Vitamin self study week 1 Flashcards
What are the fat soluble vitamins? What is a main difference btwn fat and walter soluble vitamins as it pertains to storage? What kind of compounds are vitamins?
Vitamins are chemically unrelated organic compounds that can not be synthesized by humans and must, therefore, be taken in through the diet. Vitamins are divided into two categories, the fat soluble and the water-soluble. The fat-soluble are vitamins A, D, E, and K and, unlike water-soluble vitamins that need regular replacement in the body, they are stored in the liver and can be slowly metabolized. Structurally, they are all isoprenoids: 5-carbon compounds.
T or F: Foods that contain fat soluble vitamins should be consume raw because cooking will cause the nutritional value of these vitamins to be lost.
False. Foods with fat soluble vitamins (A, D, E, K) will not lose them when cooked.
How are fat soluble vitamines released, absorbed, transported, and excreted? Where are they stored?
- The fat-soluble vitamins are released, absorbed, and transported with the fat of the diet. They are not readily excreted in the urine.
- Because they are soluble in fat, these vitamins tend to be stored in the body’s fat tissues, fat deposits, and liver.
T or F: Because fat-soluble vitamins are stored for long periods, they generally pose a greater risk for toxicity than water-soluble vitamins when consumed in excess.
True. Megadoses of vitamins A, D, E or K can be toxic and lead to health problems.
Where is most of the body’s vitamin A stored? What is the precursor molecule for vitamin A?
- liver
- carotenes
What are the forms of vitamin A? (just list)
retinol
retinal
retinoic acid
beta carotene
What is the function of retinol?
How is retinal derived?
How is retinoic acid derived?
How and where is beta carotene converted to vitamin A? What function does beta carotene have?
- retinol: It serves as a glycosyl donor for some glycoproteins.
- retinal: an aldehyde derived from the oxidation of retinol. Retinal and retinol can be readily interconverted.
- retinoic acid: an acid derived from the oxidation of retinal. It can not be reduced in the body, and therefore, can not give rise to either retinal or retinol.
- β-carotene: plant foods (carrots) contain β-carotene and it can be oxidatively cleaved in the intestine to yield two molecules of retinal (so it is a precursor of vitamin A). In humans, this conversion is inefficient and the vitamin A activity of β-carotene is about 1/6 that of retinol. It is an antioxidant.
What is the mechanism of action of vitamin A?
Retinoic acid binds to specific receptor proteins in the nucleus of target tissue such as epithelial cells. The activated retinoic acid-receptor complex interacts with nuclear chromatin to stimulate retinoid-specific RNA synthesis, thus resulting in the production of proteins that mediate several physiologic functions.
What are the functions of vitamin A? (there are 6). Be specific about which forms play a role in each function.
- vision: vitamin A (in the form of retinol/ retinal/or beta carotene) is a component of the visual pigments of rod and cone cells.
- growth: vitamin A (as retinol/ retinal/or beta carotene) is essential for bone growth.
- However, the Retinoic acid form promotes growth and differentiation of epithelial cells, but it is inactive in maintaining reproduction and in vision; thus, animals given vitamin A only as retinoic acid from birth are blind and sterile.
- taste: vitamin A (as retinoic acid) is necessary for proper keratinization of the taste buds, and without it there is a loss of appetite.
- reproduction: retinal and retinol (but not retinoic acid) are essential for normal reproduction by supporting spermatogenesis in the male and by preventing fetal resorption in the female.
- maintenance of epithelial cells: Vitamin A is essential for normal differentiation of epithelium and mucus secretion.
In what form is retinal typically used therapeutically? Retinoic acid?
Although chemically related, retinoic acid and retinol have different therapeutic applications. Retinol and its precursor are used as dietary supplements, whereas various forms of retinoic acid are used in dermatology.
What conditions may dietary deficiencies in vitamin A lead to? (just list)
night blindness
xerophtalmia
anemia
acne
psoriasis
What role does vitamin A play in night blindness and xerophthalmia?
What can xerophthalmia lead to?
night blindness: one of the earliest signs of vitamin A deficiency. It becomes difficult to see in dim light. Prolonged deficiency leads to irreversible decrease in the number of visual cells. Severe vitamin A deficiency leads to xerophthalmia, a pathologic dryness of the conjunctiva and cornea. This can lead to corneal ulceration and, ultimately, blindness due to the formation of scar tissue.
How can vitamin A deficiency lead to anemia?
anemia: can result since Vitamin A is necessary for transferrin (the iron transport protein) synthesis.
How can acne and psoriasis be treated using vitamin A? (what form)
What group of people should not have this form of vitamin A and why?
Acne and psoriasis: these conditions can be effectively treated with retinoic acid or its derivatives. However, retinoic acid should not be taken by women in whom pregnancy is a possibility since it leads to birth defects.
In what groups of people/situations have vitamin A toxicities been seen? What does overdose of vitamin A lead to at the cellular level?
Vitamin A toxicity : has been found in arctic explorers who have eaten polar bear livers, in patients undergoing acne treatment, and in individuals taking mega doses of vitamin A. Overdosing leads to over-stimulation of growth factors and mitosis with higher cell turnover and death.
