A, K, Antioxidants, Supplementation

Question 1

relationship of b-carotene and vit A?

Answer 1

b-carotene is a precursor for vit A. But not all is converted to vit A. Absorption of b-carotene is not as efficient as that of vit A

Question 2

how is vit A activity from precursors measured?

Answer 2

as retinol activity equivalents (RAE)

Question 3

what roles does vit A play in the eye?

Answer 3

1. helps maintain cornea (transparent membrane covering outside of the eye)
2. participates in the conversion of light energy into nerve impulses at the retina (nerves lining the back of the inside of the eye. consists of rods and cones)

Question 4

what happens when light passes through the cornea?

Answer 4

• strikes the cells of the retina
• rhodopsin responds by changing shape and configuration (cis to trans)
• trans-retinal can’t remain bonded to opsin
• retinal is released
• opsin changes shape and disturbs the membrane of the cell
• an electrical impulse is generated and travels along the cell
• message is sent to the brain
• retinal is converted back to cis form and binds with opsin protein to regenerate pigment rhodopsin
• some retinal may be oxidized to retinoic acid (irreversible). Thus need to get replenishment from foods or retinol stores

refer to diagram

Question 5

role of vit a in protein synthesis and cell differentiaion?

epithelial tissue and mucous membranes

Answer 5

vit a helps protect epithelial tissue (skin) against damage from sunlight

epithelial tissues that line the inside of the body are mucous membranes

deficiency = decreases membrane integrity, taste, digestion ,absorption

Question 6

role of vit A in growth and reproduction?

Answer 6

men: sperm development
women: normal fetal development during pregnancy

bone remodelling:
vit A helps remove parts of the bone that is not needed

Question 7

overall roles of vit A in the body?

Answer 7

eyes/night vision:

protecting epithelial tissue (skin and lining in organs) and mucous membranes

growth/reproduction: bone remodelling and cell division

immune system

Question 8

describe vit A deficiency

process of blindness

Answer 8

• depends on adequacy of vit A stores (most is in the liver) and protein status of the body (retinol binding proteins transport of vit A)
• deficiency symptoms would not appear until after stores were depleted (ie. doesn’t happen right after not eating vit A).

1. night blindness:
   - one of the first detectable signs of vit A deficiency
   - retina (back of eye) doesn’t have enough retinal to regenerate promptly after sudden light or darkness
2. blindness (xerophthalmia)
   - caused by lack of vit A at the front of the eye (cornea)

_____
also causes:
weakened immune system:
-less mucus secretion in resp tract, GI, urinary, vagina, etc… = weakened defenses = more likeley to have infections

keratinization:

• accumulation of keratin (hard protein of hair and nails) in tissues and skin
• skin becomes dry, rough and scaly
• goblet cells in GI tract diminish = decreased secretion of mucus = less absorption and digestion = worsens malnutrition

Question 9

where is vit A mostly stored

Answer 9

90% in liver

Question 10

composition of rhodopsin?

Answer 10

retinal + opsin

Question 11

functions of vit K

Answer 11

• activated proteins used in blood clotting (prothrombin, precursor of thrombin)
• synthesis of bone protein

Question 12

describe deficiency of vit K

Answer 12

primary is rare

secondary has two causes:

1. fat absorption falters = bile production fails = no vit K absorption
2. drug (ie. antibiotics) disrupts vit K synthesis

results in

1. hemorrhagic disease:
   - no blood clotting = excessive bleeding
2. low bone density (no vit K = body can’t make the right proteins to build bones)

Question 13

how is vit K produced in the body?

Answer 13

produced by bacteria in the GI tract

not produced in newborns = need vit K shot when born

Question 14

describe the blood clotting process

Answer 14

refer to digram

vit K allows prothrombin synthesis

Ca and thromboplastin allow conversion to thrombin

thrombin + fibrinogen = fibrin = clots

Question 15

describe free radicals

how do antioxidants work to decrease free radicals?

Answer 15

when o2 sometimes reacts with body compounds and produces high unstable molecules (has one unpaired electron. wants to steal and electron from something). By stealing another electron, it creates another free radical

can be produced from UV, pollution, tobacco, etc

antioxidants work by giving an electron to the free radical. this does not produce another free radical because

Question 16

function of vit C?

Answer 16

antioxidant:

• loses electrons easily
• protects tissues from oxidative stress

cofactor in collagen formation:

• helps to form collage (structural protein of connective tissues)
• scar tissue and wound healing

hormone synthesis:

Question 17

describe vit c deficiency

Answer 17

symptoms:

• scurvy (when vit C pool falls too low, approx 1 month with no vit C)
• gums bleeding around teeth and capillaries under the skin break (hemorrhages from inadequate collagen synthesis)
• weak muscles and bones
• anemia and infections

Question 18

vit C RDA and UL?

Answer 18

women: 75mg/d
men: 90mg/d
UL: 2000mg/d

approx 50mg in a piece of fruit

Question 19

role of vit E

Answer 19

antioxidant:

• prevents oxidation of PUFAs and other lipids
• protects lungs
• reduces risk of heart disease by protecting LDL

Question 20

vit E deficiency

Answer 20

hemolysis: RBC break open (erthrocyte hemolysis)
- from oxidation of PUFAs in membranes

hemolytic anemia

Question 21

role of vit C in iron absorption?

Answer 21

vit C reduces Fe+3 to Fe+2

Fe+2 can’t be bound in protein = needs vit C