Lecture 9: Micronutrients Flashcards
what are the essential vitamins
- A
- D
- E
- K
- vitamin C
- thiamine: B1
- riboflavin: B2
- niacin B3
- pantothenic acid B5
- vitamin B6
- folate B9
- vitamin B12
what are micronutrient deficiencies seen in the population
- vitamin D
- riboflavin B2
- iron deficiency in women
what micronutrient deficiencies are associated with alcohol liver disease
- thiamine B1
- vitamin D
what micronutrient deficiencies are associated with IBS
- iron
- B1
- B6
- B12
- vitamin D
- vitamin K
- folic acid
what micronutrient deficiences are associated with obesity
- vitamin D
- copper
- zinc
where is vitamin C absorbed
- buccal mucosa
- stomach
- small intestine
what is vitamin C’s mechanism of absorption
- buccal: passive diffusion
- GI: rapidly through carrier mediated transport system
what is vitamin B1’s mechanism of absorption
- at low concentrations, by active sodium dependent processes
- at high concentrations, by passive diffusion
what does vitamin B1 deficiency cause
Wernicke-Korsakoff syndrome
what is vitamin B2’s mechanism of absorption
- released from proteins by proteolytic enzymes
- then hydrolysed by brush border enzymes
what are dietary sources of B12
- is synthesised by microorganisms
- then concentrated through food chains
- on plants, contamination by soil bacteria
how is vitamin B12 absorbed
- B12 binds to R factor in presence of HCl
- R complex degraded in jejunum and B12 binds to Intrinsic Factor (IF)
- B12-IF complex binds to receptors at distal ileum
- B12 is absorbed into plasma in presence of calcium
what does vitamin B12 deficiency cause
pernicious anaemia
what are dietary sources of vitamin A
- retinol is in long fatty acid chains in animals
- precursor carotenoids in red/orange plants
what is vitamin A’s mechanism of absorption
- retinol hydrolysed by pepsin in stomach and proteolytic enzymes in small intestine
- carotenes packaged into micelles, absorbed through membrane and converted to retinol
what are dietary sources of vitamin D
- animal foods: D2
- synthesised in body via UV light: D3
what is vitamin D’s mechanism of absorption
- absorbed form micelle by passive diffusion
- liver 25-hydroxylase enzymes convert D2 and D3 to 25-hydroxy-vitamin D
- this is then converted to the active form 1,25-dihydroxyvitamin D by the kidney and other tissues
what is calcium’s mechanism of absorption
- 20-30% is absorbed in acid medium
- when intake is low and requirement is high, via vitamin D dependent transport system in duodenum
- when intake is high, via passive processes in jejunum
what are dietary sources of iron
- haem iron in animal products
- non-haem in plant foods
what is iron’s mechanism of absorption
- very difficult to absorb as it is associated with proteins
- haem is easier to absorb than non-haem
- haem iron absorbed as intact porphyrin complex
- non-haem is oxidised from ferric to ferrous form
- this process is aided by vitamin C
