Medical brain notes 25

  VITAMINS Introduction The vitamins are a group of complex organic compounds required in small quantities by the body for the maintenance of good health. They are not normally synthesized in the body and hence they should be supplied by the diet. The vitamins are present in foods in small quantities. Unlike other groups of nutrients the vitamins are not chemically similar to each other. Each vitamin has a specific chemical structure and a specific function or functions in the living system. Most of the vitamins act as coenzymes in the body. Normally a well balanced diet will supply all the necessary vitamins in sufficient quantity.

  Classification Vitamins are generally classified into two main groups. (i) fat soluble vitamins (ii) water soluble vitamins. 1. Fat soluble vitamins The members of this group are A,D,E and K. All these vitamins are not soluble in water and readily soluble in fat dissolving organic solvents. Inside the body for their transport and metabolism they need the presence of fats.   i. Vitamin - A Vitamin A is found only in foods of animal origin. It is present in almost all species of fish, birds and mammals. The yellow plant pigments  α ,  β  and γ carotenes and cryptoxanthin are precursors of vitamin A. The body has the ability to convert these carotenoid compounds present in the diet into vitamin A. The chemical structure of  β  - carotene is such that it oxidizes to form two molecules of vitamin A, the other provitamins form only one.  b -carotene is more efficiently converted to vitamin A than  α  - or γ - carotene or cryptoxanthin. There...

  Classification Vitamins are generally classified into two main groups. (i) fat soluble vitamins (ii) water soluble vitamins. 2. Water soluble vitamins The members of this group are B complex vitamins and vitamin C. They are readily soluble in water. B Complex vitamins i. Thiamine (B 1 ) The structure of vitamin B 1  is given in Fig. 8.5. Functions Thiamine act as a coenzyme in the form of thiamine pyrophosphate in many enzyme systems. These are involved principally in the breakdown of glucose to yield energy. Thiamine also aids in the formation of ribose, a sugar that is an essential constituent of DNA and RNA, the carriers of the genetic code. The adequate level of thiamine provides healthy nerves, a good mental outlook, a normal appetite and food digestion. Sources Meats, especially pork and liver are rich in thiamine and account for about one fourth of the average intake. Dry beans, peanuts and egg are good sources. Whole grain breads and cereals supply about one third of...