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GI (Elaina) > Fat Soluble Vitamins > Flashcards

Fat Soluble Vitamins Flashcards

1
Q

EAR

A

Estimated Average Requirement. The average daily nutrient intake level estimated to meet the requirements of half of the healthy members of a particular life stage and gender group.

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2
Q

RDA

A

Recommended Daily Allowance. The 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.

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3
Q

Risks with EAR, RDA, TUL

A

EAR: Risk of inadequacy is 50%
RDA: Risk of inadequacy is ~2.5%
UL: Tolerable Upper Limit. Risk of ‘overdose’ is ~0.1%

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4
Q

redox cofactors

A

Niacin
Riboflavin
Ascorbic acid (Vitamin C)

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5
Q

ascorbic transfer cofactors

A 
Ascorbic acid (Vitamin C)
Thiamine
Pyridoxine
Biotin
Pantothenic acid
Lipoate
Cobalamin
Folate
Tetrahydrobiopterin (Ring hydroxylations; PKU)
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6
Q

Fat soluble vitamines

A

Vitamin A
Vitamin D
Vitamin E
Vitamin K

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7
Q

biologically active vitamin A

A

all-trans-retinol

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8
Q

structural elements of vitamin A

A

b-ionone ring
branched polyunsaturated acyl chain
alcohol

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9
Q

IN the body, alcohol of trans-retinol can be converted to

A

aldehyde (all-trans retinal)
carboxylic acid (all trans retinoic acid)
ester with fatty acid (e.g. palmitate) (retinyl ester)

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10
Q

main dietary forms of vitamin A

A

are retinyl-acyl esters and carotenes. They all can be converted to all-trans-retinol.

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11
Q

other forms of dietary A

A

lycopene, lutein, canthaxanthin

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12
Q

vitamin A found in

A

Red, yellow, orange fruits and vegetables.

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13
Q

how vitamin A absorbed

A

Retinoic acid is soluble enough to be transported in the blood associated with albumin.
Retinyl-fatty acid esters are transported in chylomicrons.

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14
Q

storage reservoir for vitamin A

A

Stellate cells in the liver

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15
Q

______ mediate retinol homeostasis in body

sources of vitamin A for liver homeostasis

A

hepatocytes

retinyl esters go in from chylomicrons (dietary) or stellate cells (stored)

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16
Q

how does vitamin A leave hepatocytes

A

retinyl esters to stellate cels (storage) or VLDL to tissues

retinol to serum in complex w/ transthyretin and retinol binding protein (RBP)

retinoic acid goes out to serum w/ albumin

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17
Q

Function vitamin A w/ vision (deficiency / toxicity)

A

Retinol is important for vision, and vitamin A deficiency can manifest as night blindness. Vitamin A toxicity can result in blurred vision.

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18
Q

vitamin A and vision

A

cis-retinal bound to the protein opsin is the photoreceptor rhodopsin. Light causes conversion to trans-retinal. Rhodopsin bound to trans-retinal activates a heterotrimeric G protein, closure of a Na+ channel, hyperpolarization of the rod cell, and signaling to the neuron.

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19
Q

retinoic acid as a ligand

A

Retinoic acid acts as a ligand for the retinoic acid receptors (RAR), retinoic X receptors (RXR) and some peroxisome proliferator activated receptor (PPARb and PPARd).

RAR, RXR, and PPAR act as ligand activated transcription factors.

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20
Q

functions of retinoic acid as transcription factor ligand

A 
recruitment of antibody secreting cells to small intestine
maturation of dendritic cells
apoptosis of cancer cells
differentiation of goblet cells
inhibit keratinization
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21
Q

rhodopsin =

A

cis-retinal + opsin

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22
Q

light causes conversion of rhodopsin how

A

cis-retinal –> tran-retinal ==» activated heterotrimeric G protein to close Na channel –> hyperpolarize rod cell –> signal neuron

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23
Q

vitamin A deficiency

A 
anorexia
retarded growth
increased susceptibility to infections
alopecia
keratinization of epithelial cells

eyes:
night blindness
xeropthalmia (dry eye due to keratinization)
Bitot’s spots

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24
Q

diagnosing vitamin A deficiency

A

Measure plasma retinol concentration. Give an oral bolus of retinyl-palmitate. Measure plasma retinol concentration again after 5 hours
* The higher the RDR, the more the body is relying on short term dietary Vitamin A, rather than liver and adipose stores.
RDRs > 20% indicate the liver is not maintaining serum Vitamin A.

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25
Hypervitaminosis A
``` Doses in vast excess of this can cause. . . nausea vomiting blurred vision headache desquamation of skin alopecia ataxia liver damage (from excess stellate cell growth and proliferation) conjunctivitis, eye pain ``` Vitamin A can be a teratogen in very high doses. Acne medication Accutane
26
TUL Vitamin A
3,000 micrograms RAE/day
27
carotenes
Carotenes can be cut by a monooxygenase to form to molecules of retinal. Without being cut, carotenes act as antioxidants. Their double bonds can neutralize singlet oxygen and free radicals.
28
Vitamin E includes
tocopherols, with saturated 16 carbon acyl chains tocotrienols, with polyunsaturated 16 carbon acyl chains
29
Vitamin E abundant in
plant oils, e.g. palm oil, sunflower oil, canola oil, wheat germ.
30
tocopherols, tocotrienol-acyl esters (vitamin E) broken down by ____ into _____ and absorbed into
pancreatic lipase into tocopherols and tocotrienols, absorbed into intestinal epithelial cell
31
tocopherols and tocotrienols in intestinal epithelial cell packaged into ______
chylomicrons - delivered to tissues --> chylomicron remnants --> liver --> vldl --> tissues... (only RRR stereoisomers in VLDL)
32
Vitamin E digestion and absorption parallels
fat digestion and absorption
33
tocopherols
saturated 16 carbon acyl chains (vitamin E)
34
tocotrienols
poly unsaturated 16 carbon acyl chains (vitamin E)
35
Functions of Vitamin E
Vitamin E functions in lipid bilayers in intracellular and plasma membranes. The phenolic hydroxyl can distribute and stabilize singlet oxygen and free radicals as part of cellular oxidative stress defense.
36
Vitamin E interactions
Vitamin E, when oxidized, can be regenerated by ascorbate (vitamin C). Vitamin E inhibits Vitamin K absorption and metabolism.
37
Vitamin E Deficiency
Deficiency is rare except in people with absorption problems, e.g. premature infants, Crohns, short bowel syndrome. Also can occur with inherited lipoprotein disorders. ``` Symptoms: myopathy hemolytic anemia peripheral neuropathy ataxia, loss of vibratory sense ```
38
Vitamin E toxicity
Not very toxic. TUL is 1,000 mg per day
39
Main form of vitamin K in diet and found where
Phylloquinone is the main form of Vitamin K in the diet. It is abundant in leafy green vegetables.
40
Menaquinones
Form of vitamin K Menaquinones have variable numbers of isoprenoid subunits on the acyl chain. They are produced by fermentation. (In gut, in cheese.)
41
Menadione
Menadione is a synthetic Vitamin K used in animal feed.
42
Vitamin K digestion and absorption
Parallels fat digestion and absorption (intestinal epithelial cells, chylomicrons, tissues, remnants, liver, VLDL, tissues)
43
Vitamin K stored
is stored in cellular membranes, especially the lung, kidney, bone marrow, and adrenal glands.
44
Vitamin K function
In target cells, Vitamin K acts as a cofactor for g-glutamyl carboxylase. This enzyme carboxylates glutamic acid side chains on blood clotting proteins.
45
coumadin inhibits
vitamin K epoxide reductas e
46
which clotting factors are dependent on Vitamin K
Factor IX (Christmas factor), Factor VIIa, Factor X (Stuart factor), and prothrombin are dependent on Vitamin K dependent carboxylation.
47
coumadin/warfarin inhibit
vitamin K epoxide reducatase
48
vitamin K deficiency
Rare; most people get adequate Vitamin K. Can occur in infants (milk is low in Vitamin K), people with absorption disorders. Severe deficiency manifests as coagulation disorder: increased prothrombin time, increased bleeding.
49
vitamin K toxicity
Not described; no TUL for Vitamin K Menadione causes liver toxicity at high doses
50
Vitamin D found in
food of animal origin such as liver, eggs, fatty fish. It is also present in shitake mushrooms, and is fortified in many dairy products.
51
vitamin D synthesize
de novo from cholesterol. To make the active Vitamin D3, metabolism of skin, liver, and kidney is required.
52
most important function of Vitamin D
to regulate calcium homeostasis, but it may play other beneficial roles.
53
dietary form of vitamin D
cholecalciferol
54
how is vitamin D absorbed
through passive diffusion with fat into intestinal epithelial cells. It is transported to tissue in chylomicrons, and taken up by the liver in chylomicron remnants.
55
main form circulating in blood and form measured to assess vitamin D status
25-hydroxycholecalciferol (25-OH D3) 30-40 ng/mL is considered healthy, though recommendations vary. hydroxylated in liver
56
active Vitamin D
The hydroxylation to make the biologically active 1,25-dihydrocholecalciferol (1,25-OH D3) occurs in the kidney in response to parathyroid hormone (PTH). 1a-hydroxylase
57
PTH produced where and why
PTH is produced by the parathyroid in response to low calcium concentrations.
58
vitamin D receptor
The vitamin D receptor (VDR) acts as a ligand activated transcription factor. calcitriol binds VDR - combine with retinoid X (orphan receptor) on VDRE to change gene transcription
59
proteins made by VDR activation
calcium transport proteins (calbindin, TRPV6, PMCA1b) PMCA = plasma membrane calcium pump, in gut and kidney TRPV6 at brush border calbindin in cytoplasm Also more ca atpase pumps at basolateral membrane claudins for paracellular
60
vitamin D deficiency
Rickets, characterized by seizures, growth retardation, failure of bone mineralization (osteomalacia). Vitamin D deficiency can be dietary, genetic, or secondary to an absorption problem such as Crohns.
61
Vitamin D toxicity
Vitamin D is the most likely vitamin to have toxic effects. The TUL is 4,000 IU for age 9+ Toxic effects begin when serum 25-OHD3 > 500 ng/mL calcification of soft tissues (kidneys, heart, lungs, blood vessels) hyperphosphatemia, hypertension

GI (Elaina) (7 decks)

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