Vitamin A Flashcards
T/F
Fat soluble vitamins are mostly lost when cooking with water
False
Little are lost
How many grams of fat are needed for bile secretion for absorption of fat soluble vitamins?
5-10g
Fat soluble vitamins are absorbed by what means? How are they transported?
Passive diffusion; transported with lipids in lipoproteins
Where are fat soluble vitamins found in the cell?
Lipid portions
Where are fat soluble vitamins stored?
Liver and adipose tissue
Are fat soluble vitamins toxic?
Yes, in large amounts they are toxic
What is bile, where is it made, stored and concentrated?
Emulsified made from cholesterol in the liver, stored and concentrated in the gallbladder.
What happens with fat-rich chyme enters the SI?
Stimulates CCK
What does CCK do
Gallbladder contraction causing bile secretion from the gallbladder through the Sphincter of Oddi to the SI
What should you assume when you see “cholate” in a word?
Bile acid
What are micelles?
Fatty acids, monoglycerides, fatsoluble vitamins, cholesterol & bile
What does retinol (vit A) affect?
Reproduction and growth
What does retinal (vit A) affect?
Vision
What does retinoic acid (vit A) affect?
Cell differentiation
Where is preformed vitamin A found?
Animal products: dairy products, liver, fish, eggs.
What is a retinol ester?
Retinol with a fatty acid attatched
What is proformed vitamin A?
Precursors to vitamin A
Where is proformed vitamin A found?
Plant products: orange, yellow, red colors.
T/F
Proformed vitamin A intake should equal preformed vitamin A
False,
Proformed vitamin A is only necessary when we don’t get enough preformed vitamin A in our diet
How much proformed vitamin A is necessary to equal preformed vitamin A activity?
12x as much proformed to equal preformed activity
Considering proformed vit A, how many known carotinoids are known? How many can be convered to retinol?
> 600
<10%
What is the difference between what RE and carotenoids are bound to?
Carotenoids are bound to a fatty acid,
RE’s are bound to a fatty acid and protein in food
What makes vitamin A soluble?
Bile
Free retinol and carotenoids are incorportated into…
Micelles
How much of RE are absorbed?
80%
How and where in the body is Vitamin A absorbed?
By passive diffusion in the duodenum and jejunum
What is retinol bound by?
Cellular-retinol-binding-protein (CRBP)
What happens to retinol in the enterocyte?
Retinol is reesterified to a RE by lecithin retinol acyl transferace (LRAT)
What are RE incorporated into?
Chylomicrons
What is step 1 to vitamin A absorption?
Retinol, fatty acids, and carotenoids are absorbed as part of micelles by passive diffusion in the SI. Retinol is bound by CRBP.
What is step 2 to vitamin A absorption?
Fatty acids are reesterified to retinol by LRAT, reforming a RE
What is step 3 to vitamin A absorption?
RE and carotenoids are packaged into chylomicros and sent through the lymph system
What percentage of Vitamin A is absorbed from raw veggies as opposed to cooked veggies?
5% absorbed from raw
60% absorbed from cooked
If retinol intake is low, what happens to carotenoids?
Carotenoids are metabolized to 2 retinals
If retinol intake is low, what happens to retinals?
Either:
- Retinal is bound by CRBP, reduced to retinol, esterified via LRAT and incorporated into chylomicros.
- Oxidized to retinoic acid and travels to the liver bound to albumin
What happens to retinol if intake is adequate?
Incorporated into chylomicrons
How much of vitamin A is stored in the liver?
50-80%
What problem with Vit A metabolism will occur with patients with a low protein status? What must be done to remediate the problem?
Retinol cannot be metabolized out of the liver. Must correct protein deficiency first!!!!
What is the formula for rhodopsin?
Retinol -> retinal + opsin
What is vitamin A important for vision wise?
Vision in dim light
If you decrease vitamin A what else is reduced in the vision pathway?
Rhodopsin and night vision
In cell differentiation, retinoic acid is important for rapidly dividing cells by directing…
Keratin synthesis
Vitamin A is important for catalyzing the reaction of turning keratinizing cells into what other kind of cells?
Mucus-secreting cells
What happens to mucus secreting cells, and where does it happen, when vitamin A intake is diminished?
Keratin producing cells replace mucus secreting cells in the respiratory, GI, and urinary tracts (process called hyperkeratinization)
How does vitamin A affect gene expression?
Retinoice acid interacts with DNA in nucleus. Stimulates the production of GFs and enzymes.
How does vitamin A intake affect bones?
Vitamin A deficiency stimulates osteblasts
Excessive vitamin A stimulates osteoclasts
What are 2 major functions that carotenoids have?
Affect immune system and cell growth/differentiation
Specific carotenoids may inhibit growth & proliferation of several cancer lines, but what can supplementation cause?
Increase risk of several cancers
T/F
A vitamin is an inorganic compound
False,
Organic
What is the most reduced for of vitamin A called?
Retinoic acid
What are 3 examples of conditions associated with clinical deficiency of vitamins?
Pellagra
Burning feet syndrome
Keshan’s disease
What are subclinical deficiencies of vitamins associated with?
Increased risk of chronic diseases
In vitamin A digestion, what are proteins and fatty acids removed by respectively, and where?
Proteins removed by proteases in the stomach and SI
Fatty acids removed by lipases in SI
What is the most reduced and most oxidized form of Vitamin A?
Most reduced = Retinol
Most oxidized = Retinoic acid
What is the RDA?
Recommended dietary allowance. Meets nutritional need of 97.5% of the population
What the RAE?
Retinol activity equivalents
What is the RAE for men and for women respectively?
Men = 900 RAE Women = 700 RAE
What is the #1 vitamin deficiency worldwide?
Hypovitaminosis A
What are the 2 causes of hypovitaminosis A?
- Inadequate intake
2. Fatty acid malabsorption
What are the 4 categories of symptoms associated with hypovitaminosis A
- Vision problems (e.g. night blindness, xerophlamia, dry eye, bitot’s spots, permanent blindness more common in developing countries)
- Reproduction problems
- Depressed immune system
- Skin problems (follicular hyperkeratosis caused by plugs of keratin).
Who is most at risk for hypovitaminosis A?
Children
Fatty malabs patients
What is a sign of fatty malabsorption
Steatorrhea
How much vitamin A intake happens before symptoms of acute hypervitaminosis A happens?
> 200,000 RAE
What are some symptoms of chronic hypervitaminosis A?
Dry lips (cheilitis), dry/itchy skin, alopecia, bone/joint pain, fx, liver damage.
T/F
Vitamin A taken at toxic levels is a taratogen?
True
What is the TUL (tolerable upper intake limit) For vitamin A?
3000 RAE
What is the TUL for carotenoids?
None
Chronic carotenoid consumption can lead to what condition?
Yellow/orange skin
What conditions are smokers and former smokers at risk for with carotenoid toxicity?
Increased risk of lung cancer, heart disease, death. `
