Tuesday, November 13, 2012


Q. What is the pro-Vitamin for Vitamin A?
A. Beta carotene present in plants.

Q. What is the major function of Vitamin A?
A. In vision, as the Wald's visual cycle.

Q. What causes the nerve impulse in retina?
A. Photo-isomerisation of 11-cis retinal to all trans- retinal.

Q. How is all trans-retinal regenerated?  
A. Trans-retinal is taken to liver, where it is made to trans-retinol, then isomerised to cis-retinol and then to cis retinal.

Q. What are the enzymes required for this regeneration?                                                           
A. Alcohol dehydrogenase and retinol isomerase.

Q. What are other minor biological roles of Vitamin A?                                                               
A. Normal  maintenance of epithelium  and skin, glycoprotein   synthesis, reproduction,   cell differentiation, and anti-oxidant role.

Q. What are the sources of Vitamin A?    
A. Carrot, mangoes, papaya, green leafy vegetables, and fish liver oil.

Q. What  are the  deficiency  manifestations of Vitamin A?                                               
A. Night  blindness, xerophthalmia,  keratomalacia, and keratinisation of epithelium.

Q. Nyctalopia is due to the deficiency  of  which Vitamin?                                               
A. Vitamin A.

Q. What is the daily requirement of Vitamin A?
A. 750 to 1000 microgram.

Q. How cholecalciferol is synthesised?   
A. From 7-dehydro cholesterol in the malpighian layer of epidermis, by the action of ultra violet rays.

Q. How Vitamin D is activated?                
A. Cholecalciferol from skin reaches liver. There it is hydroxylated to form 25-hydroxy cholecalciferol (25-HCC). It then reaches kidney, where further hydroxylation takes place to form 1,25-dihydroxy cholecalciferol (DHCC).

Q. What is calcitriol?                                      
A. 1,25-dihydroxy cholecalciferol, or active Vitamin  D, contains three hydroxyl  groups at 1, 3 and 25 positions. So it is called calcitriol.

Q. Which Vitamin acts as a pro-hormone?
A. Vitamin D.

Q. What is the function of Vitamin D?    
A. It increases absorption of calcium from intestine, and it also increases mineralisation of bone.

Q. How Vitamin D increases absorption of calcium?
A. Calcitriol  binds to a cytoplasmic receptor. The hormone-receptor complex interacts with  DNA  and causes  transcription  of specific genes that code  for  calbindin.  Due  to  the  increased availability of  calcium  binding  protein,  the absorption of calcium is increased.

Q. How is Vitamin D deficiency manifested?
A. Rickets in children and osteomalacia in adults.

Q. In  renal disease, oral doses of Vitamin D may not be effective, why?                            
A. Hydroxylation and activation of Vitamin is taking place in kidney.

Q. What are the causes of rickets?             
A. Chronic renal failure, liver  diseases, and under- exposure to sunlight.

Q. What is the daily requirement of Vitamin D?
A. 5-10 microgram.

Q. What is the chemical nature of Vitamin E?
A. Alpha tocopherol.

Q. What is the function of Vitamin E ?     
A. Anti-oxidant.

Q. What is the relationship of selenium with Vita- min E?                                                        
A. They act synergistically as anti-oxidants.

Q. What is the source of Vitamin E?        
A. Vegetable oils are rich sources of Vitamin  E, e.g. wheat germ oil, sunflower oil, safflower oil, cotton seed oil, and palm oil.

Q. What is the normal daily requirement of Vitamin E?                                                               
A. 15 mg or 33 international units.

Q. What is the chemical nature of Vitamin K?
A. Naphthoquinone  derivative.

Q. What is menadione?                               
A. It is synthetic water soluble Vitamin  K, widely  used in clinical practice.

Q. What is the function of Vitamin K?    
A. Gamma carboxylation of clotting factors such as prothrombin.

Q. Deficiency of  Vitamin K  can occur in  which conditions?                                               
A. Obstructive  jaundice, antibiotic  therapy,  and administration of dicoumarol.

Q. What is the mechanism of action of dicoumarol?
A. It  competitively  inhibits  Vitamin  K  epoxide reductase.

Q. So, dicoumarol  is used for what purpose?
A. To prevent intravascular thrombosis.

Q. Excess dicoumarol will produce what?
A. Bleeding tendency.

Q. Which substance will inhibit Vitamin K?
A. Dicoumarol.

Q. Excess dose of Vitamin K in neonates may lead to which condition?
A. Hemolysis and jaundice.                        

Q. Bleeding tendency is common in the deficiency  of which?                                                  
A. Vitamin  K, Vitamin  C, and platelets.

------------------------------------------ Best Wishes: Dr.Ehab Aboueladab, Tel:01007834123 Email:ehab10f@gmail.com,ehababoueladab@yahoo.com ------------------------------------------
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