Vitamin A - Advanced Nutrition II

Vitamin A - retinoids and carotenoids

Vitamin A = all compounds that can form retinoids or retinol that can be a precursor to vitamin A; a generic term that possess the biological activity of all-trans retinol

Vitamin A is also an all encompassing term for retinoids and carotenoids but are not all interchangable

B-carotene is a carotenoid with the most of the vitamin A activity. 

retinol can convert irreversibly to retinoic acid or retinyl ester

Retinol can also reversibly convert to retinal. (main form of biological activity)

You may consume retinyl ester, retinoic acid, and beta-carotene.

Beta-carotene is a carotenoid with the most vitamin A activity.

All-trans retinol is a retinol with a alcohol group. All bonds are in transformation and it contains an alcohol group. Can find in animal origin.

Retinal - has an aldehyde group

Retinal and all-trans retinol can convert back and forth reversibly.

Retinoic acid - with an acid group

All-trans retinol can form retinoic acid in growth

Retinyl esters - with a lipid group 

Structure of carotenoids 

Beta carotene is the one carotenoid with vitamin A activity. 

Beta-carotene can be split to form two molecules of retinal

mg= microgram

12 mg of carotene need to = 1 mg retinol

Ex. 36 mg of carotene = 3 mg retinol

preformed vitamin A has more activity beta carotene takes more of it to convert. 

Dietary Sources of Vitamin A

preformed vitamin A is more toxic and only found in animal sources

Preformed -retinyl ester (retinyl palmitate ex. of retinyl ester)

Liver

Egg Yolk

Dairy (fortified in United States)

Margarines (fortified)

Tuna, Sardines, Heerring

Cod Liver Oil

Beta-Carotene = exclusively in fruits and vegetables

Orange color - Carrots, squash, papayas, grapefruit, pumpkin

Green color - chlorofil over shadows the orange color - spinach, peas, broccoli, watermelon

Digestion and Absorption of vitamin A

animal sources and vegetable sources of (protein bound carotenoids and retinyl esters)

pepsin cleaves proteins (amino acids) 

carotenoid and retinyl esters hydrolases, esterases and lipases

cleaves fatty acids

free caroteinoids and free reitnol

fatty acids combine with phospholipids, monoacylglycerol, and cholesterol and bile (makes it water soluble

incorporates into micelle

true of all fats and fat soluble vitamins

goes across intestinal cell 

can either have beta carotene, retinol, or carotenoids

most are incorporated into chylomicrons that go into lymphatic system

beta carotene - can form two retinals (retinoic acid goes through the blood to the liver) or the retinal gets incorporated into chylomicrons combining with other 

Vitamin A is primarily stored in the liver so it will be released into the blood stream as its needed. 

Functions of Vitamin A

helps your vision = how you respond to bright light when its dark out

your eyes adjustment to light and dark

It's a specific form of Vitamin A : 11-cis retinal. This is a type of double bond cis is a c form. 

its on the 11th carbon there is a double bond in the cis form. whereas for all the other biological function it is…