Page 269 - Textbook of Pathology, 6th Edition

Riboflavin (Vitamin B ) 3. Dementia: Degeneration of neurons of the brain and of 253
2
spinal tract results in neurological symptoms such as
PHYSIOLOGY. Riboflavin used to be called ‘yellow dementia, peripheral neuritis, ataxia and visual and auditory
respiratory enzyme’ (flavus = yellow), now known as disturbances.
‘cytochrome oxidase enzyme’ which is important in view of
its role as cellular respiratory coenzyme. The vitamin is TOXICITY OF NIACIN. Toxicity due to administration of
usually distributed in plant and animal foods such as the high doses of niacin as therapy for dyslipidaemia has been CHAPTER 9
liver, beaf, mutton, pork, eggs, milk and green vegetables. observed but not due dietary excess. It is characterised by
Like other water-soluble vitamins, it is rapidly absorbed from flushing of skin and liver derangement.
the bowel and stored in tissues like liver.
Pyridoxine (Vitamin B )
LESIONS IN RIBOFLAVIN DEFICIENCY. Lesions due to 6
primary or conditioned deficiency of riboflavin (aribo- PHYSIOLOGY. Pyridoxine or vitamin B is widely
6
flavinosis) are as follows: distributed in all animal and plant foods such as meat, liver,
1. Ocular lesions consist of vascularisation of normally eggs, green vegetables and whole grain cereals. Pyridoxine
avascular cornea due to proliferation of capillaries from exists in 3 closely related naturally-occurring substances—
limbus. Subsequently, conjunctivitis, interstitial keratitis and pyridoxine, pyridoxal and pyridoxamine. All of these can be
corneal ulcers may develop. converted into biologically active coenzyme, pyridoxal 5-
2. Cheilosis and angular stomatitis are characterised by phosphate.
occurrence of fissures and cracks at the angles of mouth. The major physiologic functions of pyridoxine are
3. Glossitis is development of red, cyanosed and shiny related to:
tongue due to atrophy of mucosa of tongue (‘bald tongue’). fat metabolism; Environmental and Nutritional Diseases
4 Skin changes appear in the form of scaly dermatitis protein metabolism;
resembling seborrheic dermatitis on nasolabial folds on the amino acid metabolism such as decarboxylation of amino
face, scrotum and vulva. acids, transmethylation of methionine, conversion of trypto-
5. Anaemia may develop in some cases. phan to niacin;
steroid metabolism;
Niacin/Nicotinic Acid (Vitamin B ) neurotransmitter synthesis; and
3
haem synthesis.
PHYSIOLOGY. As with thiamine and riboflavin, niacin or
nicotinic acid or vitamin B is also widely distributed in plant LESIONS IN PYRIDOXINE DEFICIENCY. Vitamin B 6
3
and animal foods such as the liver, kidney, meat, green deficiency may result from inadequate dietary intake or may
vegetables and whole grain cereals. Niacin includes result from secondary deficiency such as increased demand
biologically active derivative nicotinamide which is essential in pregnancy and lactation, chronic alcoholism and intake
for the formation of 2 oxidative coenzymes (dehydrogenases): of certain drugs (e.g. isoniazid in the treatment of
NAD (nicotinamide adenine dinucleotide) which is requi- tuberculosis, penicillamine, oestrogen in oral contraceptives
red for dehydrogenation in the metabolism of fat, carbo- etc).
hydrates and proteins. The lesions of pyridoxine deficiency include the
NADP (nicotinamide adenine dinucleotide phosphate) following:
which is essential for dehydrogenation in the hexose 1. Convulsions in infants born to mothers who had been
monophosphate shunt of glucose metabolism. administered large doses of vitamin B for hyperemesis
6
LESIONS IN NIACIN DEFICIENCY. Deficiency of niacin gravidarum (pyridoxine dependence)
causes pellagra, so named because of the rough skin of such 2. Dermatitis and seborrhoea
patients (Italian pelle agra = rough skin). Pellagra may result 3. Cheilosis and angular stomatitis
from dietary deficiency in those who largely subsist on maize 4. Glossitis (bald tongue)
since niacin in maize is present in bound form and hence not 5. Neuropathy
absorbable. Since niacin can be endogenously synthesised 6. Depression, confusion
from tryptophan, a diet deficient in this amino acid or 7. Sideroblastic anaemia.
disorders of tryptophan metabolism such as in carcinoid
syndrome or Hartnup syndrome results in niacin deficiency. Folate (Folic Acid) and Cyanocobalamin (Vitamin B )
12
Lesions in pellagra are characterised by 3Ds: Both these vitamins included in the B complex group are
1 Dermatitis: The sun-exposed areas of skin develop required for red cell formation. Their deficiency leads to
erythema resembling sunburn. This may progress to chronic megaloblastic anaemia which is discussed in Chapter 12.
type of dermatitis with blister formation.
2. Diarrhoea: Lesions similar to those seen in skin may
develop in mucous membrane of the alimentary tract resul- Biotin
ting in glossitis, lesions in the mouth, oesophagus, stomach PHYSIOLOGY. Biotin is a water-soluble vitamin and a
and colon and cause diarrhoea, nausea, vomiting and member of vitamin B complex group. It is available in food
burning sensation. sources such as organ meat, soya beans, egg yolk; however