A, K, Antioxidants, Supplementation Flashcards
relationship of b-carotene and vit A?
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
how is vit A activity from precursors measured?
as retinol activity equivalents (RAE)
what roles does vit A play in the eye?
- helps maintain cornea (transparent membrane covering outside of the eye)
- 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)
what happens when light passes through the cornea?
- 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
role of vit a in protein synthesis and cell differentiaion?
epithelial tissue and mucous membranes
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
role of vit A in growth and reproduction?
men: sperm development
women: normal fetal development during pregnancy
bone remodelling:
vit A helps remove parts of the bone that is not needed
overall roles of vit A in the body?
eyes/night vision:
protecting epithelial tissue (skin and lining in organs) and mucous membranes
growth/reproduction: bone remodelling and cell division
immune system
describe vit A deficiency
process of blindness
- 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).
- 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 - 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
where is vit A mostly stored
90% in liver
composition of rhodopsin?
retinal + opsin
functions of vit K
- activated proteins used in blood clotting (prothrombin, precursor of thrombin)
- synthesis of bone protein
describe deficiency of vit K
primary is rare
secondary has two causes:
- fat absorption falters = bile production fails = no vit K absorption
- drug (ie. antibiotics) disrupts vit K synthesis
results in
- hemorrhagic disease:
- no blood clotting = excessive bleeding - low bone density (no vit K = body can’t make the right proteins to build bones)
how is vit K produced in the body?
produced by bacteria in the GI tract
not produced in newborns = need vit K shot when born
describe the blood clotting process
refer to digram
vit K allows prothrombin synthesis
Ca and thromboplastin allow conversion to thrombin
thrombin + fibrinogen = fibrin = clots
describe free radicals
how do antioxidants work to decrease free radicals?
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
function of vit C?
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:
describe vit c deficiency
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
vit C RDA and UL?
women: 75mg/d
men: 90mg/d
UL: 2000mg/d
approx 50mg in a piece of fruit
role of vit E
antioxidant:
- prevents oxidation of PUFAs and other lipids
- protects lungs
- reduces risk of heart disease by protecting LDL
vit E deficiency
hemolysis: RBC break open (erthrocyte hemolysis)
- from oxidation of PUFAs in membranes
hemolytic anemia
role of vit C in iron absorption?
vit C reduces Fe+3 to Fe+2
Fe+2 can’t be bound in protein = needs vit C
