Page 270 - Textbook of Pathology, 6th Edition

254 egg-white has a protein avidin which binds to biotin and LESIONS IN BIOTIN DEFICIENCY. Flavonoids have been
blocks its bioavailability. a recent addition to the family of vitamins. Present data on
The major physiologic functions of biotin are as under: animal experiments and human clinical studies indicates that
1. In gene expression they play a role in prevention of neurodegenerative diseases,
2. In gluconeogenesis osteoporosis and diabetes.
3. In fatty acid synthesis
4. In catabolism of certain amino acids such as leucine METALS AND TRACE ELEMENTS
4. As carrier of CO in carboxylase enzymes.
2
SECTION I
LESIONS IN BIOTIN DEFICIENCY. Biotin deficiency is Several minerals in trace amounts are essential for health
rare and develops due to inborn errors of metabolism and in since they form components of enzymes and cofactors for
patients on parenteral nutrients devoid of biotin. The lesions metabolic functions. Besides calcium and phosphorus required
of biotin deficiency are as under: for vitamin D manufacture, others include: iron, copper, iodine,
1. Mental and neurologic symptoms such as hallucination, zinc, selenium, manganese, nickel, chromium, molybdenum,
depression, paraesthesia fluorine. However, out of these, the dietary deficiency of first
2. Anorexia five trace elements is associated with deficiency states which
3. Nausea are discussed in detail in respective chapters later. These are
4. Scaly, seborrhoeic dermatitis as under:
5. In infants, hypotonia, alopecia and rash near ears. i) Iron: Microcytic hypochromic anaemia.
ii) Calcium: reduced bone mass, osteoporosis.
In concluding the discussion of vitamin B complex, it
must be mentioned that many of the animal and plant foods iii) Phosphorous: Rickets, osteomalacia.
contain vitamin B complex group of vitamins. Their iv) Copper: Muscle weakness, neurologic defect, anaemia,
deficiency, whether primary from poverty, ignorance etc, or growth retardation.
secondary from conditioning factors like chronic alcoholism, v) Iodine: Goitre and hyperthyroidism, cretinism.
is more frequently multiple vitamin deficiency. Hence, the vi) Zinc: Growth retardation, infertility, alopecia.
clinical practice is to administer combination of these vii) Selenium: Cardiomyopathy, muscle degeneration.
members of vitamin B complex.
viii) Fluoride: Dental caries.
ix) Manganese: Impaired growth and skeletal development.
CHOLINE
x) Molybdenum: Severe neurological abnormalities.
General Pathology and Basic Techniques
PHYSIOLOGY. Choline is precursor form of acetylcoline and
betaine. Choline is widely distributed as lecithin in foods such DIET AND CANCER
as egg yolk, milk, wheat and organ meat. Choline is also
synthesised in the liver. Before closing the discussion of nutritional pathology, it is
The major physiologic functions of choline are as under: worthwhile to sum up relationship of these factors to
1. In maintenance structural integrity of cell membranes carcinogenesis discussed in previoius chapter. There are three
2. In transmembrane signaling pathways possible mechanisms on which the story of this relationship
3. In cholinergic neurotransmission can be built up:
4. In metabolism of lipids and cholesterol.
1. Dietary content of exogenous carcinogens:
LESIONS IN CHOLINE DEFICIENCY. Choline deficiency i) The most important example in this mechanism comes
develops in patients on choline-free parenteral nutrients. The from naturally-occurring carcinogen aflatoxin which is
lesions of choline deficiency are as under: strongly associated with high incidence of hepatocellular
1. Fatty liver with deranged liver enzymes carcinoma in those consuming grain contaminated with
2. Skeletal muscle damage with elevated CPK levels. mould, Aspergillus flavus.
ii) Artificial sweeteners (e.g. saccharine cyclomates), food
FLAVONOIDS additives and pesticide contamination of food are implicated
as carcinogens derived from diet.
PHYSIOLOGY. Flavoonoids are a form of polyphenols
present in several fruits and vegetables and are the 2. Endogenous synthesis of carcinogens or promoters:
constituents which imparts colour, flavour and taste to these i) In the context of etiology of gastric carcinoma, nitrites,
edible products. Particular food and vegetables rich in nitrates and amines from the digested food are trans-
flavonoids are berries, grapes, apples, broccoli, onions, formed in the body to carcinogens—nitrosamines and
legumes etc. nitrosamides.
The major physiologic functions of flavonoids are as ii) In the etiology of colon cancer, low fibre intake and high
under: animal-derived fats are implicated. High fat diet results in
1. As antioxidants rise in the level of bile acids and their intermediate
2. In cell signaling pathways metabolites produced by intestinal bacteria which act as