Week 7 Flashcards
What are Free radicals?
an uncharged molecule having an unpaired valence electron. :(
Define Oxidative stress
where there is an imbalance between pro-oxidants and antioxidants, more oxidants.
Define Antioxidants
a substance that inhibits oxidation
give free radicals a electron :)
What is the difference between the endogenous and exogenous formation of free radicals?
Endogenous:
- Metabolic processes requiring oxygen produce ROS e.g. oxidative phosphorylation in mitochondria (high energy diets)
- Enzymatic oxidation
- Exercising
- Inflammation
- Obesity
Exogenous
- Radiation
- Smoking
- Dietary components: which?
- Cooking by-products
- Air-water pollution
- Exposure to pesticides solvents, environmental toxins, drugs
- Ion metal transition
Define Redox homeostasis
the balance between pro and antioxidants
Define Antioxidant “capacity”
The synergistic work between the endogenous and the exogenous, enzymatic and non-enzymatic antioxidant systems in keeping free radicals in equilibrium
What is the difference between enzymatic and non-enzymatic antioxidant defense systems?
Enzymatic:
Gene products that function as enzymes
Non-enzymatic
Plasma constituents
Food constituents
What is Nrf2 and when is it activated?
what happens when it is activated?
a transcription factor that signals the expression of genes for antioxidant enzymes
activated when there is an increase in free radicals (e.g ROS) in the cell, and by certain phytochemicals
When activated, it moves to the nucleus when it binds to the antioxidant response element, where it promotes the expression of antioxidant enzymes
what is Essentiality is based on for vitamins?
- Humans can not make their own vitamins, or not in sufficient amounts
- When not consumed, health declines and deficiency symptoms occur
- Deficiency symptoms disappear as soon as vitamins supplementation or rich food sources are given
What are the fat soluble vitamins?
A
D
E
K
what is the biologically active form of vitamin A? what are its 3 forms?
Retinoids
- Retinol or retinyl esther
- Retinal
- Retinoic acid
what are the two form vitamin A is found as?
Retinoids
carotenoids
describe the digestion of Vitamin A?
Retinyl esters split into retinol and fatty acids in GIT: via bile and pancreatic lipase activity
Provitamin A carotenoids usually bound to protein molecule in food. Split via enzymes activity in GIT to be absorbed
How much of Vitamin A is absorbed and how?
90% of retinol intake absorbed via carrier proteins
5-60% of carotenoids intake absorbed by passive diffusion
Describe the activation process of vitamin A?
Carotenoids cleaved to form retinal or retinoic acid
Retinal converted to retinol and retinoic acid
how is vitamin A transported?
In enterocytes:
- retinyl esters are reformed, packaged in chylomicrons, transported via the lymphatic system, blood stream and liver
- Retinoic acid enters blood stream directly and transported to liver
From the liver:
- Retinoids bound to retinol binding protein for transport to cells
- Carotenoids that are not transformed: carried by VLDL
where is Vitamin A stored?
90% retinoids found in liver (enough to last several months), small amounts in adipose tissue, kidney, bone marrow, testicles, eyes
how is vitamin A excreted?
Small amount in urine; carotenoid excreted as bile
What are the functions of vitamin A?
- Growth and development
- Cell differentiation gene expression
- Vision
- Immune function
- Dermatology: psoriasis and UV-light exposure damage
- Carotenoid functions
What are the deficiency signs and symptoms for vitamin A?
Night blindness
Xerophthalmia (permanent blindness) Follicular hyperkeratosis
What are the different affects of toxicity for vitamin A for acute, chronic, teratogenic?
Acute:
GIT upset/ nausea; muscular incoordination,
headaches
Chronic:
liver damage, hemorrhages, dry skin and mucous membrane hair loss, bone loss, coma
Teratogenic (if the pregnant woman consumes large amount):
fetal malformation, spontaneous abortion
what are the different food sources for vitamin A in both retinoids and carotenoids
Retinoids (preformed vitamin A)
– Liver,fish,fish oils,fortified milk,eggs
– Some low-fat dairy is fortified with vitamin A
Carotenoids (provitamin A)
– Dark green and yellow-orange vegetables/ fruit
– Beta-carotene is the dominant carotenoid
What are the different forms of vitamin E?
Tocopherols (most active)
tocotrienols
For Vitamin E absorption: what does it depend on? how is it absorbed? how much is absorbed? which form is best absorbed?
- Absorption depends on dietary fat and amount consumed
- Passive diffusion
- 20-70% of dietary intake is absorbed
- Alpha tocopherols appear the best absorbed
How is vitamin E transported?
Micelles, enterocytes: dependent on bile and pancreatic lipase
Chylomicrons, through the lymphatic system and into circulation, to the liver
Transported from liver via lipoproteins (LDL, HDL, VLDL) for tissue delivery
Where is vitamin E stored?
Stored in adipose tissue (90%), not in the liver
How is Vitamin E excreted?
Bile, urine and skin
What are the functions of Vitamin E?
Antioxidant: Neutralisation of free radicals by vitamin E in the cell membrane
A benefit in chronic inflammatory disease
Cancer protection
Dermatological use
What happens if there is a deficiency in Vitamin E?
Hemolytic anemia: premature hemolysis of red blood cells
Impaired immune function
What happens if toxic levels of Vitamin E?
Toxic levels of Vitamin E can interfere with Vitamin K activity in blood clotting and may cause hemorrhaging
