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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
Q

Hypervitaminosis A

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
Q

TUL Vitamin A

A

3,000 micrograms RAE/day

27
Q

carotenes

A

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
Q

Vitamin E includes

A

tocopherols, with saturated 16 carbon acyl chains

tocotrienols, with polyunsaturated 16 carbon acyl chains

29
Q

Vitamin E abundant in

A

plant oils, e.g. palm oil, sunflower oil, canola oil, wheat germ.

30
Q

tocopherols, tocotrienol-acyl esters (vitamin E) broken down by ____ into _____ and absorbed into

A

pancreatic lipase into tocopherols and tocotrienols, absorbed into intestinal epithelial cell

31
Q

tocopherols and tocotrienols in intestinal epithelial cell packaged into ______

A

chylomicrons - delivered to tissues –> chylomicron remnants –> liver –> vldl –> tissues… (only RRR stereoisomers in VLDL)

32
Q

Vitamin E digestion and absorption parallels

A

fat digestion and absorption

33
Q

tocopherols

A

saturated 16 carbon acyl chains (vitamin E)

34
Q

tocotrienols

A

poly unsaturated 16 carbon acyl chains (vitamin E)

35
Q

Functions of Vitamin E

A

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
Q

Vitamin E interactions

A

Vitamin E, when oxidized, can be regenerated by ascorbate (vitamin C).

Vitamin E inhibits Vitamin K absorption and metabolism.

37
Q

Vitamin E Deficiency

A

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
Q

Vitamin E toxicity

A

Not very toxic. TUL is 1,000 mg per day

39
Q

Main form of vitamin K in diet and found where

A

Phylloquinone is the main form of Vitamin K in the diet. It is abundant in leafy green vegetables.

40
Q

Menaquinones

A

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
Q

Menadione

A

Menadione is a synthetic Vitamin K used in animal feed.

42
Q

Vitamin K digestion and absorption

A

Parallels fat digestion and absorption (intestinal epithelial cells, chylomicrons, tissues, remnants, liver, VLDL, tissues)

43
Q

Vitamin K stored

A

is stored in cellular membranes, especially the lung, kidney, bone marrow, and adrenal glands.

44
Q

Vitamin K function

A

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
Q

coumadin inhibits

A

vitamin K epoxide reductas e

46
Q

which clotting factors are dependent on Vitamin K

A

Factor IX (Christmas factor), Factor VIIa, Factor X (Stuart factor), and prothrombin are dependent on Vitamin K dependent carboxylation.

47
Q

coumadin/warfarin inhibit

A

vitamin K epoxide reducatase

48
Q

vitamin K deficiency

A

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
Q

vitamin K toxicity

A

Not described; no TUL for Vitamin K

Menadione causes liver toxicity at high doses

50
Q

Vitamin D found in

A

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
Q

vitamin D synthesize

A

de novo from cholesterol. To make the active Vitamin D3, metabolism of skin, liver, and kidney is required.

52
Q

most important function of Vitamin D

A

to regulate calcium homeostasis, but it may play other beneficial roles.

53
Q

dietary form of vitamin D

A

cholecalciferol

54
Q

how is vitamin D absorbed

A

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
Q

main form circulating in blood and form measured to assess vitamin D status

A

25-hydroxycholecalciferol (25-OH D3)

30-40 ng/mL is considered healthy, though recommendations vary.

hydroxylated in liver

56
Q

active Vitamin D

A

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
Q

PTH produced where and why

A

PTH is produced by the parathyroid in response to low calcium concentrations.

58
Q

vitamin D receptor

A

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
Q

proteins made by VDR activation

A

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
Q

vitamin D deficiency

A

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
Q

Vitamin D toxicity

A

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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