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Question 1

Vitamins: Definition

Answer 1

organic compounds occurring in natural foods either as such or as utilizable precursors, that are required in minute amounts for normal growth and health.
• They do not enter into tissue structures, unlike proteins.
• Do not undergo degradation for providing energy unlike CHO & lipids.
• Several B complex vitamins play an important role as coenzymes
differ from hormones: not being produced within the organism,

Question 2

Differences Between Water & Fat SolubleVitamins

Answer 2

Absorption :Directly into the blood.
Transport Travel freely.
Storage :Not Generally.
Excretion: Kidney detect & excrete excess in urine. Possible to reach toxic levels if consumed from Needed in frequent doses (may 1 to 3 days).
Defeciency :manifested rapidly as there is no stores

Fat-Soluble Vitamins :

Absorption
First into the lymph then the blood.( they need bile lipids for absorption)
Many require protein carriers.
Excretion: Less readily excreted; tend to remain in fat-storage sites.
Possible to reach toxic levels if consumed from Toxicity supplements.
Needed in periodic doses (may weeks or even months).
Defeciency :manifested only when stores are depleted

Question 3

Causes of Hypovitaminosis

Answer 3

 Inadequate intake.  Irregular absorption.  Impaired metabolic use.  Increased requirements

Question 4

Causes of Hypervitaminosis

Answer 4

 Long-term accumulation in the body.  Short-term administration of high dose particularly with fat-soluble
vitamins like A & D.

Question 5

…………..,…………..are important naturally occurring
antioxidants.

Answer 5

Beta-carotenes & vitamin E

Question 6

Structure of Vitamin A:
Three important forms of vitamin A:

Answer 6

1. Retinol: primary alcohol containing
   β-ionone ring with an unsaturated
   side chain. It’s found in animal
   tissues as retinol ester (with long-
   chain FA).
2. Retinal: The aldehyde derived from
   the oxidation of retinol.
3. Retinoic acid: The acid derived
   from the oxidation of retinal.

Question 7

Vitamin A can be obtained from
certain carotenoids which are
called

Answer 7

provitamins A. They are α,
β and γ-carotenes.

Two molecules of vitamin A are formed by oxidative split of β-
carotene while only one molecule is obtained from α & γ carotenes.

Question 8

Forms of vitamin A:

Answer 8

Vitamin A1 has 1 double in β-ionone ring while
vitamin A2 has 2 double bounds.

The usual form vitamin A1 predominates and is found predominantly in major species of animal, except in fresh water fish which contain vitamin A2.

Vitamin A1 is more potent in its activity than vitamin A2 and can be obtained from carotenes, while vitamin A2 can not.

Question 9

Transport of Vitamin A:

Answer 9

1. Transport to the liver:
   • Retinol esters in diet by hydroxylation → Retinol + Free Fatty Acids.

• β-carotenes by oxidation → 2 Retinal, then reduced by the enzyme retinene reductase in presence of NADH+H+ → 2 Retinol.

In intestinal epithelia, retinol is esterified with FAs to form retinyl esters
which are then taken up by chylomicrons via lymphatic system then to
the blood stream to the liver.

Question 10

Storage of Vitamin A:

Answer 10

in the liver as retinyl esters (retinyl palmitate).

Released from the liver as retinol and is carried by plasma retinol-
binding protein (RBP) to the target tissues.

Question 11

Mechanism of Action of Vitamin A:

Answer 11

Retinoic acid receptor complex binds to
response elements on DNA → resulting
in control of the production of specific
proteins that mediate several physiologic
functions.

Question 12

Vitamin A-protein complex, retinol-RBP, is distributed to the various
tissues, particularly …….,……,….. & binds to specific sites
on the cell membrane, so it acts as a ……………

Answer 12

intestine, liver & eyes

hormone

Question 13

Vitamin A plays a role in:

Answer 13

1. Night Vision.
2. Reproduction.
3. Maintains integrity of cornea, epithelial cells, skin & mucous
   membrane.
4. Bone and tooth growth
5. Immunity
6. Antioxidant effect of beta-carotene

Question 14

• Retinol and retinal are essential for normal reproduction They support

Answer 14

support spermatogenesis in males and prevent fetal resorption
in the females.

Question 15

Vitamin A & the visual cycle:

Answer 15

In the retina of the eye there are photoreceptor celled rod cells &
cone cells that contain light-sensitive proteins, called OPSINS.
• In rod cells , 11-cis retinal and the opsin protein form rhodopsin,
which is used in night vision.

Question 16

Vitamin A RDA is….

Prolonged intake of vitamin A supplement →

Answer 16

 RDA is 3 mg/day. Amounts exceeding 7.5 mg/day of retinol should be avoided.

Vit A is teratogenic in large amounts.

Prolonged intake of vitamin A supplement → ↑LDL/HDL ratio →↑risk of CHD.

Question 17

Acute hypervitaminosis A:

Answer 17

drowsiness, anorexia, headache & vomiting.

Question 18

Chronic toxicity: Vitamin A

Answer 18

scaly skin (flakes), hair loss, brittle nails &
hepatosplenomegaly.

Question 19

Vitamin A deficiency Leads to:

Answer 19

1. Night blindness: may progress to xerophthalmia
2. Other symptoms like skin changes due to hyper-keratosis.

Question 20

Causes of vitamin A deficiency:

Answer 20

 Alcohol consumption.
 Fat-malabsorption diseases like biliary tract and pancreatic diseases & hepatic cirrhosis.