Topic B5

Question 1

Biochemical role

Biochemical role of calciferol (vitamin D)

Answer 1

• Major role: maintain plasma calcium and phosphate at a level at which plasa is supersaturated with respect to bone minerals → allowing calcification
• Must undergo biochemical change before it can exert its metabolic function
• Have an effect on:
  
  • Intestines
  • Kindey
  • Bone

Question 2

Biochemical role

Effect on the intstines

Answer 2

• Result: movement of calcium from the intestinal lumen to the blood of v. porta is promoted

Question 3

Biochemical role

Effect on the kidney

Answer 3

• Kidney tubular reabsorption: vitamin D increases the reabsorption of calcium and phosphate
  
  • Increased tubulary reabsorption leads to increased circulating Ca²⁺ and phosphate
• CBP (Calcium Binding Protein) → reabsorption of Ca²⁺ + Pin

Question 4

Biochemical role

Effect on the bone

Answer 4

• Young animals
  
  • Increases mineralization of newly formed bones (Ca²⁺ + Pin built in)
• Eldery animals
  
  • Demineralization if pre-existing bones due to PTH-like activity of vitamin D

Question 5

Deficiency / hypovitaminosis of vitamin D

Answer 5

• Young animals:
  
  • Decreases mineralization of newly formed bones (soft bones)
    
    • Rickets
• Elderly animals
  
  • PTH-like activity ↑ - demineralization ↑ (fragile bones)
    
    • Osteomalatia
• Reasons for deficiency:
  
  • Car: 7-dehydrocholesterol concentration ↓
  • Sus, polutry, ca: intensive growth
  • Polutry: Egg production needs increased Ca²⁺ + Pin
  • Ø sunshine
• Prevention for deficiency:
  
  • Cod liver oil
  • Milk
  • Sun-cured hay
  • Irradicated yeast
  • Vitamin D injection

Question 6

Toxicity of vitamin D (hypervitaminosis)

Answer 6

• Vitamin D is the most toxic vitmain
• Ca²⁺ + Pin ↑ in blood
  
  • Atherosclerosis
    
    • ​​Calcification of organs, tissues and membranes
• Ca²⁺ + Pin reabsorption ↑ in kidney → precipitation in lumen → kidney failure
• Ø increase in alkaline phosphatase activity
• PTH-like activity = Ca²⁺ + Pin dissolution from bones
• GI-problems
• Slow growth

Question 7

Hypovitaminosis VS hypervitaminosis

Answer 7