Vit A

Question 1

three different forms of vit A

Answer 1

retinal, retinol and retinoic acid

the three forms are active in the body and each one performs specific roles.

Most cells have the ability to convert these forms of the vitamin.

Question 2

Sources of retinol in the Diet

Answer 2

liver & products
Kidney & offal products
Oily fish & cod liver oils
Eggs

Question 3

Sources of beta-carotene in the Diet

Answer 3

carrots
Red peppers
Spinach
Broccoli
tomatoes

Question 4

Functions of Vitamin A

Answer 4

retinol - transport, reproduction

retinyl esters - storage

retinal - Vision

retinoic acid - Epithelial differentiation, gene transcription, reproduction

Question 5

Functions of Vitamin A

Answer 5

Main function for vision.

Retinal is bonded to a protein in the eye called opsin and together form the rhodopsin molecule. Rhodopsin is found in the light sensitive cells of the eye called rods.

Rods are involved in the visual processes that occur in dim light and covey objects as black-and white images. Retinal needs to be supplied by the diet to support the synthesis of rhodopsin.

Question 6

The Regulation of Gene Expression by Retinoic Acid

Answer 6

Also involve with RXR: Retinoid receptor ; RAR: RA receptor and RARE: RA response Element

Increases expression of proteins involved in cellular differentiation and cell specilisation

Question 7

Intestinal metabolism of vitamin A

Answer 7

beta-Carotene break down by [dioxygenase]

• -> retinal with [reductase]
• -> Retinol with [ acyl-CoA:retinol acyltransferase (ARAT)]
• -> Retinyl ester

Question 8

vitamin A deficiency

Answer 8

Night-blindness (reversible by Vitamin A, temporary blindness) –> Permanent blindness (Xerophthalmia) –> death

eye becomes vulnerable to infections and lesions, followed by hardening (keratinization) and opacity of the cornea

• rare in the UK; the leading cause of non-accidental blindness worldwide
• major nutritional deficiencies in young children (aged 6 months to 6 years).
• More than 500,000 young children per year lose their sight due to vitamin deficiency and many die shortly thereafter from infectious diseases.

Question 9

vitamin A toxicity

Answer 9

Eczema –> fractures –> hepatoxicity –> death

Acute or chronic overdose of vitamin A during pregnancy, presents a teratogenic risk and interferes with normal development

Question 10

Signs of Vitamin A toxicity

Answer 10

~ Muscle and joint pains, headache
~ Erythema [skin]
~ [Mucous membranes] Conjunctivitis
~ Liver Dysfunction
~ Thinning and fracture of long bones
~ Secondary vitamin K deficiency