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Vitamin A, Retinol, Carotenoids


Vitamin A, retinol

Biochemistry
carotenoids convert to vitamin A primarily in the intestinal mucosa
carotene -> retinol -> trans retinol -> cis retinol -> rhodopsin

Metabolism
most ingested retinol is stored in the liver

Function
retinol combines with opsin to form rhodopsin
retinoic acid is essential in the differentiation of bone cells
needed for differentiation of basal cells into mucus epithelial cells
maintains the integrety of mucus membranes
required by enamel forming epithelial cells to develop
involved in steroid hormone synthesis

Requirements
men - 5,000 iu, women - 4,000 iu
optimum - 15,000 iu retinol, 25,000 iu beta carotene


Deficiency
Etiology
intestinal malabsorption (as in sprue or after intestinal bypass surgery)
abnormal storage (liver disease)
enhanced destruction or excretion (proteinuria)

EENT
night blindness, dry eyes, keritinization, opacity of the cornea
Biots spots -> xerosis conjunctiva -> xeropthalmia
xerosis - dryness of the bulbar conjunctiva
Bitot's spots- small gray plaques with foamy surfaces
keratomalacia - ulceration and necrosis of the cornea
Immune
Vitamin A-deficient children appear to be particularly susceptible
to the complications of measles.


Vitamin A Toxicity
Children
drowsiness, fatigue, irritability, vomiting
Adults
bone pain, headaches, dry skin, brittle nails, alopecia
gingivitis, chelosis, hepatosplenomegaly, visual disturbances
Pregnancy
avoid during early pregnancy - may increase birth defects in large doses
(controversial, 10,000 iu qd, minimized with multi-vitamin)
Acute toxicity
abdominal pain, nausea, vomiting, papilledema
headache, dizziness, sluggishness
Chronic toxicity
after ingestion of 25,000 units or more daily for protracted periods
bone and joint pain, hyperostoses (hypertrophy of bone)
hair loss, dryness and fissures of the lips, pruritus
anorexia, weight loss
benign intracranial hypertension
low-grade fever and hepatosplenomegaly.

Therapeutics
EENT
night blindness, dry eyes, chalzion, macular degeneration
Dermatology
wound healing, prevention of sunburn, acne, psoriasis
seborrheic keratosis, ichthyosis, follicular hyperkeratosis
Gynecology
menorrhagia, cervical dysplasia
Immunology
lupus
measles - deficiency makes kids susceptible to the complications
Onclogy
cancer - retinoids are being used to treat skin cancer

 

 

 

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