Define EAR (Estimated Average Requirement)
Average daily nutrient intake level estimated to meet the requirements of of half of the healthy members of a particular life stage and gender group
Define RDA (Recommended Daily Allowance)
Average daily dietary nutrient intake level sufficient to meet the nutritional requirements of nearly all (97-98%) healthy persons in a particular life stage and gender group
Define Tolerable Upper Limit:
Risk of “overdose” is approx. 0.1%
Biologically active form of vit A:
all-trans-retinol
- B-ionone ring
- branched polyunsaturated acyle chain
- alcohol
Three things all-trans-retinol can be converted to:
- aldehyde
- carboxylic acid
- ester w/ fatty acid (eg. palmitate)
Three dietary forms of vit A:
- retinyl palmitate
- B-carotene
- a-carotene
Vit A metabolite that can be transported in blood with albumin:
Retinoic acid
Vit A metabolites that are transported in chylomicrons:
Retinyl-fatty acid esters
Reservoir for vit A storage in liver:
Stellate cells
retinal cycle in photoreceptors?
cis-retinal + opsin = rhodopsin
rhodopsin + UV light = opsin + tras-retinal
trans-retinal –> G-protein rec. –> closes Na+ channels –> hyperpolarization of rod cell –> signals neuron
trans-retinal recycled back to cis-retinal
4 roles of retinoic acid ligand based transcription factors (RAR, RXR, PPAR):
- differentiation of goblet cells (inhibits keratinization)
- apoptosis of cancer cells
- maturation of dendritic cells
- recruitment of antibody secreting cells to small intestine
Vit A metabolites that act as antioxidants:
carotenes (double bonds bind free radicals)
Bitot’s spots in the eye?
Vit A deficiency
Dry eye due to keratinization?
xeropthalmia
due to vit A deficiency
Vit E form with SATURATED 16-C acyl chains:
tocopherols
Vit E form with polyUNsaturated 16-C acyl chains:
tocotrienols
Vit E absorption and distribution parallels _____?
fat digestion and absorption
Vit E functions?
- lipid bilayers
- intracellular plasma membranes
- cellular oxidative stress defense
Vit that can inhibit Vit K absorption and metabolism:
Vit E
Vit E deficiency: Causes? Symptoms?
Causes:
- premature infants
- Crohns
- short bowel syndrome
Sx:
- myopathy
- hemolytic anemia
- peripheral neuropathy
- ataxia, loss of vibratory sense
Main form of dietary vit K:
Phylloquinone
green leafy vegetables
Vit K produced by fermentation:
Menaquinones
Vit K absorption paralells _____.
fat
Vit K stored in _______.
cell membranes of lung, kidney, bone marrow, adrenal glands
Coumadin blocks what enzyme?
vit k epoxide reductase
**increases PTT
Clotting factors reliant on vit K dependent carboxylation:
VIIa
IX
X
Main circulating form of vit D:
25-hydroxycholecalciferol
Biologically active form of vit D:
1,25-dihydrocholecalciferol
Where does vit D get activated:
kidney
**in response to PTH
Enzyme in kidney responsible for activating vit D:
1-a-hydroxylase (+ PTH)
Ca++ channel on brush border:
TRPV6
Vit D deficiency characterized by seizures, growth retardation, failure of bone mineralization (osteomalacia):
rickets
Most toxic vitamin?
D
Vit associated with reduced colorectal carcinoma:
vit D
Most abundant metal ion in the body:
Calcium
HOw does Ca++ get across basolateral membrane?
Ca++ ATPase
Transcellular movement of Ca is regulated by?
calcitrol
Pericellular transport of Ca is regulated by?
Claudin
Inhibits PTH?
calcitonin
Intracellular signalling by calcium is mediated by?
calmodulin
How does Ca decrease cholesterol?
traps bile salts and fatty acids in undigestable soaps –> diverts cholesterol to bile salt synthesis
Saturable transport of Mg+ across brush border?
TRPM6
Basolateral transport of Mg+?
- 2Na+ / Mg2+ antiporter
2. 2K+ / 3Na+ ATPase (creates favorable Na conc for #1 above)
Functions of Mg++?
bone
ATP
kinases
polymerases
Best measurement of Mg++?
renal excretion
SLC12A3 mutation
Gitelman Syndrome
Intracellular processes dependent on Mg++:
ATP associated processes