Normally less than 10%
of iron in the diet is absorbed and generally the 15-20 mg of total iron in
Western diets is sufficient to meet adult requirements. Inorganic and haem iron arc chiefly absorbed in the upper
jejunum and duodenum, where luminal conditions, including the influence of gastric secretions and acid, facilitate
bioavailability. Many components of
the diet influence absorption by formation of soluble or insoluble complexes or
iron and by actions on the oxidation state of elemental iron.
Cyanocobalamin is readily converted into
the coenzyme forms which as methylcobal-amin, is converted with conversion of homocysteinc to methionine,
and, as deoxyadenosy-lcobalamin in
conversion of methylmalonyl - CoA to succinyl - CoA. The active coenzymes,
enzymes, methyl - cobalamin and 5 - deoxyodenosylcobalamin, arc essential for cell growth and replication. In man, failure
of this pathway due to cobalamin deficiency leads to a megaloblastic
anaemia and to a neuropathy.
In thiamine
deficiency, the hexose monophosphate pathway of glucose oxidation is retarded at the level of the transkctolase,
so pentose sugars accumulate to levels three times the normal.
The requirement for
riboflavin depends on the carbohydrate intake and is increased during pregnancy, lactation and in woman taking
oral contraceptive agents. Riboflavin requirement is also increased by prolonged administration of drugs such as
phenothiazines. Riboflavin reduces the antibacterial activity of solutions of
streptomycin, erythromycin, tyrothriein, carbomycin and fetracyline, in the
case of tetraeyelines, the reaction is a photochemical oxidation. Inactivation
also occurs with chloramphenicol, penicillin or ncomycin. |
Back 
