Lecture 14 - Absorption and What Goes Wrong Flashcards
What are vitamins?
organic compounds that are required in small quantities for a variety of biochemical functions
water soluble vitamins?
B complexes (B12 & B9)
c or ascorbic acid
Fat soluble vitamins?
A or retinol
D or cholecalciferol
E or tocopherol
K
What is B12 known as?
cobalamin
where is B12 synthesised?
solely by microorganisms
Where do ruminants obtain B12 from?
the foregut
Human source of B12?
animal origin e.g. meat, fish, diary products
What are free from B12?
vegetables, fruits and other non-animal foods unless contaminated by bacteria
Who are more at risk of developing B12 deficiency?
vegetarians and vegans
RDA of B12?
1.-2.5 mcg/day
How much B12 does a western diet contain?
5-30 mcg
what are the body stores of B12?
2-5 mg
how much B12 a day does an adult lose?
1-3mcg (~0.1% of body stored)
how is B12 lost from the body?
in urine and faeces
How much B12 is stored if the supply is cut off?
enough for 2-5 years
two mechanisms for B12 absorption?
passive absorption and active transport
Passive absorption of B12?
through buccal, duodenal and ileal mucosa
rapid but insufficient
How much of an oral dose of B12 is passively absorbed?
<1%
active transport of B12?
normal physiological mechanism
Where does active transport of B12 occur?
through the ileum
What mediates active transport of B12?
gastric intrinsic factor
How much B12 is absorbed by active transport?
~70% of ingested amount
where is haptocorrin produced?
salivary glands
where is intrinsic factor produced?
secreted by parietal cells, secretion parallels that of gastric acid
it is a glycoprotein