Topic B3

Question 1

Biochemical role of vitamin A

Answer 1

1. Maintainance of epithelial cell
2. Mucoprotein synhtesis
3. Chondritin sulphate synthesis
4. Synthesis of male/female steroid hormone
   
   • Pregnenolone → progesteron
5. Visual cycle
   
   • Retinoic acid can not subsitute for retinol and retinal in the visual processes
   • 11 cis retinal + opsin + rhodopsine → retina (rod) → visual function (night vision)
6. Antioxidant
   
   • Double bonds

Question 2

Deficiency

General

Answer 2

• Vitamin A has an overall effect on cellular growth and will therefor affect:
  
  • Growth
  • Development of bone
  • Reproduction
  • Vision
• Lack of vitamin A leads to lack of apetide due to keratinization of taste buds

Question 3

Deficiency

Maintainance of epithelial cells

Answer 3

• Xeropthalmia
  
  • ​Dryness of cornea and conjuctiva
  • Abnormal keratinization of GI and airways

Question 4

Deficiency

Mucoprotein synthesis

Answer 4

Skin and mucous membranes damaged from lack of mucous

Question 5

Deficiency

Chondritin sulphate synthesis

Answer 5

Abnormal bone development

Can lead to CNS damage (nervous system and bone growth grow in different pace)

Question 6

Deficiency

Synthesis of male/female steroid hormone

Answer 6

• Disorders of reproductive system
• Uterus + testes epithelium proliferation + keratinization will be abnormal → problems with fertilization

Question 7

Deficiency

Visual function (nigth vision)

Answer 7

• Nyctalopia = night blindness
• One of the earliest signs of vitamin A deficiency
• Visual treshold is increased
• Severe deficiency leads to xeropthalmia
  
  • Dryness of cornea and conjuctiva

Question 8

Visual function

Location

Answer 8

Retina (rod)

Question 9

Visual function

Give the visual cycle

Answer 9

Question 10

Hypervitaminosis

Answer 10

• Consequence same as hypovitaminosis
• β-carotene nevers causes hypervitaminosis
  
  • Efficiency of conversion of β-carotene to retinol depends on the level in diet
    
    • If more β-carotene consumed, less is converted and rest is stored in fat reserves
• Storage of retinylester in liver results in hypervitaminosis if consumed in excess
• Excessive vitamin A acts by stimulating the release of lysosomal enzymes → resorption of bone