. (12 Dec 1998) |
| vitamin A unit | The specific biologic activity of 0.3 ug of vitamin A (alcohol form). See: Sherman-Munsell unit. (05 Mar 2000) |
| vitamin B | A group of water-soluble substances originally considered as one vitamin. (05 Mar 2000) |
| vitamin B1 | <biochemistry> A member of the water-soluble B vitamin group, necessary for energy production and carbohydrate metabolism. Deficiency is known as beriberi. (27 Sep 1997) |
| vitamin B12 | <biochemistry> Member of the water soluble B vitamin group, important in the proper function of the nervous system and important in proper carbohydrate, protein and fat metabolism. (27 Sep 1997) |
| vitamin b 12 | <chemical> A cobalt-containing coordination compound produced by intestinal micro-organisms and found also in soil and water. Higher plants do not concentrate vitamin b 12 from the soil and so are a poor source of the substance as compared with animal tissues. Pharmacological action: haematinics. Chemical name: Vitamin B12 (12 Dec 1998) |
| vitamin B12 absorption test | <investigation> This test measures the amount of vitamin B12 in the urine after ingesting a dose of B12. This test evaluates vitamin B12 absorption. The cells in the stomach produce a substance known as intrinsic factor. This substance combines with B12 to allow absorption in the distal ileum. The patient is given a small dose of radioactive B12 which can then be detected in the patients urine. Pernicious anaemia is the clinical result of B12 deficiency. Conditions that can result in an abnormal Schilling test include: deficiency of intrinsic factor, malabsorption or the development of an antibody to intrinsic factor. The Schilling test can be performed with or without administration of intrinsic factor to determine what the underlying cause for pernicious anaemia. Laxative use, renal insufficiency and hypothyroidism can all interfere with the results of this test. (27 Sep 1997) |
| vitamin B12 deficiency | A form of anaemia (low red blood cell counts) that results when the bone marrow fails to produce adequate numbers of red blood cells due to a deficiency in vitamin B12. Intrinsic factor, necessary for normal B12 absorption, may be the underlying cause for B12 deficiency if is not produced in the gastric glands (in the stomach). (27 Sep 1997) |