Page 234 - Concise Pathology for Exam Preparation ( PDFDrive )

9 Environmental and Nutritional Pathology 219

Q. Enlist the manifestations of vitamin A deficiency.

Ans. Manifestations of vitamin A deficiency
• First symptom of vitamin A deficiency is decreased night vision (vision in dim light).
• Ocular changes due to vitamin A deficiency are collectively known as xerophthalmia (dry eye).
• First change is dryness of the conjunctivae, wherein, normal lacrimal and mucous-secreting
epithelium is replaced by keratinized epithelium.
• This is followed by accumulation of keratin debris as small opaque plaques called Bitot
spots. There is erosion of surface of cornea, inducing formation of corneal ulcers, which
may later lead to softening and destruction of cornea (keratomalacia) and blindness.
• The epithelium lining upper respiratory passage and urinary tract is replaced by keratin-
ized squamous epithelium (squamous metaplasia).
• Loss of mucociliary apparatus predisposes to secondary bacterial infections.
• Desquamation of keratinous debris in the urinary tract leads to renal and urinary
bladder stones.
• Hyperplasia and hyperkeratinization of epidermis results in plugging of ducts of adnexal
glands producing follicular or papular dermatosis.

Q. Write briefly about the metabolism of vitamin D.
Ans. Vitamin D is necessary for the formation, growth and repair of bones. It also enhances
immune function and improves muscle strength. Requirement for vitamin D increases as
people age. It is stored mainly in the liver.

Forms of Vitamin D
The following are the two forms of vitamin D important for nutrition:
1. Vitamin D 2 (ergocalciferol): This form is synthesized from plants and yeast precur-
sors. It is also the form used in very high dose supplements.
2. Vitamin D 3 (cholecalciferol): This form is the most active form of vitamin D. It is formed
in the skin when the skin is exposed to direct sunlight. The most common food source is
fortified foods, mainly cereals and dairy products. Vitamin D 3 is also present in fish liver
oils. Human breast milk contains only small amounts of vitamin D 3 .
Vitamin D 2 and D 3 are not active in the body. Both forms must be metabolized by the liver
and kidneys into an active form called calcitriol (Flowchart 9.2).

Absorption from UV irradiation of
dietary sources 7-dehydrocholesterol
(small intestine) (in skin)
Transported via
chylomicrons and UVB radiation
lymphatic system

Vitamin D 3 or cholecalciferol (in the blood)
25 hydroxylase (in the liver)
25-hydroxycholecalciferol
α-1-hydroxylase (in the kidney)
1, 25-dihydroxycholecalciferol

Increases calcium and phosphorus absorption

Normal serum levels of calcium and phosphorus and
bone mineralization maintained
FLOWCHART 9.2. Metabolism of vitamin D.

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