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Fat soluble vitamins and health - Vitamin A

31 important questions on Fat soluble vitamins and health - Vitamin A

What are the 4 forms of vitamin A?

Retinol (most of the vitmain A)
Retinyl ester, retinol that is stoared in the fat tissue of the body (more stable then retinol)
Retinal, oxydised form of aldehyde compound
Retinoic acid, oxidized for of retinal

What is beta carotene?

Beta-carotene is the most abundant and most efficient pro-vitamin A in our foods. So is converted to a vitamin

From what sources do you get vitamin A and form what sources pro vitamin a?

Vitamin A: comes form animals
Pro vitamin A: comes form plants in the form of carotenoids.

In what form is vitamin a stored in the liver?

the form of retinyl -esters

In what liver cells in vitamin A storred?

Stellate cells

What happens to the enzyme splitting beta-carotene when you eat a lot of vitamin a?

The activitie goes down.

How does vitamin A travel trough the blood?

It is bound to the plasma retinol binding protein (RBP), this protein is synthesized in the liver.

How is excretion of the retinol bound to a transport protein by urine prevented?

It is coulbed to a transtthyretin (TTR) and now you have a RBP-TTR-retinol comples and this prevents it.

How does the RBP-TTR-retinol complex deliver retinol?

It binds to a receptor on the surface of the target cell. The reteinol is released and taken up by the cell. Now it can be sorted in the liver until it is needed or emediatly converted to the bioactive for of vitamin A.

What are the main functions of vitamin A?

Promoting vision
Participating in protein synthesis and cell differentiation (and thereby maintaining the health of epithelial tissues and skin)
Supporting reproduction, growth and immune system functioning

What is the main funciton of retinol?

Retinol supports reproduction and is the major transport and storage form of the vitamin

What is the main function of Retinoic acid?

Retinoic acid acts like a hormone, regulating cell differentiation, growth, and embryonic development.

What is the main function of retinal?

11 cis Retinal is active in vision and is also an intermediate in the conversion of retinol to retinoic acid.

What is the influence of vitamin A on vision?

Vitamin A (11-cis retenal) plays two indispensable roles in the eye: it helps maintain a crystal-clear outer window because of its actions in the cornea (hoornvlies), and it participates in the conversion of light energy into nerve impulses at the retina (netvlies).

How does the conversion of light into an nerve puls with vitamin A go?

11-cis retenal is bound the the rod and cone cells with a opsins in the retina (hornvlies) and serve as the light sensitive part.
A signal is generated because of the change in structure of 11-cis-retenal. It becomses all trans retinal and the retinal is released/ This is called bleaching. A signal is send to the visial center of the brain.

The all trans retenal can change back to a 11-cis-retenal and bind to the opsins agian. So the signal can repeat itself.

What are the different cells in which vitamin a influences the protein synthesis?

it affects epithelial cells found in the lungs, trachea, skin, gastrointestinal tract, blood vessel walls, and the cornea. Vitamin A helps to maintain the normal structure and function of these epithelial cells.

What vitamin A's regualte genes?

9-cis retinoic acid and all trans retionoic acid

What are the nuclear receptors that vitmamin A used in gene regulation bind to?

9-cis retinoic acid binds to RXR and trans retionoic acid binds to RAR. One domain binds to the acid and one to the specific DNA sequences. Without binding the receptors are inactive. So it works as a transcription factor.

How does RXR and RAR bind to DNA?

Trough Hetrodimerization.

RXR and RAR form a receptor complex witch can bind with the DNA.

RXR can also bind with thyroid hormone, bile acid vitamin D and faty acid.

All of these complexes have a different fuction and bind to a different sequence in the DNA.

What acounts for the diversity in actions of vitamin A in the body?

Retinoic acid influences metabolic signalling by DNA regulation.
It is able to turn on a large number of geners in a veriety of tissues in the body.

Where is a lot of vitamin A deficiency and what are the concequences?

In africa and southeast asia. It is the leading cause of preventible childhood blindness. Also the children are more vonible to diseases and diarrhea

How are the symtoms of a toxic overdose of vitamin A called and what are they?

Hypervitaminosis A.

Overdose
It causes nausea, vomiting, headaches,

High over dose:
Drowsiness, malaise, itching and exfoliation of the skin.

How much vitamin A do you need to eat a day in order to get toxidity?

7.5-9 mg per day

Why should pregnant women stay away from vitamin A suplements?

Excessive vitamin A during pregnancy leads to abnormal cell death in the spinal cord, which increases the risk of birth defects. High intake of vitamin A before the seventh week of pregnancy appear to be the most damaging.

Why did explorers not eat the liver of a polarbear?

Because some animal levers have a overload of vitamin A and you get symtomes of a overdose of vitmain A.

What can happen if you eat a over load of carotes?

You take in to many carotenoids, this does not cause hypervitaminosis A because they ar limetly absorpted and converted to retinol.
However you can get carotenemia, a harmless condition with witch your skin turns yellow.

What is the top vitamin A sources in the us and what it the top source of provatiamin A?

vitamin A:
dairy products, liver, fish, and fortified cereals

provitamin A:
carrots, broccoli, cantaloupe, and squash.

What are vitamin A suplements usualy a mix of?

A mix of beta-carotene and preformed vitamin A

How many gram of mixed carotenoids is equual to 1 microgram of preformed retinol?

people need to consume 24 micrograms of mixed carotenoids to equal the consumption of 1 microgram of preformed retinol.

How many grams of beta-carotene is used to get 1 microgram of retinol?

2 micro gram of beta carotene

What is the RDI for vitamin A?

900 mg for men and 700 mg for woman

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Food components and health

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