Nutrition- Vitamin A

Front 1

How was Vitmamin A originally found?

Back 1

Originally found by its ability toprevent night blindness (xerophtlamia).

Front 2

What is Vitamin A a generic descriptor for?

Back 2

It is a generic descriptor forcompounds with the qualitative biological activity of retinol.

Front 3

What does Vitamin A include?

Back 3

Vitamin A includes:

Active form retinoids(retinol, retinal, retinoic acid).

Inactive forms carotenoids (e.g.B-carotene, a-carotene, lycopene, and lutein).

Front 4

Explain the retinoids

Where are the retinoids found?

Back 4

Note about the retinoids:

Retinal can interconvert reversiblewith retinol. Retinal can convert irreversibly toretinoic acid.

Retinoids-Retinol, retinal, retinoicacids are found in animal products.

Front 5

Where are carotenoids found?

Back 5

Carotenoids are pigments made inplants.

Carotenoids are found in animals, but they derive fromdietary sources.

Front 6

What is B-carotene a precursor for?

Back 6

In the organism, B-carotene, which is aprecursor of Vitamin A (provitamin) is converted into two retinal molecules.

Front 7

Explain absorption of Vitamin A + Carotenioids

Back 7

Efficiency of absorption in the gutdiffers between Vitamin A and Carotenoids.

70-90% of dietary vitamin A is absorbedas long as the meal contains at least 10g of fat.

This is because Vitamin A is ahydrophobic molecule that requires fat to serve as a vehicle for its transportinto the enterocyte.

Front 8

What happens to Vitamin A before it enters chylomicron?

Back 8

Retinol is esterified to palmitate bylecithin retinol acyl-transferase (LRAT) to form retinyl palmitate, which isthen incorporated along with phospholipids, TG, cholesterol esters, carotenoidsand Apoproteins into chylomicrons.

Front 9

Explain liver storage of Vitamin A

Back 9

Primary storage of Vitamin A in body.

It clears 70-75% of chylomicronretinoids from the circulation – the retinyl palmitate.

The absorption of carotenoids variesconsiderably, depending on food processing, but is typically less than that of VitaminA.

Front 10

Explain Adipose Tissue storage of Vitamin A

Back 10

The adipose tissue, which takes upretinyl esters from chylomicrons, stores about 15-20% of the body’s Vitamin A.

The adipose tissue is also a major sitefor storage of B-carotene.

Regular ingestion of foods rich incarotenoids turn palms of hand yellowish.

Since B-Carotene is a precursor of Vitamin A and notfully active, excess stored does not cause toxicity

Front 11

How is retinol moved through the blood?

Back 11

Once mobilized from liver and adiposestores, retinol is transported to peripheral tissues by carrier protein in theplasma called retinol-binding protein-RBP.

Front 12

What are the primary functions of Vitamin A?

Back 12

Needed to make rhodopsin and otherlight receptor pigments- necessary for ability of the eyes to adjust to changesin light.

Required for sperm production in menand fertilization in women.

Contributes to bone development –regulates the activity of osteoblasts and osteoclasts- mediated by retinoicacid.

Assists cell differentiation- retinoicacid mediated.

Contributes to maintenance of healthyimmune function.

Front 13

Explain role of Vitamin A in vision

Back 13

Cis-retinal and opsin are boundtogether in rhodopsin.

(1) Light hits the retina

(2) Rhodopsin in the rod cells iscleaved into opsin and cis-retinal-causing depolarization of the cell.

(3) Cis-retinal is converted into transretinal.o (4) Trans-retinal is converted back into cis-retinal. Trans form only occurs for a short amount of time.

(5) Rhodopsin is reformed by theattachment of cis-retinal and opsin- crucial for the visual cycle to operate.

Rod cells serve as photoreceptorscapable of detecting small amounts of light, important for night vision.

In a dim/dark environment, a flash oflight that hits the retina promotes the transformation of rhodopsin (cis totrans) in rod cells.

This generates electrical impulses thatare sent along the optic nerve to the brain where it translates to vision.

Without Vitamin A, this process failsor is severely delayed causing night blindness.

Front 14

Symptoms of Vitamin A deficiency

Back 14

Xerophtlamia, impaired growth, impairedimmunity, impaired reproductive function

Front 15

Symptoms of Vitamin A toxicity

Back 15

Fatigue, bone and joint pain, spontaneousabsorption, birth defects, nausea, diarrhea, liver damage, blurred vision, hairloss, and skin disorders