Page 239 - Concise Pathology for Exam Preparation ( PDFDrive )

224 SECTION I General Pathology

• Deficiency of niacin manifests as Pellagra (characterized by diarrhoea, dermatitis and
dementia), and is common in alcoholics, HIV patients and tryptophan malabsorption
(as is seen in Hartnup disease).

Q. Write briefly about pyridoxine deficiency.

Ans. Pyridoxine maintains sodium and potassium levels, promotes red blood cell produc-
tion, aids in decreasing the levels of homocysteine and may have a role in preventing
cardiovascular problems. Pyridoxine is precursor to pyridoxal phosphate, cofactor for
enzyme aromatic amino acid decarboxylase, which is involved in the following reactions:
- 5-Hydroxytryptophan Serotonin
- Levodopa Dopamine
• Sources of pyridoxine include milk, meat, egg yolk, fish, legumes and vegetables.
• The following predispose to pyridoxine deficiency:
• Pregnancy and infancy (due to increased demand)
• Alcoholism (acetaldehyde, an alcohol metabolite, induces rapid degeneration of
pyridoxine)
• Drug intake (isoniazid and oestrogen)
• Manifestations of pyridoxine deficiency include anaemia, nerve damage, seizures, skin
problems and oral ulcers.
Q. Write briefly about the role of diet in carcinogenesis.

Ans. The human diet is a highly complex and variable mixture of naturally occurring and
synthetic chemicals. The naturally occurring chemicals include macronutrients (fat, carbo-
hydrate and protein), micronutrients (vitamins and trace metals) and nonnutrient con-
stituents. Several carcinogens and anticarcinogens have been identified in the human diet.

Dietary Carcinogens
These are broadly classified into four categories:

1. Naturally present carcinogens: ‘Aflatoxin’, is an example of a naturally occurring di-
etary carcinogen. It is a mycotoxin produced by Aspergillus flavus, and is implicated in
the pathogenesis of hepatocellular carcinoma. Aflatoxicosis is caused by intake of grains
and nuts contaminated by the fungus.
2. Carcinogens forming during food preparation: Burnt or barbecued foods contain a
group of carcinogenic substances called polycyclic aromatic hydrocarbons, which are
produced if food is overheated. High intake of fried and broiled food, such as meats,
can increase the risk of breast, colon, prostate and pancreatic cancers.
3. Preservatives and colouring agents added to food: Artificial sweeteners (like sac-
charine and cyclamates) are known to cause bladder cancer. Cured, pickled or salty
foods contain nitrates, which have been implicated in gastric cancer.
4. Substances that are converted into carcinogens in the body: Sodium nitrite which
may be present in drinking water and vegetables gets converted to nitrosamine, which
is a carcinogen.

Cancer-Preventing Diets
• Fruits and vegetables in the diet are thought to lower the risk of cancer.
• Retinoic acid promotes differentiation of mucous-secreting epithelial cells; therefore,
diets containing b-carotene and retinoic acid can reverse metaplastic and precancerous
lesions of the respiratory tract.
• High fibre content with low animal fat content in the diet prevents colonic carcinoma
(high fat and low fibre content means high level of bile salts and acids in intestine, leading
to increased levels of free radicals and carcinogenic byproducts of bile acid metabolism).
• Folic acid, selenium, b-carotene, vitamin C and vitamin E are thought to prevent free
radical damage to cell and its DNA; thus, preventing ‘cancer initiation’. Vitamin A

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